This PDF file contains the front matter associated with SPIE Proceedings Volume 10684 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Group IV photonic materials such as Si and Ge have been used for monolithic applications including on-chip sensors and optical devices in the mid-IR spectral range. The optical properties of germanium have not been reported experimentally to the same extent as silicon in spite of expected merits over silicon. Germanium is expected to possess advantages as large nonlinear optical coefficients, a broad transparency beyond 10um, and large carrier mobility. In this paper, we report nonlinear refractive indices and multi-photon absorption coefficients over the wavelength range between 2um-5um, measured using closed and open z-scan measurements. Samples are scanned through the focal point of a plano-convex spherical CaF2 lens, where an intensity variation with respect to its spatial location exists. The transmitted laser power is measured by a power meter at different sample positions relative to the focal region. Closed Z-scan measurements utilize an aperture in front of the detector whereas open Z-scan measurements do not. Closed Z-scan measurements are typically used for the quantification of nonlinear refractive indices while open Z-scan measurements are used for the characterization of nonlinear absorption coefficients. The closed Z-scan measurement values are then divided by the open Z-scan measurement values to remove the effects of nonlinear absorption before the nonlinear refractive index is measured by fitting [B.-U. Sohn et al., APL 111(2017)] Ultrashort pulses with a temporal width of 150fs at a1kHz repetition rate are used for the measurements. The mid-infrared optical pulses originate from an optical parametric amplifier and difference frequency pumped by a Ti:sapphire regenerative amplifier. The low repetition rate of the pulses and ultrashort temporal pulse width which is much shorter than the thermal diffusion time scale of 40µs in Ge, is ideal to mitigate effects of heat phonons on the nonlinear effects under study. The nonlinear refractive index of Ge is characterized to possess the highest value, 9.1*10-5cm2/GW at a wavelength of 3um, corresponding to the two photon absorption edge. This result is supported by Kramers-Kronig relation between two photon absorption and nonlinear refractive index n2. The value of n2 is observed to vary between 4*10-5cm2/GW to 5*10-5 cm2/GW within the 3.5-5µm wavelength range. Considering Ge’s bandgap of 0.66eV, two photon absorption and three photon absorption occur in Ge at wavelengths between 2-3.6µm and 3.6-5.5µm respectively. The two photon absorption coefficient has the largest value, 25.6cm/GW at 2.2µm and possesses a relatively constant value with average of 0.71cm3/GW2 between 4-5.5µm. The four photon absorption coefficient is measured to be 0.007cm5/GW3 at 6µm. We further investigate the nonlinear figure of merit (FOM), which is proportional to n2 and inversely related to multi photon absorption coefficient. A large FOM is achieved in wavelengths where n2 is large and multi-photon absorption effects are weak. The FOM has a high value of 0.08 between 2.5 - 3 µm making germanium an efficient material for applications in nonlinear optical devices.

Optical parametric amplifiers rely on the high Kerr nonlinearities and low two-photon absorption (TPA) to achieve large optical amplification. The high Kerr nonlinearity enables efficient energy transfer from the optical pump to the signal. On the other hand, the TPA process competes with the amplification process, and thus should be eliminated. Through Miller’s rule and Kramers-Kronig relations, it is known that the material’s Kerr nonlinearity scales inversely proportional to the band-gap, while the TPA process occurs when the photon energy is larger than the band-gap energy and Urbach tails, thus presenting a trade-off scenario. Based on these requirements, we have designed a CMOScompatible, band-gap engineered nitride platform with ultra-rich silicon content. The silicon nitride material is compositionally engineered to have a band-gap energy of 2.1 eV, which is low enough to confer a high Kerr nonlinearity, but still well above the energy required for the TPA process to occur. The new material, which we called ultra-silicon-rich nitride (USRN), has a material composition of Si₇N₃, a high Kerr nonlinearity of 2.8x10^-13 cm²/W, and a negligible TPA coefficient. In optical amplification experiments, 500 fs pulses at 14 W peak power and centered around 1560 nm are combined with continuous wave signals. The maximum parametric gain of the signal could reach 42.5 dB, which is one of the largest gains demonstrated on CMOS platforms to date. Moreover, cascaded four-wave mixing down to the third idler, which was usually observed for mid-infrared silicon waveguides, is unprecedentedly observed at this spectrum.

Silicon photonics is currently moving towards the Mid Infrared (MIR), which attracts plenty of emerging technologies, from integrated spectroscopy to quantum communications. However, the development of MIR-photonics is hindered by the lack of efficient detectors and light sources. A possible solution could be an integrated system able to link the MIR with the near infrared, where detectors and light sources have been already developed for telecommunications. Because of this, the possibility to perform broad and tunable wavelength conversion and generation is of great interest. In particular, the generation and conversion can be accomplished by means of Four Wave Mixing (FWM), a nonlinear optical process in which two input pump photons are converted into signal and idler photons of different frequency. Crucial for efficient FWM is the phase matching condition, which determines the spectral position of the maximum efficiency of the process. In order to achieve large spectral translation between signal and idler, we propose to use Intermodal FWM (IMFWM), which exploits the dispersion of the higher order waveguide modes to achieve the phase matching condition. In IMFWM, the pump, signal and idler propagate on different waveguide modes. With respect to common phase matching techniques, IMFWM does not require anomalous GVD, resulting in an easier handling of the phase matching condition. Moreover, due to the sensitivity of the higher order mode dispersion with the waveguide geometry, the spectral position of the intermodal phase matching can be easily tuned by engineering the waveguide cross-section, achieving also large detunings from the pump wavelength. Another advantage is the high tolerance to the fabrication defects, related to the large widths of the multimode waveguides used. In our work, we report the first experimental demonstration of spontaneous and stimulated on-chip IMFWM using Silicon-On-Insulator (SOI) channel multimode waveguides. We used a pulsed pump laser at 1550 nm with 10 MHz repetition rate and 40 ps pulse width. The excitation of the higher order modes is attained by displacing horizontally the input tapered lensed fiber with respect to the center of the waveguide facet. We investigated an intermodal combination involving the pump injected on both the first and second order modes, the signal on the second order mode and the idler on the first order mode, with transverse electric polarization. We used a 3.8-um-wide waveguide, of 1.5 cm length, to perform a spectral conversion of 140 nm with -21 dB efficiency. With the same waveguide, we measured -85 dB between the pump and the spontaneously generated idler. The coupled peak pump power was about 2 W. We then measured the spectral position of the idler as a function of the waveguide width, achieving a maximum wavelength detuning between the idler and the signal wavelengths of 861 nm in a 2-um-wide waveguide, corresponding to the generation of 1231 nm idler and 2092 nm signal. IMFWM enables effective and viable wavelength conversion and generation. It also promotes the development of emerging technologies, like mode division multiplexing and modal quantum interference, whose working principle relies on the higher order waveguide modes.

A common strategy for increasing the efficiency of Stimulated and Spontaneous FourWave Mixing (SFWM) in integrated optical devices, is to enhance the intensity of the propagating optical field through nanoscale geometrical engineering. Typically, this is accomplished by confining light into microresonators or into sequences of mutually coupled cavities. Usually these structures are treated as a whole, with tens or hundreds of repeating units. In these structures, long grange periodicity is deliberately sought to tailor the frequency wavevector band diagram, in order to increase the group index while keeping the group velocity dispersion as low as possible. Having to deal with a large number of unit cells inherently precludes the study of the impact of the internal degree of freedom on FWM. The implementation of complex and extended structures precludes the observation of FWM regimes which are in general hidden, or overhung, by the long range periodicity, and that can emerge only by acting at the single resonator level. In this work, we study SFWM in a system made by two Silicon microring resonators (photonic dimer) of radius 7 um, quality factor Q = 10000 and separation 53.1 um, which are indirectly coupled by means of two waveguides with a coupling gap of 160 nm. We independently change the inter-cavity phase f, and the resonator eigenfrequency detuning d, by respectively implementing a Peltier cell and micro-heaters placed on the top of the resonators. We experimentally and theoretically demonstrate that, in the parameter space spanned by (f, d), the efficiency of SFWM can be enhanced, left unchanged or being completely suppressed with the respect to a single uncoupled resonator. This plethora of regimes can not be easily resolved and accomplished in large structures, where the structural periodicity makes slow light to overwhelm any other side effect. Here, a FWM enhancement of 7 dB with respect to each single constituent of the molecule is demonstrated, and attributed to the increase of internal field enhancement of one of the resonator induced by the presence of the other. We theoretically prove that this phenomenon is linked to the excitation of a sub-radiant mode in the structure. FWM suppression arises from the coherent destructive interference between the signal waves generated in the two resonators which are scattered into a common waveguide channel. We find that in the region where SFWM is enhanced, also the efficiency of Spontaneous Four Wave Mixing, the quantum counterpart of the stimulated process, is increased. This opens a plenty of possibilities for the implementation of this device for the generation of correlated photon pairs. We suggest that pairs could be deterministically bunched into a single scattering channel with a brightness that overcomes the one of a critically coupled resonator. This could beat the effective 50% of losses which suffer All-Pass and Add-Drop resonators, and could show superior brightness with respect to asymmetric microrings or dual Mach-Zehnder-microrings devices, whose maximum achievable field enhancement is inherently limited by the level attained at critical coupling.

Gallium phosphide (GaP) is an attractive material for non-linear optics because of its broad transparency window (λ_vac > 548 nm) and large Kerr coefficient (n_2 ~ 6 × 10^-18 m^2/W). Though well-established in the semiconductor industry as a substrate for visible LEDs, its use in integrated photonics remains limited due to fabrication challenges. Recently we have developed a method to integrate high quality, epitaxially-grown GaP onto silica (SiO2) based on direct wafer bonding to an oxidized silicon carrier wafer. Here we exploit this platform to realize unprecedentedly low loss (Q > 3 × 10^5) GaP-on-SiO2 waveguide resonators which have been dispersion-engineered to support Kerr frequency comb generation in the C-band. Single-mode, grating-coupled ring resonators with radii from 10 – 100 μm are investigated. The threshold for parametric conversion is observed at input powers as little as 10 mW, followed by 0.1 – 1 THz frequency comb generation over a range exceeding 400 nm, in addition to strong second- and third-harmonic generation. Building on this advance, we discuss the prospects for low-noise, sub-mW-threshold soliton frequency combs with center frequencies tunable from the mid-IR to the near-IR. Applications of such devices range from precision molecular spectroscopy to ultrafast pulse generation to massively parallel coherent optical communication.

Merging the fields of plasmonics and nonlinear optics authorizes a variety of fascinating and original physical phenomena. In this study, we specifically study the combination of the strong light confinement ability of surface plasmon polaritons (SPP) with the beam self-trapping effect that occur in nonlinear optical Kerr medium. Although this idea of plasmon-soliton has been the subject of several theoretical or numerical articles, no experimental evidence has been revealed yet. One reason is that in the proposed configurations the requested nonlinear refractive index change amplitude to generate a plasmon-soliton is too high to be reached in available material. Another limitation is due to the large propagation losses associated with plasmons. In the present study, a proper architecture has been designed and then fabricated allowing the first experimental observation of hybrid coupling between a spatial optical soliton and a SPP in a metal-Kerr dielectric structure. To be able to trigger the nonlinearity at moderate light power and simultaneously to allow propagation over several millimetres distance, a metal-dielectric structure was designed. It consists of a four-layer planar geometry made of a transparent Kerr dielectric layer placed on a lower refractive index medium, with on its top surface a thin dielectric layer covered by a metallic film deposited on top. The Kerr medium is a 3µm thick chalcogenide film (Ge28.1Sb6.3Se65.6) with a high refractive index deposited by RF magnetron sputtering on an oxidized silicon substrate. The thickness of the thin SiO2 layer is 10 nm while the top gold layer is 30 nm. Samples are about 5-6 mm along propagation direction (z-axis). As shown by numerical simulations, the designed planar nonlinear waveguide with its top silica and gold layer supports a fundamental TE mode profile at NIR wavelengths whose transverse profile along y (perpendicular to the layers) is not affected by the metal layer while the TM mode is clearly localized near the SiO2-metal-chalcogenide interfaces due to its plasmonic part. The estimated nonlinear parameter γ of the TM mode is nearly three times larger than the TE one. Consequently, in nonlinear regime an enhanced self-focusing effect is expected for this TM wave. Experiments are performed with a tunable optical parametric oscillator emitting 200 fs pulses at 1.55 µm with a repetition rate of 80 MHz. The experimental analysis consists in injecting a typical 4 × 30 μm2 (FWHM in x-y cross section) elliptical laser beam into the waveguide and monitoring the output beam spatial profile evolution versus light power. Different arrangements are tested that unambiguously reveal the plasmon-soliton coupling. For instance, experiments are conducted with and without the metallic layer and for both TE and TM polarizations. In addition, different positions on the sample of the metal part with several lengths chosen between 0.1 to 2mm are tested. Additional experiments are in progress to analyze the beam evolution with near-field scanning microscopy and simulations of the beam propagation in the full structure are developed to reach a better and fully quantitative description of the observed phenomena.

A series of waveguides were inscribed in lithium niobate by tightly focused femtosecond-laser pulses of 11-MHz repetition rate and 790-nm wavelength. To establish the inscription conditions for optimal low-loss waveguides, within each sample we varied laser pulse energy, speed and direction of translation stage movement, and focus depth of the beam. We deployed two new approaches to enhance the inscription results: 1) increase of the pulse energy with increasing focus depth inside the material to compensate for the corresponding decrease of refractive-index modification, and 2) decrease of the laser energy for the modification tracks closer to the waveguide’s core region to reduce scattering losses due to high-laser-energy driven non-uniformities. All waveguides had an optical-lattice-like hexagonal packing geometry with track-spacing of 9.9 μm (optimized for effective suppression of high-order modes). Each structure comprised 84 single-scan Type-II-modification tracks, aligned with the crystalline X-axis of lithium niobate. After heat treatment at 350 °C for 3 hours, the lowest propagation loss of less than (0.4±0.1) dB/cm and (3.5±0.3) dB/cm for the ordinary and extraordinary light polarization states, respectively, were achieved at the 1550- nm wavelength. These low-attenuation waveguides were obtained with the inscription energy varying between 50.6 nJ and 53.6 nJ and the translation speed of 10 mm/s. The corresponding refractive-index contrast of individual tracks was (–1.55±0.04)×10^-3 . The waveguides also showed low attenuation in the visible and near-infrared portion of the spectrum (532 nm to 1456 nm). Our results offer promising means for the development of low-loss waveguides with preserved-nonlinearity and high thermal stability.

High resolution gas spectroscopy in the mid-infrared in a transportable device is a big challenge allowing to address numerous applications: air quality or industrial process monitoring, defense and security, medical diagnostics... Together with high tunability in the mid-infrared, spectral purity, narrow bandwidth, compactness and robustness are needed. Nested Cavity doubly resonant OPO (NesCOPO) fulfill all those requirements. This architecture is already commercialized (in the X-FLR8 portable gas analyzer from Blue Industry and Science) and allows to reach low threshold compatible with the use of compact micro-chip nanosecond YAG laser. A wide spectral range can be obtain (2 - 10 μm). In the most mature version NesCOPO takes benefit of down-conversion of a laser radiation at 1.064 μm in a PPLN bulk crystal and give rise to two secondary radiation around 1.5 μm and between 3.2 and 4.25 μm. This last radiation is used to probe rovibrational absorption lines of species of interest using absorption or transmission spectroscopy. Speed in the selection of the emitted wavelength can be an important requirement especially when security is involved. We use engineering of the crystal using fan-out configuration. Evolution of the bandwidth and phase shift between the three waves after reflection onto the end cavity mirror has to be managed to maintain high conversion efficiency. Experiment show more flexible behavior than expected with theory. This lead to fine wavelength control on the overall emission spectrum (over 1 μm) without using crystal temperature tuning that slow down tuning speed.

Low-loss commercial optical fibers are known as perfect candidates to explore the richness of the dynamics of nonlinear physics. Indeed, the excellent knowledge of linear and nonlinear properties of these optical waveguides is a key ingredient to carry out experimental demonstration of the theoretical solutions of the nonlinear Schrödinger equation (NLSE). As soon as the early 80s, solitons were demonstrated in single-mode optical fibers with anomalous dispersion. More recently, taking advantage of the components of the telecommunication industry, more complex breather solutions have been experimentally generated. Such structures can also be detected in deep water and other nonlinear medium governed by the NLSE. Normally dispersive fibers have also stimulated recent experimental research, mainly driven by the interest in the study of dispersive shock waves. Most of the time, nonlinear dynamics observed in both anomalous and normal dispersion regimes of propagation are regarded as two completely different cases: one dominated by bright soliton-like structures and modulation-instability that provides an analogue to deep-water conditions; the other one ruled by dispersive shock waves (DSW) that satisfies the so-called nonlinear shallow water equations. However, recent theoretical works have stressed that a shock wave may appear in the regime of focusing nonlinearity with weak dispersion, thus leading to the emergence of dispersive dam break flows in the NLSE box problem. A DSW-like nonlinear wave train regularizes an initial sharp transition between the uniform plane wave and the zero-intensity background. In particular, theoretical solutions essentially describe a modulated soliton train. This provides a new semi-classical interpretation of what has been previously described in the spatial domain as a nonlinear Fresnel diffraction. The box problem (i.e., an initial square profile) then gives rise to two counter-propagating modulation dynamics of opposite velocities, whose interaction may turn into a cluster of breathers. In the present contribution, we confirm some of the above theoretical predictions by providing a detailed experimental observation of the regularization of sharp transitions from a super-Gaussian pulse in the presence of focusing nonlinearity and weak anomalous dispersion. Our results recorded in the temporal domain and based on an all-fibered test-based platform confirm the former qualitative behavior observed in the spatial domain as well as the strength of the space/time duality. After an initial shock induced by the overlap of the highly chirped and sharp wings of the pulse with the top region, strong temporal oscillations appear and nonlinearly reshape into a Peregrine-like structure at each maximum compression. This transient evolution is then marked by the breathing of the wave structures, both in the temporal and spectral domains. This transition may be followed by an asymptotic stage dominated by solitons. Finally, we also characterize the interaction event of the two counter-propagating dispersive dam break flows. Dispersive shock waves and Peregrine breathers have been shown to locally coexist, thus providing new insights into spontaneous pattern formations and novel possible interactions.

High repetition-rate coherent femtosecond sources of tunable near-IR radiation are widely used for time resolved spectroscopy and optical microscopy. We have developed a compact femtosecond optical parametric oscillator (OPO) for the near-IR in a novel configuration based on MgO doped periodically poled LiNbO3 (MgO:PPLN) synchronously pumped by a Kerr-lens-mode-locked (KLM) Ti:sapphire laser at 76 MHz. The singly-resonant OPO in a four-mirror X-cavity arrangement incorporates an 86-cm-long single mode fibre with one silver coated facet functioning as an end mirror. By coupling the resonant signal into the fibre comprising 63% of the total cavity length, the total OPO footprint is kept highly compact, while maintaining the repetition rate at 76 MHz. Moreover, the use of the optical fibre drastically alters the cavity dispersion profile compared to a free-space OPO, with the zero-dispersion wavelength shifted to ~1.3 μm. At a pump wavelength of 800 nm, the signal wavelength is tunable across 1128–1243 nm in the normal dispersion regime, and 1358–1600 nm (degeneracy) in the anomalous dispersion regime, by variation of cavity length and the crystal grating period. Tuning curves are compared to those predicted using the Sellmeier equations for MgO:PPLN and fused silica, confirming close agreement with experiment. Using a maximum pump power of ~850 mW, up to 50 mW of average signal power is extracted at 1468 nm using a 13% output coupler, and the oscillation threshold is measured to be ~600 mW. The output power is limited by an estimated coupling loss of 2.2 dB at the fibre coupler, and imperfect cavity mode-matching. Excellent passive spectral stability is observed, and a power stability of 1.1% rms is recorded. The signal beam is of high spatial quality with a TEM00 profile. Signal pulses are characterised using intensity autocorrelation, yielding pulse durations of ~130 fs at 1192 nm, very similar to those of the pump. Spectra in the anomalous dispersion regime are well-defined single peaks, while those in the normal dispersion regime exhibit a rich variety of features including symmetrical sideband formation and evidence of optical wave breakup. These features are modelled and verified using simulations based on the nonlinear Schrodinger equation. The wavelength offset of sidebands of order N is seen to follow a N0.5 dependence, analogous to those observed in the spectrum of a mode-locked soliton laser operating in the anomalous dispersion regime. To the best of our knowledge, this represents the first fibre-feedback OPO configured using a fibre facet as an end mirror; and the first time tuning in both dispersion regimes has been achieved. The combination of high intracavity dispersion and a broad phase matching bandwidth enables rapid continuous tuning across the near-IR using cavity delay, and excellent spectral stability. With suitable optics, the idler beam across 1.6–3 μm could also be extracted. This OPO represents a promising compact source for high repetition-rate ultrafast spectroscopic applications.

We report here evidence of phase-matched optical wave mixing in the extreme ultraviolet (XUV) region. This process has been studied with a collinear two-colour high-order harmonic generation scheme. An 800 nm, 30 fs driving field is used to produce a small bandwidth comb of odd harmonic orders (wavelength around 30 nm) in a long cell filled with argon gas. Mixing frequencies in this spectral range are produced by applying a second weak control-field of 1,400 nm, 40 fs. Low order (third- and fifth-order) nonlinear optical wave mixing is observed to be a phase-matched process. The dependence of the intensity of the harmonic orders and the mixing frequencies on different control-field intensities, gas pressure, and interaction length is analysed to verify the phase matching process.

Intense terahertz (THz) pulses with MV/cm peak-field amplitudes have become experimentally feasible with the advents in table-top THz generation methodologies. Such fields provide a new control-handle over the rotations of polar molecules in the gas phase, as they primarily interact with molecular rotors via their permanent dipole moments, differing yet complementing ultrashort optical pulses that interact with molecules via their polarizability tensor. When applied to linear molecules, optical pulses induce molecular ALIGNMENT while THz pulses induce ORIENTATION. In linear molecules both the dipole vector and the most polarizable axis coincide at the inter-atomic axis of the molecule, thus serving to rotate the molecules about the same axis. However, for asymmetric tops like SO2, the dipole and the most polarizable axes lie along different molecular frame axes, turning optical and THz fields as two distinct rotational handles. Well-orchestrated application of these pulses can provide complete three-dimensional control over the molecular angular distribution of such molecules - a long standing goal in molecular physics and chemistry. In the first part of the talk I will present our recent experimental and theoretical results of optical induced alignment and THz induced orientation in gas phase SO2 molecules that highlight the different rotational dynamics induced by these two distinct rotational handles. On the theoretical front, simulating the rotational dynamics of asymmetric molecules like SO2 at room temperature remains a highly demanding computational task that is effectively impossible by exact methods for dynamics. We overcame this issue by employing the Random Phase Wave Functions method [1,2] that was also verified by experimental results [3]. In the second part I will present a decay phenomenon that was recently unveiled in by a series of time-resolved measurements of the rotational dynamics induced by an optical pulse and a THz-field. We have found that despite their exact same pressure and temperature, transiently oriented molecules decay at a faster rate than aligned molecules [4]. This is attributed a coherent radiative decay mechanism that we believe is general to all resonantly induced dynamics, however has been discarded previously. I will present our recent experimental results and suggest a theoretical model that incorporates a coherent radiative term into the typical Hamiltonian of the problem. References [1] D. Gelman and R. Kosloff, Chem. Phys. Lett., 381, 129 (2003). [2] S. Kallush, and S. Fleischer, Phys. Rev. A, 91, 063420 (2015). [3] R. Damari, S. Kallush, and S. Fleischer, Phys. Rev. Lett. 117, 103001 (2016). [4] R. Damari, D. Rosenberg, and S. Fleischer, Phys. Rev. Lett. 119, 033002 (2017).

A major concern of High Harmonic Generation (HHG) is the small conversion efficiency at the single emitter level. Thus, ensuring that the emission at different locations are emitted in phase is crucial. At high pump intensities, it is impossible to phase match the radiation without reverting to ordered modulations of either the medium or the pump field itself, a technique known as Quasi-Phase-Matching (QPM). To date, demonstrated QPM techniques of HHG were usually complicated and/or lacked tunability. Here we demonstrate experimentally a relatively simple, highly and easily tunable all-optical QPM technique in which different spatial modes are superposed together to create a pump beam in which either the intensity or the polarization is periodically modulated. With these we demonstrate on-the-fly, tunable QPM of harmonic orders 25 to 41 with up to 40 fold enhancement of the emission at pressures ranging from 15 to 100 Torr.

In this proceeding, we present a software Fit@TDS that enables to retrieve the refractive index of a sample from a timedomain spectroscopy experiment. The software include commonly used methods where the refractive index is extracted from frequency domain data. This method has limitations when the signal is too noisy or when the absorption peak saturates the absorption. Thus, the software includes as well a new method where the refractive index are directly fitted using a model (the Drude-Lorentz for example) in the time domain. This method uses an optimization algorithm that retrieves the parameters of the model corresponding to the studied material. In this proceeding, we explain the methods and test them on fictitious samples to probe the feasibility and reliability of the proposed model.

We analyze the nonlinear propagation of a one dimensional Airy beam inside a photorefractive medium. Under nonlinear focusing conditions, the Airy beam splits into a weak accelerating structure and a soliton-like beam called ”off-shooting soliton”. Experimental measurements and numerical results related to the soliton-like structure are compared to conventional gaussian solitons and find good agreement in terms of profile, width and amplitude. We demonstrate that its profile is also preserved through propagation over long distances. Finally we identify the different parameters for generating the ideal Airy beam off-shooting soliton i.e. the one closest to the conventional theoretical soliton.

Hot carriers are energetic photoexcited carriers driving a large range of chemicophysical mechanisms. At the nanoscale, an efficient generation of these carriers is facilitated by illuminating plasmonic antennas. However, the ultrafast relaxation rate severally impedes their deployment in future hot-carrier based devices. In this paper, we report on the picosecond relaxation dynamics of hot carriers in plasmonic monocrystalline gold nanoantennas. The ultrafast dynamics of the hot carriers is experimentally investigated by interrogating the nonlinear photoluminescence response of the antenna [1]. From this investigation, we reveal some leverages to control the dynamics of such hot carriers within nano antenna. In particular, an increase by a factor up to five of this dynamics (from 0.5 ps to 2.5 ps) is observed for resonant nanoantenna compared to off-resonance antenna and when excitation power increases. By a two temperature model we model quantitatively the dynamics of hot carriers and we demonstrate the nonlinear generation of these carriers. The control over the carrier dynamics should allow to employ their energy more effieciently within physico-chemical processes. In a second part, we investigate the hot carrier dynamics with a spectrally resolved two-pulse correlation configuration, and demonstrate that the relaxation of the photoexcited carriers depends of their energies relative to the Fermi level. We find a 60% variation in the relaxation rate for electron−hole pair energies ranging from ca. 0.2 to 1.8 eV. The quantitative relationship between hot-carrier energy and relaxation dynamics is an important finding for optimizing hot-carrier-assisted processes and shed new light on the intricacy of nonlinear photoluminescence in plasmonic [2]. [1] O. Demichel et al, ACS Photonics 3, 791 (2016) [2] R. Méjard et al, ACS Photonics 3, 1482 (2016)

Nowadays the long-range dipole-dipole interaction between highly-excited Rydberg atoms at micrometer distance become promising way to establish the atom-atom quantum entanglement and to implement the two-qubit logic gate. For alkali metal atoms, single-photon excitation from the ground state to the desired Rydberg state demands powerful narrow-linewidth ultra-violet (UV) laser, which is very challenging. Maybe just because of this, the studies of single-photon Rydberg excitation of alkali metal atoms are rare. Alternatively people have employed the two-photon or three-photon Rydberg excitation scheme. However, comparing with the single-photon Rydberg excitation, the two-photon or three-photon scheme has following drawbacks: atomic decoherence due to the photon scattering from the lower and upper transitions, and light shift of the involved ground state and Rydberg state due to the lower and upper transition laser beams. Thanks to the efficient laser frequency conversion technology with PPXX material and the well-developed commercial fiber laser as well as fiber amplifier, we have implemented a tunable 318.6-nm UV laser system based on the cavity-enhanced second-harmonic generation following the single-pass sum-frequency generation of 1560.5-nm and 1076.9-nm fiber-amplified lasers. More than 2-Watt output of the 318.6-nm UV laser has been achieved with a typical linewidth of smaller than 10 kHz. Employing the UV laser system we have demonstrated a single-photon Rydberg excitation spectroscopy of cesium (Cs) atoms. Partial Cs atoms can be directly excited from 6S_1/2 ground state to nP_3/2 (n = 70 - 100) Rydberg states, and Rydberg excitation spectra are obtained with transmission enhancement of a probe beam locked to Cs 6S_1/2 (F = 4) - 6P_3/2 (F’ = 5) cycling transition because partial population on the ground state (F = 4) are transferred to Rydberg state. The quantum defect for Cs nP_3/2 (n = 70 -100) Rydberg states is determined experimentally. Further more, the demodulated single-photon Rydberg excitation spectrum is employed to stabilize the UV laser to specific Cs Rydberg transition to improve the laser frequency stability. References: [1] Opt. Express 25 (2017) p.22510; [2] J. Opt. 19 (2017) 045501; [3] J. Opt. Soc. Am. B 33 (2016) p.2020; [4] Opt. Commun. 370 (2016) p.150. Funding: the National Natural Science Foundation of China (61475091).

Correlated single photons provide a means to drive applications such as quantum computing and quantum communications. Correlated single photons can be generated via parametric down conversion in second–order nonlinear media or spontaneous four–wave mixing in third–order nonlinear media. In particular, complementary metal–oxide–semiconductor (CMOS) technology allows for seamless integration with electronics, providing the potential for a completely on-chip solution for quantum information processing. Ultra–silicon–rich nitride platform is a backend CMOS compatible platform, that has already been used to obtain high gain optical parametric amplification, wideband supercontinuum and enhanced nonlinearity in photonic crystal waveguides due to its large nonlinearity. In this work, we demonstrate correlated photon pair generation based on spontaneous four–wave mixing using ultra-silicon-rich nitride waveguides for the application in CMOS–based optical quantum technologies. A CW pump at a wavelength of 1555.747nm amplified using an EDFA is filtered through five wavelength division multiplexers (WDM) with a bandwidth of 1.2nm, providing 175dB suppression of EDFA induced pump sideband noise. The filtered quasi–TE pump, adjusted using a fiber polarization controller, is coupled into an ultra–silicon–rich nitride waveguide using a lensed fiber. A SiO2 cladded waveguide with a width of 550nm and height of 300nm possesses a high nonlinear parameter of 530W^-1/m with anomalous dispersion necessary for spontaneous four-wave mixing. The waveguide output is coupled into a lensed fiber and 7 cascaded WDMs are used to provide 245dB of residual pump filtration. The pump–suppressed output is spectrally separated into signal/idler part using WDMs. We refer to lower (higher) frequency photon as the signal (idler). The spontaneously generated signal and idler photons are filtered using cascaded tunable band pass filters (OTF) centered at 1571.24nm and cascaded WDMs centered at 1540.56nm, respectively. The bandwidth of the tunable OTF and WDM is 0.5nm and 1.2nm, therefore the correlated signal/idler photons are observed within the bandwidth window of 0.5nm induced by the OTF. The signal and idler photons are measured using InGaAs/InP avalanche photodetectors. The time correlation between signal and idler photons is obtained using a time interval analyzer with a detection efficiency of 20% and dead time of 15μs.The time bin is set to 81ps and the photon collection time is 240s. The coincidence peak is located ~11ns in the time–bin histogram due to the optical-path difference between the tunable OTF and WDM at respective signal and idler sides. The experimental raw coincidence counts (Hz), calculated by subtracting the accidental rate from the coincidence peak, show a quadratic increase with respect to coupled pump power. At the maximum coupled power of 5mW, the raw coincidence count is ~1Hz. We achieve a raw coincidence–to–accidental ratio (CAR) of up to 3. Therefore, we succeeded to observe correlated photon pair generation based on spontaneous four–wave mixing using the ultra–silicon–rich-nitride waveguide as a CMOS compatible platform, for future applications in quantum technologies.

We experimentally broke the temporal Fourier focusing limit of an ultra-short optical pulse and used it to demonstrate temporal super-resolution detection of a temporal event [1]. The envelope function of the pulse is synthesized in the form of a Super-Oscillating Beat (SOB) signal, made of pairs of optical modes (i.e. beat modes) centered around a common carrier frequency. The mathematical form for the synthesis of the SOB signal is based on a known super-oscillatory function [2]. Suited with the right amplitude and phases these beat modes interfere to create a lobe in the temporal waveform of the field’s envelope which can be arbitrarily narrow, at the cost of reduced amplitude at the fast oscillation. In our case, we achieved a temporal feature that is approximately three times shorter than the duration of a transform-limited Gaussian pulse having a comparable bandwidth while maintaining 30% visibility of the super-oscillating feature. We then used this SOB signal to demonstrate experimentally temporal super-resolution. Specifically, the SOB signal was used to resolve the existence of a temporal double-slit, a pair of adjacent pulses which are detected as a single temporal event by a transform-limited Gaussian pulse having the same bandwidth. Formally, this experiment constitutes a temporal analogue to super resolution imaging by using a super oscillating point-spread-function [3,4]. Numerical simulations analyse in which cases the SOB signal outperform transform-limited signals for detection of short temporal events. [1] Y. Eliezer, L. Hareli, L. Lobachinsky, S. Froim and A. Bahabad, “Breaking the Temporal Resolution Limit by Superoscillating Optical Beats”, Physical Review Letters, 119, 043903 (2017). [2] M. V Berry and S. Popescu, "Evolution of Quantum Superoscillations and Optical Supperresolution without Evanescent Waves," J. Phys. A. Math. Gen. 39, 6965 (2006). [3] A. M. H. Wong and G. V Eleftheriades, "An Optical Super-microscope for Far-field, Real-time Imaging Beyond the Diffraction Limit" Sci. Rep. 3, (2013). [4] E. T. F. Rogers, J. Lindberg, T. Roy, S. Savo, J. E. Chad, M. R. Dennis, and N. I. Zheludev, "A Super-oscillatory Lens Optical Microscope for Subwavelength Imaging," Nat. Mater. 11, 432 (2012).

We consider a model nondispersive nonlinear optical fiber channel with additive Gaussian noise at large SNR (signal-to-noise ratio) in the intermediate power region. Using Feynman path-integral technique we find the optimal input signal distribution maximizing the channel’s per-sample mutual information. The finding of the optimal input signal distribution allows us to improve previously known estimates for the channel capacity. We show that in the intermediate power regime the per-sample mutual information for the optimal input signal distribution is greater than the per-sample mutual information for the Gaussian and half-Gaussian input signal distributions.

Four–wave mixing (FWM) serves as the physical basis for various nonlinear phenomena including wavelength conversion, parametric amplification, and frequency combs. FWM on a chip has been implemented using CMOS platforms, chalcogenide glasses and III–V materials. On-chip, waveguide based stimulated FWM techniques have been mostly demonstrated using a coherent pump and coherent signal to focus on broadband spectral tuning for operation in high–speed and multi–channel wavelength division multiplexing network. Though FWM using incoherent light has the potential to provide large optical conversion efficiency, such demonstrations remain largely confined to fiber–experiments and involved narrow–band signals/idlers. Furthermore, the FWM based on a pulsed laser and a broadband incoherent source has yet to be implemented. In this work, we demonstrate integrated ultra–silicon–rich nitride parametric converters that perform wavelength conversion of a broadband incoherent source with a bandwidth of ~100nm at the -20dB level. A 500fs pulsed pump is combined with an incoherent superluminescent diode (SLD) as the signal and parametric gains between 12dB – 27dB is demonstrated as well as cascaded FWM. A 500fs pulsed laser centered at 1.555μm and an incoherent SLD with a 20dB bandwidth spanning from 1.6 – 1.7μm are used as the pump and signal respectively. The pump and signal are combined with a wavelength division multiplexer and coupled into an ultra–silicon–rich nitride waveguide with 10mm length, 700nm width and 400nm height. The waveguide is designed to have a larger nonlinear parameter of 330W^-1/m while possessing anomalous dispersion of -0.92ps^2/m, necessary for phase matched parametric conversion. At a coupled peak power of 4.6W, an idler spanning from 1.43 – 1.52μm at the -20dB level is generated. At a maximum input signal power of 0.71mW, a second idler appears at the blue side of the first generated idler because of cascaded FWM induced between pump of 1.555μm and the first idler peak of 1.48μm. At a coupled peak power of 2.8W, an idler spanning from 1.46 to 1.52μm is generated. The experimental idler bandwidth agrees well with the calculation based on degenerate FWM phase–matching condition. The broadened idler powers are calculated by integrating the energy of each signal and idler with respect to wavelength to obtain optical conversion efficiencies. The integrated idler power is 3.4dBm and 13.4dBm, corresponding to idler parametric gain of 12dB and 18dB respectively at a coupled peak power of 2.8 and 4.6W, respectively. The application of the SLD signal to a supercontinuum that is generated at a coupled peak power of 26W spectrally spanning 1.1 – 1.7μm is observed to generate an idler power of 14dBm within the wavelength range of 1.18 – 1.42μm as well as an idler conversion efficiency/gain of 27dB. Therefore, we achieved broadband wavelength conversion based on stimulated FWM using a pulsed pump and broadband incoherent signal that facilitate the spectrum spanning from 100nm, sufficient to cover parts of the E– and S–bands an representing large conversion efficiency and parametric gains of 12dB – 27dB.

The propagation of intense ultra-short optical pulses in a Kerr medium such as an optical fibre still remains a critical issue for the performance of many optical systems such as beam delivery, optical communication or pulse amplification systems. This is because the self-phase modulation (SPM) of the propagating pulse usually causes a broadening of the pulse spectrum that is typically accompanied by an oscillatory structure covering the entire frequency range. Several strategies have been proposed and successfully deployed to counteract the deleterious effects of SPM in fibre-optic systems. These include spatial or temporal scaling to reduce the impact of nonlinearity via the use of very large mode area fibres or chirped pulse amplification. A different class of approaches relies on the exploitation of the peculiar properties of parabolic shaped pulses and self-similar evolution, the use of other types of pre-shaped input pulses, and the compensation of nonlinear phase shifts with third-order dispersion. However, none of these last techniques preserves the pulse temporal duration. A simple technique to compensate the nonlinear phase due to SPM and related spectrum broadening of nanosecond or picosecond optical pulses consists in using an electro-optic phase modulator to impart the opposite phase to the pulses. This method, which emulates the use of a material with a negative nonlinear index of refraction, has proved successful in fibre-optic and free-space optical telecommunication applications using phase-shift keying systems and in the generation of high-peak-power nanosecond pulses. We have recently experimentally demonstrated that for Gaussian shaped input pulses, the use of a simple sinusoidal drive signal for the phase modulator with appropriate amplitude and frequency is sufficient to reduce the nonlinear spectrum broadening to a large degree, and to significantly enhance the spectral quality of the pulses while their temporal duration remains unaffected. In this paper, we present a comprehensive analysis of the SPM-mitigation method involving the use of a sinusoidal phase modulation. Most of the previous works are primarily experimental in nature and have not discussed the sensitivity of the technique to the initial pulse characteristics. First, we recall the concept of our method and overview our proof-of-principle experiment. Next, we derive an exact closed formula for the rms spectral width of an initially Gaussian pulse after undergoing SPM and with the corrective phase applied, which confirms the substantial reduction of the SPM-induced spectrum broadening attainable with the phase compensation. Then, we describe the impact of the initial pulse shape and duration on the effectiveness of the technique through numerical simulation of the governing equation. We show that for hyperbolic secant pulses, optimisation of the parameters of the modulating sinusoid through a scan of the amplitude-frequency space outperforms the parameter choice based on simple analytic guidelines. By varying the initial pulse duration across an order of magnitude, we highlight the significant differences in performance between pre- and post-propagation compensation schemes, and show that remarkable SPM mitigation is attainable even in the presence of non-negligible fibre dispersion.  

We report the generation of continuous-wave (cw) tunable mid-infrared (mid-IR) radiation across 4608-4694 nm with multi-tens of mW level output power using difference-frequency-generation (DFG) in the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). A 40-mm-long OP-GaP (Λ=85.1 μm) is used for DFG, pumped with a cw Tm-fiber laser and a home-built cw Yb-fiber-pumped MgO:PPLN-based optical parametric oscillator (OPO). By varying MgO:PPLN crystal temperature and simultaneously adjusting the phase-matching temperature in OP-GaP, with an input pump power of 34 W at 2010 nm and OPO idler power of >2.9 W across 3505-3557 nm, we achieved DFG tuning across 4608-4694 nm, providing >30 mW of output power across 96% of the full tuning range with 43 mW at 4608 nm. The output at 4608 nm exhibits high beam quality, with a passive power stability of 2.5% rms over 1.5 mins. The performance of the system at high pump powers, temperature acceptance bandwidth, DFG spectral characteristics, and spatial quality has been investigated.

Optical Parametric Oscillator (OPO) is a well-known solution when wide tunability in the mid-infrared is needed. A specific design called NesCOPO (Nested Cavity doubly resonant OPO) is currently integrated in the X-FLR8 portable gas analyzer from Blue Industry and Science. Thanks to its low threshold this OPO can be pumped by a micro-chip nanosecond YAG (4 kHz repetition rate and a 30 GHz bandwidth). To achieve very high resolution spectra (10 pm of resolution or better), the emitted wavelength has to be finely controlled. Commercial Wavemeter do not meet price and compactness required in the context of an affordable and portable gas analyzer. To overcome this issue, Blue first integrated an active wavelength controller using multiple tunable Fabry-Perot (FP) interferometers. The required resolution was achieved at a 10 Hz measurement rate. We now present an enhanced Wavemeter architecture, based on fixed FP etalons, that is 100 times faster and 2 times smaller. We avoid having FP ‘blind zones’ thanks to one source characteristic: the knowledge of the FSR (Free Spectral Range) of the OPO source and thus, the fact that only discrete wavelengths can be emitted. First results are displayed showing faster measurement for spectroscopic application, and potential future improvement of the device are discussed.

Plasma-based particle accelerators driven by either lasers or particle beams are an important new technology in order to reduce the large size of conventional accelerators and to minimize the construction costs. Using laser driven plasma wakefield accelerators, the synchronization between electron bunch and the ultrashort laser is crucial to obtain a stable acceleration. In order to minimize the electron bunch arrival-time jitter, the development of a new shot to shot feedback system with a time resolution of less than 1 fs is planned. As a first step, stable Terahertz pulses (THz pulses) should be performed by optical rectification of high energy femtosecond laser pulses in a nonlinear crystal. It is planed that the generated THz pulses will energy modulate the electron bunches shot to shot before the plasma to achieve the time resolution of 1fs. The selection of the nonlinear material for optical reptification is a critical aspect for the development of laser driven THz sources. In this contribution we systematically investigate the influence of the optical properties, and in particular adsorption coefficient of lithium niobate crystal as well as the theoretical description of the THz generation on the conversion efficiency of the generation of short THz pulses.

Hybrid quantum networks will be based on nodes that operate at different wavelengths, requiring quantum channel standardization via quantum frequency conversion (QFC). QFC is typically based on highly efficient sum- or difference-frequency generation in second-order nonlinear materials, such as periodically poled lithium niobate waveguides. The presence of the strong pump beam in such a nonlinear medium leads to unwanted nonlinear processes that produce noise. One of these noise processes is spontaneous Raman scattering (SRS). Typically, the pump is chosen to be the longest wavelength in the second-order nonlinear mixing process so that noise photons at the signal wavelength are produced by the less efficient anti-Stokes Raman scattering process rather than the Stokes scattering process. Since SRS is a temperature-dependent process, lowering the temperature reduces the Raman-scattered photons. We discuss the theory of temperature-dependent Raman scattering and present experimental results of the temperature dependence of dark count rates in a guided-wave QFC device.

The propagation of high peak-power beams in the atmosphere has been observed in field trials with visible-near infrared (VNIR). Longer infrared (IR) wavelengths beams have some propagation characteristics not tested in the VNIR field experiments. We identify some unique characteristics of IR ultrashort- ulse air propagation: greater transmission, much lower dispersion-induced chirp, lower sensitivity to atmospheric turbulence, and much larger critical power. We summarize the results of self-focusing theory applied to IR ultrashort pulse characteristics, apply the theory to predict the IR self-focusing distance, and show the theory is in close agreement with detailed numerical simulations including extinction and turbulence.

Dissipative soliton resonance (DSR) is an efficient way to achieve high energetic pulses without wave breaking. In fiber laser, DSR operation manifests as square pulses emission. Based on this principle, we have experimentally demonstrated pulses in the micro joule range. Experiments have been conducted using double-clad Er:Yb-doped fiber lasers in different optical configurations. In particular, we demonstrate 10 μJ DSR emission in an optimized cavity and also the possibility to observe wave breaking in DSR regime. In the latter case, harmonic mode-locking of square pulses is demonstrated.

Owing to its strong optical characteristics, graphene has emerged in the field of ultrafast lasers as a prominent saturable absorber. In this communication, we present a passively mode-locked Er:Yb doped double-clad fiber laser using a graphene deposited tapered fiber (GDTF). Averaging 20 μm of diameter with a length of 6 mm, the taper enables a strong light–graphene interaction owing to the evanescent field of the excited cladding mode. To create the saturable absorber device, graphene solution is carefully deposited via a micro syringe so that the waist of the taper is completely immersed into the aqueous solution. Then, a continuous wave laser with output power up to 95-mW centered at 1550 nm is injected into the taper. Deposition of graphene onto the taper by the optical tweezers effect started when the transmitted power dropped significantly. Afterwards, the GDTF is implemented in a fiber cavity to test its mode-locking performance. At the maximum available pump power, we obtain the 326th harmonic mode locking of soliton bunches with average output power of 520 mW.

One of very interesting phenomena under the frequency conversion appears, if incident intensity of basic wave is enough high. In this case due to self- and cross-modulation of basic wave and wave with doubled frequency a synchronous mode of laser pulses changing appears under certain condition as well as color soliton formation. For both processes the main role plays frequency modulation of the interacting waves. Therefore, investigation of the pulse chirp appearance is very important for color soliton formation. First, we investigate the phenomenon using the analytical approach without applying the basic wave energy non-depletion approximation. Based on original approach we derive the solution of Schr¨odinger equations, describing the SHG for femtosecond pulses, that describes correctly the energy conversion with propagation distance, which is much greater than the dispersion length and nonlinear length, for incident Gaussian shape (or other shape) of pulse with basic frequency. Using this solution we compare the frequency modulation of both interacting pulses for various incident temporal distribution of wave with basic frequency.

The ability of a low repetition rate pulsed-nanosecond supercontinuum source (SC) have been recently demonstrated as able to generate multiphoton images with a quality similar as those obtained with a standard titanium sapphire source. In this publication, the phenomenon involved is theoretically and experimentally studied and detailed. First, the interest of a SC source for multiphoton microscopy (MPM) is reminded and this point is illustrated with a numerical comparison of the effect of the combination of pulse duration and repetition rate of the source on the TPA of photons by a fluorophore. Then, a theoretical comparison of excitation sources used in MPM is presented. Finally, an experimental focus on the effect of the repetition rate on the image quality and the axial and lateral resolutions are highlighted. The results pave the way for simultaneous multiplex MPM.

We demonstrate broadband supercontinuum generation from 560 nm up to 2350 nm by coupling a Q-switched picosecond microchip laser at 1064 nm into a 15 μm-core step-index germanium-doped silica fiber, designed to support five spatial modes at 1064 nm. It is further shown that multiple cascaded intermodal four-wave mixing and Raman processes take place in the fiber with large frequency detuning up to 150 THz. The multimode properties of this fiber yield a number of intermodal nonlinear coupling terms and the parametric sideband wavelengths have been obtained from the phasematching condition for intermodal four-wave mixing.

Thermal and nonlinear optical characteristics are evaluated for a novel ionic liquid, BMIOMe.NTf₂, by means of the well established thermally managed eclipse Z-scan technique (EZ-scan). Nevertheless, this method still requires samples with good optical quality in order to provide a reasonable signal-noise ratio (SNR) when the material’s nonlinearity is small. Two different procedures where then introduced to improve the SNR against sample linear inhomogeneities and scattering. Both procedures are based in a subtraction of noisy background signals from the nonlinear signal of EZ-scan output. The first is applied to thermal effects and slow sample’s response, based on the perform a subtraction of the initial exposure time from the steady state signal, eliminating the linear noise. In this case, we could verify an increment of SNR from 1:2 to 40:1. The second procedure is related to fast response, e.g., arising from the electronic nonlinear polarizability. This consists in performing two sequential measurement, one with a decade of intensity higher than the first. After performing the subtraction between them, linear background suppression can be verified, with improvement of SNR to 2:1, amount about 10 times the signal value. Performing these procedures, we present a study of properties of ionic liquid BMIOMe.NTf₂. This presents a steady cumulative effect of multiple pulse absorption leading to thermal lensing as measured by the thermally managed EZ-scan technique. The photoinduced conductivity effect observed for this ionic liquid is discussed based on the observed photothermal conversion. Also a fast response corresponding to a nonlinear refractive index was also registered when the time evolution is extrapolated for short times.

Temporal cavity soliton (CS) emerges as a balance between dispersion, nonlinearity, external pump source and total losses occurring within an optical cavity. In this work, we assume the pump loss into account as the pump field propagates within the circular trajectory of the cavity. We study how the CS evolves under the effect of pump depletion. The dynamics of intra-cavity field can be evaluated numerically with the help of spatio-temporal Lugiato-Lefever equation (LLE). Here, we consider whispering gallery mode (WGM) CaF₂ resonator of radius 2.5 mm for the simulation purpose. Initial pump power has been selected such that it always remain on the lower branch of the optically bistable region under decay. A linear pump loss coefficient α_loss = 10⁻³ has been imposed on the external pump source. For this specific pump loss coefficient, we observe that generated cavity soliton undergoes in a non-uniform decay. For finding the occurrence of this transition from stable to unstable regime, phase of CS has been evaluated. A spiral pattern in the phase-space diagram dictates the formation of a stable cavity soliton. Unstable soliton regime begins when the phase becomes negative and that happens when external pump undergoes some threshold value regulated by loss coefficient.

We study different regimes of spatial-temporal pulses propagation in a waveguide under conditions of second harmonic generation. In comparison with a homogeneous medium the waveguide geometry allows us to increase the number of input parameter sets for which light bullets can be observed. We demonstrate that provided defocusing nonlinearity combined with a focusing waveguide the formation of spatial-temporal solitons is possible due to the waveguide geometry only. Stable propagation of two-component light bullets at normal dispersion is confirmed numerically.

We theoretically model a dissipative system which exhibits self-defocussing non-Kerr type of nonlinearity and numerically study the dynamics of dissipative solitons (DSs) whose evolution is governed by a complex GinzburgLandau equation (GLE). We show that, the formation of DSs are not restricted by positive nonlinearity and negative dispersion. The DSs can still be excited in normal group velocity dispersion regime, provided the nonlinearity is negative. To study the complete dynamics, we excite DSs in four different nonlinear-dispersive domain i.e., both in the Kerr and non-Kerr type medium (separated by zero nonlinearity wavelength (ZNW)) where the group-velocity dispersion may be normal or anomalous (separated by zero dispersion wavelength). For each case we modify the GLE and rewrite the dissipative system parameters of DS ansatz. We adopt semianalytic variational technique to study the overall pulse dynamics under various perturbations. The spectral and temporal evolutions of the DS induced by the perturbations due to the third-order dispersion (TOD) and higher-order nonlinearities are studied numerically in all four domain and are then compared with variational results. Our semi-analytic results match reasonably well with the numerical results and are useful for gaining physical insight into complex soliton-evolution processes. It is also observed that the frequency of dispersive wave generated due to TOD is also tailored by introducing the ZNW.

The generation of broadband terahertz radiation by optical rectification in a gradient planar waveguide is investigated. The conditions for the capture of optical and terahertz pulses and collinear propagation of their bound states are studied. The waveguide structure significantly reduces the diffraction spreading of generated terahertz pulses in comparison to a homogeneous bulk medium.

A novel technique for the measurement of low optical absorption coefficients of the massive crystal boules of an arbitrary shape is proposed. It is based on the concept of equivalent temperature of the crystal interacting with laser radiation. Optical absorption coefficient of the LBO boule was measured. The accuracy of the method was theoretically estimated.

Convectional laser-wave-communication-systems canalize only the linear momentum in time (or mutually in space) domain, therefore neglecting all the non-linear signal power related to the angular momentum and losing the related information, whilst in time-space-domain the power-information is carried by the spin-angular-momentum (SAM) the orbital-angular-momentum (OAM) and the linear-momentum (LM) related to the signals. This paper concerns with an innovative technique which uses the non-linear-power of the beam-waves-modes to canalize/extract simultaneous independent signals, in Coulomb gauge conditions and paraxial accuracy, to enable information space-time-domain-canalization with extremely large bandwidth regardless of the given frequency carrier. The paper illustrates verification tests results developed using an EM or optical laser ground-communication-system implementing a health-care-tele-assistance and patient health-care-tele-examination in data, audio and video star-link configuration using any UHF/VHF-frequency-carrier.

In this paper, we reported what we believed to be potential improved performance for a Nd:YVO4 discrete path Innoslab amplifier configuration based on a plane-plane resonator system. A 95W, 30KHz laser output was obtained with the Innoslab amplifier. The corresponding optical to optical efficiency was 28.8%. The beam quality factors of M² were 1.54 in the horizontal direction and 1.43 in the vertical direction, respectively.

Variable-free spectral range frequency comb (FC) and composite FC can be generated through dual-pumped microresonator (MR) which are very useful candidates for WDM communications. In such configurations, temporal cavity soliton (CS) rests on an oscillatory background and can exhibit enriched nonlinear dynamics. In this work, we investigate the super cavity soliton (SCS) states in MR under bi-chromatic pumping scheme. The SCS states are known to exist under the application of high pump power when the Kerr induced phase shift exceeds 2π. This leads to the observation of multi-stability and supports several exciting nonlinear states which we observe in dual-pump configurationakin to single-pump driven MR system under similar scenarios. We have performed numerical simulations of such systems based on the Ikeda formalism. We explore the possibility of optical lattice formation in dualpump MR configuration for the SCS states. We find that the optical lattice formation takes place conditionally for the case of SCSs. The analytical relation to describe the steady state of the optical lattice in the context of dual-pump driven MR is derived. We observe that the CS resting on a CW background allows the formation of an optical lattice. Even if the CS originates from chaotic MI region randomly, it gets slowly attracted to the nearest equilibrium position. However, we observe a breakdown of this optical lattice formation in case of CS existing on MI induced temporal background. Apart from indicating the caveats in the process of lattice formation with regards to the SCS states, our work will help to gain an insight into the process of the formation of cavity solitons from MI and the resulting phase of the generated solitons in the context of bi-chromatic pumping.

We propose a novel technique for measuring the surface temperature distribution of optical elements interacting with high power laser radiation. This technique is based on measuring the temperature sensitive piezoelectric resonance frequencies of nonlinear-optical crystals that are transparent at involved laser radiation wavelengths. Using small thermoresonators made of lithium niobate (LiNbO3) crystals the kinetics of the surface temperature distribution of the silica lens heated by 11W CW laser radiation at 1064 nm was measured. Modeling of the experiment results reveal the optical absorption coefficient of the lens to be 6×10^-5 cm^-1.

The high-intensity nanosecond laser pulses scattering in strongly absorbing colloidal solutions of СdSe/ZnS quantum dots has been investigated. Different types of nonlinear Tyndall scattering mechanism was revealed as a function of excitation radiation intensity. At the low laser pulses intensity (up to 15 MW/cm² ) saturation of the basic exciton transition in strongly absorbing colloidal solution of СdSe/ZnS quantum dots was observed. In this case of average laser pulses intensity (15-200 MW/cm² ) the dominant scattering mechanism is scattering on dipoles induced by the electric field and scattering on density fluctuations of the dispersed medium around bleached quantum dots. At the higher intensity (200-4000 MW/cm² ), the predominant scattering mechanism is the scattering on bubbles of gas formed around local heating centers – colloidal quantum dots.

In this research, the effect of temperature on the absorption of rubidium vapor cell D₂ line was studied by Two-photon absorption spectroscopy. The diameter and length of cylindrical rubidium vapor cell used in this research are 25.65 mm and 82.12 mm, respectively. The temperature of rubidium cell was varied from room temperature to approximately 80 °C using a peltier-thermoelctric module. The laser diode at 778 nm was used as a light source for two-photon absorption spectroscopy. The absorption spectra of rubidium D₂ hyperfine transitions were recorded in the range of 200-1100 nm .The results show that the absorption peak at high temperature is higher than that of lower temperature.

We report a pulsed optical parametric generator (OPG) and optical parametric oscillator (OPO) based on the newly developed semiconductor nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP), pumped by a Q-switched Nd:YAG laser at 25 kHz repetition rate. Using a 40-mm-long OP-GaP crystal under temperature tuning, we have generated signal and idler output tunable across 1721-1850 nm and 2504-2787 nm, respectively, with a single grating period of 15.5 μm. For a pump power of 2 W, a total output power of up to 18 mW was obtained. Transmission measurements of pump polarized along [100] axis of the OP-GaP crystal show a drop in transmission with increasing temperature. The OPG threshold increased from 0.6 W at 25 kHz to 4.7 W at 90 kHz. In the singly-resonant OPO operation, a higher idler power of 12.7 mW at 2670 nm was generated for a pump power of 2.2 W. The OPO idler power varied from 9.1 mW at 2530 nm to 7.9 mW at 2752 nm, with a highest power of 10.9 mW obtained at 2626 nm. For a fixed pump pulse energy of 88 μJ, when increasing the repetition rate from 25 kHz to 65 kHz, the OPO idler power at 2670 nm dropped from 12.3 mW to 0.7 mW. The OPG total output power exhibited a passive stability of 0.9% rms with mean values of 18.15 mW whereas the OPO idler exhibited a passive power stability of 1.2% rms with a mean value of 12.68 mW at 2670 nm.

Laser radiation limiters can be made on the basis of working substances, which have strong nonlinear effects after reaching a certain critical value (threshold limiting). Thus, it becomes possible to obtain a high transmission for a safe beam and a sharply reduced transmission for a hazardous beam. To determine the nonlinear and linear optical properties of these materials there were carried out comprehensive spectroscopic studies, experiments by Z-scan methods with an open aperture and a fixed location of the limiter. Working substances was developed which is suspension of conjugates J-type phthalocyanine dimers Zn or Mg with single-walled carbon nanotubes (SWCNTs) in water. Created conjugates can be used not only for protecting eyes and light-sensitivity elements, but for forming three-dimensional tissueengineered structures. Using conjugates J-type phthalocyanine dimers Zn and Mg with SWCNTs will increase the optical absorption in the wavelength range of laser processing by reducing the thermal effect on other substances in the composition of this structure. The Nd:YAG laser was used as the laser radiation source for generating pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape of Gaussian type. The threshold of limiting, linear and nonlinear absorption coefficients were determined by output characteristic, that was obtained by fixed location of the limiter. Created working substances have values of the following order: linear absorption coefficient ~ 3 cm^-1 for layer of 0.2 cm thickness, low limiting threshold ~ 1 MW·cm^-2 and high value of the nonlinear absorption coefficient ~ 550 cm GW^-1 . Knowing the nonlinear optical parameters, Z-scan data with an open aperture can be calculated for comparison with experimental data.

We report a stable and compact CW THz source, based on fiber coupled photoconducting antennas pumped with monolithically integrated dual mode distributed Bragg reflector semiconductor laser diode (DBR LD). Two DBR lasers are monolithically integrated on single substrate with a Y-shaped waveguide structure and made to emit two wavelengths simultaneously at 785nm center wavelength, with stable spectral wavelength difference of 0.6 nm. Ion implanted GaAs log spiral antennas are used to generate and detect THz radiation in homodyne set up. The detected THz frequency corresponds well to the value obtained for the optical beat frequency of the two modes. We analyze the use of this system for simple THz non-destructive testing applications like moisture measurement on leaves and different papers. The results obtained demonstrate the feasibility of a compact, simple, and cost-efficient CW THz system which could gain application in industrial non-destructive testing measurements.

The polarization entangled state produced via spontaneous parametric downconversion (SPDC) has relativephase maps in frequency and momentum domains which give an almost complete picture about the distinguishability and purity loss in the conjugate time and space domains. We demonstrate experimentally the tunable compensation of directional relative-phase profile for entangled photons generated by two cascaded / crossed crystals and captured over ultra-wide spatial window. We use a phase-only spatial light modulator (SLM) programmable via a personal computer to flatten (or correct for) the spatial relative-phase profile and also to add on-demand spatial phase profile. A fast, yet accurate, technique is introduced for frequent relative-phase measurements based on the tilt angle of a quarter wave plate (QWP) acting on the diagonally polarized pump beam and nulling the relative-phase of the entangled state at that direction. Our experimental measurements verify previous theoretical models for tunable compensation of the polarization two-photon state produced by the cascaded crystals arrangement.

In the present paper we analyze peculiarities of CdSe/ZnS colloidal quantum dots (QDs) nonlinear optical properties due to the one- and two-photon excitation of basic electron-hole (exciton) transition by means of ultra-short laser pulses. We also revealed the main mechanisms of optical nonlinearities which result in the laser beam divergency. To find out the role of quantum dots, two different types of solvents were investigated - toluene or hexane based colloidal solutions.

We have investigated the nonlinear absorption of CdSe-based nanoplatelets (NPLs) with different thicknesses of shell in the case of resonant one-photon stationary excitation of exciton transitions by nanosecond pulses of mode-locked Nd:YAP laser. Decrease in absorption at the wavelength of whether light hole – electron and heavy hole – electron exciton transitions was revealed. Induced changing of both absorption doublet components was attributed to phase space filling effect and exciton energy conversion mechanism.

We report the first experimental realization of spatial soliton formation by the Gaussian beam at 632.8 nm in the azobenzene liquid crystal (LC) layer with planar orientation of LC director. By appropriate anti-parallel rubbing of alignment layers on the upper and lower substrates of the cell LC molecules were oriented along the glass substrates nearly perpendicular to the input window of the cell with a small pre-tilt angle of ~2.6⁰ relative to the beam propagation Z direction. The strong self-focusing effect and soliton formation for laser beam with vertical Y-polarization and beam diffraction for horizontal X-polarization have been observed in the absence of an external electric field. The physical model is considered which implies that the interaction of azobenzene molecules with a laser field is much stronger due to a larger coefficient of orientation nonlinearity compared to other LCs, as well as they are not rigidly anchored to the cell boundary. Thus the molecule alignment can be readily varied by a low-power laser field even for a small pre-tilt angle of molecules which leads to the refractive index change and beam self-focusing regime. The numerical integration of the propagation equation for spatial solitons describes the experimental data very well.

In this paper, we proposed a multipurpose graphene all-optical sensor based on the nonlinear effect in a multimode interference (MMI) coupler. The use of a graphene as a core for this device is because of its high optical nonlinearity value and thin layer which makes its bandgap relatively small. Graphene also has a lot of great characteristics to be used as sensor material such as high thermal and electric conductivity, light yet durable and also almost transparent due to its being a single layer atom. The graphene will be sandwiched with a substrate that have a varying value of refractive index. By changing the refractive value of the substrate, an external wave will interact with the input waveguide thus lead to a change in the intensity of the output waveguide which will be analysis for the sensor output. The result shows the high distinguished changes on modal expansion and output distribution in various refractive indices of surrounding layer.

In this paper we report the results of studied nonlinear optical properties of DMABI-Ph6 in form of solutions with chloroform as solvent and guest-host thin films with poly(methyl methacrylate) as host material. We implemented the Zscan method for studies of Kerr and two-photon absorption of selected material. During experimental measurements we used 1064 nm Nd:YAG laser with 30 ps pulse duration and 10 Hz repetition rate. From acquired values of Kerr coefficients we calculated values for real part of third-order susceptibility, as well as second-order hyperpolarizability. Acquired data for DMABI-Ph6 were compared with data for other ABI derivatives studied previously to describe how different donor and acceptor groups influence third-order nonlinear optical properties.

Short THz pulses can be generated by focusing an ultrashort laser pulse and its second harmonic simultaneously in ambient air and generating plasma. The process is efficient in the right circumstances, but sensitive to the relative phase between the two pulses and the initial group delay dispersion (GDD) of the fundamental beam. Previously it was found that zero initial dispersion and π/2 relative phase is the optimal for most cases. In this work, the connection between the nonlinear crystal thickness and the spectral phase properties has been also studied for THz generation. It has been found there are conditions where the THz spectral bandwidth can by continuously tune in the function of the GDD value. It has been also found that the optimal crystal thickness strongly varies with the laser energy, hence with the peak intensity.

With the development of laser technology (for example, widespread use of diode pumping), the availability of powerful radiation sources is rising, which leads to an increase in demand for devices controlling powerful laser irradiation. The KGd(WO₄)₂ (short: KGW) crystal is one of the most famous due to a very high threshold of laser damage: up to 180 GW/cm² for τ = 20 ns pulses [1]. It is widely used in laser technics as lasing material. It was shown it has rather good acousto-optical properties, as well as the group of double potassium rare-earth tungstates KRE(WO₄)_2, where RE = Yb, Lu, and Y. It has been demonstrated for the first time that their AO figure of merit M₂ is comparable with that of LiNbO₃ and better than M₂ of SiO₂. Moreover, these monoclinic crystals are optically biaxial, transparent in visible and infra-red ranges (0.4-5.5 μm), and demonstrate significant anisotropy.

Stimulated low frequency Raman scattering (SLFRS) in submicron single-crystal diamond films (SCD) with a graphitized layer built-in is investigated. The value of SLFRS frequency shift lies in gigahertz range (8.4-9.3 GHz) and shows the morphological dependence (inverse dependence on the thicknesses of SCD layers). Experimentally estimated SLFRS conversion efficiency and threshold evidence about the coherent phonon mode excitation in submicron SCDs as a result of nonlinear interaction of high-power laser wave with an eigen vibration of nanosized graphitized layer built-in.

Model of fibre ring laser with an intracavity interferometer mode-locked through dissipative four-wave mixing is considered. The conditions required for mode locking are formulated. Characteristics of numerically simulated pulse trains at different repetition rates and gain levels are obtained. Admissible ranges of gain and repetition rate, for which successful mode locking is possible, are found. It is shown that for normal dispersion cavity the laser can generate a train of dark solitons with an energy much greater than that in the case of cavity with anomalous dispersion.

In digital holographic microscopy, wavefront aberrations suppressions techniques are very matured from the perspective of the reference wave, i.e. aberrations was suppressed by numerically manipulating the reference wave. There are techniques that deal with the noises that arise from the object arm, but were mostly numerical procedure in the reconstruction stage. We found out that a better approach would be suppressing the noises, particular scattering noise from the object arm, prior to the recording stage via phase conjugation technique. By using phase conjugation technique, it is possible to trace back to the object plane where scattering is minimum; hence, achieving optical noise suppression prior to the recording stage.

Stimulated Raman scattering microscopy allows vibrational contrast mechanism for imaging with high spectral and spatial resolution along with three-dimensional sectioning. In this paper, the implementation of a Stimulated Raman Scattering microscope (SRSM), obtained by the integration of a femtosecond SRS spectroscopy set-up with an optical microscope equipped with a scanning unit, is described. Femtosecond Stimulated Raman Scattering microscope is equipped with three femtosecond laser sources: a Ti:Sapphire (Ti:Sa), a synchronized optical parametric oscillator (SOPO) and a frequency converters for ultrafast lasers, i.e. a second harmonic generator optimized for the SOPO. The proposed implementation allows to cover all the regions of Raman spectra, taking advantage of two different laser combinations. The first, Ti:Sa and SHG laser combination can cover in SRL modality the fingerprint region (500 − 1700 cm⁻¹ ) and the silent region. The second, Ti:Sa and OPO, can cover the C-H region or O−H region (2800 − 3200 cm⁻¹ ) in SRG modality. In order to demonstrate its successful realization Stimulated Raman Gain (SRG) and Stimulated Raman Losses (SRL) images of polystyrene beads are reported and discussed.

The monocrystalline Bi₂Te_3-xSex and Bi_2-xSb_xTe_3-ySey films of various compositions and thickness were synthesized by MOCVD on sapphire substrates¹ . The transmission of laser pulses (duration τ≈35 ps, wavelength λ=1064 nm) through the films was measured as a function of radiation intensity with the aim to optimize functionality of these films deposited on different substrates as saturable absorbers for the application in passively mode-locked 1-2 μm wavelength lasers. There was investigated nonlinear absorption of films of various compositions and thickness with measured saturation intensity ≈ 20 MW/cm² for Bi₂Te_3-xSe_x and 45 MW/cm² for Bi_2-xSb_xTe_3-ySe_y. Data obtained can be explained by the classical nonlinearity – phase space filling in a quantum well² . As it was established earlier³ , the semiconductor conductivity type of the film without light interaction can be changed to the metallic conductivity type in the case of light interaction with the film, that is strongly nonlinear depends on the light intensity. At the same time, with a metallic conductivity type, the film becomes vulnerable for high light intensity.