L. Vicari

Optical applications of liquid crystals

OPTICAL PROPERTIES AND APPLICATIONS OF FERROELECTRIC AND ANTIFERROELECTRIC LIQUID CRYSTALS E.E. Kriezis, L.A. Parry-Jones, and S.J. Elston Introduction Material properties Alignment Optical properties of smectic structures Interaction with electric fields Displays Non-display applications ELECTRO HOLOGRAPHY AND ACTIVE OPTICS N. Hashimoto Electro holography Active optics Conclusions ON THE USE OF LIQUID CRYSTALS FOR ADAPTIVE OPTICS S.R. Restaino Introduction Adaptive optics: definition and history Image formation: basic principles The effect of aberrations Active and adaptive optics Characterization and control of nematic LC devices Wavefront sensing techniques Conclusions POLYMER DISPERSED LIQUID CRYSTALS F. Bloisi and L.R.M. Vicari Introduction PDLC preparation techniques The physics involved in PDLCs PDLC electro-optical behavior Applications of PDLCs NEW DEVELOPMENTS IN PHOTO-ALIGNING AND PHOTO-PATTERNING TECHNOLOGIES: PHYSICS AND APPLICATIONS V.G. Chigrinov, V.M. Kozenkov, and H.S. Kwok Introduction Mechanisms of LC photo-alignment LC surface interaction in photo-aligned cell Applications of photo-alignment technologies New developments Conclusions INDUSTRIAL AND ENGINEERING ASPECTS OF LC APPLICATIONS T. Sonehara Practical spatial modulation Spatial addressing technologies Amplitude modulation and applications Phase modulation and applications Scattering and deflection modulation

Effects of solar irradiation conditions on the outdoor performance of photovoltaic modules

Abstract Energetic losses, relative to the standard conditions of testing, in photovoltaic modules in outdoor operation, were analyzed and the role of the optical effects is discussed. The following four loss effects were estimated: (a) reflection of unpolarized light, (b) spectrum, (c) intensity of the light and (d) temperature of the module. Four independent models were used to describe these four losses. The models were validated by the experimental data of an outdoor measurement campaign performed on 0° tilted modules at 41°N latitude in South Italy. Disagreement reaching 5% under clear sky conditions was found between theoretical predictions and experimental data for the instantaneous total loss. As a result of a critical analysis of the literature data on this subject, it could be explained by invoking the presence of a fifth loss mechanism: the polarization of the incident light. Final relative losses, due to the particular state of the incident sunlight, amount to about 7–8% of a total of 14–15%. Of these, 3% is due to the low irradiation level, 1–2% to the polarization of the skylight and 3% to the reflection of the incident light on the front cover of the module. The spectral effects are negligible (less than 1%). The remaining 7% loss is due to temperature effects on the module. All the loss data are reported as a function of the air mass (AM). The maximum operating efficiency is reached at AM≈1.5.

Truncation of non diffracting beams

Abstract Physically realizable finite-aperture approximations to non-diffracting beams have been shown to posses extremely large depth of field. A new beam shape based on truncation of Weber function is presented. The propagation features of this beam are discussed by means of numerical simulation and appear to have some advantage when compared to the previous ones.

Self-phase modulation in nematic liquid-crystal films: detailed measurements and theoretical calculations

We present a detailed study of self-phase modulation in nematic liquid crystals, performing a quantitative comparison with the theory of diffraction. A quite satisfactory fit is obtained at low optical power by taking into account only orientational effects, as it is found that experimental observations are affected by laser-induced heating of the sample at higher optical power. Finally, new features in the saturation region are reported.

Electro-optic phase modulation by polymer dispersed liquid crystals

We present a mathematical model to describe the optical phase shift induced by polymer dispersed liquid crystals (PDLCs) on light impinging transversely on the sample. PDLCs are dispersions of liquid crystal microdroplets in a polymeric binder. Droplets appear as optically uniaxial spheres randomly oriented so that the material is optically isotropic. The application of an external electric field results in a reorientation of the liquid crystal and therefore in an electrically controllable optical uniaxicity of the material. The model is discussed by comparison with experimental data and with previous theory [F. Basile, F. Bloisi, L. Vicari, and F. Simoni, Phys. Rev. E 48, 432 (1993)].

Matrix assisted pulsed laser deposition of melanin thin films

Melanins constitute a very important class of organic pigments, recently emerging as a potential material for a new generation of bioinspired biocompatible electrically active devices. In this paper, we report about the deposition of synthetic melanin films starting from aqueous suspensions by matrix assisted pulsed laser evaporation (MAPLE). In particular, we demonstrate that it is possible to deposit melanin films by MAPLE even if melanin (a) is not soluble in water and (b) absorbs light from UV to IR. AFM images reveal that the film surface features are highly depending on the deposition parameters. UV-VIS and FTIR spectra show both the optical properties and the molecular structure typical of melanins are preserved.

Photoinduced long-term memory effects in n-type organic perylene transistors

In this paper, the photoexcitation response of high mobility n-type organic field-effect transistors is analyzed. White light exposure of N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8H) transistors is demonstrated to promote the occurrence of metastable conductance states with very long retention times, similar to what has been previously reported for p-type compounds. Even in the absence of a gate-source voltage VGS, the complete recovery of the initial electrical condition can take up to 20 days. However, the initial state restoring is electrically controllable by the application of a positive VGS. These effects suggest that PTCDI-C8H is an interesting n-type material for the development of light-sensitive organic circuitry.

Matrix representation of axisymmetric optical systems including spatial filters.

A matrix approach is presented that allows one to describe a complex optical system by a matrix relating the field at the output plane to the field at the input one. The elements of the optical system may be all those characterized by an ABCD ray-transfer matrix, as well as any kind of film which introduces a wavefront modulation that can be described by a complex radial transmittance function. These include, as particular cases, stops and limiting apertures. No integral has to be computed. The method holds only for circularly symmetric optical systems and laser beams.

PDLC: influence of droplet order parameter in light transmittance

A Polymer Dispersed Liquid Crystal (PDLC) is a dispersion of liquid crystal microdroplets in a polymeric binder. The material is opaque white and becomes transparent when a low frequency electric field is applied. In this paper we present experimental results about the PDLC transmittance as a function of the applied voltage. We also present a mathematical model able to describe the optical behavior of the material in the framework of Anomalous Diffraction Approach light scattering theory.

Optoelectronic polarizer by PDLC

Abstract We present a new device based on Polymer Dispersed Liquid Crystals (PDLC). Applying a transverse low frequency electric field, the scattering cross section increases or decreases depending on the polarization of the impinging light. Depending on the choice of the refractive index of the polymeric matrix, such a device can be operated as a polarizer, or as an inverse shutter. In the first case one polarization component of an unpolarized beam is transmitted, while the other is scattered. In the second case an impinging polarized beam is totally scattered when an external electric field is applied and becomes partially transmitted when the external field is switched off.