Acousto-optic Light Research Articles

Imperfections and their influences on optical homogeneity of PbMoO 4 single crystals grown by Czochralski method

Various imperfections and their optical effects in PbMoO 4 crystals grown by the Czochralski method are presented. Observation of defects were carried out by X-ray techniques, etched patterns, Twyman-Green interferometer, photoelastic patterns through crossed polarizer and scattered light from Ar laser beam path in the finished crystals. For quantitative evaluation of the optical homogeneity of the crystals, the signal/noise ( S/ N) ratio, the transmitted laser beam divergence ratio (α) and the scattered light intensity ratio (β) were definied. These are very important quantities for high capacity and high precision acousto-optic light deflectors. In the crystals with macro-imperfections, S/ N ratios were less than about 10 and α-values were more than 0.1. On the other hand, a maximum S/ N ratio of 85 and a minimum beam divergence ratio of 0.008 were obtained for a crystal free from macro-imperfections.

Acoustooptic deflection

Acoustooptic light deflectors are finding their way into a wider range of applications by offering a viable means for fast and accurate beam scanning with sufficient resolution to make them very attractive for such applications as TV recording, laser-addressed light valves, large-bandwidth facsimile systems, and flying spot scanners and displays. There are a variety of materials available for light deflection, among these being Paratellurite (TeO2), which, by exploiting its birefringence to circularly polarized light, has emerged as a most attractive acoustooptic material for laser scanning in the visible range. Its high figure of merit (M2 = 525) and anomalously low shear wave velocity (vs = 0.0617 × 105 cm/sec) make possible light-deflector designs which offer high resolution and efficiency. The anisotropic Paratellurite also offers a substantially expanded angular range over which Bragg interaction can take place thus allowing operation deeper into the Bragg regime. For example, an anisotropic Paratellurite deflector with a 0.225-cm interaction length can achieve 70% deflection efficiency with 40 mW of rf drive power and is capable of 525 linearly resolvable spots with a 0.5-cm optical aperture. The assets and liabilities of using this material for light deflection are discussed in detail.

Acousto-optical light diffraction in thin films

The diffraction of optical guided waves in thin films through an acousto-optic effect is treated. The diffraction of the bounded optical waves in thin films is a rather complicated phenomenon as compared with that of the free waves in bulk media. An expression for the diffraction efficiency has been derived using coupled-wave equations. Acousto-optical figure of merit and the mode coupling factor applicable to the diffraction in thin films are defined. The TE0 and TM0 waves in an As2S3 film deposited onto a LiNbO3 substrate were diffracted by Rayleigh waves with 93 and 72% efficiency at electrical input powers of 150 and 50 mW, respectively. The present experiment revealed that approximately 5% of the total acoustic power penetrated into the film and took part in the diffraction.

Use of the acoustooptic light deflector as an optical isolator

In many uses of lasers, the minimization or elimination of power reentering the laser is necessary to ensure its stability. It is pointed out here that the frequency-shifting properties of an acoustooptic light deflector can be used for this purpose. By using the deflected beam from a Bragg deflector, stability of the laser is obtained when the frequency of the acoustic wave is chosen such that the frequency(ies) of the light reentering the laser, shifted by twice the acoustic frequency from the light leaving the laser, does not correspond to a cavity resonance. Experimental results demonstrating this isolation property are presented and are found to be in general agreement with other results of injection locking of lasers.

Acoustooptic deflection materials and techniques

The physics and technology of acoustooptics are reviewed mainly from the standpoint of designing laser-beam deflection devices and their applications. The ultrasonic light diffraction theory in a form useful for device application is outlined, beginning with the well-known Raman-Nath equation and covering both normal and abnormal types of Bragg reflection. Various acoustooptic materials are evaluated on the basis of two main factors, i.e., acoustooptic figures of merit and acoustic attenuation, as well as availability and optical quality. Guidelines for the selection of materials are discussed in some detail, although they are still insufficient for the complete prediction of new suitable materials. Elements of the acoustooptic light deflector are presented, and the importance of the fabrication techniques is stressed. As examples of the performance characteristics of the deflector, those of TeO 2 [001] longitudinal-wave and [110] shear-wave deflectors are described. Applications of the deflector to several kinds of apparatus and systems are considered on the basis of the present and the future states of the art.

Acousto-Optic Light Deflection: Design Considerations for First Order Beam Steering Transducers

Acousto-Optic Light Deflection: Design Considerations for First Order Beam Steering Transducers

Acousto-optical light deflector using TeO 2 single crystal (Bragg reflection of laser light by ultra-sound in TeO 2 single crystal) : Uchida, N., Ohmachi, Y. Japanese Journal of Applied Physics, Vol 9 No 1 (January 1970) pp 155–156 (2318)

Acousto-optical light deflector using TeO 2 single crystal (Bragg reflection of laser light by ultra-sound in TeO 2 single crystal) : Uchida, N., Ohmachi, Y. Japanese Journal of Applied Physics, Vol 9 No 1 (January 1970) pp 155–156 (2318)

Acousto-optic light deflection: the design and operation of a simple X–Y deflection system: Pinnow, D.A., Williamson, S.R., LaMacchia, J.T., Paper WG20, 1969 Spring Meeting of Optical Society of America (11–14 March 1969, San Diego, California, USA)

MgGd0.1Fe1.9O4 ferrite with improved electrical and dielectric properties has been synthesized by conventional ceramic technique. X-ray analysis confirmed the single-phase inverse spinel structure of the ferrite. The dc resistivity is increased by one order of magnitude as compared to Magnesium ferrite. The dielectric loss of the sample investigated at room temperature is only 3 × 10−3 at 3 MHz. High resistivity and low dielectric loss can be correlated with better compositional stoichiometry, size and nature of the additives. The variation of dielectric properties of the sample as a function of frequency in the range 0.1–20 MHz has been studied at different temperatures. In addition to this, the electric and dielectric properties have been studied as a function of temperature. Possible mechanisms contributing to the results have been discussed minutely in this paper.

Design Considerations for a Semipermanent Optical Memory

The potential of high-speed optical memories using electro-optic or acousto-optic light deflection for address selection is examined. It is shown that for such memories the total memory capacity decreases as the third power of the addressing rate and that capacities in excess of 108 bits are feasible with a random access rate of 106 addresses/sec. A specific semipermanent memory design is then described which uses a laser light source, an acoustic xy light deflector and an array of 104 holograms as information storage elements. Each storage element contains 104 bits which appear as a pattern on a semiconductor read-out matrix when the storage element is illuminated through the xy deflector. Accordingly, the system has a total capacity of 108 bits with an access time of less than 10 μsec.