The accurate theory describing interaction of two coherent light beams with ultrasonic wave where one of the light beam is incident at positive Bragg angle while the other at negative was developed by Leroy and Blomme in 1984 . The assumed geometry in this theory resembles an interferometer wherein ultrasonic beam plays a role of the output beam splitter of the light. The output light intensity is modulated with ultrasonic frequency as a result of interference between the light in diffraction orders in which the frequency is changed due to the Doppler effects with those diffracted with unchanged frequency. Temporal modulation of the light intensities in diffraction orders, that was foreseen by Leroy and Blomme, was confirmed experimentally and the results will be presented. In addition, the Leroy-Blomme theory has been extended to include the effect of the initial phase of the ultrasonic wave on the phase of modulation of light intensity in diffraction orders. According to the best knowledge of the author, Leroy and Blomme theory has not been verified experimentally, although many years have passed. This theory could be applied to the quantum optics phenomenon when pairs of entangled photons are incident on ultrasonic wave instead of two coherent light beams. The geometry of interaction of two coherent light beams with ultrasonic wave in Leroy-Blomme theory is the same as for Hong-Ou-Mandel interferometer wherein a beam splitter is replaced by the ultrasonic wave. Similarities and differences between Leroy-Blomme and Hong-Ou-Mandel interferometers will be presented.
Decay characteristics and polarization of DMABN luminescence at far longwavelength Antistokes excitation by picosecond semiconductor laser radiation at 403 nm are reported. Characteristics of DMABN emission have been registered in different regions of spectra.
A theoretical model is presented for the study of the near field of light diffracted by ultrasound in an isotropic medium which becomes birefringent in the presence of an acoustic wave. Due to the interference with the sound wave, the diffracted light wave in its near field is seen to act as a quasi-monochromatic light wave which is partially polarized. The degree of coherence ins sen to coincide with the degree of polarization and can be controlled acoustically. Hence coherent laser light can be transformed into incoherent light by sending it through an isotropic material with acoustically induced birefringence. In the experimental part of the work, the non-diagonal elements of the diffracted light beam coherency matrix were measured and a good agreement with the theoretical model was obtained.
Light-diffraction tomography is a non-invasive measuring technique for mapping ultrasonic fields. Provided that there is weak acousto-optical interaction, data acquisition at normal light incidence is the appropriate technique. In the range of strong acousto-optical interaction, data acquisition and evaluation are as easy to perform as for weak acousto-optical interaction provided that Bragg incidence is used. Both techniques are complementary to each other and can be utilized in a frequency range which has not been accessible so far.
Light-diffraction tomography is a noninvasive measurement technique for mapping ultrasound fields and provides a high spatial resolution. In the range of the Raman-Nath approach, this technique can be successfully applied to frequencies of approximately 5 MHz to ultrasound fields of any geometry. Beyond this frequency range, however, light diffraction implies peculiarities that strongly affect data acquisition. It is the aim of this review to outline the capability of the method, including its range of applicability, and to discuss new steps for its extension.
Polarization effects that arise during diffraction of an arbitrarily polarized light by an acoustic wave in an anisotropic medium are studies both theoretically and experimentally. Peculiarities of these effects in the cases of isotropic and anisotropic scattering of the light are considered in detail. Results of polarization state measurements performed with a paratellurite acousto-optic cell in the zeroth order of diffraction are presented as well.
In the ultrasonic light diffraction phenomena in an isotropic medium in the intermediate range (between Raman-Nath and Bragg) variations in polarization state of diffracted light have been predicted and experimentally observed. In the paper some experimental and numerical results for 0 order of light diffracted by ultrasonic wave of 50 MHz frequency are presented. A possibility of continuous control of the polarization state from linear to elliptical or circular against the Raman-Nath parameter has been confirmed in good agreement between theoretical and experimental values.
Light diffraction by ultrasonic waves has been studied for many years, however we still can not say that the phenomenon has been examined completely. During the last decade the near field investigations received a particular attention. The new results obtained, both in the near field and in the far field of ultrasonically difracted light, forced us not only to change our point of view concerning this phenomenon but also to modify the formulas describing it. A brief review is given of some of the results which have been obtained up until now, both theoretical and experimental ones. Some new theoretical suggestions, based on the N-th order approximation (NOA) method are presented.
Some conclusions resulting from the solution of the Raman-Nath system of difference- differential equations relating to the amplitude and phase of diffracted light by an ultrasonic wave for the Raman-Nath, the intermediate, and the Bragg regions are presented and exemplified by some numerical and experimental results.
Double ultrasonic beam acousto-optical modulators require high precision driving electric signals for stable control of frequency ratio and phase shift. The high precision digital synthesis method has been developed for the generation of high quality periodic signals. Maximum frequency range of synthesized waveforms is determined by the speed of available random access memory (RAM) and an available D/A converter. A computer-based digital function generator can generate any arbitrary type of signal in the frequency range determined by the speed of RAM and the D/A converter. Frequency stability is determined by the quartz clock of the D/A converter and is in the order of 1/107. Periodic waveforms can be synthesized, stored, and then played continuously by looping through the RAM buffer.
Light diffraction by ultrasound waves is discussed in the wide range from weak acousto-optic interaction to strong acousto-optic interaction in terms of numerical simulations and experimental investigations for normal incidence. Particular emphasis has been placed on the complex nature of the diffracted light amplitude. The paper is intended as a contribution towards a unified representation of the general phenomenon.
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