Nonlinear Scattering of 248 nm Wavelength Light in High-Pressure SF₆ and CH₄ Gases for the Temporal Compression of a 20 ns KrF Laser Pulse

The nonlinear compression of narrowband (Δν ≈ 0.2 cm−1) 20 ns KrF laser pulses in SF6 at 10 atm and in CH4 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 SF6 and CH4. In SF6, 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 × 107 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 CH4, while, in the forward direction, SRS pulses shortened to 3–4 ns at reduced pumping.