Nonmechanical image rotation with an acousto-optic dove prism

Imaging the brain in action: a motorized optical rotary joint for wide field fibroscopy in freely moving animals

SIGNIFICANCE

The study of neuronal processes governing behavior in awake behaving mice is constantly boosted by the development of technological strategies, such as miniaturized microscopes and closed-loop virtual reality systems. However, the former limits the quality of recorded signals due to constrains in size and weight and the latter suffers from the restriction of the movement repertoire of the animal, therefore, hardly reproducing the complexity of natural multisensory scenes.

AIM

Another strategy that takes advantage of both approaches consists of the use of a fiber-bundle interface to carry optical signals from a moving animal to a conventional imaging system. However, as the bundle is usually fixed below the optics, its torsion resulting from rotations of the animal inevitably constrains the behavior over long recordings. Our aim was to overcome this major limitation of fibroscopic imaging.

APPROACH

We developed a motorized optical rotary joint controlled by an inertial measurement unit at the animal's head.

RESULTS

We show its principle of operation, demonstrate its efficacy in a locomotion task, and propose several modes of operation for a wide range of experimental designs.

CONCLUSIONS

Combined with an optical rotary joint, fibroscopic approaches represent an outstanding tool to link neuronal activity with behavior in mice at the millisecond timescale.

Structured illumination in compact and field-portable 3D-printed shearing digital holographic microscopy for resolution enhancement

A compact and field-portable three-dimensional (3D)-printed structured illumination (SI) digital holographic microscope based on shearing geometry is presented. By illuminating the sample using a SI pattern, the lateral resolution in both reconstructed phase and amplitude images can be improved up to twice the resolution provided by conventional illumination. The use of a 3D-printed system and shearing geometry reduces the complexity of the system, while providing high temporal stability. The experimental results for the USAF resolution target show a resolution improvement of a factor of two which corroborates the theoretical prediction. Resolution enhancement in phase imaging is also demonstrated by imaging a biological sample. To the best of our knowledge, this is the first report of a compact and field-portable SI digital holographic system based on shearing geometry.

Wollaston prism-based structured illumination microscope with tunable frequency

This work proposes an alternative structured illumination (SI) system based on a Wollaston prism (WP) illuminated by the diffracted field of an incoherent linear source. The proposed WP-based SI system presents several advantages. First, the generated fringes can be approximated by a pure sinusoidal pattern; thereby, computational methods developed for sinusoidal SI can be used without the need for additional processing. Second, the SI pattern's period can be continuously varied up to the cutoff frequency of the native widefield system. Most significantly, the phase shifting of the SI pattern required for demodulation in SI microscopy can be easily accomplished using a de Sénarmont compensator, which provides accurate lateral displacement of the fringes independently of the lateral modulation frequency. Experimental verifications confirm the presented theoretical predictions.

Tunable-frequency three-dimensional structured illumination microscopy with reduced data-acquisition

The performance of a tunable three-dimensional (3D) structured illumination microscope (SIM) system and its ability to provide simultaneously super-resolution (SR) and optical-sectioning (OS) capabilities are investigated. Numerical results show that the performance of our 3D-SIM system is comparable with the one provided by a three-wave interference SIM, while requiring 40% fewer images for the reconstruction and providing frequency tunability in a cost-effective implementation. The performance of the system has been validated experimentally with images from test samples, which were also imaged with a commercial SIM based on incoherent-grid projection for comparison. Restored images from data acquired from an axially-thin fluorescent layer show a 1.6× improvement in OS capability compared to the commercial instrument while results from a fluorescent tilted USAF target show the OS and SR capabilities achieved by our system.

Experimental demonstration of ray-rotation sheets

We have built microstructured sheets that rotate, on transmission, the direction of light rays by an arbitrary, but fixed, angle around the sheet normal. These ray-rotation sheets comprise two pairs of confocal lenticular arrays. In addition to rotating the direction of transmitted light rays, our sheets also offset ray position sideways on the scale of the diameter of the lenticules. If this ray offset is sufficiently small so that it cannot be resolved, our ray-rotation sheets appear to perform generalized refraction.

Rapid super-resolution line-scanning microscopy through virtually structured detection

Virtually structured detection (VSD) has been demonstrated to break the diffraction limit in scanning laser microscopy (SLM). VSD provides an easy, low-cost, and phase-artifact-free strategy to achieve super-resolution imaging. However, practical application of this method is challenging due to a limited image acquisition speed. We report here the combination of VSD and line-scanning microscopy (LSM) to improve the image acquisition speed. A motorized dove prism was used to achieve automatic control of four-angle (i.e., 0°, 45°, 90°, and 135°) scanning, thus ensuring isotropic resolution improvement. Both an optical resolution target and a living frog eyecup were used to verify resolution enhancement.

Dove prism with increased throughput for implementation in a rotational-shearing interferometer

An analytical expression is derived for the tilt introduced into a wave front by a Dove prism with manufacturing errors in the prism's base angles and pyramidal angle. We found that the tilt decreases when the base angles are increased above the values of traditional design. The increase in the length-aperture ratio of a prism is detrimental to the prism's performance. However, a Dove prism with a widened aperture increases throughput and maintains a manageable prism weight for implementation in a rotational shearing interferometer. Thus we propose a Dove prism designed with a widened aperture to increase throughput in a rotational shearing interferometer and with larger base angles to minimize the wave-front tilt introduced by manufacturing errors. Experimental results implemented in a rotational shearing interferometer demonstrate the feasibility of this design.

Acoustically steered and rotated true-time-delay generator based on wavelength-division multiplexing

The acoustically steered and rotated (ASTRO) true-time-delay (TTD) generator, capable of two-dimensional (2D) multiple beam generation without causing extraneous beams, is described. It is based on wavelength-division multiplexing to encode and decode various linear chirp time delays with wavelengths. An array of equally spaced light stripes with linear chirp time delays among them is formed and is subsequently rotated to a desired angle by use of our nonmechanical acousto-optic dove prism, believed to be novel. Our architecture reduces hardware complexity significantly by avoiding redundancy in conventional TTD generators. Experimental results to prove the concept of 2D multiple beam generation are shown. Also, an extension of the system for bidirectional communications is proposed. Various technical issues for practical applications are discussed.