Novel optical resonators and thermal lensing

The maximum power range over which a laser resonator supports stable oscillation is mainly determined by the (thermal) material constants of the active medium and by the cooling scheme. The power range for stable fundamental-mode operation can be shifted to higher powers with special cavity designs and intra-cavity optics but the width of the stability range will be unaffected. Moreover, increasing the pump intensity in the active medium also aggravates the aspheric components of the thermally induced distortions. It is therefore of major importance to analyze these thermal effects when developing novel resonators. We present investigations on thermally induced distortions and on a novel multi-rod laser cavity, known as the variable-configuration resonator (VCR). The thermal effects have been studied both numerically and experimentally. We present a comparison of various pumping and cooling schemes. It is found that composite rods provide the most effective cooling for end-pumped lasers. The VCR was developed to scale the power range of fundamental-mode lasers. Due to its capability to run either as a Fabry-Perot resonator or as a ring cavity it overcomes the stability problems associated with conventional multi-rod resonators and allows for a novel Q-switching technique.