Broadband amplification and thermal lensing in a combination of Yb:YLF and Yb:YAG crystals

Broadband amplification of laser radiation in a combination of Yb:YLF and Yb:YAG crystals was demonstrated. It was shown that, with the input spectrum width of 20 nm, the width at the output spectrum can reach 17 nm. A thermal lens induced in the Yb:YAG crystal is partially compensated by the lens in the Yb:YLF crystal due to the different signs of the ∂ n /∂ T coefficients of the crystals. The thermal lens in the Yb:YLF crystal in the thin and thick (“long-the-side pumped”) rod geometries was studied theoretically and experimentally. An analytical model of thermally induced phase distortions in uniaxial crystals caused by the piezo-optical effect was developed for the thin-rod geometry.