CW and pulsed operation of a diode-pumped Bessel-Gauss laser

We demonstrated passively Q-switched operation of the Bessel-Gauss laser. To prevent excessive thermal load on the laser crystal, we used a quasi-CW pumping consisting of 1-ms pulses at a 200-Hz repetition rate. The pump power level was adjusted so that a single Q-switched pulse was obtained from a single pump pulse. By adding a Cr⁴⁺:YAG crystal with an initial transmission of T₀=90% to the 80-mm cavity, we obtained two beams of 30-ns Bessel-Gauss pulses with a pulse energy of 3 μJ. The one- and two-dimensional profiles of these Bessel-Gauss pulses at different distances from the waist were similar to those of the corresponding CW beam. By using a Cr⁴⁺:YAG crystal with T₀=45% and shortening the cavity length to 38 mm, 3-ns-long, 7.5-μJ pulses were generated. We observed, however, that the far-field pattern of these short pulses was somewhat different from that of the CW beam.