EXTRA RESONANCES IN TIME-DOMAIN 4-WAVE-MIXING

We show that extra resonances, such as those caused in frequency-domai n nonlinear wave mixing by pure dephasing or laser fluctuations, can a lso be induced by operation in the time domain. These pulse-length-ind uced extra resonances arise in transient-grating experiments when the laser pulses are short enough that a steady state cannot be achieved d uring the excitation process. We show theoretically that these resonan ces increase in strength with decreasing excitation pulse length until the pulse length becomes shorter than the dephasing time of the mediu m and quote an experimental example to support this interpretation.