Abstract

Passage of far-ultraviolet radiation (1050–2000 Å) through the imperfect vacuum maintained by mechanical and oil-diffusion pumps results in the buildup of films opaque to far-uv radiation. Such films quickly coat lamp windows and other optical surfaces. The films can be removed by washing with petroleum ether or by exposure of affected surfaces to a hydrogen gas discharge. Transmittance vs time studies support the view that the films are produced from photodissociated vacuum-pump oil molecules. Passage of 2×1015 photons cm−2 through a 2.5-cm gap maintained at 10−4 Torr pressure results in two films of 50% combined transmittance measured at about 1200 Å.

© 1965 Optical Society of America

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References

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  1. Frederic Palmer, J. Chem. Phys. 2, 292 (1934).
    [Crossref]
  2. P. Warneck, Appl. Opt. 1, 721, (1962).
    [Crossref]
  3. J. M. Young, U. S. Naval Research Laboratory, Washington, D. C. (private communication).

1962 (1)

1934 (1)

Frederic Palmer, J. Chem. Phys. 2, 292 (1934).
[Crossref]

Palmer, Frederic

Frederic Palmer, J. Chem. Phys. 2, 292 (1934).
[Crossref]

Warneck, P.

Young, J. M.

J. M. Young, U. S. Naval Research Laboratory, Washington, D. C. (private communication).

Appl. Opt. (1)

J. Chem. Phys. (1)

Frederic Palmer, J. Chem. Phys. 2, 292 (1934).
[Crossref]

Other (1)

J. M. Young, U. S. Naval Research Laboratory, Washington, D. C. (private communication).

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Figures (5)

F. 1
F. 1

Hydrogen discharge lamp, showing the detectors attached to the housing at the ends of the lamp.

F. 2
F. 2

Response-vs-time curve of detector viewing lamp through vacuum path, curve I; and through air path, curve II,

F. 3
F. 3

Decrease in detector response accompanying film formation. Curve I: film forming on lamp window. In this study the detector window was protected from film buildup by a shutter except during measurement. Curve II: film forming on lamp and detector window. Both lamp and detector were continuously left unprotected during lamp operation. Curve III: film forming on lamp and simulated detector window. A simulated detector window was continuously exposed to the lamp, but the detector itself was protected by a shutter except during measurement.

F. 4
F. 4

Film elimination by use of hydrogen discharge. Curve I: decrease in detector response accompanying formation of film in vacuum. Curve II: increase in detector response accompanying removal of film by hydrogen discharge.

F. 5
F. 5

Comparison of the experimental and theoretical decrease in flux from lamp with time, due to film formation on the lamp window. Solid line represents experimental data. Broken line represents calculated curve using 1 × 10−15 cm2/quanta for A.

Equations (5)

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d I / d t = a I ( d x / d t ) ,
d x / d t = b Q V ,
Q = 2 n c l I ,
d I / I 2 = A d t ,
I t = I 0 / ( 1 + I 0 A t ) .