Abstract

In the first demonstration of cascaded four-wave mixing (CFWM) of femtosecond pulses in bulk x⁽³⁾ media [1] it was shown that two noncollinear pump pulses with different frequencies overlapping in a nonresonant Kerr medium generate a series of angularly separated multicolored pulses. These pulses have broad bandwidths and frequencies extending from the infrared to the ultraviolet. The required phase matching was achieved over a broad range by adjusting the interaction angle of the pumps, and the overall conversion efficiency was 10%. In a simple picture, the two-color pump pulses with central frequencies ω₀ and ω₁ drive the nonlinear medium at the beat frequency ω_m= ω₁ - ω₀, and this periodic modulation gives rise to multiple sidebands separated by ω_m, but unlike in resonant Raman-based processes, both the central frequency of the generated broadband spectrum and the sideband spacing can be freely adjusted. The efficient extension of CFWM generation down to 160 nm in gas-filled hollow waveguides [2] further evidenced the universal nature of nonresonant CFWM processes.

© 2009 IEEE