Direct measurement of the frequency response function by means of frequency-domain four-wave mixing spectroscopy (FD-4WM)

A new type of frequency-domain four-wave mixing (FD-4WM) spectroscopy is developed using an amplified Ti:sapphire laser as pump pulses and a Q-switched YLF laser locked to the Ti:sapphire laser as a probe pulse. This method enables us to directly obtain frequency information of the material, which is difficult to obtain by means of homodyne-detected time-domain four-wave mixing. We have measured the frequency-domain four-wave mixing spectrum for liquid samples and have shown that these spectra agree well with the results obtained by optically heterodyne-detected optical Kerr effect measurement. Furthermore, we have demonstrated the polarization-selected frequency-domain four-wave mixing. We also discuss the distortion of the frequency-domain four-wave mixing spectrum observed frequently even under low pump intensity.