Modeling the thermal response of materials to high-power continuous-wave laser irradiation is essential for directed energy applications. We present a newly developed simulation framework that predicts burn-through times by solving heat diffusion in cylindrical coordinates on a two-dimensional grid. The model accounts for anisotropic and inhomogeneous material properties, phase transitions between solid, liquid, and gas, and erosion of cells that reach a defined phase threshold. Robin boundary conditions are implemented to capture realistic surface and interface heat exchange. The software includes a flexible material database that allows for easy integration of user-defined target designs and material properties. Laser irradiation can be applied using arbitrary spatial intensity distributions. To simplify usage, common intensity distributions like Gaussian and top-hat profiles are implemented. The program produces spatio- temporal maps of temperature fields and phase boundaries, which can be exported as graphs and animations for interpretation. The framework is implemented in Python with modular code structure for easy extension. It targets scenarios requiring efficient prediction of thermal penetration and material removal thresholds, such as determining burn-through times for directed energy applications. While not limited to burn-through prediction, the focus is on macroscopic heat transport and phase transitions. The framework provides a versatile and computationally efficient tool for evaluating material response under intense laser irradiation.

Material Processing tends to demand high pulse energies as well as high average output powers. For the past decade one successful technology is the thin-disk based multi-pass amplifier which can achieve 1 kW of average power and ultrashort pulses combined with excellent beam properties at up to 700 mJ of pulse energy [1], [2].

Over the last decade, multipass thin-disk amplifiers have allowed astonishing laser properties to be achieved, but one drawback of these systems lies in their size and complexity. We show here an alternative approach with a wedged thin-disk crystal significantly shrinking and simplifying multipass thin-disk amplification.

Amplifying ps-laser radiation to high pulse-energies as well as a high average output power is a challenging task. In the past it was shown that thin-disk multipass amplifiers can achieve excellent properties for ultrashort laser pulses at over 1 kW of average power. Furthermore, systems combining multipass and regenerative thindisk amplifiers achieved 700mJ of pulse energy at a repetition rate of 1000 Hz. These systems reaching such excellent properties are complex, extensive and typically need dozens of mirror-optics and the corresponding space associated with those. With the introduction of our monolithic wedged thin-disk (WTD) concept we were able to demonstrate small signal laser amplification of up to 10 (+10 dB) for cw-systems with a drastically reduced amount of mirror optics as well as space needed. By adding a redirecting mirror to introduce two multipasses in the WTD we were able to amplify a 2 ps-laser source with a small signal gain of up to 55 (+17 dB) and at 20W seed power by a factor of 5 (+7 dB) reaching up to 100W of output power.

Creating a laser system with a high average output power and at the same time high pulse energies is a challenging task. In the past it was shown that thin-disk multipass amplifiers can achieve excellent properties for ultrashort laser pulses at over 1 kW of average power [1]. Furthermore, systems combining multipass and regenerative thin-disk amplifiers achieved 700 mJ of pulse energy at a repetition rate of 1000 Hz.

Space debris laser tracking is a versatile tool for mitigation of collision risks in low earth orbit. Thin Disk lasers are highly suitable to provide the required laser parameters. A transportable kW-class pulsed laser system was developed and tested. New Thin Disk concepts promise a more compact future system. Beyond monitoring, the Thin Disk can also be part of a ground-based laser debris removal system.

We analyze the conceptual idea whether already a single high energy laser pulse, emitted from a laser station on ground, might cause material ablation at the surface of a debris object generating recoil for a sufficiently high velocity change to allow for space debris collision avoidance. In our simulations we assess the effects of atmospheric constraints like laser power loss due to aerosol extinction as well as laser beam broadening and pointing jitter as a result from atmospheric turbulence. For the compensation of turbulence, the usage of adaptive optics is explored in terms of a suitable transmitter configuration in combination with a laser guide star. Based on the ESA DISCOS catalogue, virtual targets with simplified geometric shapes are employed to investigate laser-matter-interaction with rocket bodies, mission-related objects and inactive payloads. In addition, the NASA Standard Breakup Model serves as a reference for fragments from collisions and explosions yielding an ensemble of 9101 debris targets in the Low Earth Orbit. For these objects, a study on laser-ablative recoil is carried out using a raytracing-based code considering both the unknown target orientation as well as residual laser pointing errors constituting sources of randomness in overall 5 dimensions (3 rotational, 2 translational) which are addressed in a Monte Carlo approach. Laser momentum coupling is calculated for the computed laser fluence distribution at the mean altitude of the particular debris object. As input for the calculation of laser-matter interaction, experimental data from the irradiation of aluminum, copper, and steel as representative space debris materials are employed. The simulation results on laser-imparted momentum are discussed in terms of irradiation elevation angle, displacement on the orbital trajectory, momentum transfer uncertainty, success probability, debris material and limitations due to debris size, mass, and the required minimum fluence for the initiation of a laser ablation process.

Thin-disk lasers are indispensable in photonics research as well as in a multitude of industrial applications. They represent a unique class of laser and amplifier architecture that provides kW output power with excellent properties concerning beam quality, long-term stability, thermal management, and power scalability. For many applications, a reduced complexity of the laser and its size would be highly beneficial. The necessary multipass transitions in thin-disk lasers and amplifiers typically require sophisticated multi-mirror arrangements. Here, we present a monolithic version of the pump concept for thin-disk lasers and amplifiers, where the thin disk is replaced by a thin, wedged gain medium acting as a wedged optical trap. The wedge is coated in a peculiar manner in order to allow for efficient in- and out-coupling of the pump and laser radiation from the wedge. This concept transfers the complexity of the multi-mirror optics into the thin disk itself in a monolithic fashion. With this concept, we achieved 890 W of CW output power, 59% slope efficiency, optical-to-optical efficiency of 50%, and a gain factor greater than 10 for small signals. This demonstrates that this new concept is capable of reaching the kW power regime with minimum complexity and size.

We present a new pump geometry for compact thin disk lasers. Multi-pass pumping without external pump optics is realized with a uniquely coated wedged laser medium. CW output powers of 700 W are achieved.

Laser propagation is severely affected by atmospheric turbulence. The capability of a tiled aperture coherent coupling approach is investigated numerically regarding the mitigation of such turbulent aberrations w.r.t. the number of emitters and other parameters. © 2019 The Author(s)

Summary form only given. Throughout the past years the scaling of laser brightness by building larger laser oscillators stagnated. Therefore, alternative methods termed coherent beam combining moved to the centre of interest in research to increase the laser brightness using multiple separate laser systems. Especially, in the case of master oscillator (MO) power amplifier (PA) systems the control of phase noise introduced by the power amplifier posts a promising approach [1, 2]. Our thin disc PA system tends to introduce large phase strokes over a large range of frequencies, which typically would be approached by the use of a "woofer / tweeter" arrangement. Woofer and tweeter setups add to the complexity of the servo loop. Therefore, we decided to amplify the phase stroke of a piezo phase modulator optically to work towards a high phase stroke of several lambda as well as several 10 kHz of servo loop bandwidth. We will show the results for the capabilities of the phase modulator to extant the optical phase stroke by a factor of > 40 at frequencies up to 100 kHz and how to possibly extend the use of the WOLIT arrangement into the power amplifier itself.

Due to the low absorption of pump light in a thin disk laser, the pump light has to be redirected multiple times onto the active medium in order to achieve high pumping efficiency. Therefore, the pump optics in current systems require a large volume compared to the thin disk itself and multiple optics have to be aligned correctly with each other. Our wedged optical lasing chamber for ytterbium disks (WOLCYD) consists of an optical long-pass filter placed at a small angle directly in front of the thin disk. By this, an in-place multiplication of the number of pump passes is achieved. This results in a compact pump optic without the need of sophisticated alignment efforts. We demonstrate a laser oscillator setup and a laser amplifier setup on the basis of the WOLCYD geometry.

We present simulations of thin-disk amplifiers considering amplified spontaneous emission (ASE), as the ASE can have a crucial influence on achievable gain, especially for high energy, medium rep-rate pulse amplifiers. The model needs to incorporate the full spatial distribution of inversion and - due to the quasi-3-level nature of the typical active ion Yb 3+ , i.e. the temperature dependence of effective cross sections [1]-the temperature distribution in the thin disk. ASE-photon flux has to be resolved with high spatial and spectral resolution to incorporate the spectral emission distribution [2]. Furthermore, we also need to take into account the radiation guiding effect of the thin disk, i.e. the multiple reflections of ASE and fluorescence at the back- and front side of the disk [3]. Due to the significantly non-linear dependence between inversion and ASE, a transient model, reproducing the temporal evolution of absorbed pump power, amplified laser power and ASE-photon flux is required [4]. A fast implementation in Python allows us optimizations with variations on large parameter sets in the future.

The design of the Thin Disk main amplifer for a projected transportable pulsed laser system with 1 kW average power was optimized based on numerical modelling. The numerical models include spatially resolved ASE effects, thermomechanical modelling of the disk and beam propagation effects inside the amplifer.

Signifikante Steigerungen der Brillanz von Halbleiterlasern in den letzten Jahren fuhren zu einem vermehrten Ersatz von Festkorperlaser-Systemen durch die direkte Anwendung von Halbleiterlasern. Auch fur Hochenergielaser wurde eine direkte Anwendung von Halbleiterlasern Vorteile bieten, vor allem bezuglich Masse, Volumen und Wirkungsgrad. Allerdings ist derzeit die absolute Leistung der Einzelemitter mit guter Strahlqualitat noch zu gering, so dass fur hohe Leistung bei guter Strahlqualitat Kopplungskonzepte unabdingbar sind. Die Moglichkeiten der spektralen Kopplung sind aufgrund der verfugbaren atmospharischen Fenster fur Hochleistungsanwendungen uber grose Entfernungen stark eingeschrankt; bei passiver Kopplung skaliert die Effizienz schlecht bei hoher Emitteranzahl. Aktive koharente Kopplungskonzepte fur Einzelemitter bilden deshalb die Schlusseltechnologien fur Lasereffektoren der Multi-Kilowattklasse.

We present a side-respectively end-pumped Nd:YAG laser system at a laser wavelength of 1116 nm. The third harmonic of this wavelength at 372 nm can be used for LIDAR detection of molecular iron in the middle atmosphere at the height of about 70 to 120 km. Such measurements give information about temperature profiles and wind speeds in this atmospheric region and thus help in validating and calibrating global circulation models [1, 2].

Space debris presents an increasing threat to the lifetime of commercial and military space assets. Laser-based space debris removal systems could potentially mitigate this threat by targeting debris objects in the cm-range. In order to reach this goal a minimum fluence of a few J/cm² on the debris object and a pulse repetition rate of several 10 Hz are necessary. These requirements can be met by coupling 1000-2000 independent 10 J laser sources coherently and employing a sending telescope with a diameter of 5 m. We analyze which parameters are critical to the effectiveness of the transmission system and deduce design guidelines. In particular the effects of non-optimum filling factors, secondary mirror size, emitter intensity distribution and phase jitter of the individual emitters are discussed and compared.

During the early 1990s, collaboration between the German Aerospace Center and the University of Stuttgart started to work on the Thin Disk concept. The core idea behind the thin disk design is the use of a thin, disk-shaped active medium that is cooled through one of the flat faces of the disk. This ensures a large surface-to-volume ratio and therefore provides very efficient thermal management. Today, the thin disk concept is used in various commercial lasers – ranging from compact, efficient low power systems to multi-kW lasers, including cw lasers and also pulsed (femtosecond to nanosecond) oscillators and amplifiers. The whole development of the Thin Disk laser was and will be accompanied by numerical modeling and optimization of the thermal and thermo-mechanic behavior of the disk and also the heat sink structure, mostly based on finite element models. For further increasing the energy and efficiency of pulsed Thin Disk lasers, the effects of amplified spontaneous emission (ASE) are a core issue. Actual efforts are oriented towards short pulse and ultra-short pulse amplifiers with (multi-)kW average power or Joule-class Thin Disk amplifiers, but also on new designs for cw thin disk MOPA designs.

Die Zielsetzung der hier vorgestellten Arbeit ist die Entwicklung eines deformierbaren Spiegels fur hohe Laserleistungen. Dieser Spiegel soll verwendet werden, um thermisch induzierte Phasenstorungen im laseraktiven Medium zu kompensieren. Grundlegendes Funktionsprinzip ist hierbei die gezielte lokale Deformation eines hochreflektierenden Laserspiegels. Diese Deformation wird durch lokales Aufheizen des Glassubstrats des Spiegels erzielt. Diese Aufheizung wird durch raumlich strukturierte Beaufschlagung mit Strahlung bei einer vom Glassubstrat absorbierbaren Wellenlange erreicht. Die Intensitatsverteilung der Bestrahlung wird mittels eines DLP (Mikrospiegelarray) gesteuert. Als Bestrahlungsquelle wird ein fasergekoppelter Diodenlaser verwendet. Fur die Auslegung des Spiegels wurden numerische Simulationen durchgefuhrt und die erzielten Deformationen des Spiegels analysiert. Wichtige Auslegungsparameter sind die erreichbare Auflosung sowie der maximale Phasenhub. Basierend auf diesen Berechnungen wurden die Komponenten entwickelt und hergestellt. Fur die experimentelle Charakterisierung des Spiegels wurde dessen Oberflachendeformation mit einem Shack-Hartmann Sensor gemessen. Hierbei wurde vor allem das Verhalten des deformierbaren Spiegels bei verschiedenen Bestrahlungsintensitaten und Intensitatsverteilungen untersucht.

The large and rising number of space debris particles in low earth orbit (LEO) is posing an increasing danger to LEO satellites and the ISS. For example, even sub-centimeter particles can cause significant damage to solar panels; cm-class objects can destroy satellites. In the medium term, this threat can limit the use of popular orbits that have a high density of space debris. A first step in dealing with space debris entails locating and tracking even small debris objects with high precision to calculate orbital data and evaluate the threat they pose to satellites. After an initial passive optical detection of particles, a ground-based, high energy laser is required to obtain precise distance information through time-of-flight measurements. For this purpose, a 1 J, 1 kHz laser system with good beam quality based on thin-disk laser amplifiers is under development. Here we present the current status of the experiment and give an overview of the planned laser setup.