Abstract

The present state of grating spectroscopy is reviewed with special emphasis on the far ir. The review includes the discussion of the properties of diffraction gratings, the intensity distribution among different orders of echelette gratings, Wood anomalies, ir and submillimeterwave filters, detectors, grating spectrometers with thermal sources, rules for the construction of far ir and submillimeterwave grating spectrometers, diffraction at the monochromator slits, comparative performance of interferometers and grating spectrometers, and spectroscopy of far ir laser emissions. Extensive references are presented.

© 1969 Optical Society of America

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Figures (5)

Fig. 1
Fig. 1

Echelette grating with 90° grooves: W = width of grating, d = distance between grooves, D = width of incident beam, = angle of facets, n = normal to the plane of the grating.

Fig. 2
Fig. 2

Intensity distribution among different orders of an echelette grating [from J. F. Moser, H. Steffen, and F. Kneubühl, Helv. Phys. Acta 41, 607 (1968)]. Upper half: Measured with microwaves, λ = 3 cm and ϕ = 24°. The data of the grating are: d = 4.48 cm, = 20°, N = 34. The electric field was perpendicular to the grooves, for the incident beam as well as for the antenna of the detector. Lower half: Measured with the 0.337-mm emission of the HCN laser and ϕ = 24°. The data of the gratings are d = 0.5 mm, = 20°, N = 100. The electric field of the incident beam was perpendicular to the grooves.

Fig. 3
Fig. 3

Reflectivity of reststrahlen crystals. (Private communication, L. Genzel, 1966.)

Fig. 4
Fig. 4

Spectral region of the P(14) ν3 band of HCN at 3268.2235 cm−1, measured with the 6-m Ebert double-passed vacuum prism grating monochromator of the Physics Department, The Ohio State University, Colombus, Ohio. The echelle grating is 12.7 cm by 25.4 cm, has 73.25 grooves/mm and a blaze angle of 63°26′. The detector is PbS-cooled with dry ice and acetone mixture. The absorption of the main band is 40% for a path length of 1 m and a pressure of 5 mm Hg. The satellites are c and d P(8) of the 0 11 0 →0 11 1 transition near 3267.9 cm−1 (Ref. 100).

Fig. 5
Fig. 5

Upper half: Wavenumber dependence of the intensity in first order of diffraction for echelette gratings with = 20° measured in a grating spectrometer. Lower half: Calculated spectral resolution for the different gratings as function of the slit width. [From J. F. Moser, F. H. Steffen, and F. Kneubühl, Helv. Phys. Acta 41, 607 (1968).]

Tables (2)

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Table I Infrared Detectorsa

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Table II Interferometers and Grating Spectrometers with Spectral Resolutions of 0.1 cm−1 or Better

Equations (9)

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m λ / d = m / ν d = 2 cos ( ϕ / 2 ) sin ( ϕ / 2 - φ ) .
R g = λ / Δ λ = ν / Δ ν = m W / d = m N = m D / d cos φ < 2 W / λ .
+ φ 0 = ϕ - - φ 0 or φ 0 = ( ϕ / 2 ) -
m 0 λ 0 / d = m 0 / ν 0 d = 2 cos ( ϕ / 2 ) sin             ( e . g . = 0.67 ) .
G r = π 2 m 2 ( e / d ) 2 ,
λ R / d = 2 m + 2 k 1 2 sin ( ϕ / 2 ) [ ( m k + k 2 ) 1 / 2 / ( m + 2 k ) ] 1 + [ m tan ( ϕ / 2 ) / ( m + 2 k ) ] 2 ,
R - 1 = R g - 1 + R s - 1 = ( 1 / m ) [ ( d cos φ / D ] + ( 1 / m ) ( s / f ) [ ( d / λ ) 2 cos 2 ( ϕ / 2 ) - ( m / 2 ) 2 ] 1 / 2 .
R max - 1 = ( 1 / m ) ( d / W ) { 2 + [ cos ( ϕ - φ ) / cos φ ] } = ( 1 / m ) ( d / D ) [ 2 cos φ + cos ( φ - φ ) ] .
L q m n = λ / 2 [ q + N - 1 ( p n m / 2 π ) 2 ] ,

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