Many-pulse infrared Raman laser

An investigation was made of the main characteristics of a liquid-nitrogen Raman laser pumped longitudinally by a neodymium laser. Pumping lasting 200–600 μsec and it consisted of a series of ~30 pulses of 0.1–0.3 μsec duration each. This made it possible to increase considerably the pump energy compared with the case when only one pulse was used. A study was made of narrow-band excitation (in this case the pump spectrum Δν_p≈0.05 cm^–1 was narrower than the spontaneous Raman scattering line of liquid nitrogen Δν_l= 0.067 cm^–1) and of wide-band excitation (Δν_p = 80 cm^–1>> Δν_l). The Raman laser emitted a series of 30 pulses with a total energy up to 40 J. The average efficiency was ~15%. The output power exceeded 15 MW. The output beam diameter was ~1 cm and its divergence was (0.5–1.5)X10^–3 rad. A great proportion of the output energy was contained in the first Stokes component (λ_s = 1.41 μ).