Acousto-Optic Effects

The very specific nature of the acousto-optical effect requires one to consider some particular issues regarding device performance. These include ... 

Electro-optic and magneto-optic phenomena contain terms of nonlinear optics effects (see Eqs. (4.32), (4.33), (4.36), and (4.39)). On the other hand, acousto-optic effects which arise from a periodical density fluctuation of the medium, analogous to the Brillouin scattering phenomenon, do not contain terms of nonlinear optics, as a general rule.5) The perturbation of light propagation by sonic waves differs from that induced by electric and magnetic fields. As the electric susceptibility, xe, is a function of the density of the medium, it will be influenced by the periodical density fluctuation induced in a medium by sound waves. 

Consequently, we can understand that sound waves change the refractive index of a medium according to Eq. (4.31). In a piezoelectric medium sound waves can induce a new electric field. This phenomenon is very complex because the induced electric field relates to a change in the refractive index of the medium. In general, the acousto-optic effects are classified into two phenomena depending on the frequency of the sound waves, the Raman-Nath diffraction and the Bragg diffraction (see Table 4.10). 

Another common switch, based on the acousto-optic effect, is sketched in Fig. 18. A piezo-electric transducer... 

IV. Optical Image Processing Using the Acousto-Optic Effect... 

II. THE ACOUSTO-OPTIC EFFECT AND ITS PLANE-WAVE SCATTERING MODEL... 

IV. OPTICAL IMAGE PROCESSING USING THE ACOUSTO-OPTIC EFFECT... 

Our discussion on the acousto-optic effect applies to both bulk and thin-film materials. In this section we will study devices using SAW. The SAW device is lighter and more compact, and for a given acoustic energy its diffraction efficiency is greater than that of corresponding bulk-effect devices. 

Acousto-optic effect Mechanical strain produced in a material by the passage of an acoustic wave, causing a change in the index of refraction in the material via the photoelastic effect. 

A modification of the Debye-Sears effect, i.e., the modulation of the refractive index by acoustical waves functioning as tunable grating, is now applied to fast scanning NIR spectroscopy The Acousto-Optic Tunable Filter (AOTF), (Harris and Wallace, 1969 Chang, 1981). In combination with array detectors, chemical imaging is possible (Treado et ah," 1992). 

FIGURE 18 The basic operation of an acousto-optic device is to reduce the intensity of a transmitted beam by diffraction from a refractive index grating that is generated, via the photo-elastic effect, by the RF power supplied to the transducer. The device depicted is used for Q-switching and cavity dumping. If configured as a resonator for the acoustic wave, it serves as a mode-locker. 

ACOUSTO-OPTICS deals with the interaction between sound and laser. It can result in laser beam deflection, laser intensity modulation, and phase modulation and frequency shifting of laser. Devices and systems based on acoustooptic interaction have been playing a major role in various types of optical information processing as well as optical display systems. In Section II, we cover and review some basics of acousto-optic interactions and discuss a plane-wave scattering model for the sound-light interaction. In Section III, we discuss how intensity and frequency modulation of a laser beam can be accomplished by the acoustooptic effect. Applications such as laser beam deflection and laser TV display will then be discussed. In Section IV, we present modem applications of acousto-optics... 

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