Fresnel-Zone Scaling of Micro-Raman Edge Responses near a Silicon Boundary

Micro-Raman line scans acquired across a cleaved silicon edge reveal a reproducible intensity maximum located away from the geometric boundary. Measurements obtained with objectives producing different effective spot sizes show that the peak position defines a first Fresnel-zone scaling length. When normalized by this length scale, the Raman edge-response profiles collapse onto a common dimensionless curve. The observed response is consistent with a diffraction-modulated optical field sampled by the effective Raman-system point-spread function (PSF), which incorporates the combined effects of excitation, collection, and spatial filtering. This scaling behavior is further exploited to estimate the effective Raman spot size directly from edge-scan measurements. The results establish Fresnel-zone scaling as a useful framework for comparing Raman edge responses and assessing the spatial characteristics of fiber-coupled micro-Raman systems near sharp boundaries.