用于去除非共振背景的圆偏振宽带CARS光谱研究

相干反斯托克斯拉曼散射(CARS)是一种受激拉曼现象，在显微成像时，存在非共振背景，会导致光谱产生峰位偏移和谱线变形。本文利用飞秒激光作为光源，通过光栅滤波系统产生窄带泵浦光，飞秒激光激发光子晶体光纤产生超连续谱作为斯托克斯光，两束光被调制为圆偏振光后同时激发样品产生CARS光谱。通过模拟计算说明圆偏振光可以有效去除各向异性材料CARS光谱中的非共振背景，从而使CARS光谱具有和自发拉曼相似的谱线形状。聚苯乙烯微球和液晶样品的CARS光谱实验结果与模拟计算基本相符，说明圆偏振是一种有效去除CARS光谱非共振背景的方法。

Circularly polarized broadband CARS spectroscopy for non-resonant background removal

Coherent Anti-Stokes Raman Scattering (CARS) is a stimulated Raman process, which has the non-resonant background (NRB), leading to peak shift and spectral distortion in the spectrum. In this letter, we use a femtosecond laser as the light source and a grating filter system generating narrow-band pump light. The femtosecond laser excites photonic crystal fiber, producing a supercontinuum spectrum as Stokes light. Two beams excite the samples simultaneously after modulated to circular polarized lights to produce CARS spectrums. We illustrate that circularly polarized light can effectively remove the non-resonant background in the CARS spectrum of anisotropic materials by simulation. Thus, the CARS spectrum has a similar spectral line shape to that of spontaneous Raman. The experimental results of CARS spectrums of polystyrene and liquid crystal samples generally agree with the calculations, proving that circularly polarized CARS spectroscopy is an effective method to remove the NRB of CARS spectrum.