Nonlinear Scattering of 248 nm Wavelength Light in High-Pressure SF[sub.6] and CH[sub.4] Gases for the Temporal Compression of a 20 ns KrF Laser Pulse

The nonlinear compression of narrowband (Δν ≈ 0.2 cm[sup.−1]) 20 ns KrF laser pulses in SF[sub.6] at 10 atm and in CH[sub.4] at 50 atm pressure was studied. Both SBS and SRS optically phase-conjugated backward-reflected radiation was registered with an energy reflectivity of 10–14% in SF[sub.6] and CH[sub.4]. In SF[sub.6], the SBS pulses gradually shortened from 10 ns to 2–3 ns with a decrease in pumping to the SBS threshold of ~10 mJ, while the SRS pulse had the shortest length of 30–60 ps for the maximal pumping of 120 mJ and broadened near the SRS threshold of ~30 mJ. For the SRS pulse energy, the ~2 mJ peak power 5 × 10[sup.7] W was tenfold higher than the pump power. The theoretical model predicted a soliton-like SRS pulse compression to a temporal length of the order of the vibrational relaxation time. There was no pulse compression of backward SBS and SRS radiation in CH[sub.4], while, in the forward direction, SRS pulses shortened to 3–4 ns at reduced pumping.