This PDF file contains the front matter associated with SPIE Proceedings Volume 7115, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

A simple scheme for efficient generation of mid-IR laser radiation is reported. Using a 50 W thulium fibre laser to pump a Q-switched Ho:YAG laser 27.3 W of average output power is achieved with an M² of 1.5 (optical to optical conversion efficiency 65%) at a wavelength of 2.1 μm. The holmium laser is used to pump a ZGP OPO generating 12.6 W of average output power in the 3-5 μm waveband (optical to optical conversion efficiency 52%) with a worst case M² of 2.7. These efficiencies were maintained at 25% and 50% duty cycle operation.

The advent of non-linear photonic crystal fibres with engineered optical properties has enabled the production of compact high-brightness super-continuum sources with a spectral power density in excess of 1 mW/nm throughout the visible and near-infrared spectral regions. Such sources have intrinsically good beam quality and, when properly collimated, the various spectral components propagate in a co-linear fashion, thus retaining spectral fidelity along the beam path. These properties are ideal for an active hyper-spectral remote sensing system. We report the construction and testing of a white light transceiver for measurement of the spectral reflectivity of remote targets. The transmission section of the transceiver comprises a commercial white light source with apochromatic optics to ensure simultaneous collimation at all wavelengths. The receiver section comprises a telescope coupled to a fibre-optic visible band spectrometer. A portion of the received light is directed onto a camera to facilitate accurate pointing of the system. The transceiver has been used to measure the spectral reflection from both diffuse and retro-reflecting targets at an outdoor range. The spectral return from retro-reflective targets was successfully measured at ranges up to 1.2 km. For diffuse targets, the useful range was limited to a few hundred metres, beyond which the signal was dominated by ambient daylight. The propagation of the white light beam along the 1.2 km has been studied. The fidelity of measured spectra was affected by atmospheric turbulence which caused the beam to break up into a time-varying pattern of coloured regions. This effect imposed a lower limit on the integration time required to measure individual spectra, independent of the signal to noise ratio.

790nm-pumped Tm-doped fibre lasers provide a number of distinct benefits for integration into next generation DIRCM systems. Incorporation of Tm-doped fibre technology into mid-IR laser systems has been demonstrated in two main architectures to date; in early works the fibre laser was used as a low quantum defect pump source for Q-switched solidstate holmium laser which was subsequently shifted to the mid-IR using a ZnGeP₂ OPO [1] and more recently, a pulsed fibre laser systems was used for directly pumping the OPO [2]. He we present two fibre laser systems for integration into DIRCM systems. Firstly we present a 70W MOPA system (pump power limited) operating at 1908nm with 53% slope efficiency from the amplifier stage for pumping Ho:YAG. Secondly we present a pulsed fibre laser system producing over 4kW peak power at 1910nm using all single-mode fibres.

CASAM (Civil Aircraft Security Against Manpads) is a Framework Program 6 (FP 6) Project launched by the European Commission, DG Research-Aeronautics, binding together a group of 18 companies and research institutions from majors to SMEs. The global objective of the CASAM Project is to design, build, test and validate on ground a closed-loop laser-based DIRCM (Directed IR Countermeasure) equipment for jamming an infrared guided missile fired against a commercial airliner. The broad expertise of the CASAM team allows to address all technical, financial and legal matters dealing with the challenging topic of protecting civilian aircrafts against MANPADS. This paper reviews the main aspects of the projects.

We report on the development and characteristics of infrared semiconductor lasers as compact and robust light sources for Directed Infrared Countermeasures (DIRCM). The short-wavelength side of the 2-5 μm wavelength band of interest can be covered by GaSb-based optically pumped semiconductor disk lasers (OPSDLs), delivering a continuous-wave (cw) or temporally modulated multiple-Watt output with a high beam quality (M²<3). For the 3.7-5 μm wavelength range InP-based quantum cascade (QC) lasers are the best suited semiconductor laser source, delivering several hundreds of mW of average output power in a nearly diffraction limited output beam (M²<2). Further up-scaling of the output power can be achieved for OPSDLs by intra-cavity coupling of several semiconductor chips as gain elements in a multiple-disk cavity arrangement. For a 2.3 µm emitting dual-disk OPSDL, a doubling of the maximum roomtemperature output power compared to that of a comparable single-chip OPSDL has been demonstrated. For QC lasers power scaling by beam-quality-preserving beam combining has been demonstrated via polarization coupling of the output beams of two individual QC lasers, yielding a coupling efficiency of 82%.

SELEX Galileo has been involved in the development, manufacture and support of high performance electro-optic pointing and stabilisation systems for over forty years. The Company currently supplies the pointer/trackers for the AN/AAQ-24(V) NEMESIS DIRCM system, for which over 1,000 combat-proven units have been produced and deployed in the US, the UK and other nations. In 2007, SELEX Galileo embarked on an internally funded programme to develop ECLIPSE, a new advanced, lightweight, low-cost IRCM pointer/tracker, exploiting the extensive knowledge and experience gained from previous targeting and IRCM programmes. The ECLIPSE design is centred on a low inertia, two-axis servo mechanism with a strap-down inertial sensor and advanced sightline control algorithms, allowing effective tracking through the nadir and providing superior sightline performance. The programme involved the production of three demonstrator units in 2007, and two pre-production units in 2008. The demonstrator units were first trialled as part of a NEMESIS DIRCM system in late 2007, and in April 2008 100% success was achieved in jamming live-fire demonstrations. Helicopter installation and ground testing of a UK only trials system is complete, initial flight testing has just begun, and the airborne test and evaluation scheduled for late summer 2008 will bring the ECLIPSE System to technology readiness to level 7 (TRL7). This paper describes the Eclipse performance demonstrated to date.

Laser beam propagation through adverse turbulent environments such as the region close to a jet engine exhaust need to be studied in order to predict performance degradations on airborne laser systems. The turbulent plume region may introduce severe perturbations which accumulate and cause beam degradation in terms of beam wander, intensity scintillations and beam broadening at longer ranges. Applications of interest with respect to laser beam propagation in jet engine plume environments include e.g. directed infrared countermeasures (DIRCM) and active imaging. By characterising and evaluating the perturbation effects schemes for compensation or avoiding performance degradation can be devised. The turbulence effects in the plume region occur by mixing of hot exhaust flow from the jet engine with surrounding ambient air causing spatial and temporal fluctuations in the refractive index. In comparison to atmospheric turbulence considerably shorter outer- and inner scales have been observed. Typical values of the structure constant within the plume region range from 10^-10 to 10^-9 m^-2/3 making the turbulence several order in magnitude stronger in contrast to propagation through the atmosphere. Of importance in characterisation of the jet engine plume with respect to laser beam propagation are turbulent length scales, the extent of the turbid region, variation of the structure constant and temporal flow properties. In this paper reported experimental results and modelling approaches aimed for predicting laser beam propagation degradation in jet engine plume regions are reviewed. The results will be discussed in perspective of system performance.

Optical radiation passing through compressible turbulent shear layer is distorted due to fluctuations in the index of refraction. Most of the known data comes from measurement of the optical phase change. Knowledge of the fluctuating density field within the shear layer enables us to calculate the optical distortions. In the present work, a series of models are presented with different type of complexity. All the expressions presented are dependent on the turbulent kinetic energy and dissipation rate calculated by CFD codes. Calculations based on the models are compared with available experimental results. Some examples of application to aero-optics are given.

Airplane based laser systems for DIRCM, active imaging and communication are important applications attracting considerable interest. The performance of these systems in directions where the laser beam points close to or through the exhaust plume from the jet engines may be severely reduced. A trial to study these phenomena using a downscaled jet-engine test rig was carried out. The results on propagation of laser beams along and across the plume from these trials are presented. For laser beams propagation along the engine axis an OPO based source producing co-propagating laser beams at 1.52 and 3.56 μm was used. The beams were projected on a screen and imaged with separate IR cameras to study beam wander and spot degradation. Propagation across the plume was studied with a 532 nm laser projected on a screen and imaged by a high speed camera. The engine thrust and the distance between the engine nozzle and the laser beams were varied to study the effects of changing conditions. Scaling to full size engines and performance implications for DIRCM is discussed.

Airborne laser countermeasure applications (DIRCM) are hampered by the turbulence of jet engine exhaust. The effects of this source of perturbation on optical propagation have still to be documented and analyzed in order to get a better insight into the different mechanisms of the plume perturbations and also to validate CFD/LES codes. For that purpose, wave front sensing has been used as a non-intrusive optical technique to provide unsteady and turbulent optical measurements through a plume of a jet engine installed at a fixed point on the ground. The experiment has been implemented in October 2007 along with other optical measuring techniques at Volvo Aero Corporation (Trollhättan, Sweden). This study is part of a European research programme dealing with DIRCM issues. The Shack- Hartmann (SH) wave front sensing technique was employed. It consisted of 64 x 64 lenslets coupled to a 1024x1024 pixel Dalsa CCD sensor working at a sampling rate of 40 Hz. A 15 ns pulsed laser synchronized with the SH sensor enabled "freezing" turbulence in each SH image. The ability of the technique to substract a reference permitted a simple calibration procedure to ensure accurate and reliable measurements despite vibration environment. Instantaneous phases are reconstructed using Fourier techniques so as to obtain a better spatial resolution against turbulent effects. Under any given plume condition, overall tilt aberration prevails. Phase power spectra derived from phase statistics are drawn according to the plume main axis and to normal axis. They compare favorably well to the decaying Kolmogorov power law on a useful high spatial frequency range. Averaged phases are also decomposed into Zernike polynomials to analyze optical mode behavior according to engine status and to plume abscissa. With overall tilt removed, turbulent DSP's amplitude drops by a factor of 30 to 40 and mean aberrations by a factor of 10 from an abscissa 1 meter to another 3.5 meters away from the engine nozzle, due to quite different turbulent conditions.

In several laser radar applications detection of targets with high resolution and range accuracy, is of importance. Time-of-flight time-correlated single-photon counting (TCSPC) provides a method to accomplish range profiling at longer ranges with high accuracy and resolution. The performance of a TCSPC system used for optical range profiling suffers from the influence of atmospheric turbulence effects causing perturbations of the registered time histograms. This is mostly manifested in propagation paths close to the ground. In this work a TCSPC system based on a monostatic transmitter/receiver head, a picosecond laser operating at high pulse-repetition frequency, a single photon detector and acquisition electronics with high timing resolution was used to study the influence from atmospheric turbulence on registered pulse responses from test targets. The turbulence conditions were monitored during the experiments and the influence from turbulence effects on the pulse response are discussed. The experimental results are considered in relation to existing turbulence models. Implications on system performance for a TCSPC time-of-flight range profiling system are illustrated.

Laser based missile defence systems (DIRCM) are being increasingly employed on aircraft. In certain circumstances the laser must pass through the exhaust gases of the aircraft engine. In order to predict the degree of divergence and dispersion of the laser, an understanding of the exhaust gas structure and its influence is required. Specifically the effect of parameters such as temperature, carbon dioxide, turbulence intensity and length scales as well as the laser beam wavelength and beam diameter. A parametric study under laboratory controlled conditions was undertaken to examine these effects. The results of beam propagation through high temperature turbulent flows and for various CO₂ and H₂O concentrations are presented in this paper for wavelengths 632.8 nm and 4.67 μm. It was found that the beam displacement showed an approximate inverse square relationship to temperature. At high combustion temperatures the 632.8 nm beam was significantly broken-up and dispersed. Displacement of both beams appeared to be asymptotic above 600°C. Carbon dioxide absorption effects were found not to significantly influence the beam displacement at the wavelengths and temperatures studied. Quantifying these effects at high temperatures will assist with the development of a parametrically based laser beam propagation model.

We have demonstrated audio communications with a mid-IR laser. The laser is a frequency doubled Q-switched CO₂ system producing approximately 12ns pulses at 4.6μm. The audio signal was encoded on the beam by means of pulse frequency modulation (PFM) with a carrier frequency of 37kHz. A 1mm diameter, low noise thermoelectrically cooled IR photovoltaic detector with electrical bandwidth 250MHz was used to detect the laser beam. A custom-built circuit stretched the resultant electrical pulses to approximately 1.5μs, before being demodulated. High quality audio signals were received and recorded, and still images were successfully transmitted using slow scan television techniques. The demonstration was conducted at the Defence Science & Technology Organisation's laser range at Edinburgh, South Australia in July 2008. The distance was 1.5km, with a slant path (8m to 1.5m). The maximum range using this system is estimated to be tens of kilometres.

Laser based missile defence systems (DIRCM) are being increasingly employed on aircraft. In certain circumstances the laser must pass through the exhaust plume of the aircraft engines. In order to predict the degree of divergence and dispersion of the laser beam an understanding of the exhaust gas structure and its influence is required. Specifically the effect of parameters such as temperature, carbon dioxide, turbulent intensity and turbulence scale sizes within the flow are of interest, in addition to the laser beam wavelength and beam size. A parametric study under controlled laboratory conditions was undertaken to examine these effects. The results of beam propagation through a high temperature turbulent flow at various turbulence intensity levels are presented in this paper. Beams with wavelengths 632.8 nm and 4.67 μm at various beam diameters are used to study laser beam interaction with various turbulence intensity and eddy scales. The effect of the relative size of the beam diameter with respect to the turbulence scale is also reported. It was found that the beam displacement was strongly related to turbulence intensity and beam diameter. Scale lengths, path length and turbulence intensity were found to influence beam displacement. Quantifying these parametric effects at high temperatures will assist with development of a parametrically based laser beam propagation model.

In current laser countermeasure technology concepts where frequency conversion is required, each active component has its own laser source. During this paper we show that by using microstructured fibre technology as a delivery system, output in multiple wavebands can be efficiently generated at locations remote from the laser pump source. We demonstrate that laser radiation (with specifications close to those currently on airframes) can be delivered without significant spectral, temporal or modal degradation over lengths representative of that in an airframe. This fibre delivered radiation is used as a pump source for active frequency conversion, generating tuneable laser output in the 2 μm, 3.5 μm and 0.532 μm regions, i.e. in wavebands of interest to countermeasure applications. A Nd:YVO₄ laser (λ = 1.064 μm) with 16 W of average power in a train of 15 ns pulses acts as the single pump source for our system. Different types of microstructured fibre are assessed for high power delivery over lengths greater than 6.5 m. Three frequency conversion devices were constructed here to demonstrate the quality of the fibre-delivered radiation - the devices are all based around periodically poled lithium niobate (PPLN) crystals and consist of two optical parametric oscillators converting the pump source to wavelengths of ~2 μm and ~3.5 μm and a second harmonic generator to double the frequency to 0.532 μm. The efficiencies of the frequency conversion sources are comparable whether radiation is delivered through free space or by microstructured fibre.

The paper deals with laser range finding (LRF) technology for tracking fast-moving objects with kHz laser repetition rates. The LRF is based on time-of-flight measurement, where a short emitting laser pulse is transmitted and its time-of-flight is accurately measured by the electronics with respect to the received impulse from a non-cooperative target. The emitted laser energy is in the near infrared wavelength region. The detector is based on a single-photon detection principle of a silicon Avalanche photodiode, operated in so-called Geiger mode. A solution was devised to utilise single photon detection even at strong daylight conditions. The LRF has been integrated in a robust and compact technology demonstrator, and has successfully ranged to rapidly-moving and accelerating small targets. A detailed mathematical model was developed to predict the ranging performance of the LRF for evolution of application-specific designs. The current technology allows ranging up to a maximum range of 1.5 km with ± 0.5 m accuracy against large stationary targets, as well as tracking of small targets of 75 mm diameter moving up to a range of 300 m with a speed resolution of ± 5 m/s. The LRF device uses a standard serial protocol for device communication and control, and operates at a temperature range from 0 °C - 55 °C.

A review of the development of nonlinear materials suitable for use in the mid-IR (3 to 5 μm) is presented. This examines the properties, performance, limitations and availability of a range of materials, including birefringently phasematched crystals and engineered quasi-phasematched materials. Higher-order nonlinear processes in alternative materials are also considered and a discussion on material suitability for down-conversion of near-IR lasers into the mid-IR to meet various application requirements is also presented.

Efficient laser sources in the 3 - 5 μm wavelength range are needed for directed infrared countermeasures, but also have applications in remote-sensing, medicine and spectroscopy. We present new results on our tandem optical parametric oscillator (OPO) scheme for converting the radiation from a 1.06 μm Nd³⁺-laser to the mid-infrared. Multi Watt level output power in the 3-5 μm range at 20 kHz pulse repetition frequency is reported. Our setup uses a type I quasi phase-matched PPKTP crystal in a near degenerate OPO to generate 2.13 μm radiation. A volume Bragg grating resonant close to, but not exactly at the degenerate wavelength, is used as a cavity mirror to reduce the bandwidth and ensure singly resonant operation. Both signal and idler from the PPKTP OPO are used to pump a ZGP OPO generating high power radiation in the 3-5 μm region. Using this scheme for each pump photon it is possible to generate four photons for each pump photon, all in the interesting wavelength range, thus enabling high efficiency conversion.

The initiation of pyrotechnic substances by a laser light has been studied for more than 30 years. But until recently the use of this technology for defence applications encountered three main technical problems: the volume and the mass of lasers, the linear loss of optical fibres and their possible damage caused by the transport of strong laser power. Recent technical progress performed in the field of electrical and optical devices are now very promising for future opto-pyrotechnic functional chains. The objective of this paper is to present a demonstrator developed in order to initiate in a synchronous way four optical detonators and to measure the dispersion of their functioning times. It includes four compact Q-switched Nd:Cr:GSGG solid laser sources, pumped by flash lamp (energy ≈110mJ, FWHM ≈8.5 ns), two ultra-fast electro-optical selectors (based on RTP crystals) used to steer the laser beam and six optical fibre lines to transmit the laser pulses to the optical detonators. The set-up integrates also complex control and safety systems, as well as cameras allowing an optimal alignment of optical fibres. Experiments led us to initiate in a synchronous way four detonators with a mean scattering of 50 ns. The perspectives in this domain of initiation concern mainly the miniaturization and the hardening to the environments of electrical and optical components.

Nonlinear optical conversion of high-energy 1.064 μm pulses from a Q-switched Nd:YAG laser to the mid-infrared is demonstrated. The experimental setup is based on a two-stage master-oscillator/power-amplifier (MOPA) design with a KTiOPO₄ based MOPA in the first stage and a KTiOAsO₄/ZnGeP₂ based MOPA in the second stage. The setup can be tuned to provide output at wavelengths within the transparency range of ZnGeP₂. We obtain more than 8 mJ at 8 μm, and up to 33 mJ in the 3-5 μm wavelength region. The measured beam quality factors are in the range M² =2-4 for both wavelength regions.

Guided weapons, are a potent threat to both air and surface platforms; to protect the platform, Countermeasures are often used to disrupt the operation of the tracking system. Development of effective techniques to defeat the guidance sensors is a complex activity. The countermeasure often responds to the behaviour of a responsive sensor system, creating a "closed loop" interaction. Performance assessment is difficult, and determining that enough knowledge exists to make a case that a platform is adequately protected is challenging. A set of metrics known as Countermeasure Confidence Levels (CCL) is described. These set out a measure of confidence in prediction of Countermeasure performance. The CCL scale provides, for the first time, a method to determine whether enough evidence exists to support development activity and introduction to operational service. Application of the CCL scale to development of a hypothetical countermeasure is described. This tracks how the countermeasure is matured from initial concept to in-service application. The purpose of each stage is described, together with a description of what work is likely to be needed. This will involve timely use of analysis, simulation, laboratory work and field testing. The use of the CCL scale at key decision points is described. These include procurement decision points, and entry-to-service decisions. Each stage requires collection of evidence of effectiveness. Completeness of the available evidence can be assessed, and duplication can be avoided. Read-across between concepts, weapon systems and platforms can be addressed and the impact of technology insertion can be assessed.

CounterSim is a countermeasures modelling and simulation application developed by Chemring engineers to study the use of expendable countermeasures in air, land and naval scenarios. The CounterSim transmissometer model was originally developed in order to validate an obscurant model using measurement data from trials. In principle, it can also be used to assess line of sight transmission and detection times in military scenarios such as vehicle self protection, projected smoke to cover battlefields and littoral operations by ships supporting land operations. Ships could be facing land based threats in littoral operations. Smokes can be regarded as a nuisance rather than an asset and users will want to minimise self obscuration of their EO/IR systems. The transmissometer model offers a means of monitoring obscuration in simulations for blue on red and red on blue effectors. The paper describes a simple littoral scenario and some of the issues that arise with the transmissometer model used to monitor lies of sight to and from platforms through ambient temperature obscurants and hot smoke. Requirements for the future development of a tracking transmissometer are outlined.

We describe the development of a time dependent thulium laser model. The model is used to predict both the CW and temporal behaviour of a Tm:YAG laser. Experimental results from a diode-pumped Tm:YAG laser are obtained and the model is used to obtain good agreement with these observations for both the CW and temporal behaviour of the laser. Particular results relate to switch-on time delays and the effect of pump diode modulation on Tm laser efficiency. The laser model has been extended to the case of the Ho:YAG laser where other important effects due to ground state depletion and self re-absorption must be taken into account. The holmium laser model has recently been used to predict reported experimental results from a thulium fibre laser pumped Ho:YAG laser.