Stigmatic observations of laser-produced plasmas with a grazingincidence spectrograph.

A stigmatic spectrograph composed of a toroidal mirror and a concave grating both working at grazing incidence has been built and applied to the observation of laser-produced plasmas. Spatial resolution of 20-30 microm over a region of 1-mm extension and spectral resolution of approximately 1500 have been obtained with a considerable increase in speed of the spectrograph. By varying the relative positions of the optical elements, it is possible to change the wavelength of stigmatic condition in the range 10-300 A. Examples of observations of a beryllium plasma are shown.

Toroidal grating obtained on an elastic substrate.

The performance of a grating that is elastically deformed from a sphere into a toroid is that expected from ray traces assuming an ideal toroidal surface. Thus, it has become possible to select the wavelength range, in which a toroidal grating spectrograph is near stigmatic, by adjusting the forces acting on the elastic grating substrate. The possibility of producing toroidal gratings by replication of an elastically deformed blank is pointed out.

Thin-film photodetectors for the vacuum ultraviolet spectral region.

We report on thin-film photodetectors optimized for detecting the vacuum UV and rejection of the visible spectrum of electromagnetic radiation. The devices are made of hydrogenated amorphous silicon and silicon carbide on a glass substrate. At room temperature the photodetectors exhibit quantum efficiencies of 52% at lambda = 58.4 nm, 1% at lambda = 400 nm, and 0.1% at lambda = 650 nm. The response time for UV pulses from an N(2) laser gives signals of 6-mus full width at half-maximum and 500-ns rise time.

Imaging extreme ultraviolet spectrometer employing a single toroidal diffraction grating: the initial evaluation.

A high-efficiency extreme ultraviolet (EUV) imaging spectrometer has been constructed and tested. The spectrometer employs a concave toroidal grating illuminated at normal incidence in a Rowland circle mounting and has only one reflecting surface. The toroidal grating has been fabricated by a new technique employing an elastically deformable submaster grating which is replicated in a spherical form and then mechanically distorted to produce the desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The fixed toroidal grating used in the spectrometer is then replicated from this surface. Photographic tests and initial photoelectric tests with a 2-D pulse-counting detector system have verified the image quality of the toroidal grating at wavelengths near 600 A. The results of these initial tests are described in detail, and the basic designs of two instruments which could employ the imaging spectrometer for astrophysical investigations in space are briefly described, namely, a high-resolution EUV spectroheliometer for studies of the solar chromosphere, transition region, and corona and an EUV spectroscopic telescope for studies of nonsolar objects.