Optimization of VIPA-based Brillouin spectrographs: the benefits of numerical simulations and electro-optical modulation

Virtually Imaged Phased Array (VIPA) spectrometers coupled with confocal microscopes are commonly used for Brillouin scattering measurements. However, they are limited by their low contrast in the presence of strong back reflections or in highly scattering media. Using numerical simulations to guide the design of a new diffraction mask and experiments to validate it, we demonstrate here that a two-stage VIPA-based spectrometer and a single diffraction mask can achieve 85 dB with negligible insertion loss. Additionally, we implemented a calibration and drift correction arm based on an electro-optically modulated (EOM) laser signal operating at gigahertz frequencies. Up to eight EOM peaks, covering the free spectral range of the spectrograph, can be obtained in a single image. This allows for an absolute pixel-to-frequency scale conversion at the desired rate.