This PDF file contains the front matter associated with SPIE Proceedings Volume 10797, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The paper reviews topics presented at past conferences on “Technologies for Optical Countermeasures”, summarizes current optical countermeasures technologies, and illuminates technology trends which might be of interest in the future.

Power and, especially, brightness are important characteristics of quantum-cascade lasers (QCLs) for many applications. Brightness is a measure of the intensity of a laser’s emission that can be delivered by an optical system. Applications based on vibrational-mode gas spectroscopy or mid-infrared illumination benefit from a higher brightness beam providing a better signal-to-noise ratio, external-cavity tunable QCL systems gain efficiency when more of the beam power can be re-focused into the active region, and, of course, infrared countermeasures depend on optical power delivered by a lens system to a distant target. For a given wavelength, brightness requires both optical power and beam quality. The optical power emitted by a QCL depends on its efficiency and its active region volume. The efficiency can be optimized through design features, quality of epitaxy, thermal management, and facet reflectance. The active region volume is governed by the number of cascades and the width and length of the emitter. For a given efficiency – and QCL efficiency is close to optimized today – the route to power is either through a larger number (20–40) of cascades combined with a narrow stripe or a small number (5–15) of cascades using a broad-area emitter. For a given input power – which means for a given laser volume – a broad-area laser will have the same output power and better thermal conductance than a narrow-stripe buried-heterostructure laser. Further, because both emission power and thermal conductance of a broad-area QCL with around 10 cascades scales with area, such broad-area QCLs cascade number can be scaled to higher emission power [1,2,3]. But, wide stripes are notorious for poor beam quality and the reduced cascade number reduces efficiency. The realization of good beam quality from broad-area QCLs has been achieved through several approaches. Angled facets to suppress non-fundamental modes, tapered stripes that combine large area with a section that favors the fundamental mode, photonic crystal facets, constricted stripes to filter high-order modes, and engineered waveguide loss that suppress high-order modes have been demonstrated. Further, the reduced efficiency has been demonstrated to be acceptable down to about 10 cascades. This talk will discuss the paradigm shift to broad-area, reduced-cascade-number QCLs for high brightness applications, including the optimization of efficiency and beam quality. [1] W.T. Masselink, M.P. Semtsiv, A. Aleksandrova, and S. Kurlov, “Power scaling in quantum cascade lasers using broad-area stripes with reduced cascade number,” Optical Engineering 57(1), 011015 (2017); http://dx.doi.org/10.1117/1.OE.57.1.011015. [2] W.T. Masselink, M.P. Semtsiv, Y. V. Flores, A. Aleksandrova, and J. Kischkat, “Design issues and physics for power scaling of quantum-cascade lasers,” Proc. SPIE 9989, 99890B (2016). [3] P. Figueiredo, M. Suttinger, R. Go, A. Todi, H. Shu, E. Tsvid, C.K.N. Patel, and A. Lyakh, “Continuous wave quantum cascade lasers with reduced number of stages,” IEEE Photonics Tech. Lett. 29, 1328–1331 (2017).

Building on Leonardo’s unique experience in this domain, the Miysis DIRCM System is the culmination of over ten years of extensive development, test, validation and certification, resulting in a twin-head, spherical coverage DIRCM system that is less than 40kg and is capable of protecting the full range of platform types from the smallest helicopters to the largest transport aircraft.

This paper discusses some of the benefits that have been achieved from the application of advanced EO technology to the Miysis DIRCM System, and also considers some of the system trades a designer may have to undertake.

The extensive test and evaluation that was undertaken at every stage of the programme, including simulation, laboratory testing, platform and target dynamic testing in a System Integration Laboratory (SIL), flight trial, missile live-fire, environmental testing and reliability testing, all of which was required in order to ensure that the system provides the requisite levels of protection against the latest, sophisticated all-aspect IR MANPADS is also covered.

In particular, recent developments and system level testing will also be discussed in some detail.

Mode-locking of lasers has led to breakthroughs in numerous scientific fields and applications.Today, all mode-locked lasers are based on resonators that support a single transverse spatial mode. In the early days of laser development, locking of a few transverse and longitudinal modes of a laser was considered. In the intervening 50 years, almost no attention has been paid to locking of multiple transverse modes. In the past year, theoretical and experimental observations of locking of multiple transverse and longitudinal modes of a fiber laser have been reported. Strong spatial and spectral filtering in the laser underlie the formation of multimode ultrashort wave packets in the laser. Understanding of spatiotemporal mode-locking requires generalizing concepts from conventional 1-D mode-locking into higher dimensions: spatiotemporal dispersions (chromatic and modal dispersion) and saturable absorption, nonlinear coupling between spatiotemporal (3+1-D) modes, and spatiospectral filtering. Interactions between modes through linear and nonlinear coupling lead to shifts of the resonances, to yield states with long-range order. In the time domain, these mode-locked states correspond to coherent, spatiotemporal pulse trains. Several qualitatively-new types of mode-locking have been identified. Investigations of new 3D lasing states should be a fertile scientific direction. In addition, the peak power of spatiotemporally-mode-locked lasers scales by more than the mode area, which should lead to unprecedented performance from fiber lasers.

Engine ignition using a laser requires very high peak power levels, that can be produced by solid-state lasers such as Yb:YAG passively Q-switched lasers. We developed high repetition rate diode pumped Yb:YAG micro-lasers to study the effect of cumulated pulses on the engine ignition process. The Yb:YAG laser oscillator is pumped by a 5-Hz quasi-continuous wave diode laser emitting 3-ms long pump pulses with up to 20 W peak power. It’s passively Q-switched using a Cr:YAG crystal. Various Yb:YAG dopant concentrations and crystal length have been tested and different initial transmittance values for the Cr:YAG crystal have been compared. As a result of quasi-continuous wave pumping and passive Q-switching, bursts of short pulses are emitted at the 5-Hz repetition frequency of the long pump pulses. The control of the intra-burst repetition rate is achieved through tuning the pump power between a few watts and 20 W. The energy per pulse ranges from 250 μJ to 300 μJ, with a lower than 5 ns pulse duration. The intra-burst repetition rate can go up to 20 kHz. An amplifying stage comprised of one single Yb:YAG crystal is added after this laser oscillator.

High-power lasers at 2 µm are required for optical countermeasure applications, but can also be used for processing of materials where the mid-infrared laser wavelength provides an advantage. These applications can benefit from power scaling the 2 µm output, with the requirement to maintain a compact footprint. In particular, a Tm-doped slab laser design can be very compact, as an alternative to high power Tm:fiber lasers at 1.9 µm. It can be used directly for modulated continuous-wave output or for pumping Ho-doped lasers and amplifiers that emit at 2.1 µm. We have directly compared Tm:YLF and Tm:LLF slab crystals (1.5 mm x 11 mm x 20 mm), in an otherwise identical diode end-pumped laser configuration, to evaluate the power scaling to 150 W of these two related materials. We will present the analysis of the thermal lens behaviour of that could not be fully supressed for Tm:LLF in the slab architecture when pumped at 450 W of incident pump power from the high-brightness 793 nm laser diode stack (Lasertel T6 Diode). Further power scaling to the 300 W output power level of Tm:YLF in a dual-end-pumped slab laser configuration will be presented, in which parasitic internal lasing has been supressed through careful consideration of the slab geometry. The improved Tm:YLF laser will be used to pump a Ho:YAG slab (1.5 mm x 10 mm x 55 mm) to amplify seed pulses from a nanosecond Q-switched oscillator. A spatially and temporally resolved model has been developed to determine the optimal pump configuration and crystal dimensions to amplify seed pulses from 7 W average power at 10 kHz repetition rate, to upwards of 150 W at 2.1 µm. The model is based on rate equations and determines the distribution of thermal load throughout the crystal, permitting accurate prediction of saturation- and thermal-induced aberrations in the amplifier.

When imaging over long horizontal paths it is often the case that the isoplanatic patch size is on the order of, or smaller than, the diffraction-limited sampling rate of the imaging system. In these scenarios it is also common for the atmospheric Fried parameter to be only slightly smaller than aperture size. If the integrated turbulence strength is relatively low the main effect of the turbulence volume is to introduce shift-variant tip and tilt distortions to what is otherwise clear image. I refer to this condition as extreme anisoplanatism. In this talk, I will outline a theory for this anisoplanatic image formation following a light-field approach. Also, I will provide some insights into the performance of some image recovery techniques in the presence of extreme anisoplanatism. Finally, I will suggest how angular diversity may be used as a technique for improving scene recovery in these conditions.

A simulation method is proposed which approximates the atmospheric beam path as an extremely large aperture hollow waveguide containing a numerically sufficient subset of linearly polarized lossless propagation modes. The proposed method is shown to agree numerically with the standard angular spectrum of plane waves method in a single transverse dimension simulation and is readily expandable into two transverse dimensions but currently limited by available hardware. The method is expanded to involve coupling matrices describing the transition through each phase screen and the intermediate free-space portions. The coupling matrices are combined into a single multimode coupling matrix describing the propagation for one instance of atmosphere. The proposed matrix method has potential to evaluate multiple input beams simultaneously or condense high turbulence simulations requiring many phase screens. The input beam can be constructed by multiplying the decomposition of the desired output profile with the pseudo-inverse of the coupling matrix; however, the matrix cannot be realized in experiment. Therefore, the opportunity for beam shaping to compensate optical turbulence is evaluated by principal component analysis of the compound coupling matrix. It is shown that an average of the lowest order eigenmode across multiple simulations produces a super-Gaussian-like beam with improved power delivery and stability. The implication for optical countermeasure beam control is the potential to create any desired beam shape at the target plane.

Defence and security require both invention and innovation. Invention is the opportunity to create completely new capabilities and solutions. Innovation is the opportunity to recognise that advances are being made in adjacent markets which can be exploited beneficially to meet the needs of defence and security customers. In this paper a case study is presented on a laser directed energy weapon programme whereby early stage feasibility concepts used open innovation. This led to the identification and exploitation of laser technology from an adjacent market and the application of phased array radar theory at optical wavelengths. Additionally, this project stimulated an underpinning research activity into novel phase locking and beam combination techniques. Currently, innovation programmes are receiving substantial support from a number of defence and security organisations globally and other open innovation defence and security photonics opportunities are presented.

When studying the impact of laser dazzle on the human vision, three categories of parameters are of influence: those related to the human eye, the characteristics of the laser source itself, and environmental parameters such as target size and contrast, position of the target with respect to the laser dazzler, and ambient light level. The effects are most often translated into a decrease of the field-of-view of the eye but the question remains how this translates into human task performance degradation. More specifically, the research question for this study is the following: can we quantify the performance degradation of military specific tasks in a land environment when being dazzled by a portable laser system? Two main measurement campaigns have been organized to answer this question: a driving test to allow benchmarking with the literature, and a shooting test. The registered time and scoring of the specific tests have been statistically analyzed to determine the significant effects. The results of the driving test confirm those described in the literature; the results of the shooting test give insight in the main parameters of interest. Moreover, the outcomes of the two trials show that there is a need for a specific test protocol to find the correct compromise between environmental validity of a trial and the number of independent variables that can be controlled.

Infrared imaging sensors are a vital component of modern military weapons and surveillance systems, which for land operations is dominated by uncooled thermal imagers using microbolometer array detectors. These sensors, just as for all electro-optical and infrared devices, are vulnerable to the ever-increasing threat of in-band laser weapons, which can perturb or destroy their operational effectiveness. Importantly, this can happen even for relatively low laser output power. In this article, we analyze the experimentally measured results of laser dazzle and subsequent damage on an uncooled long-wave thermal imager. The imager has a vanadium oxide microbolometer array of size 640x480 pixels. A tunable quantum cascade laser is used with power output less than 100mW and fixed at a wavelength of 10.6 micron. The laser power was increased in incremental steps with the imager positioned only a few meters away. We discovered that the pixels covered by the laser spot saturate, leading to damage from accumulated exposures of only a few seconds. Additionally, we recorded circular diffraction effects and blooming of the array. In summary, we observed that damage was inflicted to pixels on the microbolometer array well before any significant dazzling was achieved.

In light of the potential threat to aircraft from missiles using Ultra Violet (UV) wavebands, it is important to understand the signature of an aircraft and how this can be predicted. This study compares empirical UV signature data to modelled data from CAMouflage Electro-Optical SIMulation (CAMEOSIM) to determine how well the contrast between the object and the background in the scene can be predicted. CAMEOSIM uses the standard MODerate resolution atmospheric TRANsmission (MODTRAN) model from Spectral Sciences (and the US Air Force) to estimate the radiative transfer through the atmosphere. Both MODTRAN and CAMEOSIM are well validated in visible and infrared radiative transfer. Work, including by Smith [1] has shown that MODTRAN can accurately predict UV radiative transfer through the atmosphere. Unfortunately, the work so far has concentrated on bulk transfer to describe the sky background in the UV. The aircraft scene is typically a negative contrast ‘hole’ in a positive sky background. Importantly, path-topath scattering is a key consideration in this scene since it is this that will tend to blur the edges of an object and reduce the contrast associated with it. MODTRAN, and therefore CAMEOSIM are not designed to work well for this particular scene so developed understanding of the limitations through testing is required. It was determined that prediction was possible up to ranges of less than 5km. The local visibility (in km) was required for this prediction but more accurate descriptions of the atmosphere were not.

One of the very useful aspects of a laser is its well-defined beam, delivering high intensity to a defined location. Directing that beam and specifying the location is generally done with adjustable mirrors. Directing the beam in time varying manner most often requires galvanometer scanning mirrors which translate in one dimension. These mirrors, though now a mature technology, are in general speed limited due to their inertia and can be heavy, power hungry and expensive. There are then benefits to be gained from non-mechanical means of beam steering particularly in terms of speed and weight. This paper gives an overview of methods employed to implement beam steering and then concentrates on methods that do not rely on independent phase control. The use of a micromirror array for 3-dimensional beam control will be presented with the pros and cons that this entails.

For detection of a small target using electro-optical systems, multi-band 2D image sensors are used such as visible, NIR, MWIR, and LWIR. However, 2D imaging systems are not capable to detect a very small target and they are also not capable of calculating target 3D position coordinates to develop the strategic counter method. 3D sensors (e.g. Lidar, RGBD and stereo camera) are utilized to control unmanned vehicles for detecting threats and response for specific situations. Conventional Lidar systems are unable to detect small drone threat at distances higher than their maximum detecting range of 100 ∼ 120 meters. To overcome this limitation, laser radar (LADAR) systems are being developed, which allow the detection at distances up to 2 kilometers. In the development of LADAR, it is difficult to acquire datasets that contain cases of long distant targets. In this study, a fusion data generation with virtual targets technique based on minimum real LADAR initial map dataset is proposed, and precise small target detection method using voxel-based clustering and classification are studied. We present the process of data fusion generation and the experimental results for a small target detection. The presented approach also includes effective visualization of high-resolution 3D data and the results of small target detection in real time. This study is expected to contribute to the optimization of a drone threat detection system for various environments and characteristics.

The LADAR system is a device that generates a depth map using reflected laser range information after irradiating a laser pulse onto a terrain or target. In recent years, it is important to acquire accurate 3D coordinates of target objects with target identification from 3D raw data.^1–3 The existing LADAR system does not have the function to calculate the target coordinates, but recently, its coordinate system LADAR is actively researched to find the target coordinates. In order to accurately calculate the target coordinates, accurate position information (GPS) of the LADAR system and distance to the target and angle of the laser are required. Generally, digital magnetic compass (DMC) should be used to obtain accurate angles. However, in a region in strong magnetic fields, DMC cannot guarantee its accuracy and its usage is limited. In this paper, we propose a coordinate calibration system to replace DMC and a method to extract accurate angle information using GPS and encoder for robust target coordinate extraction to the magnetic field variation. As experimental results of the proposed system, it is confirmed that it is a robust system in the magnetic field environment compared with the coordinate system using the existing DMC. This is an improved technique for obtaining accurate target coordinates in various environments. Using the proposed LADAR system, it is possible to construct a smart defense system to extract the precise target latitude and longitude coordinate system and to transmit the information to the associated Missile base and command center.

In pursuit of real time/on-the-fly image processing, a sensor with embedded algorithms for tracking is tested to determine its aliasing window whilst under laser interrogation. The characterization of the sensors and this interaction are explored, as well as the limitations thereof. This is follow on work to previous studies, in which both fixed frame rate sensors and adjustable frame rate sensors were tested to show the difference in response and functionality when subjected to Quantum Cascade Laser (QCL) modulation. A MIRAGE^[1] Infrared Scene Projector (IRSP) is used to add baseline signature for the sensor to follow before the laser signal is introduced. Discussions of further advancements in anti-aliasing algorithms are included as well.

We report on the temporally controlled combination of the emission of multiple quantum cascade laser modules. The combination is demonstrated and allows for temporal pulse shaping at a target position. The laser chips are packaged individually in stand-alone modules that can provide an average optical output power on Watt-level. Timing is provided by integrated microcontrollers which allow for comfortable output synchronization of several modules. Thus we have reached a timing accuracy in the order of better than 10 ns. The operation is demonstrated for a wavelength of λ = 4 μm, but can be easily adapted to other wavelengths that are relevant for sensing, free space communication or directional infrared counter measure applications.

Laser interception technique is a precision measurement technology which takes advantage of laser interferometry to detect weak vibrations caused by acoustic excitation with high precision. It has been greatly valued by national intelligence agencies, with pervasive application to counter-terrorism, crime investigation and other national security and defense affairs in various countries. This paper proposes an interception scheme based on acousto-optic frequency shifting laser self-mixing interferometry. In the case of weak light, the vibration information of the target object could be acquired in real time with high precision. And it is applicable for the development of miniaturized laser interception equipment. We use self-developed acousto-optic frequency shifters to stabilize the heterodyne frequency of the two laser beams at kHz level and heterodyne beat signal as carrier signal for micro-displacement detection. Besides, the self-balanced detection technology is applied to eliminate the common-mode noise of detection system, so as to ensure the signal-to-noise ratio of weak signal detection at nano-watt-level of laser power under long-distance interception conditions. By means of modulation phase recovery technique, combined with cavity frequency modulation method, Fourier transform phase extraction principle and Kalman filter method, the program realizes high-precision recovery of self-mixing interferometric displacement under weak feedback conditions and can effectively suppress low-frequency noise of laser source.

Mid-infrared (mid-IR or 3.5 – 5.0 μm) laser sources are widely employed in applications such as laser projectors, remote sensing of the atmosphere and countermeasures against heat seeking missiles. In this paper, we describe the development of a mid-IR laser source which can be used as a ground-based system for remote sensing applications and testing countermeasure effectiveness in the field. For this purpose, we developed an optical parametric oscillator (OPO) based on a ZnGeP₂ (ZGP) crystal for converting a 2.1-μm pump laser into mid-IR. The pump laser is an acousto-optically Q-switched Ho:YAG laser pumped by a continuous-wave (cw) Tm:fiber laser. The maximum possible average mid-IR power obtained is 6.5 W at a pump power of 20 W with a 33% power conversion efficiency. The pump pulses resulting from the Q-switched operation of the Ho:YAG laser have a pulse width of 30 ns (FWHM) at a pulse repetition rate (PRR) of 50 kHz. Between the pump laser and the OPO, we use a Faraday isolator for protecting the pump laser from back reflections of the output beam coupling into the pump laser cavity, we also use a polarization rotator and a lens which focuses the pump beam down to a spot of 275 μm (1/e2 , diameter) at the center of the 15-mm long and 55°-cut ZGP crystal located in the middle of a 19-mm long cavity formed by two flat mirrors. The OPO cavity is doubly resonant, the input mirror is a high transmitter at 2.1 μm and a high reflector in mid-IR whereas the output mirror is a high transmitter at 2.1 μm but a partial reflector with a reflectance of 50% in mid-IR. The mid-IR and residual pump beams are separated from each other using a dichroic mirror. We characterized the performance of the OPO in terms of the mid-IR power, power conversion efficiency and pump depletion as functions of the input pump power. We recorded the wavelength spectrum of the midIR beam.

We provide a unified framework for the evaluation of number of dazzled pixels of camera sensors for free space laser dazzling applications considering laser, beam director, sensor, camera optics and atmosphere parameters. In addition, we present a comparison of our analytical approach to experimental results, where a 1070 nm fiber laser and a CCD based sensor are utilized, for dazzling analysis based on system parameters. This framework can be applied to a variety of free space optical system configurations operating in various optical bands (e.g. UV, SWIR and MWIR) for dazzling performance analysis.

We present an optical concept for imaging sensor systems, designed to reduce considerably the sensor’s image information loss in cases of laser dazzle, based on the principle of complementary bands. For this purpose, the sensor system’s spectral range is split in several (at least two) spectral channels, where each channel possesses its own imaging sensor. This long-known principle is applied, for example, in high-quality 3-sensor colour cameras. However, in such camera systems, the spectral separation between the different spectral bands is far too poor to prevent complete sensor saturation when illuminated with intense laser radiation. We increased the channel separation by orders of magnitude by implementing advanced optical elements. Thus, monochromatic radiation of a dazzle laser mainly impacts the dedicated transmitting spectral channel. The other (out-ofband) spectral channels are not or – depending on the laser power – only hardly affected. In this paper, we present our system design as well as a performance evaluation of the sensor concerning laser dazzle.

Imaging systems have found widespread applications in science and technology, in the civilian and military domains, ranging from detection, identification, recognition and videosurveillance. The interaction between laser light and the electro-optical sensors and optical devices present in these imaging systems is of great relevance, as they are very sensitive to intense light fluxes. From this point of view, coherent light sources such as lasers can prevent proper operation, or even cause irreversible damage to the sensors. In this work, visible and near-infrared lasers were employed to dazzle CCD and CMOS cameras, including wide field of view (WFOV) optics, commonly present in actual micro unmanned aerial vehicles (micro-UAVs). The influence of various parameters such as laser wavelength, irradiance and incidence angle on dazzling were studied. The present work contributes to a better understanding of dazzling effects on CCD and CMOS optical sensors, and will be useful in designing optoelectronic countermeasures.

The laser-induced damage thresholds of commercial off-the-shelf visible and shortwave infrared cameras are measured under laboratory and outdoor conditions for infrared laser exposure times varying from microseconds to continuous wave. The damage threshold results are compared with a simple thermal model, which shows strong correlation with the experimental data, allowing the model to be used to predict camera damage thresholds across a range of exposure durations and wavelengths.

Optical camouflage painting, as a basic measure against optical reconnaissance and optical sighting weapon attack, is a general method of optical camouflage of small vessels. By utilizing this method, we can design the camouflage pattern according to basic features of vessel background, paint the camouflage pattern to equipment target surface with camouflage coating, and imitate the natural background or the outline of segmentation targets in color and texture, thus reducing the exposure signs of equipment targets. Due to the fact that most of existing qualitative evaluations on camouflage effectiveness are quantitative evaluation or evaluation based on experts' judgment, this paper put forward a new evaluation method of optical camouflage effectiveness of marine target based on target identification probability and similarity between the target and the background, carried out practical measurement test on optical camouflage effectiveness of marine targets, and calculated quantitative camouflage evaluation results of 50 collected images according to actual contribution of feature indexes. A mathematic relation model of optical identification probability and similarity of marine targets was built after comparison with manual interpretation results of identification probability. The results indicate that: the higher the similarity, the lower the identification probability. If the target and background are totally different, the corresponding target identification probability is 1, which indicates that the lower the similarity, the more the exposure features of the target, and the easier the target to be detected; if the target and background are similar, the corresponding target identification probability is 0, which indicates that the higher the similarity, the less the exposure features of the target, and the more difficult the target to be detected.