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A Hartmann-Shack wavefront sensor consists basically of two elements: a microlens array and a photosensitive detector. This paper presents a technique to fabricate close-packed microlens arrays compliant to the sensor requirements. The method is based on bulk-silicon anisotropic etching and requires a single etch mask. We first etch a micromirror array in a KOH solution and use it later as a mold for the replication of microlens arrays. The elements in the fabricated microlens arrays feature excellent fit to a parabolic mirror surface, 100% optical fill factor, excellent parallelism of the optical axes and very high precision of the array pitch. The uniformity of the focal length of the microlenses is high (in the order of 5%) and the surface roughness — expressed in terms of wavefront — is of the order of 8–13 nm. This technology also enables simple single-mask fabrication of arbitrary aspherical optical surfaces.

In the classical Hartmann test analysis, the transverse aberrations are represented by small straight segments joining two consecutive measured points in the pupil. In the analysis presented in this paper we propose the wavefront to be synthesized by many nonflat functions whose domains are the squares defined by the square unit cell defined by an array of holes in the Hartmann screen placed at the exit pupil of the system. Two advantages of this method are that a higher precision in the wavefront retrieval is obtained and second that the local curvatures and astigmatism with their corresponding axes are obtained.

An intracavity 37-element deformable membrane mirror (DMM) has been used in order to control the transverse mode profile of a diode-pumped solidstate laser. Automatic spatial mode and output power optimisation of Nd:YVO end-pumped and Nd:YAlO side-pumped lasers are demonstrated using a closed-loop genetic algorithm. Transverse mode and power optimisation of a diode-pumped, grazing incidence Nd:GdVO laser has been performed successfully. The optimisation procedure featured a genetic algorithm ensuring the global maximum is attained. Using a Michelson interferometer with the DMM operating intracavity, the DMM was found to present negligible deformation when used with a power density of 115W/cm but noticeable deformation appeared with a power density of 1.25 kW/cm.

10mm and 15mm diameter adaptive membrane mirrors have been implemented into a Nd:YVO laser. The laser performance has been investigated and compared to a similar laser without an adaptive mirror. While some membrane mirrors did not change the laser behaviour, several other membrane mirrors lead to a switching between transverse modes. With less than 3 kW/cm, the maximum intensity on the mirror membrane was small compared to a damage threshold of more than 144 kW/cm.

This paper presents an adaptive optical closed loop system with a bimorph mirror as a wavefront corrector and a Shack-Hartmann wavefront sensor to compensate for the aberrations of high power lasers. An adaptive system can correct for the low-order aberrations in the real-time — the frequency of corrected aberrations is less then 25 (30) Hz. The amplitude of such aberrations — about 7 microns. These parameters are mostly determined by the utilized Shack-Hartmann wavefront sensor. Number of corrected aberrations — up to 30th Zernike polynomial (excluding tip-tilt). We are presenting the results of the use of our adaptive system in several TW laser systems such as ATLAS, LULI and Beijing Institute of Physics.

Beam quality and efficiency of high-power solid state lasers are limited by aberrations of the active medium. The aberrations are due to temperature gradients in the laser crystals that in turn are due to the inevitable heat generation in the crystal. The aberrations lead to high diffraction losses of the laser resonator and reduced output power.

We use a birefringence-compensation scheme consisting of a relay-imaging telescope and a 90° polarization rotator to eliminate the stress-induced birefringence. In order to further improve the beam quality, the remaining aberrations of the thermal lens have to be eliminated. It is important to know the type and strength of the aberrations to determine the requirements of the adaptive mirror.

We present the investigation of aberrations in a MOPA cw-Nd:YVO/Nd:YAG laser system in which we employ an adaptive membrane mirror in order to compensate for the aberrations of the power amplifier. A genetic algorithm is used to control the adaptive mirror. A suitable power-in-the-bucket measurement behind a diffraction-limited aperture generates the beam quality signal for the feedback loop. The beam quality (M) is improved by a factor of 2.8.

The wavefront aberrations in inertial confinement fusion (ICF) laser system consists of static aberration such as material inhomogeneous, optical figure error and assemble error and so on, and dynamics aberration such as pumping induced thermal distortion, nonlinear effect induced index fluctuation and so on. Two Years ago, an adaptive optical system with 45 correction elements was established for the wavefront control of ICF laser system. And the static aberration correction had been realized. Recently this adaptive optical system has been used to correct the lamp pumping induced thermal distortion. For the nanosecond scale pulse laser output, the directly close-loop operation of adaptive optical system is impossible. So the pre-correction method of the wavefront control has been adopted. The dynamic thermal distortion pre-correction has been realized. The system also successfully corrected the compound aberration both of static and thermal aberration. This work would be helpful for shortening the operation period of the ICF laser system.

We demonstrate the implementation of a feedback controlled pulse shaping device in a femtosecond high-power Ti:sapphire laser system. The laser system consists of a mirror dispersion controlled oscillator and a multipass amplifier with a pairing double prism compressor. The system provides pulses with a duration of 30 fs and an energy of up to 1.2 mJ per pulse at 1 kHz repetition rate. The phase distorted output pulses are phase modulated with a high resolution spatial light modulator (SLM). The pulse shaper consists of an all-reflective zero-dispersion compressor equipped with a liquid crystal array. For adaptive compression of the amplified pulses a feedback loop is implemented. A two-photon process is used to monitor the temporal pulse characteristics. To achieve the shortest possible pulse an evolutionary algorithm controls the pulse shaper utilizing the two-photon signal as feedback. With this set-up transform limited pulses are achieved. Detailed investigations of algorithm parameters and their effect on convergence behaviour have been performed and are compared with the experimental findings.

The PHELIX (Petawatt High Energy Laser for Heavy Ion Research) laser project has been initiated to build a high energy, ultra high power laser for research purposes in connection with the heavy ion accelerator of the GSI. The PHELIX laser should provide ns-pulses with an energy up to 5 kJ and, alternatively, fs-pulses reaching 1 petawatt with an energy of 500 kJ. Aberrations due to beam transport and due to the amplification process limit the focus ability and the intensity on the target. For the amplification of the fs-pulse, the CPA (chirped pulse amplification) technique is used. Distortions in the phase also entail longer pulses during the compression in the CPA process.

Information is given about the Projects # 1929 and # 2631 supported by ISTC and concerned with improving laser beam quality and interesting for adaptive optics community. One of them, Project # 1929 has been recently finished. It has been devoted to development of an SBS phase conjugation mirror of superhigh conjugation quality employing the kinoform optics for high-power lasers with nanosecond scale pulse duration. With the purpose of reaching ideal PC fidelity, the SBS mirror includes the raster of small lenses that has been traditionally used as the in Shack-Hartmann wavefront sensor in adaptive optics. The second of them, Project # 2631, is concerned with the development of an adaptive optical system for phase correction of laser beams with wavefront vortex. The principles of operation of modern adaptive systems are based on the assumption that the phase is a smooth continuous function in space. Therefore the solution of the Project tasks will assume a new step in adaptive optics.