| Abstract [eng] |
In this thesis, analysis of thermal effects and various approaches for their mitigation in diode end pumped ultrafast lasers is presented. Experimental investigations were performed by employing Shack-Hartmann wavefront sensor which was adapted for measurements of thermal lens in diode end pumped lasers. During research, operation of high average power, diode-pumped, Nd:YVO4 laser with aspheric aberration corrector was investigated. Actual thermal lens measurements were conducted in order to design properly shaped aberration corrector that was manufactured using a thin film deposition technology. This allows us to conclude that employment of proper thermal lens aberration compensator allowed for laser threshold reducing and ensured improved output beam quality parameter M2 in wide pump power range. Prospects of output pulse energy scaling in diode end-pumped Yb:YAG laser by employing elliptical mode geometry was investigated. During our experiments, maximum average power in of ~ 5.5 W was obtained at repetition rates of 30-100 kHz, while in CW operation mode the 8 W output power was achieved. In spite of strongly astigmatic thermal lens due to optimized cavity design the output beam exhibits high spatial quality: beam quality parameter M2 in both vertical and horizontal plane was close to unity. Detailed comparative study of thermal effects in Yb doped KGW crystals with different orientation was performed. Measurements confirm, that anisotropic optical and thermal properties of Yb:KGW along with asymmetric cooling and pumping conditions for longitudinally pumped thin slab shaped active elements leads to formations highly asymmetric thermal lens. By varying parameters, such as crystal orientation, cooling geometry and pump channel shaping we can significantly reduce negative impact of thermal effects on laser characteristics. We have also shown, that end bulging contributes up to 50% to thermal lensing in end pumped Yb:KGW lasers. Moreover, we have investigated potential of laser output power scaling by implementation of symmetric cavity with two Yb:KGW active elements. |
