Sensitive and Selective Detection of Low-Frequency Vibrational Modes Through a Phase-Shifting Fourier Transform Spectroscopy

We introduce a sensitive technique for the measurement of impulsively excited vibrational Raman modes. A linear sweep in the instantaneous frequency of the probe pulse isolates Raman sidebands from noise, enhancing sensitivity. The temporal interference between two stretched, time-delayed pump pulses allows us to selectively excite specific modes. The method is shown to be applicable to different phases of the samples.