Abstract

An improved infrared microspectrometer is described. A figure of performance or merit for infrared spectrometers using certain types of specimens is suggested. An experimental value is given for this performance figure for the instrument now in use in our laboratory. The increased performance of the microspectrometer may be observed in the spectral data shown for typical specimens.

Spectral resolving power and sample size requirements for infrared microspectroscopy are considered for typical organic chemical substances. It now appears that for many applications the limiting factor on sample size is the difficulty in the preparation and handling of the sample rather than the performance of the instrument.

© 1951 Optical Society of America

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References

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  1. (a) Blout, Bird, and Grey, J. Opt. Soc. Am. 39, 1052(A) (1949); (b)Ibid. 40, 304 (1950).
  2. Barer, Cole, and Thompson, Nature 163, 198 (1949).
    [Crossref] [PubMed]
  3. D. L. Wood, Rev. Sci. Instr. 21, 764 (1950).
    [Crossref]
  4. It is recognized that with such a system all the radiation from the source is concentrated on the sample and that thermal effects may occur. In our work, however, we have experienced no difficulty from heating of the samples by the source, possibly because they are mounted on silver chloride disks, which in turn rest on a silver support. With low melting (<45°C) crystals, it may be undesirable to irradiate with the unchopped beam for long times. The energy content of the radiation and the ease of construction and manipulation with the “microscope-preceding-monochromator” arrangement would seem to warrant its use except in the special cases where the arrangement generally used in ultraviolet microspectroscopy (monochromator-preceding-microscope) might be indicated.
  5. M. J. E. Golay, Rev. Sci. Instr. 18, 347, 357 (1947).
    [Crossref]
  6. Other cases will be considered by R. Clark Jones in a forthcoming publication.
  7. R. Clark Jones, J. Opt. Soc. Am. 39, 344 (1949).
    [Crossref]
  8. C. S. Rupert and J. Strong, J. Opt. Soc. Am. 40, 455–59 (1950).
    [Crossref]
  9. D. S. Grey, J. Opt. Soc. Am. 41, 183–92 (1951).
    [Crossref]
  10. Designed by D. S. Grey and constructed by Bausch and Lomb Optical Company.

1951 (1)

1950 (2)

1949 (3)

(a) Blout, Bird, and Grey, J. Opt. Soc. Am. 39, 1052(A) (1949); (b)Ibid. 40, 304 (1950).

Barer, Cole, and Thompson, Nature 163, 198 (1949).
[Crossref] [PubMed]

R. Clark Jones, J. Opt. Soc. Am. 39, 344 (1949).
[Crossref]

1947 (1)

M. J. E. Golay, Rev. Sci. Instr. 18, 347, 357 (1947).
[Crossref]

Barer,

Barer, Cole, and Thompson, Nature 163, 198 (1949).
[Crossref] [PubMed]

Bird,

(a) Blout, Bird, and Grey, J. Opt. Soc. Am. 39, 1052(A) (1949); (b)Ibid. 40, 304 (1950).

Blout,

(a) Blout, Bird, and Grey, J. Opt. Soc. Am. 39, 1052(A) (1949); (b)Ibid. 40, 304 (1950).

Clark Jones, R.

R. Clark Jones, J. Opt. Soc. Am. 39, 344 (1949).
[Crossref]

Other cases will be considered by R. Clark Jones in a forthcoming publication.

Cole,

Barer, Cole, and Thompson, Nature 163, 198 (1949).
[Crossref] [PubMed]

Golay, M. J. E.

M. J. E. Golay, Rev. Sci. Instr. 18, 347, 357 (1947).
[Crossref]

Grey,

(a) Blout, Bird, and Grey, J. Opt. Soc. Am. 39, 1052(A) (1949); (b)Ibid. 40, 304 (1950).

Grey, D. S.

D. S. Grey, J. Opt. Soc. Am. 41, 183–92 (1951).
[Crossref]

Designed by D. S. Grey and constructed by Bausch and Lomb Optical Company.

Rupert, C. S.

Strong, J.

Thompson,

Barer, Cole, and Thompson, Nature 163, 198 (1949).
[Crossref] [PubMed]

Wood, D. L.

D. L. Wood, Rev. Sci. Instr. 21, 764 (1950).
[Crossref]

J. Opt. Soc. Am. (4)

Nature (1)

Barer, Cole, and Thompson, Nature 163, 198 (1949).
[Crossref] [PubMed]

Rev. Sci. Instr. (2)

D. L. Wood, Rev. Sci. Instr. 21, 764 (1950).
[Crossref]

M. J. E. Golay, Rev. Sci. Instr. 18, 347, 357 (1947).
[Crossref]

Other (3)

Other cases will be considered by R. Clark Jones in a forthcoming publication.

It is recognized that with such a system all the radiation from the source is concentrated on the sample and that thermal effects may occur. In our work, however, we have experienced no difficulty from heating of the samples by the source, possibly because they are mounted on silver chloride disks, which in turn rest on a silver support. With low melting (<45°C) crystals, it may be undesirable to irradiate with the unchopped beam for long times. The energy content of the radiation and the ease of construction and manipulation with the “microscope-preceding-monochromator” arrangement would seem to warrant its use except in the special cases where the arrangement generally used in ultraviolet microspectroscopy (monochromator-preceding-microscope) might be indicated.

Designed by D. S. Grey and constructed by Bausch and Lomb Optical Company.

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Figures (5)

Fig. 1
Fig. 1

Infrared microspectrometer showing the microscopespectrometer assembly. The microscope eyepiece (A) used for locating and viewing the sample with visible light is of course removed when spectral measurements are made. The spherical mirror (B) may be moved vertically to vary the magnification of the sample on the entrance slit of the spectrometer.

Fig. 2
Fig. 2

Spherical reflecting objectives for the infrared. The two-mirror system has a numerical aperture of 0.63 with 13 percent of the area (calculated) obscured by the convex mirror. The objectives are convertible to higher numerical apertures by the addition of refracting elements which are added between the specimen and the convex mirror. “A” is a thallium bromide-iodide element which gives a numerical aperture of 0.89 in a dry system; “B” is a potassium bromide hemisphere which is used as an immersion element with mineral oil to give a numerical aperture of 0.96.

Fig. 3
Fig. 3

Comparison of the infrared data of androsterone. Top spectrum obtained with mineral mull run using a macro sample (about 10 milligrams) with high resolution. The blank spaces are regions of mineral oil absorption. Middle spectrum obtained from single crystal run at high resolution using 0.63 N.A. objectives. Bottom spectrum obtained using same single crystal with lower numerical aperture objectives. In each case the Δλ (width of wave-length band resolved) is indicated below the spectra.

Fig. 4
Fig. 4

Comparison of the infrared data of progesterone. Top spectrum obtained with a macro sample (about 10−2 g) with high resolution, the blank spaces being regions of mineral oil absorption. The bottom spectrum is that obtained from a micro sample (10−5 g) deposited from solution on a silver chloride slide. The Δλ for each spectrum is indicated below it.

Fig. 5
Fig. 5

Top spectrum is that of cytosine hydrate obtained as a mineral oil mull. The bottom spectra were obtained using polarized radiation on a single crystal of the material. The Δλ for each spectrum is indicated above it.

Equations (2)

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P ( λ ) = [ 1 Δ λ · ( 1 τ ) 1 2 · 1 A · 1 Δ T ] · [ λ 1 2 c 1 2 ] ,
P ( λ ) = K · ( N A m ) 2 · R ( λ ) · F D · L ( λ ) ,