Erbium-doped laser active media allow to generate a laser radiation close to the 3 μm which is interesting for many applications, e.g. medicine, spectroscopy, or for further mid-infrared conversion using OPO [1, 2]. The uniaxial Er:YLF crystal which can generate a naturally polarized laser radiation at 2.8 μm (laser transition 4I11/2→ 4I13/2)  together with semiconductor saturable absorber mirror (SESAM) were chosen to generate a Q-switched pulse. The SESAM allow building a very compact laser resonator without requirements on additional power sources or special crystals, also it is a simple method to obtain the short pulses at ~3 μm. Moreover, the Er:YLF is low phonon energy crystal (ħωph = 560 cm−1), so the self-termination effect is partly suppressed and the CW laser regime can be easily reached. In this paper, to the best author’s knowledge, the passively Q-switched compact Er:YLF laser was build for the first time and nanosecond pulses were successfully generated.
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