Acousto-optic Lens Research Articles

Cerebellar granule cell axons support high-dimensional representations.

In classical theories of cerebellar cortex, high dimensional sensorimotor representations are used to separate neuronal activity patterns, improving associative learning and motor performance. Recent experimental studies suggest that cerebellar granule cell (GrC) population activity is low dimensional. To examine sensorimotor representations from the point-of-view of downstream Purkinje cell ‘decoders’, we used 3D acousto-optic lens two photon microscopy to record from hundreds of GrC axons. Here we show that GrC axon population activity is high dimensional and distributed with little fine-scale spatial structure during spontaneous behaviors. Moreover, distinct behavioral states are represented along orthogonal dimensions in neuronal activity space. These results suggest that the cerebellar cortex supports high dimensional representations and segregates behavioral state dependent computations into orthogonal subspaces, as reported in the neocortex. Our findings match the predictions of cerebellar pattern separation theories and suggest that the cerebellum and neocortex utilize population codes with common features, despite their vastly different circuit structures.

Precompensation of 3D field distortions in remote focus two-photon microscopy.

Remote focusing is widely used in 3D two-photon microscopy and 3D photostimulation because it enables fast axial scanning without moving the objective lens or specimen. However, due to the design constraints of microscope optics, remote focus units are often located in non-telecentric positions in the optical path, leading to significant depth-dependent 3D field distortions in the imaging volume. To address this limitation, we characterized 3D field distortions arising from non-telecentric remote focusing and present a method for distortion precompensation. We demonstrate its applicability for a 3D two-photon microscope that uses an acousto-optic lens (AOL) for remote focusing and scanning. We show that the distortion precompensation method improves the pointing precision of the AOL microscope to < 0.5 µm throughout the 400 × 400 × 400 µm imaging volume.

Real-time 3D movement correction for two-photon imaging in behaving animals.

Two-photon microscopy is widely used to investigate brain function across multiple spatial scales. However, measurements of neural activity are compromised by brain movement in behaving animals. Brain motion-induced artifacts are typically corrected using post hoc processing of two-dimensional images, but this approach is slow and does not correct for axial movements. Moreover, the deleterious effects of brain movement on high-speed imaging of small regions of interest and photostimulation cannot be corrected post hoc. To address this problem, we combined random-access three-dimensional (3D) laser scanning using an acousto-optic lens and rapid closed-loop field programmable gate array processing to track 3D brain movement and correct motion artifacts in real time at up to 1 kHz. Our recordings from synapses, dendrites and large neuronal populations in behaving mice and zebrafish demonstrate real-time movement-corrected 3D two-photon imaging with submicrometer precision.

Rapid acousto-optic focus tuning for improvement of imaging performance in confocal microscopy [Invited

We demonstrate the application of focus-tunable acousto-optic lens technology in confocal microscopy for a high-speed axial scanning of the object. The advantages of the proposed approach include high axial scan rate, no mechanical sample movement, no additional non-symmetric aberrations, and the control of the effective depth of focus. The acousto-optic lens operating at the focus tuning rate of 300 kHz is developed and implemented in scanning laser confocal microscopy. The performance of the instrumentation is presented using test targets. Rapid focus tuning may enhance in vivo three-dimensional imaging in confocal microscopy.

Random-access scanning microscopy for 3D imaging in awake behaving animals.

Understanding how neural circuits process information requires rapid measurements of activity from identified neurons distributed in 3D space. Here we describe an acousto-optic lens two-photon microscope that performs high-speed focusing and line scanning within a volume spanning hundreds of micrometers. We demonstrate its random-access functionality by selectively imaging cerebellar interneurons sparsely distributed in 3D space and by simultaneously recording from the soma, proximal and distal dendrites of neocortical pyramidal cells in awake behaving mice.

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

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.

Development and application of a ray-based model of light propagation through a spherical acousto-optic lens.

A spherical acousto-optic lens (AOL) consists of four acousto-optic deflectors (AODs) that can rapidly and precisely control the focal position of an optical beam in 3D space. Development and application of AOLs has increased the speed at which 3D random access point measurements can be performed with a two-photon microscope. This has been particularly useful for measuring brain activity with fluorescent reporter dyes because neuronal signalling is rapid and sparsely distributed in 3D space. However, a theoretical description of light propagation through AOLs has lagged behind their development, resulting in only a handful of simplified principles to guide AOL design and optimization. To address this we have developed a ray-based computer model of an AOL incorporating acousto-optic diffraction and refraction by anisotropic media. We extended an existing model of a single AOD with constant drive frequency to model a spherical AOL: four AODs in series driven with linear chirps. AOL model predictions of the relationship between optical transmission efficiency and acoustic drive frequency including second order diffraction effects closely matched experimental measurements from a 3D two-photon AOL microscope. Moreover, exploration of different AOL drive configurations identified a new simple rule for maximizing the field of view of our compact AOL design. By providing a theoretical basis for understanding optical transmission through spherical AOLs, our open source model is likely to be useful for comparing and improving different AOL designs, as well as identifying the acoustic drive configurations that provide the best transmission performance over the 3D focal region.

A 2D/3D switchable autostereoscopic display system, an acousto-optic lens approach

A novel autostereoscopic display system with the characteristics of variable viewing distance control, real-time 2D/3D switchable display, and adjustable lens pitch using an acousto-optic lens (AOL) is proposed. With the unique property of an AOL array, the proposed system can provide viewers to select suitable viewing distances by adjusting the acoustic signal that is applied to the AOL array. With the same property, the system can also be adjusted with an appropriate interpupillary distance (IPD) for personal entertainment applications. The proposed system with adjustable lens pitch, can adopt to different display panels with various resolutions and/or composited images. The operation principle of the system is analyzed with a set of design parameters and a set of simulation results to facilitate the implementation of the system and to verify the validity of the approach.

Beam deformation within an acousto-optic lens.

The acousto-optic lens (AOL) is becoming a popular tool in the neuroscience field. Here we analyzed the deformation of the diffraction beam after passage through an AOL consisting of a pair of acousto-optic deflectors using both theoretical and experimental data. The results showed that, because of the high sensitivity of optical spatial frequencies of acousto-optic deflectors, the boundary strength of the diffraction beam of the AOL decreases significantly. When the focal length of AOL diminishes, the deformation of the diffraction beam becomes more serious with a smaller beam size. This deformation of the diffraction beam finally leads to a decreased illuminative numerical aperture, which worsens the image's spatial resolution.

Microscopic OCT imaging with focus extension by ultrahigh-speed acousto-optic tunable lens and stroboscopic illumination.

We develop high-resolution optical coherence tomography (OCT) system with high-speed acousto-optic tunable lens. Stroboscopic pulsed illumination is used for the first time to perform time-resolved OCT imaging with acousto-optic tunable focusing. The operation of ultrahigh-speed tunable acousto-optic lens is demonstrated theoretically and experimentally. Focal position tuning at MHz frequency range is experimentally shown in the imaging system leading to OCT images with extended depth of focus. Imaging with active optical elements is helpful for improvement of photon collection efficiency, depth of focus and enhancement of the image quality.

Monitoring synaptic and neuronal activity in 3D with synthetic and genetic indicators using a compact acousto-optic lens two-photon microscope

BackgroundTwo-photon microscopy is widely used to study brain function, but conventional microscopes are too slow to capture the timing of neuronal signalling and imaging is restricted to one plane. Recent development of acousto-optic-deflector-based random access functional imaging has improved the temporal resolution, but the utility of these technologies for mapping 3D synaptic activity patterns and their performance at the excitation wavelengths required to image genetically encoded indicators have not been investigated. New methodHere, we have used a compact acousto-optic lens (AOL) two-photon microscope to make high speed [Ca2+] measurements from spines and dendrites distributed in 3D with different excitation wavelengths (800–920nm). ResultsWe show simultaneous monitoring of activity from many synaptic inputs distributed over the 3D arborisation of a neuronal dendrite using both synthetic as well as genetically encoded indicators. We confirm the utility of AOL-based imaging for fast in vivo recordings by measuring, simultaneously, visually evoked responses in 100 neurons distributed over a 150μm focal depth range. Moreover, we explore ways to improve the measurement of timing of neuronal activation by choosing specific regions within the cell soma. Comparison with existing methodsThese results establish that AOL-based 3D random access two-photon microscopy has a wider range of neuroscience applications than previously shown. ConclusionsOur findings show that the compact AOL microscope design has the speed, spatial resolution, sensitivity and wavelength flexibility to measure 3D patterns of synaptic and neuronal activity on individual trials.

A compact acousto-optic lens for 2D and 3D femtosecond based 2-photon microscopy

We describe a high speed 3D Acousto-Optic Lens Microscope (AOLM) for femtosecond 2-photon imaging. By optimizing the design of the 4 AO Deflectors (AODs) and by deriving new control algorithms, we have developed a compact spherical AOL with a low temporal dispersion that enables 2-photon imaging at 10-fold lower power than previously reported. We show that the AOLM can perform high speed 2D raster-scan imaging (>150 Hz) without scan rate dependent astigmatism. It can deflect and focus a laser beam in a 3D random access sequence at 30 kHz and has an extended focusing range (>137 mum; 40X 0.8NA objective). These features are likely to make the AOLM a useful tool for studying fast physiological processes distributed in 3D space.

Acousto-optic lens based on interaction of narrow laser beam with cylindrical ultrasound

Experimental studies of narrow light beam interaction with cylindrical standing ultrasonic wave are presented. As the focusing and defocusing effects are observed, the considered arrangement appears to be an acousto-optic lens. The proposed system acts as an equivalent optical spherical lens whose focal length changes periodically. Additionally, the system based on cylindrical ultrasound serves as an efficient laser light modulator with the rise time of 100ns. The parameters of both considered modalities (lens and modulator) can be easily controlled.

Acousto-optic lens with very fast focus scanning

We propose and experimentally demonstrate an acousto-optic cylindrical lens with a very fast (400-kHz) focal scanning. The lens is realized by use of two adjacent acousto-optic scanners with counterpropagating acoustic waves that have the same frequency modulation but a pi phase difference. This scheme completely suppresses the lateral scan but adds the linear chirp of the two waves and thus functions as a fast focal-scan lens. We also demonstrate the use of this scanning lens in a very fast confocal profilometer.

Laser tuning with an acousto-optic lens

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Fourier transform properties of acousto-optic lens

A rf pulse of 4 μs swept linearly over 10 MHz, about a center frequency of 100 MHz, has been compressed to 110 ns. Fourier and Mellin transforms property of the surface acousto-optic lens has been discussed.

Fast acousto-optic lens Q switch

A fast acousto-optic Q switch has been demonstrated which relies on a linear FM pulse of acoustic energy to act as a moving lens. While one corrdinate of the focus of the lens is fixed by the rate of frequency sweep, the other coordinate is ’’swept’’ in time by the frequency variation of the pulse. The on time of the switch is proportional to the reciprocal of the pulse bandwidth. Experiments have been conducted which verify the characteristics of this technique. A TeO2 Bragg cell was used in a successful attempt to Q switch a Nd/YAG laser with the acousto-optic lens approach.