We propose a new technique for three-dimensional (3-D) imaging in arbitrary spectral intervals. It is based on a simultaneous diffraction of two divergent stereoscopic light beams on a single acoustic wave propagating in a uniaxial birefringent crystal. We discuss in detail this configuration of acousto-optic (AO) interaction, derive basic relations, and experimentally demonstrate the applicability of the proposed approach to 3-D spectral imaging. A stereo-imager of this type may be produced as an ultra-compact embeddable optical element, which is promising for many imaging applications.

Spatiospectral structure of wave phase matching in birefringent crystals has a strong dependence on the geometry of the acousto-optic interaction and incident light spectrum. This dependence defines details of light beam profile transformation. It is especially important for imaging applications related to a large angular aperture and a wide spectral bandwidth of the incident light. In this paper, we demonstrate accurate three-dimensional plotting of a light transmission pattern without small birefringence approximation. The rather complicated shape of the phase-matching locus in the spatiospectral domain inevitably leads to residual spatially nonuniform chromatic aberrations in the spectral image. Theoretical consideration and computational modeling are confirmed by the experiments on Bragg diffraction in paratellurite crystal. The results are especially important for the development of acousto-optical imaging devices and laser beam shaping technologies.

Spectral image filtration by means of acousto-optical tunable filters (AOTFs) has multiple applications. For its implementation, a few different optical schemes are in use. They differ in image quality, number of coupling components, dimensions and alignment complexity. To choose the optical system of AOTF-based spectral imager properly, many factors have to be considered. Though various schemes of acousto-optic (AO) filtration have been tested and discussed, their comparative analysis has not been reported up to now. In this study, we assembled the four most popular schemes (confocal, collimating, tandem and double-path) using the same AO cells and experimentally compared their main features. Depending on the application, each scheme may be the basis of compact cost-effective spectral imaging devices.

A rather narrow field of view (FOV) has always been considered as an essential limitation of spectral imagers based on acousto-optical tunable filters (AOTFs). We demonstrate a computational technique to overcome this constraint. It is based on preliminary precise spectral-angular characterization of beam transformation caused by light diffraction on an acoustic wave and consequent correction of acquired stack of spectral images. This technique is applicable for any geometry of acousto-optic interaction and opens the way for the development of AOTFs with significantly expanded FOV.

Raman microspectroscopy has become an effective method for analyzing the molecular appearance of biomarkers in skin tissue. For the first time, we acquired in vitro Raman spectra of healthy and malignant skin tissues, including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), at 532 and 785 nm laser excitation wavelengths in the wavenumber ranges of 900–1800 cm⁻¹ and 2800–3100 cm⁻¹ and analyzed them to find spectral features for differentiation between the three classes of the samples. The intensity ratios of the bands at 1268, 1336, and 1445 cm⁻¹ appeared to be the most reliable criteria for the three-class differentiation at 532 nm excitation, whereas the bands from the higher wavenumber region (2850, 2880, and 2930 cm⁻¹) were a robust measure of the increased protein/lipid ratio in the tumors at both excitation wavelengths. Selecting ratios of the three bands from the merged (532 + 785) dataset made it possible to increase the accuracy to 87% for the three classes and reach the specificities for BCC + SCC equal to 87% and 81% for the sensitivities of 95% and 99%, respectively. Development of multi-wavelength excitation Raman spectroscopic techniques provides a versatile non-invasive tool for research of the processes in malignant skin tumors, as well as other forms of cancer.

We report on wavelength-multiplexed digital holographic imaging based on simultaneous Bragg diffraction of wideband light by several ultrasound waves of different frequencies in crystalline media. This technique is easy to implement, avoids spectral scanning, and is applicable in various digital holography schemes. It also enables single-shot acquisition of a few spectral fringe patterns by a single monochrome sensor and wavelength demultiplexing of the resulting interferogram. We have assembled a Mach–Zehnder interferometer with an acousto-optical tunable filter operating in the multifrequency mode and have validated the proposed technique by dual-, three-, and four-wavelength quantitative phase imaging of the test samples.