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.