Since a decade, wavefront shaping techniques has allowed to coherently manipulate speckle patterns. It opens the possibility to focus light through complex media and ultimately to image in them, provided that the medium can be considered as stationary during the process. However, scattering by tissues evolves over millisecond timescales, creating a fast decorrelation of the speckle pattern, thus limiting the use of this technique for in vivo microscopy. Therefore, focusing through biological tissues requires fast wavefront shaping devices, sensors and algorithms.
It has been demonstrated by Akemann et al that an Acousto-Optic Deflector (AOD) time locked on the output laser pulses of a regenerative amplifier can be used as an arbitrary 1D beam shaper: the locally modulated acousto-optic phase grating allows the spatial control of the laser pulse wavefront, with refresh rate of several tens up to several hundreds of kHz, limited by the size of the AOD aperture.
We have investigated through simulations and experiments, the use of two crossed AODs to implement 2D spatial wavefront shaping, and perform focusing by optimization through a scattering media. We have used different algorithms adapted to this grating modulator and analyzed in each case the AOD bandwidth used, the speed of convergence and the maximum intensity enhancement. In particular, we have shown that two crossed 1D modulators provide larger enhancement than a single 2D wavefront shaper with the same number of pixels. We will present our latest results towards achieving the ultimate optimization, limited by the AOD speed of 40 kHz.
Baptiste Blochet, Walther Akemann, Benjamin Mathieu, Sylvain Gigan, and Laurent Bourdieu, "Fast optimization wavefront shaping with acousto-optic deflectors (Conference Presentation)," Proc. SPIE 10502, Adaptive Optics and Wavefront Control for Biological Systems IV, 1050205 (Presented at SPIE BiOS: January 27, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2290630.5752153058001.
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