Control of the parameters of double acousto-optic spectral filtering in digital holography

Subject of study. Off-axis digital holograms were obtained with the acousto-optic spectral filtering of broadband radiation. Aim of study. Methods for controlling the parameters of the double acousto-optic spectral filtering were evaluated in terms of increasing the coherence length of light and improving the quality of off-axis digital holograms. Method. For measurements, an off-axis digital holography setup based on a classical Mach–Zehnder interferometer was used. The lighting part of the setup contained a broadband radiation source and two acousto-optical cells with the possibility of separate control of their frequency and orientation. In the output channels of the interferometer, interference images were recorded and the spectra were measured. Digitally processed experimental data for single and double acousto-optic filtering were compared with the results of the mathematical modeling of the acousto-optic interaction. Main results. It was shown that changing the driving frequency and orientation of the acousto-optical cells under double filtering are effective methods for adaptively adjusting the recording parameters of digital holograms. In particular, with double filtering, the coherence length could be increased by a factor of 1.4 compared with single filtering. The rotation of the double filter by 10° increased the coherence length by a factor of 2 compared with a single unrotated filter. The coherence length increased by 35%–40% if the second cell was rotated by an angle of up to 3° or if the driving frequency of the second cell was shifted by less than 1 MHz; however, the peak spectral intensity decreased by 2.5 and 4 times, respectively. Practical significance. Evaluation criteria and recommendations for choosing methods for controlling the parameters of double acousto-optic spectral filtering have been developed, which expand the capabilities of multi-wavelength digital holography in biomedical and technical applications, allowing adaptive changes in the recording parameters of holograms, increasing the effective field of view, and improving the accuracy of amplitude and phase image retrieval.