Present paper focuses on correction for effect of vertical imbalance, which can make difficulties to observing
stereoscopic image in Greenough stereoscopic microscopes. In the context of geometrical optics we derive condition of
vertical imbalance elimination for all points of stereoscopic image observed in Greenough stereoscopic microscope.
Present paper describes new method for eliminating depth plane curvature stereoscopic distortion by depicting each of
two perspective images on separate flat screen with these two screens intersecting at certain angle.
Some results obtained with developed high resolution scanning acoustical microscope are shown in the present paper. Created systems are provided with the set of acoustical objectives for working frequencies from 25 MHz to 1 GHz having different apertures of sound beam and different focus distances. Designed and developed system is capable for capturing both bulk acoustical images, as well as the plane images obtained as cuts in desirable section of an object; so, so-called B-scan as well as C-scan are realized. The presence of noise strongly reduces their quality. To solve this problem it is possible to use methods of mathematical processing. The application of this method allows receiving bulk acoustic images with very high resolution. In the present work the application of four such methods in comparison is considered.
Some results obtained with developed high resolution scanning acoustical microscope are shown in present paper. Designed and developed system is capable for capturing both bulk acoustical images, as well as the plane images obtained as cuts in desirable section of an object; so, so-called B-scan as well as C-scan are realized. Created systems provided with the set ofacoustical objectives for working frequencies from 25 MHz to I GHz having different apertures of sound beam and different focus distances. Results of investigation of technical and biological objects are briefly discussed.
Interesting phenomenon - drastic suppression of diffracted light first order side lobes, has been shown as a result of numerical simulation of light and sound beams interaction with equal cross-section field distribution and equal divergences.
In this paper the main idea and method for bulk holographic video realization is considered. By digital simulation the steps of hologram recording and image reconstruction is shown. The prospects and some shortcomings of the suggested method are discussed.
At this chapter the method of 3-dimensionl image reconstruction, based on the acoustooptical interaction of reference light beam at the hologram that created by high frequency acoustic wave field, is discussed. Such, acoustically created hologram is electronically controlled and as a sequence the moving bulk scene reconstruction is possible. The mathematical modeling of step-by-step image capturing and reconstruction is discussed. The architecture of such king of system is considered.
Paper is devoted to consideration of the method of first order side lobes suppression for acoustical fields excited by disc-shape radiator. Numerical simulations results of radiator optimized variant are presented. Offered method can be applied for sound radiation directivity diagram improvement, for example, in acoustical microscopy.
There is considered theoretically the competition near the resonant acousto-optical (AO) conditions of two mechanisms which influence to the diffraction efficiency ηd variation, when the thickness L of the sample (the length of interaction) is changed: (1) the enhancement of ηd due to increase of L, and (2) degradation of ηd due to the increase of optical absorption αL in crystal. It is shown that: (1) when changing the length of interaction L the maximum diffraction efficiency ηd is changed and shifted in wavelength's scale, reaching the maximum value at defined L which depend on the particular interaction geometry; (2) for particular considered in present work crystals the variation of L is more critical to the wavelength λ change for GaAs as compared to InP; (3) when realizing the optimized geometry of AO interaction closed to resonant condition at frequency 2.5 GHz, the diffraction efficiency in GaAs crystals can reach 8% and in InP 3.5% per 1 mW of conducted electromagnetic power (correspondingly 8000 and 3500% per 1 W of RF power) when the thickness of samples is about 4 mm.
Monitoring of laser energy absorbed inside tissue is very impotent for laser thermocoagulation of tumors, laser surgery etc. Experimental results have shown that analysis of optoacoustic signal magnitude induced by short laser pulse inside tissue can give quantitative information about laser fluence absorbed by the tissue. We have investigated some tissue phantoms with absorbing objects inside. The first harmonic (1064 nm) of Q-switched Nd:YAG-laser was used for generation of optoacoustic signals.
The time-resolved detection of laser-induced stress transients makes it possible to detect absorbing structures in turbid media. We used optoacoustic technique for investigation of blood vessels in tissue. The position in depth and the size of absorbers in gel phantoms and vessels in muscle tissue were measured. The acoustic waves were induced by 15-ns 1064-nm pulses of Q-switched Nd:YAG laser. Experimental results have shown that the blood vessels can be visualized at depth up to 10 mm at that wavelength.
The method of calculation of the diffracted acoustic field amplitude distribution by Fourier transform for the round emitter in approximation of isotropic medium has been described. The numeric results in form of dependencies of the relative acoustic field amplitude on the dimensionless coordinates have been presented at four examples of acoustic heads.
In present paper the brief review of last years publication on laser opto-acoustics in medical applications is done. The short theory and main practical formulae are given. Several examples of practical applications of laser opto-acoustics in biomedicine such as opto-acoustic methods of layered tissues investigation and breast cancer diagnostics possibilities are shown. Some results of acoustic receivers investigation for opto-acoustic applications designed at Saratov State University are presented.
The way of extension of acousto-optical interaction frequency bandwidth to more than one octave is suggested. The main principle used for this aim is to design the electro-acoustical multi-element transducer with variable, along its length, parameters. In such a case to each frequency point inside chosen band exists the region of the transducer's length where, from one hand, the condition for good excitation of sound waves is fulfilled and from the other hand the Bragg condition is also fulfilled because of closed coincidence of real and necessary frequency dependencies of Bragg angle and of the angle of sound wave front inclination. This window moves from one end of the transducer to the other when frequency changes from minimum to maximum one inside the band. The closer real angle frequency dependence follows to necessary one than larger the length of transducer can be done and than more higher the diffraction efficiency can be reached.
We demonstrated in this work the possibility of application of the effect of resonant acousto- optical (AO) interaction for the creation of wide band and high efficiency Bragg cells on gigahertz frequencies. The main principle of this effect consists in heat there exists the optimum photon energy (very close to the band gap of semiconductor sample) where the optical absorption is still not big enough but the figure of merit already several times higher in comparison with one when the photon energy is fat from the band gap. We have shown theoretically that the optimization of multilayer thin film piezoelectric transducers allows to create AO Bragg cells (deflectors and modulators) working in resonant conditions and having very high diffraction efficiency (more than 10%) and very wide frequency band (up to 2 GHz). This optimization based on the use of the acoustical matching scheme-asynchronous transform, analogous to one in electrotechnics. Experimental devices represent the cells with crystal plates of GaAs and InP of (100) and (110) cut having the multilayer thin film transducer on the butt-end that has been matched with microstrip transmission line. Characteristics of created AO cells reach: 10% per 1 Watt of electrical power; 2 GHz frequency band with 8 MHz frequency resolution. The obtained experimental results show a good agreement with theoretical predictions.
We created an acousto-optical standing-wave modulator for fluorometry and laser mode synchronization in the frequency bandwidth from 20 MHz to 160 MHz without the mechanical Bragg angle correction. The special construction multi-element electro-acoustical transducer was matched electrically and acoustically in whole frequency bandwidth.
The solution of the main problem of high frequency (up to 10 GHz) acousto-optics (sound attenuation and restriction of the bandwidth) may consist in the utilization of the multielement electroacoustical transducers which ensure automatic tuning at Bragg angle in wide frequency band. The current presentation describes the consideration of different types of new high frequency multielement transducers, the theoretical advantages of the diffraction efficiency and bandwidth of acousto-optic interaction as compared with the case of the one element transducer.