Improvements in crystal growth technology have enabled us to grow 28 mm dia., 10 cm long crack- and twin-free boules of the chalcopyrite compounds AgGaS2 and AgGaSe2. While the crystals grow with optical defects (micron-size scattering centers), post-growth heat treatment procedures have been used to successfully eliminate them and produce material of near-theoretical transparency. High optical quality, oriented single crystals, 1 cm in cross-section and over 2 cm in length have been produced and are leading to new advances in IR frequency generation. The optical and phase equilibrium studies that have led to this advance in materials technology are described, as well as some of the details in the crystal growth technology itself.
The growth of large size, high quality tungsten bronze Sri_xBaxNb206 (SBN) and Ba -x Srx K1- Na Nbs01.5 (BSKNN) ferroelectric crystals has now made it possible to conduct extensive pry opey rty evaluations of these materials for potential electro-optic, photorefrac-tive, and millimeter wave applications. Recent developments in these bronzes are discussed along with results on doped material for photorefractive device applications which show sub-stantial improvement in photorefractive sensitivity and speed over undoped material. Tung-sten bronze morphotropic phase boundary materials such as Pb,_x Bax Nb206 and Ba2_4Sr,NaNb5015, are also discussed as highly promising new materials for future device applications.
We present the results of our theoretical and experimental studies of the photorefrac-tive effect in single crystal SBN:60, SBN:Ce, and SBN:Fe. Specifically, the two-beam coupling coefficients, response times and absorption coefficients of these materials are given.
Two wave mixing gain and electrical polarization were compared when a BaTiO3 crystal was placed in an alternating electric field. The electric field was used to switch the direction of polarization in the crystal. Each time the polarization was switched the direction of two wave gain changed. A relationship between the time dependent polarization and the optical gain was obtained.
The theory and pratice of tunable acousto-optic filters and their applications are reviewed. Topics discussed include the basic principle of operation, filter characteristics and configurations. Experimental results of a noncollinear Te02, filter are presented. Finally, the development of an acousto-optic monochromator using such filter is described together with some performance figures.
Alternative use of sensitizing material and improvement of ion charging in the thermoplastic optical recording device are described which were effective for getting noise free clean images. Sensitizing material that shows less absorption and scattering was chosen for the photoconductor part of active layers in the thermoplastic element. Using a scorotron charging device provided with ion decelerating grid wires, uniform noise free reconstructed images were obtained. Precise measurement and control of the temperature of the plastics revealed that repetitive use of the thermoplastic element should be stopped before hardening of the plastic occurs. The effects of the above improvements are shown by demonstrating clearer reconstructed images and more accurate processed images.
Polyacetylene films were used to generate optical third harmonics and other nonlinear optical effects. The source was a Nd-YAG pulsed laser operating at 1.06 microns. The poly-acetylene films were prepared using the Shirakawa synthesis procedure. The films were free standing, one micron to 100 microns in thickness. Nonlinear optical effects were observed using non-Bragg angle scattering. The films were mounted in a vacuum tight sample holder, nevertheless, the measurements resulted in heat damage to the films.
Results obtained recently demonstrate that many organic molecules can be designed to provide nonlinear susceptibilities far larger than lithium niobate. These molecules may be attached to polymer chains to create large area films with good mechanical properties as well as the required optical performance. Applications that have been predicted include second harmonic generation, optical modulation, optical switching, and memories. For these hopes to reach fruition, highly ordered polymer films incorporating these molecules must be fabricated. Among the most promising techniques being pursued is the Langmuir-Blodgett deposition technique in which monolayers can be extracted from a water subphase onto a substrate. Interleaving film materials permits the creation of multiple layer systems between 5Å and 5000Å in thickness. In this paper, we review both the research directed toward molecular design and the efforts to grow multilayer crystalline polymer films.
Physical studies of nonlinear optical properties of organic and polymer structures have demonstrated exceptionally large second and third order nonlinear optical responses that are important to the fields of nonlinear optics and optical device technologies. These unusual responses have been exhibited by a large number of structures, phases, and states that include organic solids and films, single crystal polymers, Langmuir-Blodgett films, liquid crystals, and liquid crystal polymers. Experimental and theoretical studies of such systems have achieved significant advances in the understanding of these exceptional macroscopic nonlinear optical responses based on theoretically calculated microscopic electronic mechanisms, especially the role of electron-electron correlations and highly charge correlated electron excited states. Combined theory and experiment have led to the recent discovery of liquid crystal polymerization of divinyldiacetylene monomers to form highly conjugated liquid crystal polymers exhibiting large second and third order non-linear optical responses.
The polydiacetylenes, which are a class of fully ordered polymeric single crystals, are very attractive candidates for nonlinear optical applications and devices. The growth techniques, nonlinear optical measurements and possible applications of these materials are discussed. Recent results on the first picosecond time resolved measurement of the third order nonlinear optical susceptibility are presented.
The second-order hyperpolarizability of certain molecular classes can be highly enhanced. Consequently many possibilities exist for creating nonlinear materials or structures. A discussion of these properties and structures is presented.
Molecular hyperpolarizabilities may be represented graphically by estimating the change in magnitude of atomic coefficients in the combination molecular orbitals formed in the mixed state of a molecule and photon. Rapid qualitative evaluation of the merit of a given molecular structure may be obtained by methods directly related to numerical evaluation of molecular polarizabilities. The conclusions correlate well with experimental observation and link electro -optical activity directly to molecular structure. The conditions for a dipolar interaction between matter and radiation define the symmetry relationship between unperturbed molecular orbitals which may combine to generate the mixed state of molecule and photon. The shift in electron density on formation of the combination orbital is controlled by the energy difference between unperturbed orbitals and the energy of the photon and the symmetry restrictions give the direction and extent of polarization. The probability of polarization is a function of the extent of in-phase overlap between the the filled and vacant molecular orbitals mixed by the interaction. A nonresonant interaction is a Franck-Condon process where the mixed state has a very short lifetime restricting molecular polarization to reorganization of the electronic states, this short lifetime brings the relative phase of the unperturbed orbitals into prominence, showing how different polarizations for different directions of the electric vector may occur in some asymmetrical molecules. The combination of different modes of polarization together with different probabilities for these polarizations suggests that some dipolar molecules possess only one observable electromagnetic susceptibility while others have unequal but observable susceptibilities for the same orientation with respect to the incident radiation.
The generalized dual field effect on the response times of liquid crystals has been analyzed and demonstrated experimentally by using both static magnetic and pulsed optical fields. An improvement in decay time higher than one order of magnitude, depending on the field strength, can be achieved. At high fields, this relaxation time is inversely proportional to the external field intensity and is independent of the liquid crystal thickness. In addition, thermal modulation of liquid crystals was investigated. The response times of the opto-optical thermal modulation are found to be much faster than the corresponding electro-optic modulation of liquid crystals.
The symmetry arguments which predict the existence of ferroelectricity in chiral smectic liquid crystals are presented. Structure of the ferroelectric liquid crystals in the thin and the thick cell configurations are reviewed. A brief description of the technique to align these liquid crystals is also given. Finally the effect of electric fields on these liquid crystals is discussed.
Advances in the technology of fabrication of large arrays of thin-film field-effect transistors for liquid crystal display applications is making available an important new component for many other applications such as spatial light modulators for optical signal processors. Hydrogenated amorphous silicon has a number of advantages over other semiconductors for such arrays relating primarily to cost and yield due to the simple, low temperature processing, and options offered by a transmissive device. There are also disadvantages stemming from the low electron mobility which is roughly 0.1% that of crystalline silicon. Still, sub-micro-second switching times are possible which is not only adequate for liquid crystal control within very large arrays but suitable for much of the row and column driving circuitry as well. In this paper we will describe the characteristics of a-Si devices, circuits, and LC cells controlled by them. We will also discuss the technology in the context of projecting what the capabilities of such devices could be for spatial light modulators and displays.
The recently developed microscopic theory of liquid crystal birefringence is reviewed. New physical insights into the origins of the visible and infrared birefringence of liquid crystals are obtained. Guidelines for selecting or synthesizing highly birefringent liquid crystal materials are established. Novel applications of liquid crystals in the infrared regions are foreseeable. In addition, mechanisms which limit the high power laser applications of liquid crystals are briefly discussed.
Recent studies in the areas of the photoactivated and CCD-addressed liquid crystal light valves, as well as improvements in the operation of the visible to IR dynamic image converter (VIDIC) will be discussed.
A quasi systems-level desirability analysis has been performed of candidate elec-trooptic materials for use in high-speed guided-wave optical devices. More than 30 inorganic, semiconducting, and organic materials have been compared. The bulk guided-wave phase modulator has been adopted as an initial basis for comparison. Drive voltage and current dynamics have been analyzed as a function of material properties and electrode architectures. Potassium niobate and lithium niobate are found to be among the more desirable materials. The III-V semiconductors and the low Curie temperature ferroelec-trics were found less desirable and, in some cases, marginal or even unacceptable for high-performance device applications.
Barium titanate (BaTiO3) is a perovskite ferroelectric material with many dielectric, acoustic and optical applications. In particular, the electro-optic tensor components of BaTiO3 are among the largest of any material, leading to favorable performance in a number of device configurations. In this paper we will present results of recent measurements on the photorefractive properties of BaTiO3 in the visible spectral region, and the electro-optic properties of BaTiO3 at millimeter wavelengths. The particular advantage of BaTiO3 for photorefractive applications is its large value of the electro-optic tensor component r42, which in turn provides large values of grating efficiency, beam coupling gain and degenerate four-wave mixing (DFWM) reflectivity. Large values of the DFWM reflectivity are particularly desirable in phase conjugate resonator applications, where BaTiO3 is generally the material of choice. In recent experiments, we have used photorefractive beam coupling to determine the relative importance of holes and electrons to charge transport, and to measure the number of empty traps. This same tech-nique provides an accurate relative measurement of the electro-optic coefficients in our samples. The promise of BaTiO3 for phase shifting at millimeter-band carrier frequencies has been recognized for some time. We have recently made the first electro-optic measurements in BaTiO3 at millimeter-wave frequencies. Specifically, we have measured the tensor component r33 at a carrier frequency of 94 GHz. The measured value (3.8 x l0 cm/V) is the largest in any material at this frequency. When account is taken of the absorption losses, BaTiO3 compares very favorably with other materials for practical device applications.
The fabrication and experimental operation of the photo-emitter membrane spatial light modulator (PEMLM) are reported. The incorporation of a grid structure into the PEMLM is demonstrated to significantly enhance the active removal of electrons from the membrane by secondary emission. The effects of the readout Schlieren optics and the microchannel plate flatness on the readout image quality are also discussed.
We report experiments on the magnitude and speed of optical-field induced changes in the refractive index of semiconductor-doped color-filter glasses. A large third-order nonlinear susceptibility of 10-13 to10-14m2/W is measured with a response time of tens of picoseconds. Low-loss (planar and channel) optical waveguides have been fabricated by ion-exchange in these glasses.
InSb has been recognized in recent years as a very good material for nonlinear optical devices because of the extremely high nonlinear index of refraction near its band edge. It has proven valuable in investigating bistable optical etalon performance, and nonlinear processes in semiconductors. Numerous schemes for using bistable etalons as basic elements for optical logic and optical computing have been recently developed. Some considerations for using InSb as a material for developing optical bistable devices, and some design considerations for a method of applying bistable optical elements to array processing for do all optical computer are discussed.
A guide for the selection of materials for large time aperture Bragg cells is presented. Effects of acoustic attenuation and acoustic nonlinearities are analyzed and the results are applied to summarize the material and performance trade-off. Since optical quality and relatively large optical aperture size are the fundamental requirements for a large time aperture Bragg cell, this analysis is limited to high quality optical materials such as Tellurium dioxide, TeD2 .
Wide bandwidth Bragg cells are of extreme importance in many acousto-optic applications. The proper choice of material and crystal orientation for the Bragg cells is critical for maximizing the performance of such a system. The physical properties of importance in the design of wide bandwidth Bragg cells of such systems will be reviewed. The advantages and disadvantages of the best currently available acousto-optic crystals will be evaluated with regard to these physical properties. Methods for selecting the optimum material and crystal orientation for a given bandwidth will be discussed.