Numerical and experimental characterization of a multi-pass cryogenically cooled Yb 3+:CaF2 laser amplifier

Abstract

Present thesis is dedicated to study and realization of cryogenically cooled solid-state multi-pass (MP) Yb3+:CaF2 laser amplifier. Within the scope of the thesis specific design questions as active medium choice, thermal behavior of the amplifier, pumping setup, as well as experimental results of the measurements of the amplifier performance will be considered. We have implemented MP scheme seeded by regenerative preamplifier stage and pumped with InGaAs diode laser stack, which can produce up to 200 W average power of pump radiation. Regenerative amplifier, developed during past years in Ultrafast Laser Group at Photonics Institute [Pugzlys, 2009] is capable of delivering up to 10 mJ energy in 500 ps broadband pulses with ~12 nm bandwidth at FWHM. In the framework of this work we aimed to reach 100 mJ output pulse energy at 100 Hz frequency. We provide extensive characterization of implemented MP amplifier, which includes small-signal gain measurement, output energy measurements, output pulse cross-section and spectrum measurements. We address the challenge of beam narrowing during amplification process and offer a solution to resolve it. Achievement of 100 mJ output pulse energy with spectral band of ~12 nm at FWHM at 50 Hz repetition rate is confirmed. We conduct numerical modelling of heat dissipation in the Yb:CaF2 crystal thermally bonded with blank CaF2 slabs. Thermal behavior of bonded structure is studied in dependence on the thickness of undoped regions and active area. Heat distribution in the case of double-sided pump is compared to the case of single-sided pump.