Efficient scattering of intense picosecond pulses by optical inhomogeneities in a self-focusing channel in compressed hydrogen

A channel formed by self-focusing of 30-ps pump pulses of wavelength 1.06 μm and energy of up to 40 mJ in high-pressure hydrogen (with a pressure of up to 120 atm) was probed by second-harmonic pulses delayed in time with respect to the pump pulses. This revealed scattering of efficiency which increased from zero to almost total scattering with increasing delay time. The effect is interpreted as scattering by optical inhomogeneities formed by an acoustic perturbation excited under conditions of a nonuniform temperature distribution along the self-focusing channel.