Institut für Dünnschichttechnologie und Mikrosensorik

The high coherence of laser light sources is a key to the application of diffractive optics usable in holographic AR/VR displays. This can be combined with switchable diffractive elements, which are advantageous for several optical functions used in immersive holographic displays such as shutters, polarization filters, for rapid beam deflection and selection. We demonstrate a compact, effective and robust diffraction wide-angle switchable beam-deflecting device based on circular polarization gratings possessing Bragg-performances (Bragg-PG) and a polarization switch. Such grating/polarization switch pair may, for instance, be a discrete switchable deflection element or as a switching element for pre-deflection with field lenses for application in holographic AR/VR displays. Micrometer-thick circular polarization gratings characterized by high diffraction efficiency (DE > 95%), large diffraction angles ( 95% in the vis spectral range) and stable symmetric and slanted circular Bragg polarization gratings were fabricated using the developed material and processing technique. The high usable diffraction angles combined with high DE make the Bragg-PG attractive for HMD AR/VR applications because of the system inherent short focus lengths and large numerical apertures needed to meet the low space budget in HMD and other optical systems.

Distributed feedback (DFB) lasers are produced directly in fluorescent azobenzene-containing materials using a single holographic optical step. Surface relief grating capable of producing images in fluorescence microscopy can be holographically formed in a number of materials.

S.2214-2217

A new material based on 1,2-naphthoquinone in polymethylmethacrylate is proposed for phase holograms showing diffusion enhancement. The spectral sensitivity of this material allows forming holograms using 488–530 nm wavelengths, while the hologram reconstruction can be implemented at 633 nm. The amplitude of the refractive index modulation achieved makes it possible to reach diffraction efficiencies close to 100% at a thickness of several hundreds of µm. It was found by means of UV–visible and NMR spectroscopy that the diffusion of 1,2-naphthoquinone caused by photoproduct attachment to macromolecules of a polymer matrix is the main reason for the hologram enhancement. A relatively high diffusion coefficient (4.8 × 10−17 m2 s−1 at 50 °C) was measured, leading to fast enhancement at moderate temperature.

Poly(2,2-dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltammetrically coated onto carbon fibre electrode as an active functionalised microelectrode. An electrochemical impedance study on the prepared electrodes is reported in the present paper under different applied potentials during electrochemical impedance spectroscopic measurements. The capacitive behaviour of the PProDOT-Me2 coated carbon fibre microelectrode was investigated by cyclic voltammetry of polymer in monomer free solution which agreed with the capacitance obtained from electrochemical impedance spectroscopy. The film thickness for the cyclovoltammetrically prepared polymer film was in the range of about 30–50 nm. The electrochemical impedance data fitted two equivalent circuit models were used to find out numerical values of the proposed components. The effect of the deposition charge on the capacitive behaviour of the film was also investigated.

Abstract A series of six new aromatic polyamides with side oxadiazole rings has been synthesized by polycondensation reaction of aromatic diamines containing pendent substituted oxadiazole groups with a silicon‐containing diacid chloride [namely, bis(p‐chlorocarbonyl‐phenylene)diphenylsilane] or with a fluorine‐containing diacid chloride [namely, hexafluoroisopropylidene‐bis(p‐benzoyl chloride)]. All polymers were easily soluble in amidic solvents, such as N‐methylpyrrolidinone and dimethylformamide, and gave thin transparent films by casting such solutions. Very thin coatings were deposited onto silicon wafers and exhibited smooth, pinhole‐free surfaces in atomic force microscopy investigations. The polymers showed high thermal stability, with decomposition temperature >400°C. Some of them did exhibit a glass transition, in the range 152–276°C, with a reasonable interval between glass transition and decomposition. Four of these polymers showed blue photoluminescence, in the range 460–480 nm, which makes them promising candidates for future use as high‐performance materials in the construction of light‐emitting devices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 714–721, 2003

We report on phosphorescence and delayed fluorescence from polyphenylquinoxalines in frozen solution and in the film at 77 K. Upon pulsed optical excitation, the following types of experiments have been carried out: (a) optical spectra detected by means of a gated optical multichannel analyzer, (b)-transient measurements employing a single photon counting setup, and (c) photoluminescence excitation spectra. We will argue that in a polymer in which the quinoxaline units are directly linked together via C−C-bonds, the delayed fluorescence is due to the recombination of Coulombically bound electron−hole pairs, which on their part are generated by direct optical excitation. This is deduced from the facts that (a) the intensities of delayed fluorescence, phosphorescence and prompt fluorescence all vary linearly with the pump intensity; that (b) both delayed fluorescence and phosphorescence decay according to a power law up to 1 s, i.e., at times exceeding the triplet lifetime; and that (c) the photoluminescence excitation spectrum of the delayed fluorescence shows an onset at 0.4 eV above the absorption edge. In an oxygen-bridged polyphenylquinoxaline, on the other hand, both geminate pair recombination and triplet−triplet annihilation play a role in the generation of delayed fluorescence.