Directly diode-pumped millijoule subpicosecond Yb:glass regenerative amplifier

Summary form only given. Ytterbium-doped laser materials have recently received a great deal of interest. The low pump saturation intensity of Yb:glass at 975 nm (/spl sim/4 kW/cm/sup 2/) can benefit from diode pumping and the fluorescence bandwidth is broad enough to support subpicosecond pulses. By using a regenerative amplifier, the challenge of efficiently extracting energy from a low emission cross-section material can be met. Such advantages make it possible for Yb:glass lasers to be compact and cost-efficient, and thus, great candidates for applications such as surgery and micro-machining. We have demonstrated, for the first time, millijoule, subpicosecond pulses from a directly diode-pumped laser system. The gain medium was a 400-/spl mu/m thick, Kigre QX phosphate glass doped with 15% wt. Yb/sub 2/O/sub 3/, shaped in a keystone slab geometry. The initial cavity was composed of 2 spherical mirrors and 2 plane mirrors: a regular X cavity. Cylindric optics were then used to improve the mode matching between the pump and the lasing beams and to generate a TEM/sub 00/-like output beam. By replacing spherical optics with cylindrical optics, we improved the tangential M/sup 2/ value of the output beam of the bare cavity from 114 to 1.7, while maintaining the sagittal M/sup 2/ value at 1.3. The free running output power of the regenerative amplifier shows more obvious thermal effects than does that of the bare cavity at higher average pump powers because the combination of thermal birefringence and polarization sensitive optics, such as thin film polarizers, results in higher cavity losses.