Abstract

Compact, tunable, moderate pulse power laser sources, operating in near infrared range of 750 – 800 nm and below 400 nm in a case of frequency doubling, are required in medical diagnostics, pollutions inspection etc. Such pulse parameters can be achieved in passively Q-switched flash-lamp or diode pumped Cr LiCAF laser with frequency doubling option. The passive Q-switching was realized for such type lasers using Cr⁴⁺.YOS saturable absorber [1]. We propose to use as passive Q-switch V³⁺:YAG [2] crystal, applied till now for Q-switching of Nd lasers operating at 1 06 μm and 1.3 μm wavelengths. Because of very short recovery time of 1-3 ns V³⁺.YAG absorbers can be also used for passive mode locking Its ground state absorption cross section is about 5 × 10⁻¹⁸ cm² for near infrared range of 780- 820 nm. We have demonstrated, for the first time, application of V³⁺.YAG for Q-switching of flash-lamp pumped Cr.LiCAF laser In the first step of experiments it was examined the free running mode of operation in the cavity consisted of 5% doped Cr:LiCAF rod of 55 mm length, a flat high reflector and a flat output coupler of about 25% transmission. It was achieved 30 mJ for pump energy of 40 J in a cavity of 30 cm length. The tunability in the range of 760 – 805 nm was demonstrated applying Lyot’s filter consisted of 5 crystalline quartz plates. To show feasibility of such method of Q-switching the experiments were carried out in the same cavity (but without Lyot’s filter) with an uncoated V³⁺:YAG Q-switch of 70% initial transmission. The near TEM₀₀, unstable pulse series consisted of 1, 2 or 3 pulses with separation about 30 ps (see Fig 1) were observed. It was achieved in preliminary experiments above 1 mJ of energy for each pulse, with 50 ns pulse duration time. The spectrum of pulses was centered on 763 nm and pulse bandwidth was less than 2 nm. The very smooth shape of pulses and narrow spectrum line indicate, that single longitudinal mode is possible. The results of V³⁺:YAG Q-switch performance examination as well as optimization of cavity parameters were presented.

© 2000 IEEE