Yb:CaF2 thin-disk laser

We present Ytterbium-doped CaF2 as a laser active material with good prospects for high-power operation in thin-disk laser configuration owing to its favorable thermal properties. Thanks to its broad emission bandwidth the material is also suitable for the generation of ultra-short pulses. The properties of the crystal as well as the challenges related to the coating, polishing, mounting and handling processes which are essential to achieve high power laser oscillation in thin-disk configuration are discussed. A wavelength tunability of 92 nm is demonstrated, which confirms the potential of Yb:CaF2 for the generation of ultra-short pulses. An output power of 250 W with an optical efficiency of ηopt = 47% was measured in CW multimode thin-disk laser operation with a pump spot diameter of 3.6 mm. Using a smaller pump spot diameter of 1 mm the fundamental mode output power was 13 W with an optical efficiency of ηopt = 34%

Improved X-ray detection and particle identification with avalanche photodiodes

Avalanche photodiodes are commonly used as detectors for low energy x-rays. In this work we report on a fitting technique used to account for different detector responses resulting from photo absorption in the various APD layers. The use of this technique results in an improvement of the energy resolution at 8.2 keV by up to a factor of 2, and corrects the timing information by up to 25 ns to account for space dependent electron drift time. In addition, this waveform analysis is used for particle identification, e.g. to distinguish between x-rays and MeV electrons in our experiment.Comment: 6 pages, 6 figure

Experimental Investigations on Power Scaling of High-Brightness cw Ytterbium-Doped Thin-Disk Lasers

The core topic of the present thesis is the improvement of the brightness of thin-disk lasers at a targeted output power of one kilowatt and beyond. For an output power of several kilowatts the intention was to approach a beam quality factor of M2≈ 8, whereas for the thin-disk lasers with an optical output power up to one kilowatt a near diffraction limited beam quality was aimed. Multi-kilowatt beams with high brightness offer advantages for fast and precise material processing applications such as remote cutting, where the beam must propagate over large distances. In the second case a thin-disk laser generating ultrashort pulses can be developed in a further stage. In order to improve the beam quality of a thin-disk laser it is essential to know very precisely how the thin disk deforms in laser operation whereby special attention has to be paid on the aspherical part of this deformation which can be in the order of a few tens of Nanometers. For this reason, an interferometric setup was developed which was optimized to measure the disk deformation during laser operation with high precision. Thus, interferometric measurements in real-time could be carried out when operating the different thin-disk lasers up to an optical output power of approximately four kilowatt. The obtained results were directly used to optimize the beam quality of each thin-disk laser individually

Design of a transportable 1 kW Thin Disk Amplifer with high pulse energy for laser range finding

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

Kohärent gekoppelte Halbeiterlaser als Stahlquellen für Laserwaffensysteme - Chancen und Herausforderungen sowie erste experimentelle Resultate

Halbleiterlaser sind Laserquellen, die eine direkte Umwandlung elektrischer Energie in optische Strahlung ermöglichen. Aufgrund ihres Funktionsprinzips ist dies mit vergleichsweise hohem Wirkungsgrad möglich, zugleich sind Halbleiterlaser sehr kompakt. Die Wellenlänge der erzeugten optischen Strahlung kann durch die verwendeten Halbleitermaterialien relativ flexibel gewählt werden. Die für die Nutzung als Hochenergielaser erforderliche Strahlqualität/Fokussierbarkeit und Laserleistung kann allerdings nur durch geeignete Kopplung vieler Halbleiterlaserquellen erreicht werden. Für die Kopplung kommen grundsätzlich zwei Verfahren in Frage: die sogenannte „kohärente Kopplung“, bei der die relative Phasenlage der Einzellaser geregelt wird und die spektrale Kopplung, die auf einer Strahlkombination durch wellenlängenselektive Bauteile beruh

Thin Disk Laser Development for Space Debris Monitoring and Mitigation

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

Single-stage Yb:YAG booster amplifier producing 2.3 mJ, 520 fs pulses at 10 kHz (Orale)

International audience520fs, 2.3-mJ pulses are demonstrated in a Yb:YAG booster amplifier delivering peak powers up to 4.4GW. To avoid damage and nonlinear-effect issues, passive divided pulse amplification is studied for the first time for bulk-amplifier. Great efforts have been deployed in the development of laser systems delivering femtosecond pulses for industrial and scientific applications. Among all available technologies, fiber lasers came out as one of the best choice due to their capability to deliver short pulse duration (typically 300 to 500 fs) together with high average power within very reliable and robust systems. Nevertheless, one of the main drawbacks remains the limited output energy available for such laser due to the strong confinement of the light. Standard femtosecond fiber lasers can deliver typically up to 10s µJ energy pulses; and lasers based on rod type technology allow to reach up to the mJ level for laboratory systems [1-2] and 200 µJ for industrial systems. We propose here to enhance the energy from fiber sources by implementing a very simple, but optimized, Yb doped YAG booster stage. This booster consists in using a cm-long crystal to have a simple high gain booster together with a rather-modest length to prevent from deleterious nonlinear effects like self-phase modulation and critical self-focusing. Secondly, the use of a simple and passive divided pulse amplification (DPA) setup [3] is also investigated, in order to exceed the energy limitation. We investigate how the DPA permits to overcome the laser threshold limits from 2.9 mJ to 4.1 mJ. This simple and straightforward amplifier geometry allows to deliver, in a nominal and safe regime, ultrashort pulses below 520fs for energy of 3mJ (before compression) 2.3 mJ after. We demonstrated then pulses up to 4.4 GW of peak power. The fiber laser source used is a standard industrial laser-developed by Amplitude Systems-that delivers pulse energy 180µJ up to 100 kHz repetition rate with duration of 350 fs. By limiting output energy below 200µJ, nonlinear effects and damages threshold in the laser are safely avoid. The Yb:YAG booster is implemented between the fiber amplifier and the compresso

High power and high energy femtosecond lasers based on hybrid architectures (orale)

International audienc