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

A pulse-periodic picosecond erbium-doped garnet (Y 3 Al 5 O 12 :Er 3+ ) 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 = 0.73 μ ) and also of the up-converted signal obtained by mixing with neodymium laser radiation ( λ = 0.78 μ ) 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 ZnGeP 2 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.