Single-frequency diode-pumped solid-state lasers
The work discussed in this thesis covers two broad areas: Novel techniques for the single-frequency operation of miniature, diode-pumped solid-state lasers and the high-power (i.e. multi-watt) operation of diode-bar end-pumped lasers in the eyesafe 2 μm wavelength region. A monolithic Nd-doped phosphate glass laser is described, in which uni-directional, hence single-frequency operation is enforced by the acousto-optic effect in the laser medium. The loss difference for the two counter-propagating waves relies on an acousto-optic self-feedback mechanism which can yield high loss differences even for very small diffraction efficiencies. Reliable single-frequency output is maintained indefinitely with an applied radio-frequency power of 0.2 W. Single-frequency output powers up to 30 mW for 400 mW of pump power are demonstrated. A technique is developed which facilitates reliable single-frequency operation of actively Q-switched lasers at repetition rates beyond the inverse lifetime of the upper laser level. Stable single-frequency operation of a Q-switched laser requires the initial establishment of a stable prelase which is free from spiking. Relying on the natural decay of spiking limits repetition rates and hence average power. Using feedback suppression of spiking, a Q-switched Nd:YAG laser is demonstrated which operates on a single frequency at repetition rates up to 25 kHz, with 88% of available cw power extracted. In the second part of this thesis, the high-power operation of diode-bar end-pumped solid-state lasers operating in the eyesafe 2 μm wavelength region is discussed. Efficient operation of a Tm:YAG laser end-pumped by a beam-shaped 20W diode bar is demonstrated. At a mount temperature of 20°C an output beam of 4.1 W with M2 values of 1.2 and 1.4 in the orthogonal planes is obtained for 13.5 W of diode power incident on the rod. This laser is then used to intracavity-pump a Ho:YAG laser, which avoids the upconversion problems usually associated with Tm3+-Ho3+-codoped lasers. At a mount temperature of 10°C for both the Tm:YAG and the Ho:YAG rods, an output power of the Ho:YAG of up to 2.1 W at 2097 nm is obtained for 9.2 W of diode power incident on the Tm:YAG rod.