Superbroadening of single 1.06 μm picosecond pulses in H2O and D2O: On the concurrence of dielectric breakdown and superbroadening

The superbroadening of single 1.06 μm picosecond pulses extracted from a passively mode-locked Nd:glass laser in H₂O and D₂O has been studied. Data on ninety degree scattering of the laser pump and visible superbroadened (SB) light, the dependence of the SB light intensity on cell length, and the polarization ratio of the SB light are reported. The results show that filament formation and breakdown is not required to produce SB light, although these catastrophic effects may occur after the formation of SB light and occur concurrently with superbroadening at high laser pump intensities. The previous conclusion that four-wave parametric interaction is solely responsible for superbroadening in water is sustained by the present results. The present results show that to minimize self-focusing and to produce a highly polarized ps continuum beam for time-resolved spectroscopic study, low pump intensities and short cells should be used.