Coherent Anti-Stokes Raman Scattering Microscopic Imaging of Melamine Crystals

The excitation source for a spectrally focused coherent anti-Stokes Raman scattering (CARS) microscopic imaging system is a single femtosecond laser oscillator. The system uses a glass rod composed of SF10 to introduce a chirp into the femtosecond pulse for an enhanced spectral resolution. For single Raman displacement detection, a melamine sample is used to perform experimental spectrally focused CARS microscopic imaging research. Moreover, a half-wave plate is inserted in the pump and Stokes optical path of the spectral focus CARS microscopic imaging system. By changing the half wave, the polarization direction of the linearly polarized excitation pulse is changed, and the variation trend of the ratio of the resonant signal/nonresonant background with respect to the deflection angle of the half-wave plate is studied. Furthermore, the deflection angle of the half-wave plate is determined using the maximum ratio of the resonant signal/nonresonant background in a specific region of the sample.