The influence of pumping beam diameter on output of the room-temperature operated Q-switched longitudinally diode-pumped Yb:YAG microchip laser was investigated. The tested microchip laser was based on monolith crystal (diameter 3mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.% Yb/Y, 3mm long) and saturable absorber (Cr:YAG crystal, 1.36mm long, initial transmission 90% @ 1031 nm). The microchip resonator consisted of dielectric mirrors directly deposited on the monolith surfaces. The pump mirror (HT for pump radiation, HR for generated radiation) was placed on the Yb:YAG part. The output coupler with reflection 55% for the generated wavelength was placed on the Cr<sup>3</sup>+-doped part. For longitudinal pumping, fibre coupled (core diameter 400 ¹m, NA= 0:22) laser diode was used. The diode was operating in pulsed regime (repetition rate 20 Hz, pulse length 3 ms, maximum pumping energy 95 mJ, wavelength 934 nm). Three various pumping optics offering pumping beam radius 0.20, 0.27, and 0.34mm were used. The wavelength of microchip laser emission was 1031 nm. The pumping beam radius did not signficantly influenced the pulse duration which was 1:5 § 0:3 ns (FWHM) in all three cases. The highest generated single Q-switched pulse energy (1.08 mJ) was obtained for pumping beam radius 0.27mm for maximum pumping. The corresponding peak power was 0.72MW.
The goal of this work was an investigation of the temperature influence (in range from 80 up to 320 K) on the laser properties of Yb:YAG/Cr:YAG Q-switched diode-pumped microchip laser. This laser was based on monolith crystal (diameter 3mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.% Yb/Y, 3mm long) and saturable absorber (Cr:YAG crystal, 1.36mm long, initial transmission 90% @ 1031 nm). The laser resonator pump mirror (HT for pump radiation, HR for generated radiation) was directly deposited on the Yb:YAG monolith part. The output coupler with reflection 55% for the generated wavelength was placed on the Cr:YAG part. The microchip laser was placed in the temperature controlled cupreous holder inside vacuum chamber of the liquid nitrogen cryostat. For Yb:YAG part longitudinal pulsed pumping (pumping pulse length 2.5 ms, rep-rate 20 Hz, power amplitude 21W) a fibre coupled (core diameter 400 μm, NA= 0:22) laser diode, operating at wavelength 933 nm, was used. The microchip laser mean output power, pulse duration, repetition rate, emission wavelength, and laser beam profile were measured in dependence on temperature. The generated pulse length was in range from 2.2 ns to 1.1 ns (FWHM) with the minimum at 230 K. The single pulse energy was peaking (0.4 mJ) at 180 K. The highest peak power (325 kW) was obtained at 220 K. The highest pulse repetition rate (38 kHz) and output mean power (370mW) was reached for temperature 80 K.