High-efficiency picosecond parametric superradiance emitted by a ZnGeP2 crystal in the 5–6.3 µ range

Highly efficient (quantum efficiency 17%) parametric superradiance was generated in a nonlinear ZnGeP₂ crystal of length 4.2 cm pumped by single (of energy ~1 mJ) ultrashort pulses (τ = 150 psec) from an erbium laser (λ = 2.79 µ). High-power (~1 MW) continuously tunable infrared radiation of wavelengths 5–5.3 and 5.9–6.3 µ was obtained. The energy and angular tuning characteristics, line width, divergence, and gain of this superradiance were determined. The nonlinear coefficient d₃₆ was found for ZnGeP₂. Depletion of the laser pumping had to be allowed for already for parametric superradiance efficiency of just 0.1%.