Cryogenically-cooled Ho:YAG laser in-band pumped by a Tm fibre laser

Scaling of laser power and brightness to meet the needs of ever-demanding applications is a demanding task which continues to preoccupy many within the laser community. In conventional 'bulk' solid-state lasers the main obstacle is heat generation in the laser medium and its associated detrimental effects. Methods for combating these problems have been the focus of much research, resulting in many novel laser geometries with improved thermal management and reduced thermal lensing, but often at the expense of increased complexity and reduced flexibility. An alternative approach, which is beginning to attract a great deal of interest, is to operate the laser with the laser medium maintained at cryogenic temperatures (~77 K), where the effects of heat loading are dramatically reduced due to a large increase in thermal conductivity and a large decrease in the temperature coefficient of refractive index (dn/dT) and expansion coefficient [1]. In host materials such as YAG the net reduction in thermal effects can be over 50 times compared to operation at room temperature. In the case of diode-pumped Yb:YAG lasers, the combined effect of a massive reduction in thermo-optic aberrations and lower re-absorption loss has allowed very impressive results to be achieved in terms of output power and beam quality from relatively simple laser resonator configurations [2]. In this paper we report on preliminary work ultimately aimed at achieving a further reduction in thermal effects by combining the advantages of cryogenic cooling with a very low quantum defect fibre-laser-pumping of bulk solid-state lasers. Here we describe preliminary results for a cryogenically-cooled Ho:YAG laser in-band pumped by a high-power Tm-doped silica fibre laser