Spectral superbroadening of self-focused picosecond laser pulses in D 20

Intense picosecond light pulses of a mode-locked Nd: glass laser at XL = 1054nm (fundamental wavelength) and \SH = 527 nm (second harmonic wavelength) are passed through a sample of D 2 0 under self-focusing conditions. Spectrally structured superbroadened, spatially bell-shaped emission in the forward direction is obtained. Primary generation processes are pump-pulse-degenerate stimulated parametric four-photon interaction (c ^ 4- uy —> u; 3 + u;4) and stimulated Raman scattering (u>i — • ojR + u; r), which occur concurrently = uL or OJSH angular pump frequency, UJR = first Stokes frequency, uv = vibrational frequency, u3 = signal frequency, u; * = idler frequency). The parametric four-photon interaction occurs under collinear non-phase-matched conditions and under longitudinally phase-matched, transver-sally non-phase-matched (Cerenkov-like) conditions/Subsequent interaction pro-cesses are pump-pulse-nondegenerate four-photon interaction of the type ujy + ÜJr u)3> + ujAr, coherent antiStokes Raman scattering (CARS, ur-o;4 — • o; 3), inverse Raman scattering (UJA UJX-hcj^), and cascading light up-conver-sion of the type u< \ + — LJR —> uj^y 1