Nonstationary Raman amplification of superluminescence in crystals

The sequential excitation of LiF crystals with F ₂ ⁻ color centers and KGd(WO₄)₂ crystals by 1047-nm laser pulses with a duration of 22 ps is investigated. Broadband (275 cm⁻¹) Stokes superluminescence appearing in the fluoride crystal undergoes nonstationary Raman amplification in the oxide crystal. The amplified pulses with a Stokes frequency shift of 767 cm⁻¹, a duration of 7 ps, and a power up to ~1.1 MW have high spatial and time coherence and exhibit time delay increasing from ~1 to 4.5 ns with a decreasing pump power. The results are discussed in terms of the cooperative Raman scattering.