Wavefront aberration measurement in a cryogenically cooled Yb:YAG slab using a wavefront sensor

P. Sikocinski; O. Novak; M. Smrz; J. Pilar; H. Jelinkova; A. Endo; A. Lucianetti; T. Mocek

doi:10.1117/12.2265933

11 May 2017 Wavefront aberration measurement in a cryogenically cooled Yb:YAG slab using a wavefront sensor

P. Sikocinski, O. Novak, M. Smrz, J. Pilar, H. Jelinkova, A. Endo, A. Lucianetti, T. Mocek

Proceedings Volume 10238, High-Power, High-Energy, and High-Intensity Laser Technology III; 102380O (2017) https://doi.org/10.1117/12.2265933
Event: SPIE Optics + Optoelectronics, 2017, Prague, Czech Republic

Abstract

We investigated wavefront aberrations in a cryogenically cooled Yb:YAG slab with a wavefront sensor using a probe beam technique under non-lasing condition. To analyze the pump-induced phase aberrations created in the crystal, the measured wavefronts were fitted with orthonormal Zernike polynomials. The Yb:YAG crystal of 2 mm thickness, 10 mm diameter, and 3 at.% doping concentration was mounted in a copper holder in a closed-loop pulse tube cryostat with cooling capacity of 12 W at 100 K. The gain medium was single-end pumped by a fiber-coupled laser diode at pumping intensity of ~6.5 kW/cm² with a maximum repetition rate of 100 Hz, pulse duration of 1 ms, and pump spot diameter of 2.5 mm. The time resolved measurement revealed that defocus, which was the main wavefront aberration, represents not only a thermal lensing effect but also an electronic lensing effect. The thermally induced defocus is more dominant at high repetition rate than the electronically induced defocus. We also measured wavefront aberrations of amplified beams in a cryogenically cooled Yb:YAG slab. A room temperature operated thin-disk regenerative amplifier was used as a seed laser. The seed beam was amplified in the cryogenically cooled crystal at 160 K in a double pass configuration. The wavefront measurement was conducted at semi-saturated conditions, at three different repetition rates: 10 Hz, 20 Hz and 40 Hz, and at five different pump intensities in the range between 6.5 kW/cm² and 14.8 kW/cm². Under lasing condition, only defocus aberration were induced. Due to opposite signs of the defocus aberration of the seed beam and pumped induced in the Yb:YAG crystal, wavefront of the amplified beam had smaller PtV (Peak to Valley) and RMS values than the seed beam.

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P. Sikocinski, O. Novak, M. Smrz, J. Pilar, H. Jelinkova, A. Endo, A. Lucianetti, and T. Mocek "Wavefront aberration measurement in a cryogenically cooled Yb:YAG slab using a wavefront sensor", Proc. SPIE 10238, High-Power, High-Energy, and High-Intensity Laser Technology III, 102380O (11 May 2017); https://doi.org/10.1117/12.2265933

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KEYWORDS

Wavefronts

Crystals

Wavefront aberrations

Temperature metrology

Laser crystals

Amplifiers

Laser beam diagnostics

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