Azobenzene undergoes trans → cisisomerization when irradiated with light tuned to an appropriate wavelength. The reverse cis →transisomerization can be driven by light or occurs thermally in the dark. Azobenzene's photochromatic properties make it an ideal component of numerous molecular devices and functional materials. Despite the abundance of application-driven research, azobenzene photochemistry and the isomerization mechanism remain topics of investigation. Additional substituents on the azobenzene ring system change the spectroscopic properties and isomerization mechanism. This critical review details the studies completed to date on the 3 main classes of azobenzene derivatives. Understanding the differences in photochemistry, which originate from substitution, is imperative in exploiting azobenzene in the desired applications.

Photoisomerization in different classes of azobenzene

We consider a class of beams that are both partially polarized and partially coherent from the spatial standpoint. They are characterized by a correlation matrix whose elements have the same form as the mutual intensity of a Gaussian Schell-model beam. We focus our attention on those beams that would appear identical to ordinary Gaussian Schell-model beams in a scalar treatment. After establishing some inequalities that limit the choice of the matrix parameters, we study the main effects of propagation. Starting from the source plane, in which the beam is assumed to be uniformly polarized, we find that in the course of propagation the degree of polarization generally becomes non-uniform across a typical section of the beam. Furthermore, we find that the intensity distribution at the output of an arbitrarily oriented linear polarizer is Gaussian shaped at the source plane whereas it can be quite different at other planes.

/pdf/partially-polarized-gaussian-schell-model-beams-1tn1rk5u1q.pdf

Partially polarized Gaussian Schell-model beams

An optical transducer comprises an optical element for directing an electromagnetic wave to a focal region and a metallic nano-structure having a longitudinal axis substantially parallel to an electric field of the electromagnetic wave, the metallic nano-structure being positioned outside of the optical element, wherein the electromagnetic wave produces surface plasmons on the metallic nano-structure. A cladding material having a refractive index differing from the refractive index of the optical element can be positioned adjacent to a surface of the metallic nano-structure. Magneto-optical recording heads that include the transducers and disc drives that include the magneto-optical recording heads are also included.

Near-field optical transducers for thermal assisted magnetic and optical data storage

Volume holography is a promising technology for high-capacity optical data storage. [1,2] When utilizing the entire volume of a medium instead of only its surface, capacities above one terabyte on a memory medium the size of a compact disc are theoretically possible. Recent developments in the field of holographic storage materials and advances in storage techniques and technology are summarized in review articles by Ashley et al. [3] and Hesselink et al. [4] Although there are still material challenges, write-once media seem to be fairly advanced. In search of rewritable media, many studies have been performed on photorefractive crystals and organic glasses. [1,4] Manufacturing single crystals of the required size is very expensive, and a major drawback of the organic photore-fractive materials is the requirement of very high electric field strengths. With increasing material thickness, the voltage necessary for creating the field becomes difficult to handle. A different potential class of rewritable media are polymers containing photoaddressable azobenzene chromophores. [5] Many studies have been performed on azobenzene-containing polymer films with thicknesses in the range of 0.5–10 l m. [3,6] However, the preparation of the thick samples required for multiplexing with sufficiently low optical density remains difficult to achieve. Because the absorption coefficient depends on the wavelength, it is in principle possible to tune a laser with an adjustable wavelength (e.g., a dye laser) to the very edge of the absorption band. [7] If writing is to be performed at a wave-length where fixed-wavelength, solid-state lasers are available (515 or 532 nm), however, a concept that allows for diluting the chromophores is required. So far, the best results have been reported by Minabe

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

An apparatus for producing a small spot of optical energy comprises a planar waveguide shaped to direct a linearly polarized electromagnetic wave to a focal point within the waveguide, and a metallic pin positioned at the focal point whereby the linearly polarized electromagnetic wave creates surface plasmons on a surface of the pin. The apparatus can further comprise means for phase shifting a portion of the linearly polarized electromagnetic wave. Recording heads comprising a magnetic write pole, a planar waveguide positioned adjacent to the magnetic write pole, the planar waveguide being shaped to direct a linearly polarized electromagnetic wave to a focal point within the waveguide, and a metallic pin positioned at the focal point whereby the linearly polarized electromagnetic wave creates surface plasmons on a surface of the pin, and disc drives that use such recording heads are also disclosed.

Apparatus and method for producing a small spot of optical energy

We examined the holographic recording properties of polyester containing cyanoazobenzene units in the side chain. It was revealed that, when a linearly polarized object beam with an arbitrary polarization direction was recorded, the retrieved beam had the same polarization state as that of the object beam, with a constant diffraction efficiency of 0.1. Moreover, two object beams with mutually orthogonal linear polarization could be recorded and retrieved separately from the same area. This is, to our knowledge, the first example of holographic polarization multiplexing. The retrieved images were found to resolve details of ?40 line pairs/mm and a 40?µm-pitched checkerboard pattern. The resolution of the system is limited by the CCD cameras that are used. Polarization encoding to increase the storage capacity and (or) the signal-to-noise ratio of holographic data recording is also discussed.

Holographic recording and retrieval of polarized light by use of polyester containing cyanoazobenzene units in the side chain

A small-sized optical head and optical disk apparatus capable of high-density recording at a high data transfer rate. A collimated light beam is incident on a first surface of a transparent condensing medium. The light beam incident on the first surface is reflected by a reflective structure, such as a metallic film or a hologram, formed on the outside of a second surface of the transparent condensing medium. The reflected light forms a beam spot on a third surface of the transparent condensing medium. Light condensed at the beam spot is emitted as near field light, and propagates to a recording medium for optical recording or reproduction.

Optical head and optical disk apparatus

PROBLEM TO BE SOLVED: To make it possible to record image edge portions having data information of signal light at a high density without the occurrence of missing of the data. SOLUTION: This optical recording method consists of executing Fourier transform of the signal light having the data information in the image edge portions by a lens. A light shielding body formed with a light transparent part 21 which shields the zero order component of the Fourier transform image of this signal light and allows the components from the first order to third order in an x-axis plus direction or in the x-axis plus direction and y-axis plus direction to transmit, is arranged in front of the optical recording medium. The signal light and reference after the Fourier transform are transmitted through this light transparent part and the optical recording medium is irradiated with this light, by which the hologram is recorded in the optical recording medium.

Optical recording method, optical recorder, optical reading method, and optical reader

A method and an apparatus capable of filtering based on desired spatial frequency characteristics without loss of Fourier spectrum frequency components, and of matched filtering of high recognition capability without losing functions of data recording and reconstruction as well as high-speed transmission and retrieval features and mass storage capacity characteristic of a holographic memory. Fourier transformed object light with 0° polarization of a target image is stored as a hologram using reference light having a spatial polarization distribution such that a daughter wavelet on scale m has 90° polarization. The hologram is retrieved using the Fourier transformed object light with 0° polarization. The hologram yields diffracted light in the form of a spatial frequency component which corresponds to scale m and is polarized 90° with respect to the other spatial frequency components. A polarizing element is used to extract only the spatial frequency component corresponding to scale m. Given reference light having a spatial polarization distribution in conformity with a shape of a spatial frequency filter, retrieval light of 0° polarization is applied for low-pass and high-pass filtering upon reconstruction.

Holographic recording method and filtering method

An optical recording medium, an optical recording and reproducing method, and an apparatus that can record and reproduce multilevel information at a high density and with a high S/N ratio. Recording light emitted from a light source is collimated by a collimation lens and introduced into a polarization rotary device. Recording light transmitted by the polarization rotary device is focused by an objective lens onto an optical recording medium. In response, a photo-induced birefringence is recorded on the optical recording medium. Multilevel recording is performed by controlling a voltage applied to the polarization rotary device to change a polarization angle θ of recording light. Reproduction is performed by detecting light reflected from the optical recording medium with an analyzer and a detector.

Optical recording medium, optical recording and reproducing method and apparatus

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