Our objective is to develop crystals that shift the light from well developed laser sources to application specific wavelengths which may be tunable. Military applications extend across the entire spectrum from ultraviolet through the far-infrared but our greatest interest has been in materials for the mid-IR (3-5 μm) and far-IR (8-12 μm) atmospheric windows. Our primary applications that drive crystal development are infrared countermeasures and remote sensing of chemical and biological warfare agents. To achieve these results we have pursued two tracks: birefringent bulk materials and quasi-phase-matched structures. Birefringent studies include the grey track problem in KTiOPO₄ (KTP) plus growth of its isomorphs, KTIOAsO₄ (KTA), RbTiOAsO₄ (RTA), CsTiOAsO₄ (CTA), and K_xRb_1-xTiOPO₄ (KRTA); chalcopyrites: ZnGeP₂, CdGeAs₂, AgGaS₂, AgGaSe₂, AgGa_(1-x)In_xSe₂, AgGaTe₂; plus GaSE, and HgGa₂S₄. A small portion of the effort is pursuing UV materials, the foremost being the borates MM'(B₃O₅)₃ where M=Sr, Ba, Pb; M'=Li,Na. Previously, work was done on LiB₃O₅ (LBO), β-bonding (GaAs), by periodic poling (LiNbO₃, LiTaO₃, KTP, BaTiO₃) and by periodic doping. Th cover the 4.5-5.0 μm band, work is being done on RTA and Pb{Mg_xNb_yTi_1-x-y}O₃ (PMNT). For periodic poling in the 8-12 μm region studies are being made on CGC (CsGeCl₃), CGB (CsGeBr₃), Tl₃PbBr₅, Tl₄PbI₆ and Tl₄HgI₆. QPM can also be obtained using total internal reflection devices (GaAs, ZnSe).

Zinc germanium diphosphide (ZnGeP₂) has proven to be an important nonlinear optical crystal for the generation of midwave infrared radiation, especially in an optical parametric oscillator configuration pumped by a Ho:YAG laser operating at 2.09 micrometers. Future applications will require higher intensity levels of the laser pump beam which are limited by the crystal's laser damage threshold and nonlinear absorption. These two quantities were measured for silver-doped ZnGeP₂ samples of which was uncoated, two had conventional anti-reflection coatings, and one had an AR coating with a quintic refractive index profile. Prominent nonlinear absorption was observed in some of the crystals; the nonlinear absorption coefficient was found to be anisotropic and a weak correlation between the values of the linear and the nonlinear absorption coefficient was observed. The values of the nonlinear optical coefficients measured in these crystals for ordinary and extraordinary polarizations of incident light are reported along with the measured values of the laser damage threshold of these newly grown crystals at 2.09 micrometers, both in the AR coated and uncoated forms.

Infrared detected materials, such as Hg_1-xCd_xTe, Hg_1-xZn_xTe have energy gaps almost linearly proportional to their composition. Due to the wide separation of liquidus and solidus curves of their phase diagrams, compositional segregation exists in both axial and radial directions of crystals grown in the Bridgman system unidirectionally with constant growth rate. It is important to understand the mechanisms, which affect lateral segmentation in order that large radially uniform composition crystals can be produced. Following the Coriell, et al. treatment, we have developed a theory to study the effect of a curved melt-solid interface shape on lateral composition distribution. The model is considered to be a cylindrical system with azimuthal symmetry and a curved melt-solid interface shape which can be expressed as a linear combination of a series of Bessel functions. The results show that melt-solid interface shape has a dominant effect on the lateral composition distribution of these systems. For small values of β, the solute concentration at the melt-solid interface scales linearly with interface shape with a proportional constant of the product of β and (1-k), where β-Vr/D, with V as growth velocity, R as the sample radius, D as the diffusion constant and k as the distribution constant. A detailed theory will be presented. A computer code has been developed and simulations have been performed and compared with experimental results. These will be published in another paper.

Triethylphosphine sulfide, [C₂H₅]₃ P(S) (abbreviated as TPS), seems to be a potential nonlinear optical organic material. Bulk single crystals of this material were grown using modified Bridgman-Stockbarger method. Commercially available triethylphosphine sulfide, procured from Johnson Matthey, was purified by physical vapor transport using low pressure sublimation (approximately 30 mTorr). The growth conditions are being optimized. The temperature gradient was chosen to be 6 - 8°C/cm, and the ampoule lowering rate was chosen to be 0.2 - 0.4 mm/hr and cooling rate after the crystal growth run was 5 - 10°C/day. Several TPS single crystals with size 10x10x15 mm³ have been grown. The second harmonic generation was measured qualitatively and has been found to be comparable to phase matched potassium dihydrogen phosphate.

3-methoxy-4-hydroxy-benzaldehyde (MHBA) is one of the new organic materials that has become important for nonlinear optics in recent years because of its large second order nonlinear optical susceptibility and good blue transparency. Single crystals of MHBA were grown by a modified solution growth method. A study has been performed to select a suitable solvent for the growth of this material and to determine the effects of the solvent on the morphology of the crystals. These solvents were first studied to see their effects on the characteristic morphology of the material. From the results of morphology studies, methanol, ethanol, and MEK were selected as possible solvents for the growth. The solubility of MHBA was measured as a function of temperature in each solvent. From the solubility data, we discovered that a mixture of methanol to water (1:1) showed the most promise as a solvent for the growth of MHBA from solution. Crystals were grown using the three solvents in an effort to confirm the results of the solubility test. The properties of the material were studied using Differential Scanning Calorimetry, Vicker's hardness, and optical absorption spectrum. The results of the above measurements are described in this paper.

Nonlinear optical (NLO) polymeric films are targeted for photonics applications including optical switches and frequency doubling devices. This work focused on improving upon the NLO activity of these materials by using a composite prepared from a χ ² active aligned biopolymer and a χ³ active mixture of a donor/acceptor tricyanovinylaniline dye (TCVA) chromophore and a silver metal colloid (Ag). Second harmonic generation was obtained by poling the biopolymer poly-L-benzyl- glutamate. The χ² values ranged from 5.4x10^-11 esu to 2.4x10^-10 esu given varying poling voltages of 1 to 3 kv/cm. The p- tricyanovinylaniline dye exhibited large third-order NLO responses when incorporated into polycarbonate films. The χ³ values varied by orders of magnitude ranging from 6x10^-12 to 2x10^-10 esu depending on the amount of TCVA and silver concentrations in the polycarbonate films.

Organic materials with large electro-optic coefficients are promising for fabrication of fast electro-optic modulators with low driving voltage. In this paper we describe the growth of micron-thick single crystal films of various electro-optic organic materials from melt using the plate- guided method. The compounds such as mNA, COANP, NPP, PNP, MBANP and DAST will be considered. The films are grown using a homemade facility, which allows to control melting and recrystallization rate and to observe the process with an optical polarizing microscope. A single crystal films will make up a planar optical waveguide integrated with a coupling prism. The light will be injected into the film using the prism. Then, after traveling a certain distance within the film, the light will be decoupled. Combination of high electro-optic coefficients of the film (10 to 100 pm/V) with relatively long travel distance of the light beam (5 mm and more) potentially gives a driving voltage of the phase modulation of the beam of 5 V and less. This is very important for the incorporation of the modulator into a standard low voltage electronic circuitry. The phase modulation can be converted into amplitude modulation using various interferometer schemes such as Mach-Zehnder (M-Z) scheme with external arm, M-Z with internal arm, polarimetric waveguide interferometer, and dual-mode single- arm interferometer. We will provide some experimental data showing the advantage of the dual-mode single-arm scheme. Potential modulation rate of the system can be 10 dB and higher.

Benzil:MNA binary organic single crystals have been grown to overcome decomposition tendency and improve mechanical properties of 2-methyl-4-nitroaniline (MNA) which is known to be one of the best organic NLO material. Single crystals of binary system have grown using a transparent Bridgman- Stockbarger system which has fabricated to monitor the growth process. The growth conditions for the flat solid- liquid interface are optimized for the different dopant concentration of benzil. The melt in the self-sealing ampoule is maintained in liquid state without decomposition up to 2 weeks which allows us to grow 20 mm long single crystals. Hardness of 5wt% benzil:MNA is measured to be 13 Kg/mm² which is 45% higher than benzil. The conversion efficiency of second-harmonic generation is found to be 1.5% with 4.5 mm interaction length. Since MNA is phase-matchable material, this efficiency could be comparable to commercial KDP. Surface quality of binary crystals has maintained its initial condition in air without absorption of water vapor which may be the main cause of surface degradation.

This work is the continuation of the whole series works, dedicated to the investigation of the resonant phenomena in various kind waveguide junctions and expansions. The development requirements of radar and SHF technique cause the wide utilization of the expansions and junctions: as antenna's paths system, wave modes changers and switches, high-Q resonators, measurement devices, frequency band- splitting devices (SHF-filters, satellite communication and TV system multiplexers) and etc. But the anisotropic dielectrics electrical characteristics measurements is of important interest. High quality materials that using in present time (as SHF-filter elements; high-Q resonators and etc.) are the anisotropic crystals. So, the waveguide junctions with anisotropic loading investigation problem is actual.

Gold nanoparticle composites are known to display large optical nonlinearities. In order to assess the validity of generalized effective medium theories (EMTs) for describing the optical properties of metal nanoparticle composites, we have used the z-scan technique to measure the third-order susceptibility of gold nanoparticle composites across the entire range of fill fractions. These materials range from low concentration statistically random gold sols, to aggregated thin (two-dimensional) composite films, to quasi-bulk thin films above the percolation threshold. These measurements allow the nonlinearity of gold to be determined both directly and by deduction from applicable effective medium theories. We compare our results with predictions which ascribe the nonlinear response to a Fermi-smearing mechanism. We demonstrate that the nonlinear susceptibility changes sign due to a phase shift between the applied field and the local field, and that this sign change occurs at the percolation threshold. Further for films whose thickness is less than an optical wavelength we introduce a 2D form of the Maxwell Garnett model.

Four main multilayer coatings are manufactured. Different combinations of these coatings allow to solve various tasks connected with the filtration of middle range infrared light. The cut-on coatings are the base of the construction, which divides all spectrum in two different parts: high transmission and full blocking. In order to obtain a cut-on- filter with good transmission and rejection characteristics, it was necessary to coat both sides of the substrate. One multilayer serves as the principal high-pass stack and the auxiliary--to achieve full blocking. The design, manufacture and optimum performance of coatings is discussed. The coatings are composed of PbTe/ZnS symmetric stacks deposited on two sides of a ZnSe(ZnS) or germanium substrate. Transmission characteristics of the different infrared interference filters are presented. It is shown that the set of materials which was chosen for such kind of coatings made it possible to get both steady optics characteristics from room temperature up to 4.2 K, high mechanical and thermal stability, as many property, which we need for cryogenic cooling: to realize stable layer in vacuum; good adhesion; dilatometric compatibility without hygroscopicity. The coatings are very simple. They contain the layers of two materials and final principal multilayers contain only ten layers. The coatings were tested on thermal and mechanical stability.

In this paper, we describe different schemes of phase conjugation during formation of the self-organized hexagonal spot array in the photorefractive crystal KNbO₃. Both forward and backward phase-conjugated beams are observed in the two-beam coupling geometry. We present also theoretical description of this multiplexed phase conjugation, introducing concept of the scattering wave-vector diagrams that visualize contributions from the transmission and reflection gratings.

Bacteriorhodopsin (BR) has been proven to be an effective non-linear media for a variety of applications, such as optically addressable spatial light modulators, volumetric memories, optical image processing systems, optical sensors, and optical correlators. However, practical realization of such systems with BR depends upon the specific characteristics of this material. In this report we present experimental results of the time evolution and intensity dependent characteristics of a BR gelatin film. In particular we studied the spectral dependence of the optical density/refraction index modulation. A holographic technique was used to investigate the exposure characteristics of photorefraction, recording versus storage time, as well as the connection between the diffraction efficiency of the recorded grating and light induced scattering (noise)--the parameters that are of primary importance for such applications as high density memory systems and optical correlators.

Conventional electronic logic circuits in today's computers impose extreme limitations on computational speed, complexity, compactness. In highly dense electronic logic circuits the connections simply cannot handle electric signals swiftly and reliably. On the other hand, optical interconnections and optical integrated circuits are sought to provide answers to future computing and compactness demands. Optical devices are immune from electromagnetic interference and free from electrical short circuits. They have low-loss transmission and provide large bandwidth (i.e. multiplexing capability), and are manufacturable in compact sizes, are lightweight and inexpensive. Recently, we demonstrated an all-optical NAND logic gate having nanosecond response time by waveguiding two collinear nanosecond white light caused by focusing a pulsed Nd:YAG laser at 1064 nm along with a cw He-Ne laser at 632.8 nm through a polydiacetylene derivative of 2-methyl-4- nitroaniline (PDAMNA) thin film. The physics involved in the process was explained based on Z-scan studies of the same polymer using He-Ne laser. These studies show an induced absorption by an excited state, resulting in a reverse saturable absorption (RSA) in the system. The RSA figure of merit in PDAMNA was estimated. The size and sign of the real and imaginary parts of the third order nonlinearity were evaluated. These studies also demonstrate for the first time to our knowledge, that reverse saturable absorption in an optical system can be used to build similar logic gates.

The bulk growth of periodic poled lithium niobate (PPLN) is made by the off-centered Czochralski technique adding an impurity to the melt. The periodic domain structures are obtained with different impurities such as Er, Yb, Nd, Cr, Fe and Y. The impurity distribution along the bulk PPLN crystals has been studied to understand the formation mechanism of the periodic domain structure. The distribution coefficient of the impurities, the temperature fields and the shape of the solid-liquid interface have been found to play a key role in the PPLN formation. The cooling rate and other growth conditions control the size of the areas where the periodic domain structure appears. It has been found that independently of the impurity added to the melt the dopant concentration is constant along the periodical domain structure, while it has been observed that exists a periodical variation of the Nb concentration which is related one to one with the periodical domain structure.

We report the photodeposition of polymeric layers of nanometer scale thickness onto two nanoparticle substrates. This was accomplished by ultraviolet irradiation of a solution of functionalized diacetylene monomers in which the nanoparticles were suspended. Following photodeposition, the coated nanoparticles were analyzed using transmission electron microscopy and UV-visible spectroscopy. Highly regular polydiacetylene films with thicknesses from 2.5 - 25 nm were produced. The thickness measurements were facilitated by the attachment of small gold nanoparticles onto the surface of silica nanoparticle substrates prior to photodeposition, to provide contrast in the final TEM image. Deposition onto gold nanoshells was also demonstrated. Photodeposition onto these particles resulted in more individual coated particles. Furthermore, short irradiation times (approximately 5 minutes) yielded coated particles without the extra oligomeric contaminants usually found. This substantiates the idea that photodeposition occurs preferentially on a substrate material. UV-visible spectroscopy of the deposited films indicate that approximately 40% less conjugation is present relative to macroscopic polydiacetylene thin films grown with the same approach. This process yields a unique `nanolaminate' coating which may be useful in the modification of the physical, chemical, or optical properties of nanoparticles.

When a praseodymium doped fluoride fiber was pumped with a 587 nm dye laser that resonantly excited the ¹D₂ level of Pr³⁺, we detected energy upconversion signals at 492 and 522 nm from the ³P_0,1 levels. We also observed violet upconversion signals at 356, 382 and 413 nm. Anti Stokes Raman signals were observed at 3500 - 4200 cm^-1 away from the laser beam.

We discuss manifestation of the channeling effect in the visualization of hexagonal patterns in KNbO₃ and phase gratings in LiNbO₃. We have shown that visualization of the domain patterns, discovered earlier in the subharmonic beam in the photorefractive BSO crystal, may be explained by the channeling effect. A wave-packet description allows us to explain backward movement of domains due to the specific dispersion law for the space-charge waves. An analogy is discussed with domain formation in the charge-density-waves, known in quasi-1D conductors. Non-linear phase shift of the couple's waves may lead to discomensuration.

Third harmonic conversion is an effective technique to generate laser radiation at 355 nm from high power solid state lasers. Numerous studies have shown that conversion efficiency depends on parameters such as laser beam quality, crystal nonlinear coefficient, crystal optical quality, and interaction geometry. Relatively little attention has been given to possible limitation in conversion efficiency due to two photon absorption (TPA) at the third harmonic wavelength (355 nm). We have conducted two photon absorption measurements in more than a dozen KDP crystals. The investigated crystals had different doping concentrations and were doped with different impurities. The results of these investigations show that TPA is always present in KDP crystals at 355 nm and is strongly dependent on crystal composition. The TPA coefficient β varied from β= 0.001 to 0.02 cm/GW.

The authors systematically investigated the second-order susceptibility of the cathode-side face of poled glass. This report consists of three parts. The first is a technique to pole a set of multi-pieces of glasses for distinguishing the second harmonic (SH) signals from the anode-side piece and from the cathode-side piece. The SH signal from the cathode- side piece was only one hundredth of that from the anode- side piece, and those from the middle pieces are further less. The SH signal increased with the number of glasses in a set. The second is a technique to give a further identification of the SH signals from each face. For this purpose, we looked for the materials, which are opaque to the second-harmonics. We found two kinds of new materials: lead silica and Pyrex glasses. They don't transmit the UV light, but transmit the visible light. We detected the second harmonics at 266 nm from the face of the glass facing to the detector. The SH signal in poled lead silica increased exponentially with the increase in the lead percentage. The third is a new technique of doping F^- into the cathode-side face, which increases the SH signal from the cathode-side face by two orders. It reached two times of that from the anode-side face.

Band edge effects such as increased density of modes, large field enhancement, and low group velocity will provide highly efficient parametric amplification if the proper phase matching conditions can be established. We derive the phase matching conditions for 1D-photonic band gap structures. Direct integration of Maxwell's equations in the time domain confirms these conclusions, and show that parametric amplification in 1D-photonic band gap structures provide much larger conversion efficiencies compared with quasi-phase-matching.

The optical whispering-gallery modes of dielectric microspheres can have extremely sharp resonances, with quality factors as large as Q = 10¹⁰. Using evanescent coupling for input and output, an effective ring resonator is produced, with a large intracavity field enhancement. It has been suggested that optical nonlinearities might be enhanced using these modes. Our effort to do so is described herein. The nonlinear medium is a composite, in which semiconductor nanoparticles are the active component and constitute a small volume fraction. This can be achieved by fabricating microspheres from semiconductor-doped glasses or by coating fused-silica spheres. Because the field distribution of a whispering-gallery mode is strongly localized near the sphere's surface and includes an evanescent tail external to the sphere, thin-film coating is a practical option, and this technique offers several advantages. The properties of whispering-gallery modes and optical coupling are discussed, the processes of fabrication and coating are described, and the operational characteristics and potential applications of nonlinear optical behavior in microspheres are considered.

Successful incorporation into military electro-optics systems requires laser sources that are compact, reliable, versatile, and inexpensive. All-solid-state devices can meet these requirements but additional power, pulse energy, and wavelength criteria must also be met. Nonlinear frequency conversion is a viable solution for generation of high power at mid-infrared (2 - 5 μm) wavelengths. Recent advances in quasi-phasematching (QPM), particularly periodically poled lithium niobate, have shown QPM devices to be highly efficient and broadly tunable in the mid-IR. In this paper we review efforts to scale both the average power and the energy per pulse of QPM optical parametric devices pumped by Nd lasers.

Up-conversion of red light with wavelength of 660 nm in Tm³⁺-doped BaY₂F₈ powder results in the two violet luminescence bands with peaks at 417 and 430 nm and two blue luminescence bands with peaks at 455 and 470 nm. The two violet bands are observed to be stronger than the blue bands. The blue luminescence is also observed by pumping with 993 nm light. The up-conversion is explained by a multiple excited state absorption process.

The effect of different factors on the quality of the grown potassium dihydrophosphate crystals was studied. The transmission values in the range of 200 - 400 nm were measured for crystals grown under different conditions. The range of the impurities having an effect on the absorption of the UV radiation by crystals and solutions was extended. The maximum transmission was observed for the samples grown from the solutions of the stoichiometric composition at the crystallization temperature 55 degree(s)C and growth rate of 1 mm/day.

The results of the study of optical absorption, bulk laser damage threshold and structural characteristics of rapidly grown KDP crystals are presented in this paper. Crystals were grown in the direction of preset angle ((Theta) equals 59 degree(s)) of synchronism at a rate of 5 mm/day. The developed technique allows to obtain blanks of nonlinear elements right during crystal growth thus decreasing material and power consumption when making products. The grown crystals have bulk laser damage threshold on the level of approximately 4.5 GW/cm² and high structural quality.

In this paper, a new kind of photorefractive Cu:KNSBN crystal with Li-replacement at A-sites ((Cu,Li):KNSBN) was reported. We studied the photorefractive properties of this kind of crystal by using the conventional two-wave mixing method. It revealed that the Li-replacement can improve the photorefractive response rate of the crystal which is very important in real time information processing. An response time of 90 ms was obtained at a total incident intensity of 3.92 W/cm². The absorption spectrum and other photorefractive properties were also measured and discussed. Experiment showed that cation replacement such as Li- replacing at A-sites provides a new way to improve the photorefractive properties of KNSBN crystals.

Second harmonic generation in Lithium Niobate (LN) thin films has been widely studied. This interest is extended to waveguides obtained by the Liquid Phase Epitaxy (LPE) technique due to the high perfection and crystallinity of the films. However the incorporation of vanadium into the film due to the growth technique is still a problem because of the absorption band of this ion in the visible zone of the spectra. In this work the LN films are obtained by the LPE technique on pure LN singledomain substrates in the horizontal LPE geometry. Several temperatures have been used in order to obtain the best crystalline quality. The starting flux used was LiVO₃ 80 mol%, with a Li rich melt of LiNbO₃.

Triangular lattice photonic crystal behaving in the electromagnetic zones constructed from fused silica cylinders in styrofoam is fabricated. The transmission spectra of the photonic crystal with and without defects are measured. On this basis, the defect modes of photonic crystal were studied, and the potential applications of the photonic crystal are discussed.