Phase-controlled polarization coherent anti-Stokes Raman scattering microscopy for highsensitivity and high-contrast molecular imaging

We report on a phase-controlled polarization coherent anti-Stokes Raman scattering (CARS) microscopy for high-sensitivity and high-contrast molecule vibrational imaging. By changing the phase difference between the two CARS signals (i.e., a weak resonant CARS and a strong nonresonant CARS signal) simultaneously generated from the same focal volume of the sample, the complete constructive (in-phase) and destructive (out-ofphase) interference CARS images can be acquired for image processing. The directly digital subtraction between the constructive and destructive interference CARS images yields a fivefold improvement in signal-tobackground ratios compared with conventional CARS while providing an approximately 20-fold amplification of a resonant CARS signal compared with conventional polarization CARS imaging. We demonstrate this technique by imaging 1 μm polystyrene beads and unstained human epithelial cells in aqueous environments.