Extreme nonresonant background reduction for rapid phase-modulation CARS spectroscopy by phase sensitive detection

We effectively suppressed a nonresonant background, which is general issue of femtosecond-laser based multiplex CARS spectroscopy, by applying phase sensitive detection for our rapid phase-modulation CARS method [3]. The modulation phase of each spectral measurement can be extracted from an interference intensity between a narrowband probe and a broadband pulse. We demonstrated the method with a sample of chloroform molecules. By using a phase sensitive detection, signal-to-noise ratio was improved from 2.7 to 9.4 dB.