UV and Higher Energy Photonics: From Materials to Applications 2024

In this work, we probe optoelectronic processes at a band edge in hBN by means of optical imaging and spectroscopy at deep ultraviolet frequencies. Our laser excitation spectroscopy shows that strong radiative recombination and carrier excitation processes originate from the pristine structure and the stacking faults in hBN. We further demonstrate prominent electroluminescence and photocurrent generation from hBN by fabricating vdW heterostructures with graphene electrodes.

The capability of lighting is essential for modern society with an exponential increase of the lighting energy consumption versus the GPD per capita. White Light Emitting Device (LED) based on solid state lighting allows for a tremendous energy saving typically around of 70% as to compared with incandescent lighting and therefore constitutes a real breakthrough in terms of low consumption technology. The life span analysis is also very positive for LEDs. The remaining issue lies in the end life of the component and recycling. We will show during this presentation based on a comprehensive approach developed within a 4 years R&D research project called RECYLED, how this issue can be solved by considering alternative disassembling technique based on energy pulse fragmentation. The later technology applied to LED bulbs allows for a recycling rate of more than 80% far above the commonly used crushing technology in recycling. The end of the presentation will be devoted to an even more eco-friendly approach based on ZnO as a rare-earth free white emission and potentially easy soluble LED material.

Microalbuminuria can be detected using urine protein test strips. However, this approach can only be used for qualitative analysis. Moreover, despite the high accuracy of commercial instruments for the clinical detection albumin, these devices is not suitable to be used for home detection due to their bulky size and additional labeling steps. Therefore, our study sought to develop a label-free method by five types of miniaturized detector devices (MDDs) for the detection of HSA and BSA. Using flip-chip (FC) ultraviolet-C (UV–C) light-emitting diodes (FC UVC LEDs) as a light source. The most accurate of the five tested MDDs consisted of a FC UVC LED light source, optical quartz fiber (OQF), a holder, and two quartz lenses (QL1 and QL2) with a light divergence angle of 1.8°. When detecting human serum albumin (HSA) and bovine serum albumin (BSA)at concentrations ranging from 0.01 to 4 mg/mL, the coefficients of determination (R2) of absorbance and concentration at 279 nm were 0.9969 and 0.9972, respectively, and the limits of detection (LOD) of BSA and HSA were 0.24 mg/mL and 0.25 mg/mL, respectively.

In this talk, I will introduce an electroluminescent (EL) device that overcomes the Schottky barrier for efficient UV to IR emission based on a metal-oxide-semiconductor (MOS) capacitor structure. It combines a MOS capacitor with a carbon nanotube network and transition-metal dichalcogenide monolayers. By applying AC voltage, it emits across a wide range of bandgaps, bypassing the need for energy level alignment. This device shows minimal dependence on Schottky barrier height, achieving bright EL in materials with varied thicknesses or mobilities. This AC EL via MOS capacitor device offers a new avenue for UV light sources and optoelectronic applications.

GaN hexagonal microrod has been used for generating exciton-polaritons at room temperature. When a GaN microrod is excited by a laser, various photonic modes and polariton modes can be simultaneously generated. Here, we compared the optical characteristics of the Fabry-Perot mode and the whispering gallery mode generated in a GaN microrod and found a method for extracting a specific mode among various photonic modes in a GaN hexagonal microrod. Excitation spot size dependence of angle-resolved photoluminescence is carried out to investigate the tendency of photonic and polaritonic modes.

The effect of size on transitions between defect-induced magnetic phases in ZnO nanowires is investigated in a temperature range from 1.8 K to 300 K using calorimetric measurements of specific heat. The obtained results demonstrated interesting magnetic phenomena in unusual magnetic nanomaterials. At low temperatures, we observed isolated magnetic ions in nanowires of diameters 45-50 nm, and ferromagnetic phases in nanowires of diameters 85-100 nm. However, at higher temperatures, we observed multiple transitions between superparamagnetic phases in the thinner nanowires and multiple transitions between spin-glass phases in the thicker nanowires.

This presentation enhances the understanding of the underlying mechanism behind the generation of higher harmonics from electronic self-phase modulation which is driven by the Electric Field E(t) of the optical, NIR, and MIR femtosecond light pulses to produce attosecond laser pulses and providing the direction to produce zeptosecond laser pulses. The HHG arises from driving the phase of the electric field, E(t) by itself to create HHG in form of odd Bessel functions in time of odd harmonics driven by laser pulse from the nonlinear refractive index of Kerr media, n2 (χ3) and extending to even HHG from n1 (χ2).The three characteristic features of HHG spectrum are initial decreasing harmonics, a plateau region of HHG, and cutoff frequency. We show theoretically in the EM Kerr electronic self-phase modulation (ESPM) model that the distinctive features of HHG arise mainly from the changes in the phase of the E(t) wave driven by the envelope of the laser pulse causing the cosine of the cosine squared for χ3 and the cosine of the cosine for χ2 in time. The outcomes are Bessel function expansions producing odd harmonics for n2 (χ3) and even harmonics for n1 (χ2).

Ensuring the safety of food remains a critical and persistent challenge globally. Each year around the world, nearly 600 million individuals fall ill from consuming contaminated food, leading to around 420,000 fatalities. Separately, fungal contaminations pose a major global challenge to food security. These issues also cause enormous economic burdens. This presentation discusses the potential of utilizing ultraviolet-light systems to tackle both issues, along with opportunities for further enhancement.

Ptychography as a means of lensless imaging is used in wafer metrology applications using Extreme Ultraviolet (EUV) light, where high quality optics are scarce. To obtain sufficient diffraction intensity, reflection geometries with shallow (ca. 20 degrees) grazing incidence angles are used, which require re-sampling the diffraction data in a process called tilted plane correction (TPC). The tilt angle used for TPC is currently obtained through either experimentally tricky calibration, manual estimation based on diffraction pattern symmetry, or numerical optimization, each with their own drawbacks. In this work we offer an alternative numerical optimization approach to TPC, where we use the flexibility offered by our Automatic Differentiation (AD)-based Ptychography approach to include the data resampling into the forward model to learn the tilt angle. We demonstrate fast convergence of the approach across a range of incidence angles on simulated and experimental data obtained on a high-harmonic generation (HHG) beamline.

Ultrawide-band-gap (UWBG) semiconductors have attracted much attention for deep-ultraviolet (DUV) photonics and high-power electronics. However, the physical understanding is in infancy, preventing the potential capacities of UWBG semiconductors to be drawn out. Therefore, the electronic and optical properties should be fully elucidated using such as DUV spectroscopy. Whereupon, another obstacle stands that DUV spectroscopy itself is immature. In the presentation, we therefore talk about the development of DUV scanning near-field optical microscope and the optoelectronic properties of AlN studied by DUV luminescence spectroscopy.

Nanophotonic structures are crucial for controlling light at scales smaller than its wavelength. While designing for linear polarization is straightforward, creating nanostructures for helically structured light, like circularly polarized light and optical vortices, is challenging due to complex near-field chiral interactions with matters in helical electromagnetic fields. In this presentation, we apply topology optimization, an intelligent design approach, to create 3D nanogap antenna structures with outstanding chiroptical functionalities. With these structures, we demonstrate giant chiral dissymmetry (up to g = 1.70), polarization conversion around the Poincaré sphere, and circularly polarized far-field emission from a linear dipole embedded within the gap. Additionally, our in-depth analysis reveals a physical connection between the flow of spin angular momentum of light within the nanostructure and the local density of optical chirality. The insight, combined with our developed structures, offers a fresh perspective for engineering chiral nanophotonic structures and finds applications in circular dichroism spectroscopy in UV.

We propose a method for separating fluorescence and Raman spectra during photobleaching process. Since the spectral decomposition is based on many spectral data with different fluorescence intensities, the fluorescence and Raman spectra are successfully resolved. As a result, the method effectively reduces the fluorescence interference in Raman spectral measurements. The method was applied to highly fluorescent samples and Raman spectra measured using UV, visible, and near-infrared lasers were compared.

This talk will consider the future of metal halide perovskite (MHP) photovoltaic (PV) technologies as photovoltaic deployment reaches the terawatt scale. The requirements for significantly increasing PV deployment beyond current rates and what the implications are for technologies attempting to meet this challenge will be addressed. In particular how issues of CO2 impacts and sustainability inform near and longer-term research development and deployment goals for MHP enabled PV will be discussed. To facilitate this, an overview of current state of the art results for MHP based single junction, and multi-junctions in all-perovskite or hybrid configurations with other PV technologies will be presented. This will also include examination of performance of MHP-PVs along both efficiency and reliability axes for not only cells but also modules placed in context of the success of technologies that are currently widely deployed.

The recent advent of robust, refractory (having a high melting point and chemical stability at temperatures above 2000°C) photonic materials such as plasmonic ceramics, specifically, transition metal nitrides (TMNs), MXenes and transparent conducting oxides (TCOs) is currently driving the development of durable, compact, chip-compatible devices for sustainable energy, harsh-environment sensing, defense and intelligence, information technology, aerospace, chemical and oil & gas industries. These materials offer high-temperature and chemical stability, great tailorability of their optical properties, strong plasmonic behavior, optical nonlinearities, and high photothermal conversion efficiencies. This lecture will discuss advanced machine-learning-assisted photonic designs, materials optimization, and fabrication approaches for the development of efficient thermophotovoltaic (TPV) systems, lightsail spacecrafts, and high-T sensors utilizing TMN metasurfaces. We also explore the potential of TMNs (titanium nitride, zirconium nitride) and TCOs for switchable photonics, high-harmonic-based XUV generation, refractory metasurfaces for energy conversion, high-power applications, photodynamic therapy and photochemistry/photocatalysis. The development of environmentally-friendly, large-scale fabrication techniques will be discussed, and the emphasis will be put on novel machine-learning-driven design frameworks that leverage the emerging quantum solvers for meta-device optimization and bridge the areas of materials engineering, photonic design, and quantum technologies.

DUV light is of great importance in applications, including nanolithography, material science, and biology. Metasurfaces, comprising well-engineered nanoresonators, promise to improve DUV technologies due to their capability to manipulate light at the nanoscale. We present metasurfaces showing high-quality-factor resonance (high-Q) in the DUV range. We combined low-loss dielectric materials, resonance mode associated with the quasi-bound state in the continuum, and various device schemes to realize the DUV high-Q metasurfaces. We demonstrate metasurfaces with functionalities including imaging-based biosensing and high-Q optical charity. Fabrication and characterization of the high-Q metasurface will be reported. This work provides a platform to advance DUV nanophotonics in sensing, quantum optics, and nonlinear optics.

Recently, we achieved highly sensitive autofluorescence imaging of living HeLa cells using deep-UV SPR with the Kretschmann-Raether configuration. A buffer solution, such as N-2-hydroxyethylpiperazine-N-ethanesulfonic acid (HEPES), is essential for observing living cells. Therefore, the refractive index of specimen layer is higher than that of the atmosphere. The commonly used quartz prism, which is generally used for exciting deep-UV SPR in the Kretschmann configuration, is not sufficient under aqueous conditions. In our research, we employed a high-refractive index prism made of sapphire. The deep-UV SPR excitation of an aluminum thin film through a sapphire prism was investigated theoretically and experimentally, revealing a 2.8-fold increase in fluorescence intensities. Deep-UV SPR enhanced the autofluorescence of cell structures, with yeast cells exhibiting particularly high sensitivity. Consequently, for water-immersed specimens, the sapphire prism-based Kretschmann configuration successfully excited SPR in the deep-UV.

Therapeutic drug monitoring (TDM) enables individually optimized antibiotic levels for best efficacy. Deep-UV Raman spectroscopy was proven highly promising in antibiotic sensing for TDM. It is suitable for monitoring low-concentrated active ingredients in complex environments like body fluids, with detection limits as low as one-digit µM or mg/mL.

This study presents a biomolecule sensor utilizing ultraviolet plasmonic-enhanced native fluorescence, enhancing sensitivity and selectivity for detecting neurotransmitters (NTs). NTs, like monoamines, fluoresce weakly in the UV range. Plasmonic nanostructures, including aluminum hole arrays and corrosion-modified magnesium alloy, amplify UV fluorescence, and this biosensor improves NT detection, which is critical for understanding neurological disorders. Traditional methods lack multi-NT probing and molecule differentiation. Tested neurotransmitters include Tryptophan, Dopamine, and Norepinephrine, and DOPAC. Corrosion boosts fluorescence by 5.45 times in magnesium alloys. Multi-layered Silica microspheres increase sensitivity in comparison with the monolayer. This research highlights UV plasmonic-enhanced fluorescence's potential for distinguishing similar NT structures.

Germanium is typically used for solid-state electronics, fiber optics, and infrared applications, due to its semiconducting behavior at optical and infrared wavelengths. In contrast, here we show that the germanium displays a metallic nature and supports propagating surface plasmons in the deep ultraviolet (DUV) wavelengths, which is typically not possible to achieve with conventional plasmonic metals such as gold, silver, and aluminum. We measure the photonic band spectrum and distinguish the plasmonic excitation modes: bulk plasmons, surface plasmons, and Cherenkov radiation using momentum-resolved electron energy loss spectroscopy. The observed spectrum is validated through electrodynamic electron energy loss theory and first-principles calculations. In the DUV regime, intraband transitions of valence electrons dominate over the interband transitions, resulting in the observed highly dispersive surface plasmons. We further employ these surface plasmons in germanium to design a DUV radiation source based on the Smith-Purcell effect. Our work opens a new frontier of DUV plasmonics to enable the development of DUV devices such as detectors, and light sources based on germanium.

Low-temperature microplasmas, efficient sources of ions, electrons, and photons, particularly from microcavity plasma arrays, offer unprecedented performance in photonics. This paper reports recent advancements across three key areas: precise timekeeping, achieved through integrating microplasma mercury ion lamps into miniature clock systems with exceptional stability; uniform and high-fluence photon generation for VUV photolithography and nanopatterning, enabling selective surface modification and low temperature dielectric depositions at nano/micro scales; and deep UV (Far UV-C) excimer emission from microplasma lamps, utilized in preventing airborne as well as foodborne pathogen transmission. Far UV-C's safety for human exposure presents potential for indoor disinfection, including wearable devices, shaping biothreat prevention strategies.

With the aim of EUV imaging of nanostructures, a table-top EUV beamline has been constructed, for which the concept of lensless imaging, also known as ptychography, has been developed. The beamline is built around a high-harmonic generation (HHG) source. The coherent quasi-monochromatic EUV light is focused on the sample by an ellipsoidal mirror. Since our application is mainly directed towards wafer metrology for lithography, we adhere to a reflection set-up: the EUV light is scattered by the nanostructures at the surface of the sample, and is reflected towards a camera, where a far-field diffraction pattern is recorded. A data-set comprising a multitude of these diffraction patterns is generated for partially overlapping positions of the focused probe on the sample. Such a data-set provides the necessary redundancy for phase retrieval of the complex-valued field of the sample. Our ptychography algorithms have been developed within an automatic differentiation framework. The multiple challenges from concept and design towards experiment and application will be addressed.

This research explores advances in the fabrication of Josephson junctions, crucial devices in superconducting quantum circuits. Our previous work has successfully fabricated these on a 12-inch substrate using an ArF immersion lithography. To enable future large-scale production, we are moving towards sputtering and dry etching techniques. After initial successful tests on a 4-inch substrate, we have now verified this process on 12-inch substrate fabrication equipment, marking significant progress despite the challenges we have faced.

Deep UV Raman spectroscopy is an extremely powerful technique for biosensing. Recently we advanced our photonic setup (laser techniques, optical hollow core fibers, etc.) for highly sensitive and selective monitoring of antibiotics in body fluids and the investigation of antimalarial active agents. We are also working of highly frequency resolved deep UV Raman spectroscopic techniques for the investigation of weak biomolecular interactions.

Complex materials inherently have complex spectroscopic signatures, limiting the use of Raman spectroscopy. We show resonance Raman for 3 complex systems to identify the presence of a moiety, and use its resonantly enhanced Raman spectra to identify molecular modifications. The large enhancement makes the Raman signal dominated by the resonant molecules. We show that heme still attached to globin remnants still exists in (complex) soft tissue extracted from B. canadensis and T. rex, but the heme outer ring has been damaged. Further, evidence of goethite on the heme still attached to the globin remnants suggests preservation modes. Modern analogs show similar trends. We separately show that methylated cytosine can be distinguished from un-methylated cytosine using resonance Raman with state-of-the-art sensitivity. Finally, phonon-allowed resonance excitation in PARes-Raman on benzene produces Raman signal gain of 3500x with an excitation wavelength change of 0.01 nm. This signal gain and narrow linewidth represents a further step to separately analyze chemical moieties in complex materials w/o sacrificing signal level but still providing Raman spectral vibration information.

The depletion of natural resources today necessitates a reevaluation of technological development, considering both material abundance and energy-efficient processes while maintaining device efficiency. In this context, SrSnO3 emerges as a superior candidate, this material's abundance, non-toxicity, and cost-effectiveness, along with the tunable bandgap, the stability and durability underscore its potential in developing environmentally friendly and sustainable UV technologies. In this research, The synthesis of homogeneous, green, crack-free SrSnO3 thin films using sol-gel was achieved. XRD measurements confirmed the purity of the perovskite phase. The films presented 80% of transparency in the visible range with a UV absorption around 300nm. The efficiency of the material was further explored by layering the doped perovskite on Silcon to create a hybrid device and initial electrical properties will be discussed. This work contributes to the ongoing efforts to develop sustainable and efficient materials for UV optoelectronic devices and underscores the pivotal role of advanced material synthesis techniques in achieving this goal.

When an intense laser interacts with a gas of atoms, high-order harmonics are generated. In the time domain, this radiation forms a train of extremely short light pulses, of the order of 100 attoseconds. Attosecond pulses allow the study of the dynamics of electrons in atoms and molecules, using pump-probe techniques. This presentation will highlight some of the key steps of the field of attosecond science.