Frequency-encoded multiplexed CARS microscopy by rapid pulse shaping

A new coherent anti-Stokes Raman spectroscopy (CARS) technique is reported for real-time detection and classification of several chemical constituents, utilizing a single detector and a single beam of shaped femtosecond pulses. The technique is based on rapidly switching between differently shaped pulses that either maximize or minimize the targeted vibrational lines excitation, thus creating temporally modulated bright and dark profiles in the total CARS signal that are measured by a single photomultiplier tube and demodulated by a multi-channel lock-in amplifier. Using a two-dimensional spatial light modulator displaying 24 different pulse shapes, we demonstrate pulse shaping at 80 kHz and chemically specific microscopy with pixel dwell times of less than 0.5 ms.