Dynamic wavefront shaping with an acousto-optic lens for laser scanning microscopy.

George Konstantinou,Geoffrey J Evans,John E Mitchell,Victoria A Griffiths,K M Naga Srinivas Nadella,R Angus Silver,Paul A Kirkby

doi:10.1364/oe.24.006283

Abstract

Acousto-optic deflectors (AODs) arranged in series and driven with linearly chirped frequencies can rapidly focus and tilt optical wavefronts, enabling high-speed 3D random access microscopy. Non-linearly chirped acoustic drive frequencies can also be used to shape the optical wavefront allowing a range of higher-order aberrations to be generated. However, to date, wavefront shaping with AODs has been achieved by using single laser pulses for strobed illumination to 'freeze' the moving acoustic wavefront, limiting voxel acquisition rates. Here we show that dynamic wavefront shaping can be achieved by applying non-linear drive frequencies to a pair of AODs with counter-propagating acoustic waves, which comprise a cylindrical acousto-optic lens (AOL). Using a cylindrical AOL we demonstrate high-speed continuous axial line scanning and the first experimental AOL-based correction of a cylindrical lens aberration at 30 kHz, accurate to 1/35th of a wave at 800 nm. Furthermore, we develop a model to show how spherical aberration, which is the major aberration in AOL-based remote-focusing systems, can be partially or fully corrected with AOLs consisting of four or six AODs, respectively.

Highlights

Acousto-optic lenses (AOLs) allow rapid, inertia-free focusing and scanning of an optical beam
We have investigated how AOLs driven with non-linearly chirped frequencies can be used to control optical wavefronts at high-speed
Using a rapid and precise, custom-designed field-programmable gate array (FPGA) control system to drive a cylindrical AOL, we experimentally demonstrate aberration-free continuous axial line scanning and 2D-spherical-like aberration correction for periods of 1-10 μs at 30 kHz rates

Summary

Introduction

Acousto-optic lenses (AOLs) allow rapid, inertia-free focusing and scanning of an optical beam. Developed for cold atom research [1], AOLs have found applications in high-speed, 3D, two-photon microscopes [2,3,4,5] to monitor signalling deep within the scattering tissue of the brain [6]. AOLs are well suited for this application because they enable 3D random-access multi-photon (RAMP) microscopy, which allows spatially distributed points of interest to be monitored at rates of 30–50 kHz [3]. AOLs use pairs of acousto-optic deflectors (AODs) to focus and deflect an optical beam (Fig. 1(a)). The names are analogous to cylindrical and spherical lenses. Focusing is achieved by driving the transducers of the AODs with linearly-chirped frequencies, while beam steering is achieved by offsetting the frequency [1]

Methods

Results

Conclusion