Heterodyne polarization coherent anti-Stokes Raman scattering microscopy

We develop a heterodyne-detected polarization coherent anti-Stokes Raman scattering (HP-CARS) microscopy for high sensitive and high contrast molecular vibration imaging. The HP-CARS technique, which utilizes interference of the weak resonant CARS signal and the relatively intense local oscillator field generated simultaneously within the same focal excitation volume of the sample for optical heterodyne detection, yields an approximately sevenfold improvement in vibrational contrast compared with local oscillator CARS, while exhibiting a 12-fold amplification of the resonant signal compared with P-CARS. We demonstrate this method by imaging both 4.69 μm polystyrene beads and unstained human epithelial cells in aqueous environments.