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Waveguiding light-emitting strips have been written in a blank LiF crystal with a femtosecond laser, by translating the sample under the pulsed focused beam. Light guiding through these buried micro-structures was observed at several wavelengths between 458 and 1550 nm. Visible photoluminescence spectra of aggregate F2 and F3 + laser active color centers were measured. The refractive index increase, estimated of the order of 10-4 in the visible and near-infrared spectral intervals, is consistent with the stable formation of electronic point defects in LiF. These results are promising for the realization of miniaturized optical waveguiding solid-state amplifiers and lasers based on color centers. © 2014 AEIT.

A single wavelength electro-optical reflection technique was used to study the creation of space charge distributions (SCDs) in an Al/PPV/ITO LED by monitoring the third order NLO response of the electro-luminescent layer, at a wavelength far from the main absorption band ( λ =632.8 nm). The polymer is a PPV derivative with oxidiazole groups grafted as side chains. The measurements show the presence of SCD given by the sum of a static contribution close to the ITO, and of a slowly changing and bias dependent one due to mobile charges injection. Taking into account Debye–Huckel screening in the polymer, we estimate the density of the fixed charges to be ρ 0 =1.5×10 24 m −3 , for a uniform distribution in a 110 nm thick layer. The dynamics of the mobile charges was investigated by time-dependent measurements. The samples were biased at a voltage V b for a time interval and the time dependence of the signal was studied after switching off V b . The measurements were performed for several temperatures between 60 and 110°C, indicating complex dynamics of the signal. Measurements performed at low temperature (88 K) show the features of dispersive transport. The dynamic measurements were investigated by the electro-absorption technique also, with wavelengths laying in the main absorption band of PPV.

We report on the design, manufacturing and testing of Alq 3 /polyvinylcarbazole (PVK) light emitting devices. The devices were obtained by spin coating PVK films on indium tin oxide coated glass substrates. Alq 3 films were then deposited by high vacuum thermal evaporation. The devices were topped by depositing magnesium/silver electrodes by thermal evaporation. After deposition, the samples were stored and operated under a nitrogen atmosphere in order to prevent damage due to oxidation. The thickness of the active layers was purposely chosen to be large in order to study the device with an electro-optic reflectometric technique.

The growth of the macroscopic second order nonlinear optical properties of side-chain and crosslinkable copolymer species is theoretically modelled. The model describes the rotational diffusion of nonlinear diazo-dye dipoles, in the presence of crosslinking sites randomly distributed in the copolymer matrix, under application of a periodic electric poling field. The time dependence of the orientational probability distribution for the crosslinked dipoles has been calculated. Such distribution have been used in order to evaluate the temporal growth of the second order nonlinear optical properties and their asymptotic value when saturation of the crosslinking process is attained. The results of the theoretical model are compared to the experimental ones, obtained for a crosslinkable copolymer, Red Acid Magly. In the experiments the r33 component of the electro-optic coefficient is measured by means of a modified electro-optic ellipsometry setup. The comparison shows a good agreement between experimental and numerical results. The model can be used in order to find the best values of the copolymer parameters, necessary in order to maximize the final second order nonlinear optical properties.

We propose a novel approach for wide-field fluorescence imaging based on dielectric multilayers on glass coverslides. It is demonstrated that the fluorescence radiated by emitters in proximity to the multilayer surface can couple to Bloch Surface Waves and subsequently leaks into the glass. The coupled fluorescence is beamed with low divergence according to the Bloch Surface Waves spectral/angular dispersion and then collected with a low-magnification imaging system. Since the coupling between emitter and surface modes is dependent on the surface local morphology, we find a strong spectral deformation of the collected fluorescence spectrum depending on the corresponding surface relieves imaged.

Biosensors based on surface plasmons have shown to be reliable and highly sensitive platforms. Here we investigate the feasibility and the potential of an alternative platform for biological sensing based on Bloch surface waves sustained by a one-dimensional photonic crystal made of dielectric materials.

Bloch surface wave (BSW) sensors to be used in biochemical analytics are discussed in angularly resolved detection mode and are compared to surface plasmon resonance (SPR) sensors. BSW supported at the surface of a dielectric thin film stack feature many degrees of design freedom that enable tuning of resonance properties. In order to obtain a figure of merit for such optimization, the measurement uncertainty depending on resonance width and depth is deduced from different numerical models. This yields a limit of detection which depends on the sensor’s free measurement range and which is compared to a figure of merit derived previously. Stack design is illustrated for a BSW supporting thin film stack and is compared to the performance of a gold thin film for SPR sensing. Maximum sensitivity is obtained for a variety of stacks with the resonance positioned slightly above the TIR critical angle. Very narrow resonance widths of BSW sensors require sufficient sampling but are also associated with long surface wave propagation lengths as the limiting parameter for the performance of this kind of sensors.

Bloch surface waves (BSW) propagating at the surface of truncated, one-dimensional crystals are valid candidates to improve sensors based on surface plasmon polaritons, usually referred to as surface plasmon resonance (SPR). The low losses introduced by the dielectric BSW stacks enable to achieve resonance widths much below the ones of SPR, thus proposing improved sensing results. A simplified, bi-linear model of the resonance intensity distribution is applied to estimate the effect of the resonance properties onto the measurement noise. This yields a limit of detection (LoD) that is used to optimize a BSW supporting thin film stack and to quantitatively compare SPR and BSW sensors. The results indicate that an order of magnitude reduction of the LoD is within reach when sufficient sampling of narrow BSW resonances is achieved.

Dye-sensitized solar cells (DSCs) have a typical sandwich structure, with the active layers between two conductive glass sheets. Their co-planarity could be an issue in the mass production of large area devices. The micrometric gap should be uniform all over the device, in order to maintain a good electrolyte layer. The frames of sealant, which isolate the adjacent cells in a module, usually work also as spacers. Nevertheless, the uniformity of the gap is not commonly tested in a systematic way. Here large area empty blanks and full DSCs were studied by means of optical interferometry, i.e., monochromatic surface scan and wavelength scan. The collected fringe patterns allowed retrieval of the microchamber’s absolute profile. In some cases, evident U-shaped bending was found, with edge-to-center variation up to Δ h / h ≈ 80%. Interestingly, despite the large absorption and the weak index contrast in the full DSCs, a good fringes’ visibility was achieved, by adopting near-infrared (IR) laser source and filtering off external reflections. Moreover, the IR n and k indexes of porous titania dyed and filled with electrolyte were retrieved. In summary, the results show that the bending effect must always be tackled for large area, by using the right sealing frames and thermal treatments. Further improved IR interferometry can be successfully implemented for in-line testing of DSCs structure and uniformity.

We report experimental results of Z-scan investigations on the photoinduced nonlinear absorption and refractive index of submillimeter bulk samples of the III–V semiconductor InSb. The measurements were carried out in the cw regime at λ = 10.6 μ m using a CO 2 laser. The results put into evidence the contribution of the nonlinear Fabry-Perot resonator, constituted by the high-refractive-index sample itself, to the transmittance of the system. Such contribution can lead to a wrong evaluation of the nonlinear optical coefficents in Z-scan experiments. The experimental data were fitted using a modified Z-scan theory in which the effect of the resonator is taken into account. The values for the nonlinear absorption and refractive index used in the fit are in good agreement with those reported in literature.

Here we report a fundamental angle resolved study on bare dye solar cells, DSCs, and those coupled to two different prisms (hemi-cube and hemi-cylinder). The natural angular enhancement of incident photon-to-current conversion efficiency of DSCs is shown to further increase in the prisms case. This is partially due to the higher external transmittance and mainly to the longer optical path, achieved thanks to the tilted surfaces and optical density of the coupling elements. Results suggest possible use of DSCs with thin active layers (below 10 μm) and micrometric refractive prisms or nanometric diffraction gratings on the surface, compensating the incomplete light absorption by an enhanced optical path. A simplified yet robust angular refractive path model, which includes Fresnel reflection, Snell’s refraction and Lambert–Beer absorption, can clearly explain the results and predict enhancements at larger angles than the used ones. The angular photo-electronic measurements revealed also an elegant tool to retrieve a dispersion curve for the effective refractive index n eff ( λ ) of such a complex and absorbing medium as the sensitized porous titania filled with electrolyte. Such information could be used in the design and simulation of different photon management structures, from the macroscopic size of 3D photovoltaics architectures to the micro- and nano-scale of anti-reflection, refractive or diffraction texturing.

The use of linear and circular subwavelength gratings for improving the fluorescence extraction from organic dyes spotted on the surface of a one-dimensional photonic crystal is demonstrated. The one-dimensional photonic crystal hosting the gratings allows Bloch surface waves (BSWs) to be coupled in the visible range. We provide experimental evidence for the distributed diffraction of BSW-coupled fluorescence that is locally excited using a microscope-based setup. By diffracting the BSW-coupled fluorescence, a significant improvement in the total fluorescence collection is obtained as compared to a flat one-dimensional photonic crystal.

We report on the investigation on the resolution of optical sensors exploiting Bloch surface waves sustained by one dimensional photonic crystals. A figure of merit is introduced to quantitatively assess the performance of such sensors and its dependency on the geometry and materials of the photonic crystal. We show that the figure of merit and the resolution can be improved by adopting a full ellipsometric phase-sensitive approach. The theoretical predictions are confirmed by experiments in which, for the first time, such type of sensors are operated in the full ellipsometric scheme.

The intensity dependent complex character of the photodarkening of virgin As2S3 samples exposed to continuous wave (CW) and pulsed laser radiation has been measured. Excitation in the CW and pulsed (picosecond) regime for the same irradiation doses leads to significant differences in the photodarkening curves. It is shown that the kinetics of the photodarkening can be decomposed into several processes related to structural transformations in As2S3: defect elimination and stabilization, polymerization of the structural entities, decomposition followed by arsenic clustering and arsenic oxidation.

Prism coupling experiments were performed on poly (1,4-phenylene-1,2-bis (4-methoxyphenyl) vinylene) low loss ( α =1 dB/cm) optical waveguides, with a picosecond ( τ FWHM =5 ps) infrared laser source ( λ =830 nm). The results show a very large influence of the amorphous nature of the polymer material on its dielectric properties. In particular, large quasi-permanent changes of the refractive index at λ =830 nm were observed, which are explained in the frame of a four-level system model, taking into account trap levels in the bandgap of the material.

We report on the measurement of the electro-optic properties of poled polymers at λ=1.55 μm via the Teng and Man technique. Measurements of the electro-optic coefficient obtained for two different sandwich structures, using either indium tin oxide (ITO) or aluminum doped zinc oxide (ZnO:Al) semitransparent electrodes, are compared. The experimental results show that the use of ITO electrodes can lead to a largely wrong evaluation of the electro-optic coefficient r33, with respect to that obtained when using ZnO:Al electrodes, whose plasma resonance is shifted to longer wavelengths. Results on the disperse red 1/methyl-metacrylate based sidechain benchmark system are reported.

We exploit the properties of surface electromagnetic waves propagating at the surface of finite one dimensional photonic crystals to improve the performance of optical biosensors with respect to the standard surface plasmon resonance approach. We demonstrate that the hydrogenated amorphous silicon nitride technology is a versatile platform for fabricating one dimensional photonic crystals with any desirable design and operating in a wide wavelength range, from the visible to the near infrared. We prepared sensors based on photonic crystals sustaining either guided modes or surface electromagnetic waves, also known as Bloch surface waves. We carried out for the first time a direct experimental comparison of their sensitivity and figure of merit with surface plasmon polaritons on metal layers, by making use of a commercial surface plasmon resonance instrument that was slightly adapted for the experiments. Our measurements demonstrate that the Bloch surface waves on silicon nitride photonic crystals outperform surface plasmon polaritons by a factor 1.3 in terms of figure of merit.

In this work we introduce the use of a patterned polymer-based surface functionalization of a one-dimensional photonic crystal (1DPC) for controlling the emission direction of fluorescent proteins (ptA) via coupling to a set of two Bloch Surface Waves (BSW). Each BSW dispersion branch relates to a micrometric region on the patterned 1DPC, characterized by a well defined chemical characteristic. We report on the enhanced and spatially selective excitation of fluorescent ptA, and on the spatially-resolved detection of polarized emitted radiation coupled to specific BSW modes. As a result, we provide an optical multiplexing technique for the angular separation of fluorescence radiated from micrometric regions having different surface properties, even in the case the emitting labels are spectrally identical. This working principle can be advantageously extended to a multi-step nanometric relief structure for self-referencing biosensing or frequency-multiplexed fluorescence detection.

An alternative method to plasmon techniques for the enhancement, control and detection of fluorescence is proposed. The role of the metallic layer is played by a silicon-based one-dimensional photonic crystal that can sustain Bloch surface waves (BSWs), which can be regarded as the dielectric analogue of surface plasmon polaritons (SPPs) for metals. Throughout the paper we explore the route that leads to an enhanced, directionally-controlled and selfreferencing fluorescence-detection scheme. We first consider a 1DPC that is functionalized with a thin, flat and homogeneous polymeric layer decorated with a fluorescent dye. The enhancement of the BSW-coupled fluorescence emission is studied against a similar scheme that uses a common thin glass coveslip. An enhancement as large as 560 is found. We further investigate the BSW coupling of the illuminating laser light into 30-nm thin polymeric waveguides. Imaging the BSW-coupled emitted fluorescence through the leakage radiation microscopy is used for the purpose. The possibility of coupling BSWs into nanometric guiding ridges makes feasible the design of a spatially-resolved and multiplexing fluorescence-detection scheme, which can be most useful for self-referencing in the biosensing field. We conclude the paper by investigating the effects on the fluorescence emission of a multistack that consists of a dielectric multilayer and a thin metallic layer deposited on top. The implications of using a metallo-dielectric structure for the coupling of the emitted fluorescence with BSW and SPP modes is discussed.

We report on the experimental characterization of the peculiar properties of surface electromagnetic waves propagating at the truncation facet of finite one dimensional dielectric photonic crystals. Such waves are generally known as Bloch surface waves. In particular we show results on the direct experimental comparison of the performance of Bloch surface wave and surface plasmon polariton based optical biosensors and on the application of Bloch surface waves in fluorescence microscopy.

We report on the direct experimental comparison of the sensitivity and figure of merit of biosensors based either on surface plasmon polaritons on metal layers or on Bloch surface waves on one dimensional photonic crystals. The comparison was carried out by making use of a commercial surface plasmon resonance platform that was slightly adapted for these experiments. Although the experimental conditions are not optimized for Bloch surface waves, our experiments demonstrate that both types of biosensors show a similar figure of merit for biochips deposited on low cost molded plastic substrates. For glass substrates with better optical quality, the increased homogeneity of the photonic crystals results in the Bloch surface wave sensors outperforming the surface plasmon polariton sensors by a factor 1.7 in terms of figure of merit. Considerations on the illumination bandwidth indicate options to further increase such a factor.

The optical properties of Rhodamine 6G doped silica-titania glassy thin films deposited onto soda-lime glass substrates, have been studied by changing the relative concentrations of SiO 2 and TiO 2 . The guided light propagation properties of the films in the planar waveguide configuration have been investigated at λ = 632.8 nm, by means of a single prism geometry.

We report on time resolved sensing experiments demonstrating the direct, label-free and specific binding of an antibody/antibody system probed by means of Bloch surface waves on silicon-based one-dimensional photonic crystals.

Lithium Fluoride (LiF) presents interesting optical properties and it has been proposed as an active optical material for colour centre (CC) lasers and amplifiers. The use of a grating to reduce the laser threshold and to narrow the line-width has also been demonstrated. More recently, LiF gained increased attention due to its unique characteristics as x-ray imaging detector for high resolution microscopy and for the development of CC lasers using gratings induced by high energy femtosecond laser pulses. We present a review of our recent work in the production of photonic structures, like photo-induced Bragg gratings and wave-guides either by laser CW illumination or by femtosecond laser irradiation. CW laser illuminated gratings were written in both coloured LiF crystals and films. Gratings and wave-guides are characterized using confocal microscopy, optical absorption and emission spectroscopy, near field scanning, scattering and insertion loss measurements.

Preliminary tests on the sensibility to external environment of an optical waveguide filter operating in the near infrared region are reported. Device consists of a hybrid sol-gel based grating loaded channel waveguide. Several techniques were implemented to obtain the final device. A hard master with gratings produced by Electron Beam Lithography was employed to fabricate a transparent soft mold. UV-nanoimprinting technique, exploiting the soft stamp, was used to reproduce on the hybrid photo- sensitive sol-gel film the planar grating. Optical lithogra- phy was finally applied to manufacture the grating loaded channel waveguide which is our final integrated sensor. The device was optically characterized by transmission measurements in the range 1,450-1,590 nm and its sensi- bility to external environment was tested in air and water.

After the introduction in 1991 by B. O’Regan and M. Gratzel, Dye Solar Cells (DSCs) have reached power conversion efficiency values over small area device as high as 11%. Being manufactured with relatively easy fabrication processes often borrowed from the printing industry and utilizing low cost materials, DSC technology can be considered nowadays a proper candidate for a large scale production in industrial environment for commercial purposes. This scenario passes through some challenging issues which need to be addressed such as the set-up of a reliable, highly automated and cost-effective production line and the increase of large area panels performances, in terms of efficiency, stability and life-time of the devices. In this work, an overview of the most utilized DSCs materials and fabrication techniques are highlighted, and some of the most significant characterization methods are described. In this direction, different approaches used to improves devices performances are presented. In particular, several methods and techniques known as Light Management (LM) have been reported, based to the ability of the light to be confined most of the time in the cell structure. This behavior contributes to stimulate higher levels of charge generation by exploiting scattering and reflection effects. The use of diffusive scattering layers (SLs), nanovoids, photonic crystals (PCs), or photoanodes co-sensitization approaches consisting in the use of two Dyes absorbing in two different parts of the visible range, have been demonstrated to be effective strategies to carry out the highest values of device electrical parameters. Finally, to increase the light path inside the DSCs active layer, the use of refractive element on the topside (a complementary approach to SL) has been shown a promising possibility to further improve the generated photocurrent.

We report on the experimental characterization of the thermal sensitivity of biosensors based on the coupling of Bloch surface waves (BSW) on amorphous silicon nitride/silicon one dimensional photonic crystals (1DPC). The results show that the silicon alloys compensate the thermo-optic effect taking place in the external medium and indicate that a class of temperature insensitive biosensors can be fabricated by properly designing the layout of the 1DPC. The experimental results are in very good agreement with numerical simulations based on a transfer matrix approach. Moreover, the BSW biosensors show a resolution of 0.03 °C for the measurement of temperature.

The power conversion efficiency (η) of a dye solar cell (DSC) with a 13 μm thick TiO2 layer increases with solar AM1.5 light’s angle of incidence by 10% at 55° ± 5° and then decreases at higher angles due to Fresnel reflection at the front air/glass interface. For cells with thin TiO2 (3 μm), the enhancement in η is substantially larger (16%). We show, also through spectral quantum efficiency measurements, that the angular enhancement for thin cells is mainly due to optical path lengthening, quantifying the relevant parameters useful for photon management strategies and for understanding the productivity of DSC modules outdoors.

The coupling of optical Bloch surface waves at the truncated end of one dimensional porous silicon photonic crystals is exploited for fast vapour sensing. Self-standing multilayered membranes bound to transparent substrates were fabricated by electrochemical etching and used in an attenuated total reflection configuration to resonantly excite the surface waves and perform real-time sensing.

We quantify the strong dependence of photocurrent on the angle of incidence of light in a dye solar cell (DSC). Under laser illumination the photocurrent increases for large incidence angles. The enhancements are different upon using or not a coupling prism. They are explained with a model including three different angular factors. The observed enhancements up to 25% can be useful for evaluating novel designs of an efficient photon management in DSCs. Even an effective refractive index neff≈2.0 for the mesoporous titania/electrolyte phase was retrieved from the angle dependent photocurrent.

We demonstrate that an ultrathin ridge (< lambda/10) can guide Bloch surface waves in a dielectric multilayer. The propagation and polarization properties of the guided modes are investigated with a multi-heterodyne scanning near-field optical microscope.

In this work, we use a multi-heterodyne scanning near-field optical microscope to investigate the polarization and propagation of Bloch surface waves in an ultrathin (similar to lambda/10) ridge waveguide. First, we show that the structure sustains three surface modes, and demonstrate selective excitation of each. Then, by numerically processing the experimental data, we retrieve the transverse and longitudinal components of each of the modes, in good agreement with the calculated fields. Finally, we provide an experimental estimation of the effective indices and the dispersion relations of the modes. (C) 2010 Optical Society of America

Recently a single beam technique for measuring both the non-linear refractive index and non-linear absorption of transparent materials has been proposed by Sheik-Bahae et al. IEEE J. Quantum Electron., vol.26, p.760, 1990; in which the transmittance of a sample is measured through a finite aperture in the far field as the sample is moved along the propagation path of a focused Gaussian beam. The sign and magnitude of the non-linear refractive index and the value of absorption changes can be deduced from the transmittance curve. In the present paper this technique has been applied to evaluate both the thermal and electronic non-linear changes of refractive index and of absorption of some Schott semiconductor doped glasses by using the CW and pulsed regime.

The thermal nonlinear response of a waveguide produced by sputtering a Corning 7059 glass film over a nonlinear substrate (Corning CS2-61) is studied with a pump–probe technique in a quasi-cw regime. The coupling efficiency is found to be a function of pump power and chopping frequency. The coupling zone is scanned with a probe beam to examine the spatial dependence of the coupling efficiency.

The Rhodamine 6G fluorescence enhanced by the surface electromagnetic waves coupled on surface of 1D photonic crystals is studied. The fluorescence-mediated surface electromagnetic waves (SEW) distribution is visualized by means of far-field fluorescence microscopy. The kinetics of Rhodamine 6G bleaching due to SEW is studied. The way of SEW visualization in reflectivity spectra via fluorescence process is shown. The prospective for SEW application in the optical sensors field is tested via direct spectroscopy of the photonic crystal covered by the ethanol and R6G thin film. Spectral flexibility of the SEW excitation depending on the effective photonic crystal dispersion controlled by its design rather than on material dispersion opens prospectives for the application of SEW-enhanced fluorescence microscopy in biocensing with increased spatial and concentration sensitivity and spectral selectivity.

The spatial distribution of surface electromagnetic waves on a one-dimensional photonic crystal with a polymeric grating on top is mapped using a multiheterodyne scanning near-field optical microscope. The grating opens a bandgap. At the band edges, a stationary field formed by two surface waves with opposite propagation constants and almost identical amplitudes is produced. Field intensity maxima are localized to the grating peaks or grooves, depending on the wavelength. Far from the bandgap, we identify surface waves coupled via either the 0 or the −1 order of the grating. The corresponding phase profiles indicate that these waves propagate in opposite directions. © 2008 American Institute of Physics.

The authors report on the measurement of the second order nonlinear optical properties of ZnO films deposited by low temperature radio frequency sputtering on ZnO:Al coated glass substrates. They show that ZnO:Al plays a crucial role as a buffer layer for the successive growth of ZnO. The effect of aluminum doping on the relaxation of the stresses acts as a template for crystallization of ZnO, allowing us to obtain partially oriented ZnO films with relatively large nonlinear coefficients. The measurements of the second harmonic tensor by the Maker fringes method are in good agreement with results for the electro-optic coefficient obtained by nonlinear ellipsometry.

We describe the use of one-dimensional porous silicon (p-Si) photonic crystals for guiding TE-polarized surface electromagnetic waves (SEWs). Although bulk and interface roughnesses might deteriorate the optical response of photonic structures, we observed reflection spectra presenting narrow (≲6nm) reflectivity anomalies associated with SEWs. In analogy with surface plasmons, SEWs are strongly sensitive to surface modifications. As a proof of principle for a sensor, we provide a direct real-time monitoring of the reversible interactions of organic vapors with the p-Si multilayer. We highlight the higher sensitivity of the SEW-based detection scheme as compared to a method exploiting perturbations of waveguide modes.

We report on an original technique for poling polymeric thin films, which allowed us to obtain a second-order nonlinear inverted domain structure, which could be used for frequency-doubling waveguides under quasi-phase-matching condition. Measurements of the local value and orientation of the electro-optic r33 tensor component were performed by a reflection microscopic electro-optic ellipsometer. The measured parameters for the nonlinear structure induced in the polymeric film result to be consistent with the expected values.

In this work the authors investigated the second order nonlinear optical properties of a group of Disperse Red 1 based electro-optic fluorinated copolymers, synthesized with two fluorinated monomers: the -fluoroacrylate monomer bearing an adamantane side group and the -fluoroacrylate monomer bearing the Disperse Red 1 chromophore. By means of nonlinear ellipsometry at =1550 nm, the poling induced electro-optic tensor main component r33 was determined. The polymer's thermostability was investigated by means of the temperature scanning and isothermal relaxation techniques, leading to the determination of the depolarization temperature Tdep=136 °C, corresponding to an activation energy for the relaxation of the orientational distribution of the active chromophores EA=105 kcal/mol. The increased thermostability of the copolymer, given by the adamantane side group, is then compared with that of other two groups of fluorinated copolymers. ©2006 American Institute of Physics

In a polyconjugated main chain polymer strip waveguide the nonlinear, nonresonant refractive index n2 was measured by monitoring the signal spectrum broadening due to self-phase modulation. The two photon absorption coefficient α2 was obtained by calibrating the inverse transmission measurement. The nonlinear coefficients were determined to be n2=0.85×10−14 cm−2/W andα2=0.08 cm/GW at a wavelength λ=885.6 nm. The used polymer was poly[1,4-phenylene1,2-di(phenoxyphenyl)vinylene]. The result is in good agreement with interferometer measurements. The material is suitable for all-optical switching.

The knowledge of the nonlinear optical properties of organic polymers has reached a stage of maturity after a couple of decades of intense investigations. In particular the second order nonlinear optical properties of poled polymer films have been widely explored; their application targets in integrated optoelectronics start to be met, opening the way to a whole generation of high frequency electro-optic modulators. However, in order to make these materials really applicable in the manifacturing of long living and reliable devices, a serie of problems still have to be completetely solved. In particular the temporal stability of the orientational distribution of the nonlinear guest chromophores, the chromophores’ chemical stability under intense illumination conditions and the presence of parasitic χ(3) contributions to the second order nonlinear optical response.

In this work we investigated the second-order nonlinear optical properties of a group of Disperse-Red-1-based electro-optic fluorinated copolymers, synthesized with two fluorinated monomers: the hexafluoroisopropyl alphafluoroacrylate monomer and the alphafluoroacrylate monomer bearing the Disperse Red 1 chromophore. Copolymers, with a concentration of chromophore substituted groups ranging from 46% to 75% molar, were synthesized and deposited as single films on glass substrates, for second-harmonic generation, and as sandwich structures with electrodes, for nonlinear ellipsometry measurements. For large concentrations of substituted groups, cracking of the films was observed and did not allow for any electro-optic characterization by nonlinear ellipsometry. The second-harmonic generation tensor main component d33 was retrieved by means of second-harmonic generation at λ=1064nm for each concentration. The results obtained for the copolymer with the lowest concentration are compared with those obtained by ...

We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at l=1064 nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples

We used two nonlinear optical techniques, single wavelength ellipsometry and electroabsorption spectroscopy, to study the creation of space charge distributions in an Al/polymer/ITO organic light emitting diode. The polymer is OXA1-PPV, a derivative of poly(p-phenylene-vinylene) in which oxidiazole groups are grafted as side chains to improve electroluminescence efficiency. Both the techniques are sensitive to the spatial profile of electric field via the nonlinear effect in the bulk of the polymer. Results indicate the creation of an asymmetric charge distribution with depletion region close to the ITO electrode. The comparison between ellipsometry and electroabsorption measurements is an original feature of this work. Such an integrated analysis shows as a further result that the mostly used electroabsorption setup, working with wavelengths in the spectral region of maximum absorption, modifies the spatial charge distribution optically reactivating trapped carriers.

We characterised second harmonic generation coefficients of GaN and Al0.08Ga0.92N crystalline thin films, deposited by MOCVD on a sapphire 0001 layer, through standard Maker fringes method. Measurements were performed at λ=1064 nm using a Nd:YAG Q‐Switched laser. From the measured ratio between d33 and d31 coefficients we were able to deduce information on crystalline degree of samples structure, that was found to be higher in thicker films.

Measurements of the second and third order electro‐optic response of side‐chain copolymer films are reported and discussed in the frame of an extended model taking into account the dependence of the nonlinearity on the orientational distribution of poled copolymers, charge injection and trapping in the films upon application of large voltage drops and screening of the electric field in the mesoscopic films.

We report the results of the morphological, electrical and optical characterisation of double-layer Alq3-based organic emitting diodes with a lithium fluoride (LiF)/Al cathode. A detailed electron microscopy investigation of their cross-section shows the presence of LiF isolated grains underneath the Al film. Due to the introduction of the LiF layer, luminance was larger than 30,000 cd/m2 at a bias voltage VB=25 V with a maximum external luminous efficiency as large as 46 lm/W at VB=20 V. Performing on/off VB cycles at a very low frequency, each time a recovery of the initial electric and luminous performance was observed. The non-exponential decay of both electric current and luminance during each on-cycle has been interpreted as the signature of dispersive transport controlled by multiple trapping on localised states in an amorphous system.