Generation of eye-safe radiation in passively Q-switched laser with three Stokes intracavity Raman conversion

Raman conversion is one of the methods for obtaining pulsed laser radiation into the eye-safe (near 1.5 µm) spectral region. Well developed lasers on Nd doped crystals generate radiation around the 1.06 and 1.3 µm wavelengths. Both passive and active Q-switchings are widely used for pulse generation at 1.06 µm wavelength. For generation at 1.3 µm wavelength an active Q-switch is primary applied, because of low efficiency of passive absorbers in this spectral range. Starting at 1.06, or 1.3 µm wavelengths Raman conversion in crystal media with Raman shifts from 900 to 1000 cm
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allows to reach the eye-safe region by three, or one Raman shifts. Such possibilities were demonstrated at the flash lamp pumping for milliJoule level of laser pulses. For laser systems with longitudinal diode pumping when pulse energy is in the microJoule range the one shift Raman conversion of the 1.3 µm laser radiation is usually used with active Q-switch laser operation. Meanwhile, a possibility to obtain the eye-safe radiation from a passively Q-switched all solid-state laser system with Raman conversion and longitudinal pumping is highly attractive due to constitutive simplicity, compactness and good beam quality.