This PDF file contains the front matter associated with SPIE Proceedings Volume 11539, including the Title Page, Copyright Information, and Table of Contents.

Welcome to the conference on Technologies for Optical Countermeasures XVII; and High-Power Lasers: Technology and Systems, Platforms, Effects IV

The observable infrared signature of naval platforms is crucial in determining survivability and is therefore an important issue in warfare. Increased detectability in the EM spectrum leads to higher susceptibility against threats like sea skimming anti-ship missiles. The infrared platform signature is not a fixed quantity but a highly dynamic property that varies significantly depending on the prevailing conditions. To reduce susceptibility, active reduction measures can be deployed that reduce surface and exhaust gas temperatures and therefore actively obfuscate the signature. Since infrared decoy countermeasures compete with the platform signature, these reduction measures can positively affect countermeasure effectiveness, enabling enhanced interruption of the kill chain. To enable accurate signature reduction, improved awareness of the platform’s current signature is required. A sensor driven system on board of a platform, combined with specialized modelling capacity is capable of monitoring the current and predicting the near future signature. The output of such a system can subsequently be used for improved countermeasure deployment by linking it to an onboard Electronic Warfare Tactical Decision Aid (EWTDA). This paper addresses a methodology for evaluating the effect of different signature reduction measures on decoy effectiveness by using engagement simulations. The importance of the fidelity in background (e.g. clutter statistics) and ship signature modelling is also discussed. Finally, an example will be given of a concept signature monitoring system consisting of sensors and signature models which is currently being deployed on an operational Royal Netherlands Navy (RNLN) vessel. Future versions of this system are expected to provide input to the onboard EWTDA to enable more effective decoy deployments.

We discuss a solution to the dilemma of high confinement energy and the high interface-scattering rate for the high-barrier InGaAs-InAlAs-AlAs QCLs, operating at wavelengths substantially shorter than 4 µm. The new design includes fewer quantum wells within a single cascade and operates at 3.6 µm. Otherwise, its performance is very similar to the best of recently-shown QCLs at 4.6 µm and 4.0 µm using the same material system.

Quantum cascade lasers are the most powerful and efficient mid-IR semiconductor technology. Their niche market has a strong annual growth and provides decisive advantages over other mid infrared laser technologies. As a semiconductor laser, QCLs are small and the direct conversion from electricity to light ensures a high conversion efficiency. mirSense has been developing quantum cascade laser-based solutions for 5 years now and ranks among the very few companies mastering this technology. The main value brought by this technology in this market is to deliver coherent and bright sources in the band II and band III of transmission of the atmosphere. We focus in particular on the application of this technology to defense applications like DIRCM. Our strong innovation propensity has lead us to build a strong IP and innovative solutions.

Thermal infrared imaging systems are increasingly vulnerable to the threat of disruption or damage from laser weapons. For laser weapons operating within the waveband of the imager, in-band, the effect is primarily dazzling of the focal plane array. In contrast, for those not in the same waveband, out-of-band, the critical interaction is thermal heating of the outer optical components leading to probable substrate damage. In this article, we analyze the impact of out-of-band high power laser radiation on an infrared telescope operating in the longwave waveband region (LWIR). In particular, we illustrate the stages from coating ablation to subsequent substrate damage. A 1.07 micron continuous-wave fiber laser illuminated the telescope for durations up to a few seconds at a maximum power of approximately one kilowatt. Both visible and LWIR imagers recorded the impact on the outer lens. Our results indicate a predictable chronological sequence of events leading to material damage and heat transfer effects across the substrate as we increased the laser power and duration time.

The development of shift-free fixed-line filters is a key technology for advancing the next generation of laser protection and is greatly desired due to the increased threat of laser attacks. Thin-film interference coatings have remained the key technology for achieving narrow bandstop filters for protection against laser light since the late 1970s. This paper presents the latest developments in fixed-line laser technology and introduces a metamaterial solution to mitigate the angular shift found in thin-film interference coatings. The metamaterial coating consists of metallic nano-particles periodically distributed within a non-absorbing dielectric material with a specific refractive index that enables the desired plasmonic resonance to exist at wavelengths that match that of the lasers. Due to the nano-particle size, the metamaterial layer can be treated as an individual homogeneous layer with properties described by an effective Drude-Lorentz approximation model. Unlike standard interference coatings where the effective index of the stack decreases with larger angles of incidence, the metamaterial’s effective index remains relatively fixed with increasing angles resulting in the narrow bandstop function remaining shift-free.

Due to their negligible cost, small energy footprint, compact size and passive nature, cameras are emerging as one of the most appealing sensing approaches for the realization of fully autonomous intelligent mobile platforms. In defence contexts, passive sensors, such as cameras, represent an important asset due to the absence of a detectable external operational signature – with at most some radiation generated by their components. This characteristic, however, makes targeting them a quite daunting task, as their active neutralization requires pinning a small angular diameter moving at a high speed. In this paper we introduce an interpretational countermeasure acting against autonomous platforms relying on featurebased optical workflows. We classify our approach as an interpretational disruption because it exploits the heuristics of the model used by the on-board artificial intelligence to interpret the available data. To remove the struggle of accurately pinpointing such an imperceptible target, our approach consists in passively corrupting, from a perception point of view, the whole environment with a small, sparse set of physical observables. The concrete design of these systems is developed from the response of a feature detector of interest. We define an optical attractor as the collection of pixels inducing an exceptionally strong response for a target feature detector. We also define a physical object inducing these pixel structures for defense purposes as a CLOAK: Countermeasure Leveraging Optical Attractor Kits. Using optical attractors, any optical based algorithm relying on features extraction can potentially be disrupted, in a completely passive and nondestructive fashion.

This paper will report on a first series of experiments of High Energy Laser effects on drones and drone components at TNO. After a description of the 30kW L3O laser facility at TNO, the experimental results will be discussed. The experiments were performed in an indoor facility and some considerations will be given on how to set up the experiments to enable “translation” of the experimental results to outdoor operational scenarios. The results illustrate that there can be large variations in the illumination time of the High Energy Laser on the target before fatal damage is observed, depending on the specific drone component selected as target. This illustrates that target aimpoint selection is critical for the result and a good understanding of the weak spots of drones is required to enable High Energy Laser systems to be effective against drones.

The performance of laser weapon system depends among others on harnessing or mitigation of transient thermal optics effects (trans-TOE’s) occurring inside High Energy Laser (HEL) and in laser optics beam forming train as well. In the developed in last year at MUT laser effector based on of 10-kW fiber HEL the optical train consists of about ten lenses, mirrors and windows including the most critical fiber endcap. We have measured the transient 2D temperature distributions in these optical elements under 10-kW laser beam exposition and compared results to numerical modeling in COMSOL Multiphysics. Applying such experimental / numerical approach the effective absorption in dielectric layers of typical mirrors and in volume of transmissive elements under high laser power were determined. The layer absorption was determined to 20 − 50 ppm for High Reflective (HR) mirrors and less than 10 ppm for Anti Reflecting (AR) coatings. The idea of dynamic self-compensation of trans-TOE’s by means of tailored design of the following transmissive and reflecting elements was proposed. The numerical model of this concept for the simplest combination consisted of 2 HR mirrors and single AR coated lens was presented.

Laser-plasma interactions have many theoretical and technological applications. One is the use of coherently accelerated electrons to provide novel sources of THz radiation. Our research focuses on simulating the cross/self-interactions between two high intensity, ultra-short, counter propagating and detuned laser pulses and an initial neutral target for controlled ionization. Unlike our previous studies of laser-matter interaction over preformed plasma, we explore the injection and collision of laser pulses to induce background plasma driven by the self-guided laser wakefield mechanism, which is then used to perturb the plasma resulting in induced dipole oscillations leading to transverse radiation. Inducing a cylindrical spatial plasma column within the laser beam radius regime provides a stable, spatially localized plasma channel. The emitted radiation from the plasma dipole oscillation (PDO) will not be affected by surrounding plasma absorption, resulting in effective radiation distribution. Results include 3D EM-PIC simulations and a comparison of the self- ionizing plasma against the preformed plasma to assess the efficiency of the mechanisms.

We study how to control the orbital angular momentum, the intensity distribution, and the coherence length of a laser beam based on fiber array coherent combining. The features of the formation of nonzero orbital angular momentum of the beams when the controls the piston phase shift of the fiber array were theoretically and experimentally studied. A new method for controlling the distribution of the intensity of a light field synthesized on the basis of fiber array coherent combining were proposed. The possibilities of controlling the degree of spatial coherence of the synthesized laser beam were studied theoretically and experimentally.

The development of the solid-state fiber laser has given a boost to the possibility of destroying a target without the need for a projectile or blind the photoreceptive element of a heat-seeker missile with laser emission. The growing presence of drones on the battlefield since 2010 and the on-board intelligence on guided missiles have given new credibility to these research programs. Solid state fiber laser, which uses optical fiber as an amplifying medium, has many advantages including efficiency, thermal and opto-mechanical stability, the elimination of free space optics using fiber components, and above all good beam quality thanks to its waveguide. In addition, these coherent sources are available at interesting wavelengths in line with military issues. However, now it is difficult to obtain a high-power fiber source (> 1 kW) while maintaining high beam quality and good spectral coherence. Power scaling whilst preserving beam quality can be achieved through coherent beam combining. The principle is to interfere constructively N mutually coherent single-mode laser beams with proper phase alignment into a single good quality beam. Conventional coherent beam combining is typically based on tiled apertures, for which theoretical maximum efficiency is 67% (due to limited lenses fill factor and secondary lobes in the far field), and for which experimental efficiency is currently below 50%. We present here a novel technique for coherent beam combining based on Multi-Plane Light Conversion. The beam combiner is designed as a spatial multiplexer which output modes form a Gaussian beam when superimposed constructively, reaching theoretically 100% efficiency. Moreover, reflective free-space design allows for high power handling up to 500W. We measure an experimental mode purity above 85% with a total efficiency of 70% (including optical losses) combining 6 beams. This system can be altered to provide error signals for easier phase-locking of the inputs.

Fiber lasers and amplifiers are capable of producing kilowatts of optical output power with diffraction-limited beam quality. We present high precision high power fiber arrays which can be used for coherent and spectral beam combining for scaling of fiber laser systems to high brightness and high power. The availability of CO2 laser-based fiber splicing systems that can control the position and size of the heating zone has opened up new possibilities in the splicing of multiple fibers (fiber arrays) to large optical elements. In our experiments we realized linear fiber arrays with PM and non-PM large mode area (LMA) fiber with no gap between the individual fiber channels (DC-PM-20/400 and DC-PM-25/250). The fibers were spliced to a large AR-coated fiber end cap. The misalignment of the PM axes of all fiber channels was less than ±1 degree and the inline tolerance of the fiber array was below ±2.5µm. Each fiber channel was tested up to an optical output power of 1kW.

While propagating in air in the filamentation regime a high-power ultrashort laser pulse experiences the self-organizing into spatially localized light channels, which represent parts of laser beam with the highest intensity and have angular divergence reduced in comparison with the beam as a whole. We present the experimental results on the main characteristics of post-filamentation channels formed by the filamentation of Ti:Sapphire-laser pulses (744 nm, 90 fs) in air. We found that these post-filamentation channels are characterized by a number of features, namely, broader spectral composition with pronounced red shift against the initial pulse spectrum, strong nonlinear phase modulation, and reduced pulse duration. We showed that the increase of initial pulse energy from 0.5 to 2 mJ does not affect post-filamentation channel energy (about 0.4 mJ) though leads to significant change in its spectrum. Thereby, relatively high intensity (more than 0.1 TW/cm²), low angular divergence (fractions of mrad) and wide spectral range of post-filamentation channel help to obtain an ultra supercontinual pulse spectrum by means of post-filamentation channel recurrent filamentation in a medium with high optical nonlinearity (e.g., solid dielectric). The obtained results can be useful in solving the practical task of high-intensive post-filamentation light channels application in laser pulse energy long-range delivery.

This paper presents the effects of M² (M square) factor of the laser source on steel materials in terms of spot size, duration of exposure and power density. Generally, laser sources are modelled as a Gaussian beam. M² factor is known as the beam quality factor and it represents the degree of variation of a laser beam from an ideal Gaussian beam. It determines how well a laser beam will focus or diverge. According to ISO 11146-1, M² is defined as BPP (Beam Parameter Product) divided by λ/π. It is also related to beam waist and divergence angle. A perfect beam would be a single mode TEM00 laser beam. Single mode fibers have smaller core diameter. It means that it can focus more easily than multi mode fiber laser can. In this study damage effects of CW lasers, which have 1070 nm wavelength, on 1 mm thick steel target plate are examined. Effects of using two different M² values at different output powers are investigated experimentally and the results are discussed. These results will help compare the theory with experimental results.

Quantum cascade laser (QCL) emitting in the mid-wave infrared atmospheric windows (3 μm to 5 μm) will be of immediate use to several civilian applications, including airborne self-defense protection system and trace gas sensing and free space optical communications. At present, the mid-infrared laser sources mainly include solid-state optical parametric oscillation lasers, fiber lasers, and QCL. In these lasers, quantum cascade laser is the only one that can realize the conversion from electricity to light. Since its invention in 1994, with the deepening of scientific research, quantum cascade laser performance has been continuously improved, and the output laser power and beam quality of single transistor has been continuously improved. In this work, the output beam quality of QCL is analyzed. the evaluating method of the laser beam quality is analized in theory based on the Gaussian beam transmittion law. The output nearfiled and farfield of the single quantum cascade laser is measured in the experiment. The output divergence angle is calculated and the output beam quality is analized by using the M² factor.

High-power laser plays an important role in many fields, such as directed energy weapon, optoelectronic contermeasures, inertial confinement fusion, industrial processing and scientific research. The uniform nearfield and wavefront are the important part of the beam quality for high power lasers, which is conducive to maintaining the high spatial beam quality in propagation. We demonstrate experimentally that the spatial intensity and wavefront distribution at the output is well compensated simultaneously in the complex high-power solid-state laser system by using the small-aperture spatial light modulator (SLM) and deformable mirror (DM) in the front stage. The experimental setup is a hundred-Joule-level Nd:glass laser system operating at three wavelengths at 1053 nm (1ω), 527 nm (2ω) and 351 nm (3ω) with 3 ns pulse duration with the final output beam aperture of 60 mm. While the clear arperture of the electrically addressable SLM is less than 20 mm and the effective diameter of the 52-actuators DM is about 15 mm. In the beam shaping system, the key point is that the two front-stage beam shaping devices needs to precompensate the gain nonuniform and wavefront distortion of the laser system. The details of the iterative algorithm for improving the beam quality and the strategy of achiving high beam quality on spatial intensity and wavefront simultaneously are presented. Experimental results show that the output wavefront RMS value is 0.06, and simultaneously the output near-field modulation is 1.38:1 and the fluence contrast is 10.5% at 3 ns at 1053nm with 40-Joule-level energy.

Today we are reliant on a growing range of space-based assets. To assess inherent space-related risks it is critical to evaluate existing and planned systems. Here we summarise 2019-2020 findings from a wide range of participants. Our analysis includes: the importance of: persistency, all-weather, night and day capabilities, satellite image resolution, and other technical requirements. Hybrid threats, cyber warfare, GPS ‘spoofing’, jamming, and EMP are part of a new generation of threats becoming relevant with rapid space domain exploitation, in addition to space weather impact [1].