As a novel material of low loss and high thermal stability, a graded index plastic optical fiber (GI POF) comprised of a copolymer of methyl α-chloro acrylate (MCA) and 2,2,2-trichloroethyl methacrylate (TCEMA) was prepared and the thermal, mechanical, and optical characteristics were investigated. Although each homopolymer had low loss and desirable high thermal stability, they had crucial disadvantages for the fiber fabrication process. To draw a MCA polymer (PMCA) fiber, it has to be heated above 270 °C. However, the polymer started to decompose at a lower temperature and produced numerous bubbles. In contrast, TCEMA polymer (PTCEMA) is too brittle to roll up during heat drawing. In this study, we succeeded to improve the strong viscoelasticity and the low decomposition temperature of PMCA and the brittleness of PTCEMA by copolymerizing MCA and TCEMA. In addition, the glass transition temperatures (T g ) of the copolymers were in the range of 133―147 °C and the transmittances of the copolymers were much higher than that of PMMA which has been commonly used as a base material of POF. A suitable GI POF was obtained using the MCA and TCEMA copolymer.

Design, synthesis, and characterization of a partially chlorinated acrylic copolymer for low‐loss and thermally stable graded index plastic optical fibers

A correction method for range walk error in time-correlated single-photon counting using photomultiplier tube

The electron density, the excitation and the gas temperatures have been obtained from optical spectrometric, microwave interferometric and thermocouple measurements in an argon rf plasma. The investigation was carried out in an active discharge and a channel region characterized by sonic laminar flow. Optical measurements of the excitation temperature were made in the 4000–5000 A range for discharge pressures of ∼ 63–644 torr and input rf power of 42–60 kW. Excitation temperatures in the discharge ranged between ∼ 7000–10,000 K. Electron densities measured by optical and microwave techniques showed good agreement. Thermocouple measurements in the channel and N2 rotational spectra from traces of N2 injected in the argon, as well as gas dynamic considerations, indicated that the gas temperature in the discharge and the channel regions were 2900–4400K and 1900–3300K, respectively. These values were substantially lower than the excitation temperatures corresponding to these regions, indicating that the plasma was in a two-temperature state in both regions. Standard tests for local thermal equilibrium (LTE) showed that the first excited level of argon constituted the bottleneck level.

Characteristics of an argon rf plasma: Active discharge and laminar sonic flow region

Publisher Summary This chapter examines the reshaping and stabilization of astronomical images. The simplest image stabilizer is a connection to the slow-motion controls of the main telescope. Much faster response can be obtained by rotating or translating a small optical element. The image stabilizer for a single object offers a different problem, for fast response is useful but at the same time the light for the measurement should not be wasted. The Richardson slicer resembles a confocal cavity or a White cell. The mirrors can be adjusted in two different ways. Multiple strips are formed along the slit, in much the same way as a Bowen slicer and each beam is superposed on the grating. Addition of a Bowen slicer to an existing coude spectrograph will shorten the exposure only to the extent that it is no longer necessary to widen the spectrum by trailing the image. The most direct method is to divert some 10% of the light by a beamsplitter. IA small part of the telescope aperture may be used to provide an offset tracking beam.

4. Reshaping and Stabilization of Astronomical Images

The applications of non-coherent bundles of optical fibres constitute the major area of utilization of this technology at the present time, and this situation is likely to continue in the foreseeable future. This is because these are the simplest assemblies of optical fibres and therefore offer the greatest scope in variations of design and construction.

Non-Coherent Bundles—Applications

Absolute and angular transmission measurements were made on a single sheathed fiber 0.15 mm in diameter and 2.1 m long, and an optical angular transfer function was defined and calculated. The effective transmission of the source brightness was calculated as a function of the f numbers of the entrance and output optics of the fiber, and these results were used to choose a suitable optical system for illumination of a spectrometer.

R. Fraser

Papers

Fiber optics for spectroscopic illumination.