A. S. Machikhin

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.

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.

An optical system for coupling double acousto-optic monochromators and eyepieces of visual optical instruments

The problem of simulating the optical coupling system when designing video spectrometers based on double acousto-optic monochromators and standard optical instruments for visual observation is considered. A three-component afocal optical system is proposed to be installed between the monochromator and the eyepiece. This configuration is shown to allow the field of view of the instrument and the illuminance at off-axis points of an image to be increased. The calculated optical coupling system has been manufactured as a finished mechano-optical module. Results of its testing with different types of visual optical instruments are presented.

Imaging system based on a tandem acousto-optical tunable filter for in situ measurements of the high temperature distribution

We present, to the best of our knowledge, the first experimental demonstration of a new imaging system for in situ measurement of the two-dimensional (2D) distribution of the surface temperature of microscopic specimens. The main component of the system is an imaging tandem acousto-optical tunable filter (TAOTF) synchronized with a video camera. A set of TAOTF spectroscopic images (up to a few hundreds) is taken by the TAOTF imaging system to fit the measured spectral curves in each pixel to the Planck radiation function and determine the temperature and emissivity of the sample using the gray body approximation. It is experimentally shown that this technique provides aberration-free spectral imaging suitable for precise multispectral imaging radiometry (MIR).

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.

A multifunctional contactless profilometer based on a tunable acousto-optical image filter

A contactless complete-field profilometer operating as an optical coherent microscope with the spectral recording is designed. Its special feature is that the spectral selection is carried out in the receiving channel. An acousto-optical image monochromator is used for this purpose. The experimental relief surface data are given.

Obtaining spectral stereo images with electronic spectral tuning and polarization separation

The problem of obtaining stereo images of objects in arbitrary narrow spectral intervals is considered. A method of accomplishing this task is proposed, according to which the two light beams forming a stereopair are simultaneously filtered in one acousto-optic cell and the output beams are separated with respect to polarization. An optimum geometry of diffraction is found and requirements to the acousto-optic filter are formulated. The main characteristics of the spectral stereo system are determined.