Background-Free Stimulated Raman Scattering Imaging via Donut-Shaped Detection

High Resolution Image Download MS PowerPoint Slide Stimulated Raman scattering (SRS) as a nonparametric process is immune to the nonresonant background, but it is accompanied by other competing nonlinear effects, especially cross-phase modulation (XPM). Here, we present an XPM suppression method based on balanced detection of spatially segmented central and peripheral regions of the pump beam in stimulated Raman loss microscopy. This donut-shaped detection scheme harnesses the principle that the SRS signal in central and peripheral regions possesses the same phase as it measures vibrational absorption, whereas the XPM signal of the two regions shows an opposite phase as it measures energy redistribution induced by the refractive index change. By separately detecting the signals in the two regions and compensating with a scaling factor, XPM is effectively suppressed. This easy-to-implement method enhances SRS image contrast and spectral specificity by flattening the XPM contribution during hyperspectral imaging, enabling the extraction of a weak SRS signal from an overwhelming background.