Research on the Influence of Modulation Depth of Phase Sensitive Detection on Stimulated Raman Signal Intensity and Signal-to-Noise Ratio

timulated Raman scattering is one of coherent Raman scattering. The signal generated by stimulated Raman scattering is significantly enhanced under the third-order nonlinear effect, and there is no interference from non-resonant background. Its spectrum is almost consistent with the spontaneous Raman spectrum. Therefore, the micro-imaging technology based on stimulated Raman scattering has the advantages of no labeling, high specificity and being non-invasive. It has been successfully used in biological cell imaging and has made many great achievements. Stimulated Raman signal has the same wavelength as excitation luminescence and is easily disturbed by excitation luminescence background noise. In order to solve this problem, the combination of optical modulation and phase-sensitive detection is often used to detect it. In the detection process, modulation depth influences the intensity and signal-to-noise ratio of the stimulated Raman signal. Because of this, this paper deeply analyzes the influence of modulation depth on stimulated Raman signal intensity and signal-to-noise ratio based on relevant theories. At the same time, considering the limitation of cell photodamage threshold on the sum of two excitation optical powers in applications such as bio-spectral imaging, the excitation optical power configuration method to obtain the maximum signal intensity and the best signal-to-noise ratio at different modulation depths is analyzed. By establishing a stimulated Raman experimental system, dimethyl sulfoxide is taken as the research object for experimental verification. The results show that when the stimulated Raman loss is detected under the limitation of photodamage threshold, at the same modulation depth, the signal intensity reaches the strongest when the optical power ratio of pump light to the one of stokes light is 1:1,and the signal-to-noise ratio reaches the best when the ratio is 1:2. When the optical power ratio of pump light to the one of stokes light is the same, the intensity and signal-to-noise ratio of stimulated Raman signal decrease with the decrease of modulation depth, and the correlation is approximately linear. The stimulated Raman spectrum of dimethyl sulfoxide obtained from the experiment also verified that the higher the modulation depth, the stronger the spectral signal and the better the signal-to-noise ratio and the better the spectral quality of the whole sample. The research results are the improvement of stimulated Raman microscopy in signal modulation and detection and can provide reference guidance for stimulated Raman spectroscopy detection and cell imaging experiments.