V. E. Pozhar

A spectral distortion correction method for an imaging spectrometer

An algorithm for calibration and spectral correction of images obtained with the aid of a spectrometer is proposed and analyzed. Using an acoustooptical microscopic imaging spectrometer as an example, the contribution of individual optical elements of the spectrometer to distortions of spectral images is determined. The accuracy of the algorithm is estimated.

Elastic and photo-elastic characteristics of laser crystals potassium rare-earth tungstates KRE(WO4)2, where RE = Y, Yb, Gd and Lu

The elastic and photo-elastic characteristics of four laser crystals KY(WO₄)₂, KGd(WO₄)₂, KYb(WO₄)₂, and KLu(WO₄)₂ are presented. The first pair was reported early, and the last two materials have been investigated for the first time. The full matrix of elastic constants of these monoclinic crystals has been determined. Also, acousto-optical figure of merit for all the basic geometries of isotropic diffraction has been measured. It is proved that potassium rare-earth tungstates has rather good acousto-optical properties and particularly can take place of fused silica in technical applications required high power laser radiation. All the results demonstrate good prospect of these optically bi-axial laser crystals for development of new effective acousto-optical devices.

Combined optical-coherence and spectral microscopy based on tunable acousto-optic filters of images

A new optical scheme for the microscopic investigation of biological objects is proposed, which combines principles of the optical-coherence and spectral microscopy. The proposed system is based on the acousto-optic filtration of images in the reception channel of a microinterferometer. A prototype of the instrument has been manufactured and it has been demonstrated that the acousto-optic filtration does not violate the interference of two beams carrying images, which makes it possible to extract information both about three-dimensional spatial features and about spectral properties of the object studied.

Elastic and photoelastic properties of KGd(WO4)2 single crystals

The elastic and photoelastic properties of a potassium-gadolinium tungstate KGd(WO4)2 crystal are determined. A complete matrix of elastic constants for the material is obtained for the first time and the velocity diagrams in the five most practically important planes are constructed on its basis. The coefficients of acoustooptic quality M2 are measured for the first time for the crystal in the case of isotropic diffraction for all basic configurations of acoustooptic interaction, which makes it possible to reveal the directions of the most effective interaction.

Double-AOTF-based aberration-free spectral imaging endoscopic system for biomedical applications

The problem of in vivo photoluminescence diagnostics of the tissues accessible by endoscopes is discussed. The spectral imaging module attachable to conventional rigid and flexible medical endoscopes is developed and described. It is based on a double acousto-optical tunable filter (AOTF) and a specialized optical coupling system. The module provides wide field of view (FOV), absence of image distortions, random spectral access, fast spectral image acquisition at any wavelength in the visible range and accurate measurement of reflectance spectrum in each pixel of the image. Images of typical biomedical samples are presented and discussed. Their spectra are compared to the reference data.

Acousto-optical tunable filter for combined wideband, spectral, and optical coherence microscopy.

A multimodal technique for inspection of microscopic objects by means of wideband optical microscopy, spectral microscopy, and optical coherence microscopy is described, implemented, and tested. The key feature is the spectral selection of light in the output arm of an interferometer with use of the specialized imaging acousto-optical tunable filter. In this filter, two interfering optical beams are diffracted via the same ultrasound wave without destruction of interference image structure. The basic requirements for the acousto-optical tunable filter are defined, and mathematical formulas for calculation of its parameters are derived. Theoretical estimation of the achievable accuracy of the 3D image reconstruction is presented and experimental proofs are given. It is demonstrated that spectral imaging can also be accompanied by measurement of the quantitative reflectance spectra. Examples of inspection of optically transparent and nontransparent samples demonstrate the applicability of the technique.

Aberration analysis of AOTF-based spectral imaging systems

Image aberrations caused by acousto-optic (AO) anisotropic diffraction in uniaxial crystals are discussed. For their analysis, we propose a simplified ray-tracing model of an AO crystal cell (AOC). With this approach, one can assign any configuration of AO interaction, any material and geometry of the crystal, and then estimate all conventional ray aberrations, such as spherical, coma, astigmatism, distortion, etc. The optimization procedure is demonstrated by the aberration analysis of three principal spectral imaging schemes based on AO tunable filters (AOTFs). The approach developed promises performance improvement of AOTF-based systems for high-quality spectral imaging and image processing.

Full-field optical coherence microscopy based on acousto-optic filtration of interference images

The problem of three-dimensional near-surface imaging of microscopic structures is discussed. Anew scheme of optical coherence microscope with detection in the spectral domain is proposed. It is based on a broadband light source and filtration of interference images by a tunable acousto-optic imaging filter placed in the detection channel. The applicability of the scheme for analyzing depth distributions of object properties is experimentally demonstrated.

An acousto-optic endoscopic imaging spectrometer

The problem of endoscopic recording of spectral images of hard-to-reach objects is considered. A prototype of the imaging spectrometer, based on a specialized acousto-optic monochromator and a rigid endoscopic probe, is created. In contrast to other similar devices, the proposed optical system, due to the double monochromatization, minimizes spatial-spectral distortions, allowing one to use the spectrometer for fast and undistorted measurements of spectra of all image elements of the studied object. Examples of the obtained spectral images are given and analyzed.

Optimal configuration of an acoustooptic modulator based on a KY(WO4)2 crystal

The elastooptic constants of a KY(WO4)2 laser crystal are determined for the first time. The angular dependences of the acoustooptic quality factor are calculated and analyzed. It is demonstrated that the control power of an acoustooptic high-power laser radiation modulator based on this crystal can be halved compared to available configurations.