Picosecond erbium-doped YAG laser (λ=2.94μ) with active mode locking

A pulse-periodic picosecond erbium-doped garnet (Y₃Al₅O₁₂:Er³⁺) laser with synchronous electrooptic modulation of losses in the resonator containing a partial polarizer was investigated. The spectral and time characteristics of the fourth harmonic of the laser radiation (λ=0.73μ) and also of the up-converted signal obtained by mixing with neodymium laser radiation (λ=0.78μ) were determined as a function of the detuning between the modulation and intermode beat frequencies. Under optimal conditions the laser operated at a repetition frequency of 1—1.5Hz and it generated a train of 25 ultrashort pulses with an energy of 0.5MJ (±3%) per spike and of 40±10 psec duration at the fourth harmonic frequency. The relationship between the duration of the pulses τ and the width of the spectrum Δν of the fourth harmonic was τΔν~2. A parametric superradiance signal formed in a ZnGeP₂ crystal pumped with the radiation from this erbiumlaser, operated in the ultrashort pulse regime, provided a reliable indication of the precision of optimization of the optical length of the resonator.