Visible Survey Spectrometers

This product is marketed for General Atomics by McPherson, Inc. The McPherson product line includes spectrometers spanning the spectral range from extreme ultraviolet to near infrared. Inquiries should be made to McPherson. Phone: 1-800-255-1055 (continental USA) 1-978-256-4512 Fax: 1-978-250-8625. Email McPherson

Applications

Plasma Diagnostics
Analytical Spectroscopy
Raman Spectroscopy

Features

Broad spectral coverage combined with high resolution (0.2 nm):
- 400 - 800 nm with a 1200 G/mm grating
- 200 - 400 nm with a 2400 G/mm grating and plastic phosphor installed over the transformer input face
High optical throughput (f/3) due to large diameter, aberration-corrected grating
Stigmatic imaging: 0.1 mm vertical resolution over 10 mm height of entrance slit
Use of first order spectrum eliminates need for order sorting
Photographic mask in focal plane permits selective attenuation of bright lines in spectrum, increasing effective dynamic range of detector
Simultaneous coverage of entire visible spectral range with no moving parts; spectrum dispersed over ~6,000 pixels

Description

This innovative visible survey spectrometer (U.S Patent No. 5,675,411) mates the customer's choice of CCD detector (intensified or unintensified) to a stigmatic, Rowland circle, survey spectrograph with high spectral resolution and high optical throughput.

The first order spectrum in the focal plane of the Rowland circle is divided into twenty spectral segments which are fiberoptically stacked into a two-dimensional image with the same rectangular format as that of the CCD sensor. Vertical grouping of the pixels during CCD readout integrates the signal brightness over the height of each spectral line image, minimizing readout time.

The legend on the schematic above describes the eight numbered optical components. The aberration-corrected holographic grating is 70 mm in diameter. The fiberoptic transformer which couples the curved focal plane of the spectrograph to the planar CCD camera may be customized to provide a large number of simultaneous viewchords (utilizing the stigmatic property of the aberration-corrected grating) or to span a very broad spectral region, whichever suits the needs of the customer.

In the photograph above, the spectrometer's detector chamber is uncovered to expose the CCD camera which is coupled to the geometric transformer by a fiberoptic reducing plug that provides the exact demagnification ratio required for size matching. The insert at top left is a computer generated color simulation of the rastered spectrum at the output tip of the transformer when the instrument is illuminated with the continuous spectrum from a tungsten-halogen light source. When the instrument is illuminated with a low pressure gas discharge, such as a Geissler tube, the characteristic spectral features of the emitting gas produce lines filling the height of a track in the CCD image. With column summing over the height of the spectral line images, dim lines are easily measurable.

The visible survey spectrometer may be purchased with an unintensified CCD camera, as shown in the photograph, or with an intensified CCD camera with fiberoptic input and output windows.
Further details may be found in the following paper:

N.H. Brooks et al, "Visible Spectroscopy in the DIII-D Divertor," Presented at 11th Topical Conference on High Temperature Plasma Diagnostics, Monterey, California, United States, 5/96;
Rev. Sci. Instrum. 68, 978 (1997);
General Atomics Document GA-A22352.

Contact McPherson, Inc. for additional information.