A Fixed-Focus Broad-Range Echelle Spectrograph of High Speed and Resolving Power

Journal Article · Wed Oct 01 04:00:00 EST 1952 · Journal of the Optical Society of America

DOI:https://doi.org/10.1364/josa.42.000706· OSTI ID:4381585

Harrison, George R. ^[1]; Archer, James E. ^[1]; Camus, Jean ^[1]

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1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

From the basic formulas governing echelle performance, simple expressions for echelle and groove dimensions are derived for producing a two-dimensional echelle spectrogram having any desired characteristics. Several possible mountings of Bausch & Lomb echelles having 200 grooves per inch and resolving powers in the range 200,000 to 500,000 have been tested with the objective of covering as much as possible of the spectral range 2000 to 7000A in a single exposure with high photographic speed. This type of spectrograph is of increasing importance for the analysis of complex spectra of materials available in only minute samples. The mounting thus far found most satisfactory involves making the light from a horizontal slit parallel with an 8-inch concave mirror of 10.5-ft focus, placing the echelle with its grooves horizontal in the resulting collimated beam nearly over the slit, and illuminating a 21-ft concave grating with grooves vertical with the slightly diverging parallel beams from the echelle. The vertical plate factor thus produced on 30 inches of plate set in the focal plane at the grating normal varies from 0.47 A/mm at 7000A to 0.14A/mm at 2000A, and the spectral region from 7000 to 2000A can be covered in a single exposure at such dispersion. The reduction of optical parts to mirror, echelle, and grating gives high speed, so that exposure times of from 20 to 60 sec suffice for most arc spectra. To combine the echelle and grating characteristics effectively, the spectrum below 3600A is made to overlap in the second order of the grating that from 7200 to 3500A in the first. Measured resolving powers vary from 220,000 at 7000A to 450,000 or more at 2537A. Even in complex Zeeman spectra of the rare earths, the statistical distribution of lines is found to be such that little interference results from the partial overlapping of two grating orders. The spectral images are found to be stigmatic and sharp out to 15 inches on either side of the normal to the grating.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• NSA Number: NSA-06-006203
• OSTI ID: 4381585
• Report Number(s): NYO--3407
• Journal Information: Journal of the Optical Society of America, Journal Name: Journal of the Optical Society of America Journal Issue: 10 Vol. 42; ISSN 0030-3941
• Publisher: Optical Society of America (OSA)
• Country of Publication: United States
• Language: English

Related Subjects

DIFFRACTION
EQUATIONS
ERBIUM
FREQUENCY
HYPERFINE STRUCTURE
LENSES
LIGHT
MAGNETIC FIELDS
MERCURY
NEODYMIUM
OPTICAL SYSTEMS
PERFORMANCE
PLANNING
PRASEODYMIUM
Physics
REFLECTION
RESOLUTION
SPECTRA
SPECTROMETERS
SPECTROSCOPY
TESTING
ZEEMAN EFFECT