Supercontinuum Generation in Gases

Supercontinua extending from the ultraviolet to the infrared are observed from high-pressure (1-40 atm) Ar, Kr, Xe, ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, or C${\mathrm{O}}_2$ illuminated with 2-psec or 70-fsec, 0.6-μm pulses with an energy ≲500 μJ. The blue spectral component is shown to display a nearly universal behavior for all gases and pulse durations. Although the maximum intensity of the focused, femtosecond pulse in an evacuated cell was ∼${10}^{13}$ W/${\mathrm{cm}}^2$, continuum generation was only observed with the femtosecond pulse when the threshold for self-focusing was exceeded.