Double acousto-optic spectral filtering in off-axis multi-wavelength digital holography

Abstract

Multi-wavelength digital holography (MDH) is a label-free technique for mapping spectral and spatial properties of samples in scientific and industrial applications. Light sources for MDH often include acousto-optic tunable filters (AOTFs) for sequential or simultaneous selection of narrow spectral bands in broadband radiation. We theoretically and experimentally evaluated the influence of the spectral transmission function of single and double AOTFs on the quality of the acquired holograms and proposed ways to improve their characteristics. We analyzed the spatio-spectral properties of the acousto-optic interaction and changed the incident angle of light to reduce the spectral bandwidth and increase the width of the high-contrast area in the interference image. Double spectral filtering using two AOTFs significantly improves the visibility distribution of the interference pattern with peak spectral transmission close to 100% and provides a good compromise between an increase in the coherence length and a decrease in the peak intensity by shifting driving frequency of the second filter. The results of the study provide valuable information for the development of AOTF technology and can be used for both optimal design and adaptive control of AOTF-based tunable light sources in MDH.