Polarization dependent photorefractive amplitude modulation production in MgO:LiNbO 3 phase modulators

We present experimental and theoretical results of the intensity dependence of residual amplitude modulation (RAM) production in electro-optic phase modulators. By utilizing the anisotropy of the medium, we show that RAM has a photorefractive origin.

Photorefractive performance of a novel multifunctional inorganic-organic hybridized nanocomposite sensitized by CdS nanoparticles

A novel multifunctional inorganic-organic photorefractive (PR) poly(N-vinyl)-3-[p-nitrophenylazolcarbazolyl-CdS nanocomposites with different molar ratios of US to poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl (PVNPAK) were synthesized via a postazo-coupling reaction and chemically hybridized approach, respectively. The nanocomposites are highly soluble and could be obtained as film-forming materials with appreciably high molecular weights and low glass transition temperature (T,) due to the flexible spacers. The PVNPAK matrix possesses a highest-occupied molecular orbital value of about -5.36 eV determined from cyclic voltammetry. Second harmonic generation (SHG) could be observed in PVNPAK film without any poling procedure and 4.7 pm/V of effective second-order nonlinear optical susceptibility is obtained. The US particles as photosensitizers had a nanoscale size in PVNPAK adopting transmission electron microscopy. The improvement of interface quality between US and polymer matrix is responsible for efficient photoinduced charge generation efficiency in the nanocomposites. An asymmetric optical energy exchange between two beams on the polymer composites PVNPAK-CdS/ECZ has been found even without an external field in two-beam coupling (TBC) experiment, and the TBC gain and diffraction efficiency of 14.26 cm(-1) and 3.4% for PVNPAK-5-CdS/ECZ, 16.43 cm(-1) and 4.4% for PVNPAK-15-CdS/ECZ were measured at a 647.1 nm wavelength, respectively.

One-dimensional modulation instability of broad optical beams in biased photorefractive-photovoltaic crystals under steady-state conditions

We present a comprehensive study of the one-dimensional modulation instability of broad optical beams in biased photo refractive-photovoltaic crystals under steady-state conditions. We obtain the one-dimensional modulation instability growth rate by globally treating the space-charge field and by considering distinction between values of Eo in nonlocal effects and local effects in the space-charge field, where Eo is the field constant correlated with terms in the space-charge field, which depends on the external bias field, the bulk photovoltaic effect, and the ratio of the optical beam's intensity to that of the dark irradiance. The one-dimensional modulation instability growth rate in local effects can be determined from that in nonlocal effects. When the bulk photovoltaic effect is neglectable, irrespective of distinction between values of Eo in nonlocal effects and local effects in the space-charge field, the one-dimensional modulation instability growth rates in nonlocal effects and local effects are those of broad optical beams studied previously in biased photorefractive-nonphotovoltaic crystals. When the external bias field is absent, the one-dimensional modulation instability growth rates in nonlocal effects and local effects predict those of broad optical beams in open- and closed-circuit photorefractive-photovoltaic crystals. (c) 2004 Elsevier B.V. All rights reserved.

Profilometry of semiconductor components by two-colour holography with Bi12TiO20 crystals

We studied the shape measurement of semiconductor components by holography with photorefractive Bi12TiO20 crystal as holographic medium and two diode lasers emitting in the red region as light sources. By properly tuning and aligning the lasers a synthetic wavelength was generated and the resulting holographic image of the studied object appears modulated by cos2-contour fringes which correspond to the intersection of the object surface with planes of constant elevation. The position of such planes as a function of the illuminating beam angle and the tuning of the lasers was studied, as well as the fringe visibility. The fringe evaluation was performed by the four stepping technique for phase mapping and through the branch-cut method for phase unwrapping. A damage in an integrated circuit was analysed as well as the relief of a coin was measured, and a precision up to 10 μm was estimated. © 2009 SPIE.

Spectrographic technique for determining refractive indices

A new experimental technique is proposed to determine refractive indices of liquids and isotropic solids at different wavelengths. A Pellin-Broca hollow prism filled with a liquid sample produces the spectrum (of the liquid prism) on the photographic plate of the camera. A plane reflector, mounted at a small angle to the normal of the exit face of the prism, also forms a direct image of the collimator slit in the plane of the same photographic plate. All the necessary information for determining the refractive indices (for different wavelengths) is extracted directly from the spectrogram without using any goniometric system. Experiments are conducted with the liquid prisms of isopropyl alcohol, water, and benzene. The results of the experiments are compared with those obtained by a Pulfrich refractometer (critical angle method). The proposed new technique gives the refractive indices for visible and invisible spectral lines to an accuracy of 2x10(-5). (C) 1997 Society of Photo-Optical Instrumentation Engineers.

Photo-induced optical bleaching in Ge12Sb25S63 amorphous chalcogenide thin films: effect of 532 nm laser illumination

The photo-induced effects of Ge12Sb25S63 films illuminated with 532 nm laser light are investigated from transmission spectra measured by FTIR spectroscopy. The material exhibits photo-bleaching (PB) when exposed to band gap light for a prolonged time in a vacuum. The PB is ascribed to structural changes inside the film as well as surface photooxidation. The amorphous nature of thin films was detected by x-ray diffraction. The chemical composition of the deposited thin films was examined by energy dispersive x-ray analysis (EDAX). The refractive indices of the films were obtained from the transmission spectra based on an inverse synthesis method and the optical band gaps were derived from optical absorption spectra using the Tauc plot. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. It was found that the mechanism of the optical absorption follows the rule of the allowed non-direct transition. Raman and x-ray photoelectron spectra (XPS) were measured and decomposed into several peaks that correspond to the different structural units which support the optical changes.

Laser-induced changes on the complex refractive indices of phase-change thin film

The refractive indices of crystalline phase-change films are usually obtained by thermal-induced crystallization. However, this is not accurate, because the crystallization of phase-change film in rewritable optical disks is laser induced. In this study, we use the initializer to crystallize the phase-change films. The dependence of the refractive index n and the extinction coefficient k of the phase-change films on the initialization conditions are studied. Remarkable changes of the refractive indices (especially k) are found when the initialization laser power density is 6.63 mW/mum(2) and the initialization velocity is 4.0 m/s. At the same time, the structure changes of the phase-change films are also studied. This dependence is explained by the structure change of the films. These results are significant in improving the accuracy of optical design and the thermal simulation of phase-change optical disks, as well as in the study of phase-change optical disks at shorter wavelengths. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Planar refractive microlens arrays in indium phosphide and quartz substrates

Large-area concave refractive microlens arrays, or concave template structures, and then the non-refractive-index-gradient type of planar refractive microlens arrays in InP and quartz substrates, are fabricated utilizing the method consisting of conventional UV photolithography, thermal shaping of concave photoresist microlenses, etching with an argon ion beam of large diameter, and filling or growing optical medium structures onto the curved surfaces of preshaped concave templates. Several key conditions for fabricating concave and also planar microlenses are discussed in detail. The concave structures obtained are characterized by scanning electron microscope and surface profile measurements. The far-field optical characteristics of quartz/ZrO2 planar refractive microlens arrays have been acquired experimentally. (c) 2008 Society of Photo-Optical Instrumentation Engineers.

Refractive index changes in photochromic SbPO4-WO3 glass by exposure to band-gap radiation

We report photoinduced photo-darkening in SbPO4-WO3 glass by exposure to 532 nm light with a power density of 143 mW/cm(2). The time of exposure was varied between 0 and 256 min following which visible photo-darkening, peaking at 850 nm was observed. Spectrophotometer measurement of absorption was performed for both treated and untreated regions of the sample. Time exposure to below band-gap light results in a single exponent Gaussian absorption function over an exceptionally wide range of wavelengths (500 nm-1600 nm), with a 1/e width of 647.5 nm. Kramers-Kronig transform of the change in the absorption indicates a negative local change in the refractive index. The dispersed refractive index change at 1550 nm, Delta n, is calculated to be similar to -5 x 10(-8). The peak absorption increases with time of exposure and the photo-darkening remains irreversible at room temperature. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Relief grating induced by photo-expansion in Ga-Ge-S and Ga-Ge-As-S glasses

We report the fabrication of relief diffraction gratings recorded on a surface of photosensitive Ga10Ge25S65 and Ga5Ge25As5S65 glasses by means of interference of two UV laser beams at 351 nm. The diffraction efficiency (eta) of first diffraction order was measured. Atomic-force-microscope (AFM) was used to perform a 3D imaging analysis of the sample surface topography that shows the superposition of an imprinted grating over the topography of the glass. The change in the absorption edge and the refractive index has been evaluated and a structural approach of the relief grating on the glass surface has been discussed.

Progress on holographic techniques to study photo-chemical reactions in solid state

In this paper it is presented recent developments in the heterodyne detection holographic techniques for studding photosensitive materials. The actual state of the technique allows simultaneous and independent measurement of the refractive index and of the absorption coefficient changes in photosensitive materials and their use to self-stabilize the fringe pattern. The modeling of the measured signal together with the fringe stabilization allow the long term-fitting of the optical properties and the study the photosensitive materials close to the saturation.

Tailoring the refractive index of Ge-S based glass for 3D embedded waveguides operating in the mid-IR region

The photosensitivity of GeSx binary glasses in response to irradiation to femtosecond pulses at 800 nm is investigated. Samples with three different molecular compositions were irradiated under different exposure conditions. The material response to laser exposure was characterized by both refractometry and micro-Raman spectroscopy. It is shown that the relative content of sulfur in the glass matrix influences the photo-induced refractive index modification. At low sulfur content, both positive and negative index changes can be obtained while at high sulfur content, only a positive index change can be reached. These changes were correlated with variations in the Raman response of exposed glass which were interpreted in terms of structural modifications of the glass network. Under optimized exposure conditions, waveguides with positive index changes of up to 7.8x10−3 and a controllable diameter from 14 to 25 μm can be obtained. Direct inscription of low insertion losses (IL = 3.1 – 3.9 dB) waveguides is demonstrated in a sample characterized by a S/Ge ratio of 4. The current results open a pathway towards the use of Ge-S binary glasses for the fabrication of integrated mid-infrared photonic components.

Highly refractive index sensitive femtosecond laser inscribed long period gratings

The distinct behaviour of femtosecond laser inscribed long period gratings, with a non-uniform index perturbation within the optical fibre core, has been studied experimentally. The non-uniform laser-induced perturbation results in light coupling from the core mode to a greater number of cladding modes than is the case with their UV laser inscribed counterparts, and this is made evident from the surrounding refractive index (SRI) grating response. Femtosecond inscribed long period gratings are shown to simultaneously couple to multiple sets of cladding modes. A 400μm LPG is shown to result in attenuation peaks that have both blue and red wavelength shifts over a 1250nm to 1700nm wavelength range. This gives rise to SRI sensitivities far greater than anything achievable by monitoring a single attenuation peak. The maximum sensitivity produced by monitoring a single attenuation peak was 1106nm/RIU, whereas monitoring opposing wavelength shifts resulted in a significantly improved sensitivity of 1680nm/RIU. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Liquid core fibre Bragg grating based refractive index sensor formed by femtosecond assisted chemical etching technique

We report the fabrication of a refractive index (RI) sensor based on a liquid core fibre Bragg grating (FBG). A micro-slot FBG was created in standard telecom optical fibre employing the tightly focused femtosecond laser inscription aided chemical etching. A micro-slot with dimensions of 5.74(h) × 125(w) × 1388.72(l) μm was engraved across the whole fibre and along 1mm long FBG which gives advantage of a relatively robust liquid core waveguide. The device performed the refractive index sensitivity up to about 742.72 nm/RIU. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

The refractive folio : exegesis and assessment in the open studio

Folio submission is universally regarded as the most appropriate means for measuring a student’s performance in the studio. However, developing meaningful and defensible assessment criteria is persistent challenge for all tertiary art educators. In discipline-based studios, the parameters provided by medium and technique provide useful points of reference for assessing creative performance. But how can student performance be evaluated when there is no discipline-based framework to act as a point of reference? The ‘open’ studio approach to undergraduate teaching presents these and other pedagogical challenges. This paper discusses the innovative approaches to studio-based teaching and assessment at QUT. Vital to the QUT open studio model is the studio rationale – an exegetical document that establishes an individualised theoretical framework through which a student’s understandings can be, in part, evaluated. This paper argues that the exegetical folio effectively reconciles the frequently divergent imperatives of creative, professional and academic skills, while retaining the centrality of the studio as a site for the production of new material, processual and conceptual understandings.