This PDF file contains the front matter associated with SPIE Proceedings Volume 13201, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Advanced resonator designs for Ho³⁺:YAG lasers and ZGP OPOs are presented. A segmented Ho³⁺:YAG crystal for power scaling was investigated. An improved power performance could not be shown up to 60W of output power, which is attributed to the low overall crystal temperature. Exploiting the Porro prism resonator concept for the first time, a 200-times increased alignment tolerance compared to a corresponding mirror resonator was achieved. The performance of a ZGP OPO could be improved by a negative lens in the resonator, which significantly enhances the beam quality.

Coherent Beam Combining (CBC) is one of the novel methods aiming to increase laser output power and intensity, especially in cases where applications require both high power and high beam quality. CBC offers a way of exceeding limitations of a single-fiber laser source, allowing for excellent scalability and high efficiency operation. Simulating and optimizing the intensity of the far-field is crucial when designing a CBC system. This paper focuses on a way of approaching numerical solution of the electric field intensity along the Rayleigh range of multiple Gaussian beams coherently combined over large distances. It aims to circumvent the restrictions of computational capacity faced by most numerical methods when solving for the optical field propagation over large geometries by combining ray and wave optics approach. Output intensity fields for coherent combination of 6, 12, and 20 channels operating at a wavelength of 1550 nm are presented, using a Cassegrain type telescope as beam combiner. Influence of design parameters and near field arrangement is examined and results are compared with previously reported experimental values.

Backwards Wave Optical Parametric Oscillators (BWOPOs) eliminate the need for a resonant cavity, offering a compact and robust alternative to traditional OPOs. In this study, a BWOPO using a PPKTP crystal with a 765 nm poling period was pumped by a Q-switched laser at 1030 nm, delivering 40 μJ pulses. The backward wave generated at 2.8 μm exhibited a narrow spectral bandwidth of 1.75 GHz, despite the pump's broad 360 GHz bandwidth. The extracted pulse energy was around 5 μJ. These results highlight the BWOPO's potential for applications requiring precise wavelength control and stability.

As new threats arise in orbit, military forces need to protect their most valuable satellites. MBDA’s long term vision is to offer reactive military capabilities in Low Earth Orbit (LEO) enabling the delivery of graduated military effects against threats to high-value assets. Technical solutions must be compatible with a lawful and responsible use of space. In such context, potential effectors include High-Energy Lasers (HEL). The lack of real-world data on potential satellite vulnerabilities against HEL led MBDA to develop new testing capabilities to provide representative environments and technologies at laboratory scale. The objective is to provide quantitative responses to be able to dimension the effector with on-board energy, laser power and engagement characteristics. This effort is supporting the development of technologies enabling neutralisation of low-orbit threats while ensuring in-orbit safety and weapon assurance. MBDA and ALPhANOV operate a common test facility called the Vulnerability Test Facility (VTF), enabling the reproduction of realistic engagement conditions. The continuous improvement and implementation of its experimental capabilities leads to the enrichment of an experimental vulnerability database of all kinds of threats subject to Laser Directed Energy Weapons (LDEW).

The use of drones and Unmanned Aerial Vehicles (UAVs) poses an increasing aerial threat in both military and civilian sectors. High-Energy Laser (HEL) systems emerge as a promising way to countermeasure these threats with excellent precision and minimal collateral damage. Considering that UAVs and drones are predominantly constructed from lightweight construction materials like Carbon Fiber-Reinforced Polymer (CFRP), investigating the vulnerability of this material class becomes crucial, as it directly impacts the resistance of these platforms against high-energy laser countermeasures. This study presents research on HEL interactions with Carbon Fiber-Reinforced Polymer (CFRP) composites, exploring the effects of Continuous Wave (CW) laser powers of up to 120 kW. We established a laboratory environment that meets the demands of operational safety requirements for laser processing of CFRP including a robot-controlled sample exchange and automatic laser beam shut-off. The interaction of the laser with the composite material was evaluated using high-speed images showing the rapid expansion of a smoke cloud, that contains fragments of fibers and a partially ionized plasma. Experiments reveal a decrease in perforation times with increasing laser power, which can be described by a power law. A detailed examination of the damaged samples, visually and via micro-focused computed x-ray tomography, offers insights into heat affected zones and ablation dynamics. Furthermore, Compression After Impact (CAI) tests assess the residual strength of the irradiated CFRP panels. A decrease of the compressive strength of a factor of about two is observed. The outcomes of this research contribute to the understanding of CFRP behavior under extreme laser conditions, providing valuable knowledge of the dynamic interactions between high-energy lasers and complex composite materials, highlighting potential applications for countermeasures in defense technology.

We have developed a method which allows us to measure a time-dependent temperature profile on the backside of a flat piece of material which is, on the front, irradiated by a high-power laser beam. This is achieved by application of a 50 µm thick strip of ResbondTM989FS – a material with known low and flat reflectivity of ∼0.12 in the range of 4–8 μm. Imaging this strip with an IR camera provides the time-dependent temperature profile which agrees well with control measurements using thermocouples. Solving the heat equation by the Greens-function method may model the time-dependent temperature field throughout the material, including the front. Experiments have been performed at three different laser power settings and with two different beam diameters. We have measured and successfully modelled steel and aluminum alloys with different coatings and without. Modelling a brass alloy requires a sudden change in laser absorption around 600°C. Measuring a titanium alloy proves challenging due to a sudden onset of an exotherm reaction with the air’s oxygen. For carbon fiber plates, ablation is found to be a more dominant mechanism than heat conduction. Overall, high-power laser absorption is found to be rather independent of the coating (which often burns away in a flash) and ∼50% less than expected from a measurement of reflectivity of the bare material at low power. Our numbers (derived at 915 nm wavelength) are also somewhat different from the ones by Reich et al. for their laser, reported at last years conference.

Unmanned Aerial Systems (UAS) and Unmanned Aerial Vehicles (UAV), commonly known as drones, are increasingly being used in both civil and military contexts. The advances in embedded computing power are enabling some UAS to operate fully autonomously, posing significant challenges to existing countermeasures. In response to this evolving threat landscape, Directed Energy Weapon (DEW) technologies, including Hiigh Energy Lasers (HEL), are emerging as promising solutions in the Counter-UAS (C-UAS) domain to complement kinetic means. This is due to their low cost per shot, virtually unlimited ammunition capacity, speed-of-light engagement, high accuracy level, and scalability of on-target effects tailored to the UAS threat level. This study aims to evaluate the effectiveness and performance of HEL technology as a killchain-integrated C-UAS solution in various scenarios, using modelling and simulation, and comparing those to what could be obtained by using kinetic effectors. Such performance is obtained by integrating simplified representations of UAS with parametric HEL and kinetic effector models. This paper contributes to ongoing efforts to improve security measures against the escalating threat of drone proliferation in today’s dynamic and complex environments.

Directed energy laser weapons are becoming more common on the global battlefield, with an increasing prevalence of both Earth-based and space-based platforms expected in the future. The thermal impact of these laser weapons can be significant and understanding the potential for thermally induced physical damage as a function of power, beam focus and time on target is critical to mission planning. Testing is often understood to be the standard for truth in this regard, but it can be difficult to depend entirely on laboratory or field testing, especially when adversarial targets and/or challenging environments are the focus of such studies. For example, the thermal impacts of directed energy laser weapons on foreign targets in inaccessible environments can be challenging to understand via testing alone. The need to understand the thermal impact of directed energy laser weapons in situations where testing is difficult or impossible motivates the use of transient thermal prediction software. Adversarial targets in inaccessible environments can be simulated, and scientific studies can be performed by varying laser power, beam focus and time on target. Additionally, the effectiveness of possible countermeasures can be evaluated by simulating with and without the countermeasure and computing the reduction in thermal impact due to the design change of interest. In this paper we report on a methodology for simulating the transient thermal impact of laser weapons on orbiting satellites. We demonstrate how critical factors such as power level, beam focus and time on target can be included. We report time-dependent physical temperatures and show how the efficacy of countermeasures can be evaluated.

We present first results from a study on the feasibility and impact of laser dazzling on drones, covering both laboratory and field tests. The research focused on the effects of laser dazzling on drone cameras and collision avoidance systems across various scenarios, including surveillance, attacks, and obstacle avoidance maneuvers with commercially available drones. These scenarios were tested in field studies using a green laser mounted on either a hand-held weapon frame or a manually tracked tripod equipped with a camera. This study highlights the potential vulnerabilities of UAVs to laser dazzling and aims to improve understanding of effective defense mechanisms in drone security.

When using a high energy laser beam in a maritime environment, a laser safety concept is required to protect personnel or uninvolved third parties from uncontrolled reflections of the laser light from the sea surface. Therefore, the knowledge of the amount and direction of reflected laser energy is crucial. These vary statistically and depend largely on the dynamics of the wavy sea surface that are mainly influenced by wind speed, wind direction, and fetch. A numerical model is used to calculate the time-dependent spatial intensity distribution of the laser beam reflected from the dynamic sea surface. The specular reflection of laser light is modeled by an analytical statistical Bidirectional Reflectance Distribution Function (BRDF) of the sea surface. The model also identifies the hazard distances where the laser intensities exceed a defined exposure limit. Thereby, the forward reflected radiation is of great interest for estimating the risk to third parties and the backward reflected radiation to the laser source for assessing the risk to own forces. The calculated time-dependent intensities are presented for observer positions on a quarter-circular arc of the specular plane of incidence with fixed radii from the center of the laser spot for the two reflection hemispheres. In addition, the determined probabilities of exceeding a defined exposure limit are shown.

Infrared (IR) imaging is crucial for military surveillance, targeting, and detection systems. In common with all electro-optical imaging devices, they are vulnerable to in-band laser strikes, causing pixel saturation, image dazzling and potential array damage. An obvious safeguard is inserting a filter that blocks the expected laser wavelengths without significantly reducing the imager’s performance. The perfect countermeasure! However, our results indicate a side effect: a high power-density laser that permits dazzling even in the transmission band of the filter. A continuous-wave Quantum Cascade Laser (QCL) with a peak wavelength of 4.57 microns and output power of approximately 300 mW irradiates the thermal infrared imager sensing in the Mid-Wave Infrared (MWIR). The IR imager has a filter wheel with two dielectric-stacked infrared bandpass filters outside the laser’s wavelength, positioned internally between the detector dewar and telescope. The images were radiometrically calibrated over four integration times under conditions with and without each filter. In summary, our observations indicate a counterintuitive result. There are dazzling effects observed through filters out of band with the laser, with the most significant being for the bandpass filter closest to that of the laser wavelength.

Research into thermal blooming effects in laser beam propagation has been initiated within ten years after the first demonstration of a laser. Results of these studies have been published in excellent review papers. Now several decades later, developments in laser technology are bringing High Energy Laser systems closer to actual operational application and to power levels where thermal blooming might affect the system performance. In support of understanding HEL performance and development of potential mitigation measures, it is of interest to be able to estimate the limits when a system will enter conditions where thermal blooming will affect performance. This will also support understanding of potential mitigation measures. This paper discusses which parameters influence thermal blooming in a High Energy Laser system in several realistic scenarios. The influence of these parameters on the laser beam are illustrated analytically for a collimated High Energy Laser beam. We provide a simplified derivation of the distortion parameter as presented in the review papers. This distortion parameter will be used to explore the effect of thermal blooming on three generic HEL systems: short range (I), medium range (II) and large range (III), with corresponding power levels for more complex beam shapes, thermal blooming effects on the power on target are analysed with wave optics simulations. Thermal blooming critically depends on the atmospheric conditions. More specifically: the molecular absorption, the wind speed component perpendicular to the beam and the atmospheric transmission losses due to scatter and absorption by aerosols and molecules in general. The averages of these parameters and their variability over location and time, have been analysed by exploring a data base over weather parameters collected over the whole of Europe in 2019. For a specific location in the Mediterranean their effect on thermal blooming in a generic large range HEL system are calculated. The combined effect of turbulence and thermal blooming has been investigated as well, to explore where one or the other effect might dominate and how the combined effect degrades HEL-system performance. Finally, some considerations on mitigation of thermal blooming effects by system design choices or change in wavelength are given.

The whole defense community recognizes the threat posed by UAV on the battlefield and the current lack of economically sustainable counter systems. MBDA’s answer is Sky Warden, a modular, scalable and evolvable system designed to integrate and control a large panel of sensors and effectors, in particular High-Energy Lasers (HEL), in order to neutralize class one and two UAVs. The lack of knowledge of HEL performance against UAV threats leads MBDA to explore experimentally HEL-UAV engagement scenarios. With tests performed at laboratory scale, we examine the level of vulnerability (Kill Probability) of UAVs in known conditions. The representativeness of dynamic laser-target interaction emulating atmospheric perturbations (absorption, diffraction, turbulence…) and target attitude evolution (incidence, speed…) is essential for the progressive development of meaningful vulnerability models. MBDA and ALPhANOV operate a versatile and common test facility, the Vulnerability Test Facility (VTF), enabling the reproduction of realistic engagement conditions. The improvement and implementation of its experimental capabilities for target vulnerability assessment lead to the continuous enrichment of an experimental database. Based on this data and a generic vulnerability approach, MBDA extends its field of knowledge in order to improve the effectiveness of destruction of UAVs by HEL.

Heat-seeking missiles continue to be serious threats to aircrafts. In recent years, open-loop DIRCM systems have proven to be efficient countermeasures against these missiles. However, closed-loop DIRCM systems seem to be more promising as they employ a jamming code based on the classification or identification of an incoming missile through retro-reflection from the seeker head. In these systems, the retro-reflected beam is influenced by the optical turbulence in both transmission and return paths. In this paper, the influence of optical turbulence on the identification performance of a closed-loop DIRCM system is investigated. A dataset is created by varying the seeker spin and carrier frequencies along with the optical turbulence levels and range. Deep neural network classifiers were trained on this dataset and evaluated in terms of their effectiveness in identifying missile seekers with the DIRCM system.

The ongoing development of High Energy Laser (HEL) weapon systems is leading to a new suite of potential anti-satellite (ASAT) capabilities among both spacefaring and non-spacefaring nations. Powerful ground-based HEL systems may be used to dazzle or damage sensors or disable entire satellites. Such uses offer several advantages over other counterspace capabilities. HEL weapons could be used both in an offensive and a defensive manner and may be difficult to attribute to a specific actor. Furthermore, in some cases the physical effects are reversible, and the use of HEL may significantly limit the creation of space debris compared to other ASAT capabilities. The very long slant-paths through the turbulent atmosphere, coupled with the necessity to track and engage fast-moving objects in Low Earth Orbit (LEO) makes this particular application an interesting cross-over between typical HEL technology, astronomical instrumentation, satellite and space debris laser ranging, and laser satellite communication. In this paper we will review some of the scenarios and physical effects that may be expected from HEL systems used as an ASAT capability. We show that HEL systems of even moderate powers may pose severe risks to the sensors of imaging satellites passing overhead. We also find that the laser fluence delivered to a satellite on a single passage could easily reach the damage thresholds of many of the components that a satellite needs in order to function. A fourth scenario in which HEL is used to provide a negative impulse to alter the orbit or even de-orbit a small LEO satellite seems unlikely but merits some attention as a potential future capability.