Pulse-picking coherent anti-Stokes Raman scattering microscopy for highly sensitive chemical imaging

Coherent Raman scattering has been developed into powerful technologies for the chemical imaging of biological samples. However, limited sensitivity remains a critical bottleneck for coherent Raman microscopes. We introduce a pulse-picking technology that can significantly increase the sensitivity of coherent anti-Stokes Raman scattering (CARS) microscopy. An acousto-optic modulator driven by a function generator allows picking collinearly combined pump and Stokes pulses at low duty cycles. This method reduces the number of pulses at each image pixel, enhances the peak power of laser pulses, and thus significantly improves the sensitivity of CARS and minimizes phototoxicity. We demonstrated an over 1000-fold sensitivity improvement for CARS imaging. Besides, we show this pulse-picking method can enhance the sensitivity of multiphoton fluorescence and second harmonic generation modalities about 20 times. Using cell and biological tissue samples, we highlight the potential of this pulse-picking technology for highly sensitive multimodal chemical imaging in biological and medical sciences.