Single-mode single-frequency glass laser emitting microsecond pulses

It is demonstrated that a single-mode single-frequency glass microsecond laser with a very simple optical system free of negative feedback components can be constructed. A long cavity was used and the passive Q switch was in the form of an LiF crystal coloured by irradiation with gamma rays. Microsecond pulses were generated in a cavity L ~ 22 m long with a configuration intermediate between semiconcentric and semiconfocal (R/L = 1.36, where R is the radius of curvature of the nontransmitting mirror). The active elements (10 mm in diameter and 300 mm long) were made of GLS22 glass and the initial transmission of the passive switch was ~60%. The transverse oscillation modes were selected by a stop with an aperture 4 mm in diameter. The longitudinal oscillation modes were selected by a pile of four plates; the cavity contained a prism selector (consisting of three TF5 glass prisms) and an additional mirror with the reflectivity ρ = 20% located at a distance of ~3 m from the pile. Single-mode single-frequency lasing was achieved at pump energies not exceeding 1.3 times the threshold energy; the energy of the output radiation pulses did not exceed 8 mJ.