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.

Acousto-optic spectral selection of light is an effective technique for interference imaging at multiple wavelengths. In this paper, we show that, depending on the location of the acousto-optical tunable filter relative to the interferometer, it is possible to enhance important characteristics of the whole system: spectral contrast, insensitivity to ambient light, performance stability, and measurement accuracy. We analyze theoretically and compare experimentally a quantitative phase imaging system based on a Mach-Zehnder interferometer with one and two acousto-optical filters located in the illumination or/and in the output channels. Visibility of the interference patterns and noise root mean square in the calculated phase maps are estimated for all cases at room temperature. It is shown that acousto-optic filtration of interfering light beams in the output channel ensures better contrast of the interference pattern and, therefore, provides better stability and higher precision of the phase measurements.

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A technique for spectral filtration of interference images in full-field optical coherence tomography is proposed, implemented and tested. It is based on the spectral selection of light in the registration channel of the interferometer by imaging acousto-optic tunable filter. It is demonstrated that the diffraction of two interfering optical beams via the same ultrasound wave does not destruct the coherence. This new technique, which can be named tunable-imaging-filter-based full-field spectral-domain optical coherence tomography (TIF FF SD OCT), is applicable for 3D surface and inner structure visualization of optically inhomogeneous biomedical objects with moderate spectral, lateral and axial resolution, however with rather high speed.

Multispectral interference techniques are widely used in biomedicine and science for quantitative characterization of morphological, chemical and other properties. These techniques, for example, multispectral digital holography and spectral-domain optical coherence tomography, require wavelength tuning in the interferometer. In this paper, we discuss the effectiveness and potential applications of acousto-optic light filtration for this purpose. We show experimentally that acousto-optical tunable filters are effective for simultaneous spectral and phase data collection not only in conventional dual-path interferometers but also in a common-path interferometer. Scheme of a compact spectral interferometric module based on such interferometer is presented.