High Spectral Dispersion Research Articles

High signal-to-noise detection of rotational Raman scattering through refluorescent and dispersive atomic filters

We introduce new methods for capturing rotational Raman scattering that simultaneously suppress background scattering and have exceedingly high spectral dispersion at low wavenumbers. These methods are based on resonant absorption and refractive index dispersion of atomic vapor, and take advantage of the availability of tunable lasers. Three different configurations are presented. The first is an atomic notch transmission filter which is based on refluorescence from an optically thick atomic vapor cell. This configuration is demonstrated in air using mercury vapor at 254 nm. The second configuration is an atomic resonance prism cell which is demonstrated in CO2 using mercury vapor, again at 254 nm. The third configuration is a density gradient atomic vapor cell which uses rubidium vapor at 780 nm. In the last two configurations, the atomic cell simultaneously blocks the elastic scattering while spatially dispersing the rotational Raman lines. In each case, a tunable Ti : sapphire laser was employed as an illuminating source. Copyright ” 2000 John Wiley & Sons, Ltd.

Achromatized transmission-type holographic screen for a multiview stereoscopic image system

The main drawback of the use of transmission-type holographic screens is poor color reproduction caused by their high spectral dispersion. For overcoming this drawback, a long, narrow diffusing slit is used as an object when recording the screen. The necessary size and position of the slit relative to the photoplate and to the recording and reconstruction beams are determined by the phase relations of the beams. By use of the slit, holographic screens of 30 cm x 40 cm are recorded with a diverging reference beam and are used to display a multiview full-color stereoscopic image. The images displayed on the screen show no sign of color separation except near the edges of the screen. The image brightness on the screen is high enough that it can be watched in a normally illuminated room.

Microspectrometer with slab-waveguide transmission gratings

An integrated transmission diffraction grating in a planar optical waveguide is presented for broadband spectroscopic analysis of liquids and gases. Silicon oxynitride slab waveguides on silicon substrates with low optical loss in the visible range are combined with a phase transmission grating exhibiting a blaze effect at 500 nm to achieve high-efficiency diffraction and high spectral dispersion. Collimated white light propagates through the waveguide and couples into air at a stepped formed planar grating. The beams of each adjacent step interfere constructively at the focal line of a cylindrical lens, its focal line positioned perpendicular to the waveguide plane. We used a common silicon photodiode array to detect the spectral data. Our approach is to develop a compact and economic spectrometer without moving parts that can be applied for UV-visible analysis and near-infrared industrial process control as well.

Emission-line galaxies in the third list of the Case Low-Dispersion Northern Sky Survey

Observations of 47 galaxies in the third Case list are reported. Thirty-five of the galaxies in the sample were selected for the presence of emission lines on the objective prism plates. At the higher spectral dispersion of the data, significant line emission was found in 46 of the 47 galaxies. Twenty-six galaxies are found to be undergoing significant bursts of star formation. Ten additional galaxies may be starburst galaxies with low-excitation spectra. Two galaxies are probably type Seyfert 2. The most distant object, CG 200, at a redshift of 0.144, has a strong broad H-alpha emission line, and is probably a Seyfert 1. Seventeen of the galaxies have been detected by IRAS. Eight of the IRAS galaxies have H-II-region-type spectra and eight have low-ionization starburst spectra. The galaxies represent a mixture of types, ranging from intrinsically faint dwarf galaxies with Mb equalling -16 mag, to powerful galaxies with MB equalling -23 mag. Galaxies CG 234 and CG 235 are interacting, as are galaxies CG 269 and CG 270.

Multiechelle grating mountings with high spectral resolution and dispersion

This paper describes a new spectrometer mounting using several echelle gratings as dispersive elements. These gratings are mounted so that a resolution equal to the sum of the resolution of the individual gratings is obtained. In the mounting the dispersions from the gratings coact resulting in very high dispersion in the focal plane. The multiechelle grating mounting can be used to build compact spectrometers with higher resolutions than can be obtained with the widest gratings ever ruled. Results from an experimental verification of the multiechelle grating mounting are given.

A Rocket Payload Using Cassegrain-Echelle Optics with Image Intensification for High Resolution Ultraviolet Stellar Spectroscopy

A description is given of a rocket payload designed to record high resolution ultraviolet stellar spectra using the star-stabilised ‘Skylark’ rocket vehicle. The system consists of a 35 cm aperture f/12 Cassegrain telescope and a spectrometer in which the high spectral dispersion of an echelle grating is crossed with that of a plane grating to separate the echelle orders. The spectrum is focussed onto an electrostatic image intensifier tube, the fibre optic faceplate of which is coated with sodium salicylate to give ultraviolet sensitivity. Photographic film is used to record the two dimensional spectrum array with a resolving power λ/dλ ≃ 104 between 1200 Å and 3000 Å. Efficiency measurements of components indicate that the photometric efficiency of the entire system will allow spectra to be recorded for early-type stars which are brighter than mr ≃ 5.