One-Step Holographic Photoalignment for Twisted Nematic Liquid Crystal Gratings

Liquid crystal gratings, in which liquid crystal molecules are periodically aligned, are fabricated by highly efficient and practical one-step holographic photoalignment method using a photocrosslinkable polymer liquid crystal (PCLC). This method is an innovative fabrication technique for liquid crystal grating containing a twisted nematic alignment, which does not require a conventional complex fabrication process. In this chapter, three types of liquid crystal gratings with twisted nematic alignment are fabricated. Periodic director distributions of these liquid crystal gratings are analyzed based on the elastic continuum theory and observed experimentally using a polarized light optical microscope. Furthermore, the polarization diffraction properties were measured by illumination with a visible laser beam. The resultant liquid crystal gratings exhibit various polarization diffraction properties depending on the director distributions and the polarization states of the incident beams. These polarization diffraction properties are well explained by theoretical analysis based on Jones calculus. These resultant liquid crystal gratings exhibit great potential for application as a diffractive optical element that can simultaneously control the various parameters of the light wave, such as amplitude, polarization states, and propagation direction

Serodiagnosis of type A hepatitis by detection of immunoglobulin M-type antibody to hepatitis A virus.

Serum specimens from 12 patients with type A hepatitis were analyzed for immunoglobulin M-type antibody to hepatitis A virus (IgM anti-HA). A recently developed solid-phase radioimmunoassay kit for IgM anti-HA (HAVAB-M, Abbott Laboratories) and a competitive binding radioimmunoassay kit (HAVAB, Abbott Laboratories) with or without 2-mercaptoethanol treatment, as modified by Yano et al. (Acta Hepatol. Jpn. 21, 704-712, 1980) were used to obtain an M-index. All specimens obtained within 60 days of the onset of illness and specimens from 2 of 4 patients later than 60 days after the onset were positive with the HAVAB-M test. This test gave negative results to sera which were positive for anti-HA by a standard HAVAB test in the following: 3 patients with type B hepatitis; 5 with non-A, non-B hepatitis; 11 healthy adults; and 10 sera strongly positive for rheumatoid factor. The M-index for type A hepatitis in sera within 30 days of the onset (mean value of the M-index, m, = 1.52; standard deviation, SD, = 0.25) was significantly higher than that for non-A hepatitis (m = 1.05; SD = 0.15) and for healthy adults (m = 1.02; SD = 0.10). The simplicity and usefulness of the HAVAB-M test in diagnosis of acute type A hepatitis over those measuring the M-index by HAVAB tests were shown by direct comparison of the results.</p

Coronagraph focal-plane phase masks based on photonic crystal technology: recent progress and observational strategy

Photonic crystal, an artificial periodic nanostructure of refractive indices, is one of the attractive technologies for coronagraph focal-plane masks aiming at direct imaging and characterization of terrestrial extrasolar planets. We manufactured the eight-octant phase mask (8OPM) and the vector vortex coronagraph (VVC) mask very precisely using the photonic crystal technology. Fully achromatic phase-mask coronagraphs can be realized by applying appropriate polarization filters to the masks. We carried out laboratory experiments of the polarization-filtered 8OPM coronagraph using the High-Contrast Imaging Testbed (HCIT), a state-of-the-art coronagraph simulator at the Jet Propulsion Laboratory (JPL). We report the experimental results of 10-8-level contrast across several wavelengths over 10% bandwidth around 800nm. In addition, we present future prospects and observational strategy for the photonic-crystal mask coronagraphs combined with differential imaging techniques to reach higher contrast. We proposed to apply the polarization-differential imaging (PDI) technique to the VVC, in which we built a two-channel coronagraph using polarizing beam splitters to avoid a loss of intensity due to the polarization filters. We also proposed to apply the angular-differential imaging (ADI) technique to the 8OPM coronagraph. The 8OPM/ADI mode mitigates an intensity loss due to a phase transition of the mask and provides a full field of view around central stars. We present results of preliminary laboratory demonstrations of the PDI and ADI observational modes with the phase-mask coronagraphs

Dispersion reduction in generation of high-order optical vortex using axially symmetric half-wave plates

We present the topological-charge-dispersion reduction scheme in optical vortex generation using axially symmetric half-wave plates (AHPs). The topological-charge dispersion caused by retardation errors of AHPs and other waveplates is decreased by eliminating unwanted circular-polarization components

Picosecond rotation of a ring-shaped optical lattice by using a chirped vortex-pulse pair

A novel method of ultrafast rotation of ring-shaped op-tical lattice in the picosecond time region was proposed and demonstrated. Our ring-lattice generator was as-sembled by a pair of linearly chirped pulses with time delay, a high-order birefringent retarder, and an axially symmetric polarization element. Using a mode-locked Ti:sapphire laser oscillator as a light source, stable two-, four-, and six-petaled ring-lattice rotations were respec-tively demonstrated with the rotation periods of 1.6 ps, 3.2 ps, and 4.8 ps. Our method has a potential to open up a new technique to resonantly excite propagating quasi-particles together with their coherent enhance-ment

Design and laboratory demonstration of an achromatic vector vortex coronagraph

A vector vortex coronagraph (VVC) is one of promising means for imaging extremely faint objects around bright stars such as exoplanets. We present a design of an achromatic VVC, in which an axially-symmetric half-wave plate (AHP) is placed between crossed polarization filters (circular polarizer and analyzer). The circular polarizer and the analyzer are both composed of a polarizer and a quarter-wave plate (QWP). We demonstrate, via Jones calculus and Fourier analysis, that the achromatic stellar elimination can theoretically be realized by optimal polarization filters, even when chromatic AHP and QWPs are used. We carried out laboratory demonstrations of the designed VVC using a photonic-crystal AHP. As a result, we observed achromatic coronagraphic performance, a light suppression level of 7 x 10(-5), over a wavelength from 543 nm to 633 nm. (c) 2013 Optical Society of Americ

High-Efficiency Characterization of Optical Vortices with Arbitrary State of Polarization Using Straight-Line and Parabolic-Line Polarization Gratings

An optical system consisting of a straight-line polarization grating (SPG) and two parabolic-line polarization gratings (PPGs) is presented for the characterization of optical vortices (OVs) with arbitrary states of polarization (SoPs). The PPG is capable of converting an OV with a specific SoP into a bright bar-like spot with 100% efficiency. The number of dark lines and their orientation respectively correspond to the magnitude and sign of topological charge (TC) of the incident OV, thereby enabling characterization of OVs with high efficiency. Furthermore, on combining an SPG with PPGs, the present system can characterize the TC of incident OVs regardless of their SoP. The feasibility of the system was demonstrated in experiments using gratings fabricated by applying the photoalignment method and employing films of a photo-crosslinkable polymer liquid crystal. The experimentally obtained efficiency is 70.2%. We furthermore demonstrate the system’s capability to characterize polarization vortices