Tunable CW and Q-switched operation in Yb:CaF2 and Yb:SrF2

Summary form only given. Diode-pumped solid-sate laser systems combined with CPA technique are promising devices for generation of highest peak intensities. With regard to the choice of a suitable gain medium its spectroscopic properties determine the scaling of a laser system towards both highest output pulse energy and shortest pulse duration. In order to saturate the absorption with a minimum number of diode lasers a long fluorescence lifetime of the gain medium is desired. Ytterbium-doped fluorides such as Yb:CaF₂ and Yb:SrF₂ comprise a broad emission spectrum and a comparable long fluorescence lifetime. At a dopant concentration of 3.3% (atm.) we measured a radiation lifetime of 2.2 ms for Yb:CaF₂ and 4.6 ms for Yb:SrF₂. It shows absorption and emission cross section whereas the latter is determined by reciprocity method. According to ISO 11254-1 standard the damage threshold of Yb:CaF₂ was measured to be 53 J cm^-2 at a pulse duration of 10 ns (FWHM) and a center wavelength of 1064 nm. We built a diode-pumped Yb:CaF₂ and Yb:SrF₂ laser with a stable cavity, a resonator length of 1 m and a glass prism for wavelength tuning. A pulsed driven stack of 25 fast axis collimated diode-laser bars for 100 W (quasi-CW) maximum output power each is applied as pump source. The laser operates in quasi-CW operation with a repetition rate of 1 Hz and a pulse duration of 2 ms. Applying a DKDP Pockels cell a quarter wave plate and a thin film polarizer the laser operates as Q-switched laser and regenerative amplifier respectively. Pulses with a duration of 23 ns and 60 mJ pulse energy were generated in Q-switched operation with Yb:CaF₂ as gain medium. As seed-pulse source a commercial Ti:Sa oscillator with 1030 nm center wavelength is used. The hard clip bandwidth after stretching to 2 ns is 32 nm. Regenerative amplification will be demonstrated.