This PDF file contains the front matter associated with SPIE Proceedings Volume 6740, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Recent advances in polymer materials have significantly increase the available electrooptic coefficients. This has now stimulated the development of new designs and configurations for high frequency optical modulators. In addition, it has opened up the field to new applications including high speed optical Digital Signal Processing. The initial areas investigated include linear modulators, true time delays and arbitrary waveform generation. More complex devices with multiple elements in series are now being investigated.

The semi-macroscopic mechanisms responsible for the surface relief gratings (SRG) formation on azobenzene-containing films are far from deep understanding.¹ We present the results of experimental studies of SRG in PMMA and PVK polymeric matrices. The Monte Carlo (MC) kinetics of polymeric movements is reported for recently proposed model,² which mimics the effect of mass transport along the direction of light modulation, resulting from multiple trans ↔ cis photoisomerisation cycles of functionalized dyes. We show that the model, symmetric on "microscopic" level, leads to a directed mass transfer from bright to dark places. Preliminary studies show that the centers of mass of polymer chains undergo a normal diffusion under the light illumination. No global light-induced ordering of polymeric chains was detected. MC studies were performed for a system consisting of half a million of model monomers.

A comprehensive model has been developed to construct phase matching conditions, including Poynting vector directions, parametrically interacting beam wavelengths, relative walk-off angles and polarization states in a biaxial nonlinear single crystal with known refractive index dispersion. The model optimizes phase matching conditions by providing a strategy for walk-off compensation that determines the optimum periodicity of twist-twin Adhesive-Free Bond (AFB(R)) composite pair designs. The model is validated experimentally by measuring the calculated walk-off angles and the crystal orientation of KTP that correlates to the given Poynting vector. The method is useful in reducing uncertainties of OPO designs, in providing walk-off compensation design data, and in confirming the final walk-off corrected design configuration. It is generally applicable to biaxial and uniaxial nonlinear crystals.

We report the excitation of the non-steady-state photoelectromotive force (photo-EMF) in high-resistance wide-gap materials: layered boron nitride (BN), GaN nanoparticles in porous glasses, polypyrrole nanostructures in chrysotile asbestos matrix. The non-steady-state photo-EMF appears in semiconductor material illuminated by an oscillating interference pattern. Non-uniform illumination gives rise to the photoconductivity and space charge gratings which periodically shift with respect to each other resulting in an alternating photocurrent. Since the conductivity and space charge take part in current generation a number of photoelectric parameters can be measured: Maxwell relaxation time, lifetime, diffusion length and mobility of carriers, concentration of impurity centers.

The authors present the design and calculated performance of a low threshold selectively oxidized Surface Emitting Laser (SEL) for operation at a wavelength of up 3.0 μm. The device is based on III-V quaternary semiconductor alloys and is grown by the Molecular Beam Epitaxy technique. The theoretical investigation of the optical properties of the compound semiconductor alloys allows for the selection of the optimum materials for highly reflective Bragg mirrors. The simulation of the designed SEL performance has been carried out by evaluation of the important laser characteristics such as threshold gain, threshold current density and external quantum efficiency. We present a design which integrates a thermoelectric controller and multi-SELs to provide continuous tunability.

We report the findings of work undertaken to develop InAs photodiodes with low reverse leakage current, for detection of mid-wave infrared wavelengths up to 3.5μm. Good quality epitaxial growth of InAs and the lattice matched ternary AlAs_0.16Sb_0.84 was developed using molecular beam epitaxy. A photodiode structure was designed, grown and characterized using an AlAs_0.16Sb_0.84 layer to block the diffusion of minority electrons. Further reductions in the reverse leakage current were achieved through studies of wet etching using a range of etchants. A sulphuric acid based etchant provided the lowest surface leakage current for a single etch step, however the surface leakage current was further reduces when a two steps etching process was employed, starting with a phosphoric acid based etchant and finishing off with a sulphuric acid based etchant. Surface profile analysis showed that higher etching rates were obtained in the direction parallel to the <100> direction. The atomic composition of the etched surface was investigated using Auger analysis. By etching a test pixel array, the potential for fabricating small pitch focal plane arrays by wet etching was evaluated.

Nonlinear optical materials play a key role in the development of coherent sources of radiation as they permit the frequency conversion of mature solid-state lasers into spectral ranges where lasers do not exist or perform poorly. The availability of efficient quasi-phasematched infrared materials is thus considered as important for the development of several defense optronics applications. This paper will review the recent progresses we achieved with thick Orientation Patterned-GaAs structures. We will present results obtained in growing thick-layer (500 µm) on 2 cm long structures with very low optical losses (less than 0.02 cm^-1). This loss coefficient is low enough to allow the realization of a high power OPO in the MIR band.

We report measurements on a series of quantum dot infrared photodetectors grown with different combinations of monolayer thicknesses (2.2. 2.55 and 2.9 ML) and quantum dot layer sheet doping densities (6×10¹⁰ cm^-2 and 12×10¹⁰ cm^-2). The dark current and noise current were higher in devices grown with sheet doping density of 12×10¹⁰ cm^-2. At a given bias voltage the dark current and the noise current was found to be lowest in devices having 2.55 ML and sheet doping density of 6×10¹⁰ cm^-2. This combination gives a sheet doping density to dot density ratio of approximately unity. Highest gain was achieved in devices with 2.55 ML and sheet doping density of 6×10¹⁰ cm^-2.

In the framework of a nonisothermal model it is shown that in the spot of cwCO₂ laser of power P the temperature of a small bare Si plate increases from T'=300[K] to an equilibrium temperature T₀(P). The moment of time t₁(P) at which T₀(P) is achieved, t₀(P) at which the oxide layer of 1 nm is formed, the sample temperature at t₀(P), the oxide layer thickness at t₁(P), the oxide layer growth rate at t₀(P), and t₁(P) are computed, for dry and wet oxidation and for <100> and <111> oriented samples. How well the computed results are in agreement with the experimental results depends on the magnitude of the effect of the processes which were not incorporated in the model. The advantage of this analysis is the possibility to obtain explicit results from which the limits of the model can be specified and special results can be gleaned. With this aim this study was undertaken.

The photo-physical and optical power limiting (OPL) properties of several new thiophenyl-containing arylalkynyl Pt(II) complexes with longer arylalkynyl groups, named ATP3, ATP4, ATP6 and ATP7 were studied. Thiophene units were introduced into the structure as an attempt to modify photo-physical properties and OPL capability. The new compounds have their thiophene rings either close to the Pt-atom (ATP7), in the middle of the chain (ATP3), or at the terminal end (ATP4). The measurement results were compared with those of the earlier studied PE3 compound. ATP6 is similar to ATP4, but with methoxy groups in the arylalkynyl ligands. Just as PE3, all thiophenyl derivatives showed large intersystem crossing capabilities and triplet phosphorescence, thus having the potential of large nonlinear absorption and good OPL performance. All compounds are characterized by absorption and emission spectra, quantum yield, luminescence decay (fluorescence and phosphorescence) and two-photon absorption capabilities at 780 nm, and compared to the properties of the PE3 compound. Also analogous triazole-containing compounds, abbreviated Z1, Z2 and Z3, were studied in the same way, and compared to the earlier studied Pt1-G1 compound. The OPL performance of all compounds were measured, and clamping levels of approximately 2.5 to 5 μJ pulse energy from 30 mM (ATP) and 50 mM (triazole) concentration samples were found. All compounds possess high transmission in the visible region and fluorescence quantum yields in the order of 10⁻² (ATP) and 10⁻³ (triazoles).

The crystallization conditions of Al₂(WO₄)₃ from Li₂O-WO₃ solvents (molar ratio 30.0:70.0, 32.5:67.5, 35.0:65.0, 45.0:55.0 and 55.0:45.0) as well as from Na₂O-WO₃ solvents (molar ratio 25.0:75.0, 27.5:72.5, 30.0:70.0 and 32.5:67.5) have been investigated. The concentration and temperature regions of crystallization of Al₂(WO₄)₃ and the density, viscosity as well as the solution losses due to evaporation have been established. On the basis of the data obtained it has been concluded that the most suitable solvent for growing Al₂(WO₄)₃ single crystals is Na₂O-WO₃ with a molar ratio of 27.5:72.5. The temperature and concentration regions of crystallization of Al_2-xMe_x(WO₄)₃ solid solutions obtained by replacement of Al2O3 in the Na₂O-Al₂O₃-WO₃ system by Ga₂O₃, In₂O₃, Sc₂O₃ or Y₂O₃ have been investigated. The crystallization regions and concentration boundaries of existence of the solutions are found to depend strongly on the nature of the replacing element. Solid solutions containing Sc and In crystallize from high-temperature solutions with a lower concentration as compared to that of pure Al₂(WO₄)₃, this being accompanied by a high distribution coefficient of the substituting ion. On the contrary, Ga and Y containing solid solutions crystallize from high-temperature solutions with much higher concentrations, the distribution coefficient of the substituting ions being relatively low. The experimental obtained data are the basis for growing bulk single crystals with preset compositions from the Al_2-X Me_X (WO₄)₃, Me=Sc, Y, Ga or In, solid solutions.