Design and Setup of a Post-Compressor Adaptive Optics Loop at PHELIX

This work aimed to provide advanced control over the focal spot of the PHELIX laser by the means of implementing a post-compressor adaptive optics loop. The ultimate goal was to increase the peak intensity on the target, which is critical for a lot of experiments that are based on laser-plasma interaction. Over the course of this thesis, I implemented an ultra-compact wavefront sensor, which could successfully measure the wavefront over the full 28 cm aperture of the PHELIX laser on a footprint of 2×1 meters for the full energy range of PHELIX. This sensor was used to run a closed control loop with a commercial deformable mirror. Furthermore, I developed a calibration routine for the sensor, which enabled finding the optimum achivable wavefront at the focal spot in the target chamber. Together with this routine, I was able to triple the intensity on target up to 1.4·10²¹ W/cm². This was the first time where an intensity of more than 10²¹ W/cm² could be reached systematically at PHELIX. Lastly, we performed an experiment in the group which provided a qualitative prove of the on-shot intensity gain by observing the transmission of the laser pulse through polystyrene foils of various thicknesses. The result verified the successful optimization of the peak intensity

A study on the effects and visibility of low-order aberrations on laser beams with orbital angular momentum

Laguerre-Gaussian-like laser beams have been proposed for driving experiments with high-intensity lasers. They carry orbital angular momentum and exhibit a ring-shaped intensity distribution in the far field which make them particularly attractive for various applications. We show experimentally and numerically that this donut-like shape is extremely sensitive to off-axis wavefront deformations. To support our claim, we generate a Laguerre-Gaussian-like laser beam and apply a selection of common low-order wavefront aberrations. We investigate the visibility of those wavefront deformations in the far field. Under use of established tolerance criteria, we determine the thresholds for the applied aberration and compare the findings with simulations for verification

WOMBAT: A modular software for wavefront sensing and optimization at PHELIX

Many experiments at large-scale laser systems require the highest on-target intensities. This is achieved only for beams with minimal aberration, which becomes more and more difficult to realize for large-aperture laser systems where the beam dimension nowadays exceeds 10 cm. Therefore, wavefront sensing and correction is crucial to suit the needs of current applications [1]. Commercial solutions in software and hardware have been available for the last two decades. However, these solutions often are specialized for a certain setup that might not fit the particular needs of the facility. Adaptions of existing systems are possible, but rather cost-intensive and do often require third-party-maintenance over the lifetime of the system.Therefore, a more flexible software for wavefront sensing and correction is currently being developed at the PHELIX facility at GSI, Darmstadt. The “Wavefront Optics Measurement and Beam Analysis Tool” (WOMBAT) is a modular LabVIEW-software that offers great flexibility while working with custom and commercial hardware. The software contains a camera-module that acquires images from arbitrary camera model, including commercial Shack-Hartmann sensors (SHS). Further modules are available to perform and analysis of its data, wavefront reconstruction as well as a modal analysis in terms of the Zernike-polynomials. The measurement quality is comparable to commercial solutions and even supersedes them in some fields. Wavefront correction can be conducted with different adaptive optics systems, including motorized mirrors, movable lenses and deformable mirrors. For this purpose, modules for response recording and wavefront control are implemented, using a driver interface that can easily be adapted for new hardware.The performance of the current state of WOMBAT has been quantitatively verified and proven in various experiments, compensating static aberrations and enabling manual optimization of the focus. Further functionality is being investigated, including continuous recording and compensation of on-shot-aberrations and an algorithm to retrieve the wavefront from far-field-images

Alignment procedure for off-axis-parabolic telescopes in the context of high-intensity laser beam transport

Off-axis parabolic telescopes are rarely used in high-intensity, high-energy lasers, despite their favorable properties for beam transport such as achromatism, low aberrations and the ability to handle high peak intensities. One of the major reasons for this is the alignment procedure which is commonly viewed as complicated and time consuming. In this article, we revisit off-axis parabolic telescopes in the context of beam transport in high-intensity laser systems and present a corresponding analytical model. Based on that, we propose a suitable setup that enables fast and repeatable alignment for everyday operation