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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Vol. 31, Iss. 25 — Sep. 1, 1992
  • pp: 5331–5340

Light-trap design using multiple reflections and solid-angle attenuation: application to a spaceborne electron spectrometer

Federico A. Herrero  »View Author Affiliations


Applied Optics, Vol. 31, Issue 25, pp. 5331-5340 (1992)
http://dx.doi.org/10.1364/AO.31.005331


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Abstract

The design and performance of a new light trap for a spaceborne electron spectrometer are described. The light trap has a measured photon-rejection ratio of 2 × 10−11, allowing only one in 5 × 1010 incident photons to reach the sensitive area of the instrument. This rejection is more than sufficient because the ambient ultraviolet in Earth orbit requires a rejection no better than 10−8 to maintain the photon interference to less than 10 count/s. The light trap uses triple reflections to keep most of the light passing through the entrance slit away from the sensitive area of the spectrometer. However, because of electron-optic requirements, the edge of one of the metallic electrodes falls within the field of view of the sensitive area, allowing double-reflection photon paths to reach the sensitive area. Assuming diffuse reflectance r, the author shows that the photon rejection can be written as ∊ = G2r2 + G3r3 with G3 approximately 10 times larger than G2. Both coefficients depend only on the internal surface geometry; G2 represents the electrode edge reflections (second-order) and G3 represents the triple-reflection (third-order) paths. As shown by the analysis and measurements taken at two different values of r, the rejection is controlled by triple reflections if r > 0.08. It is shown that the average reflectance of all the internal surfaces must be less than 0.006, which is consistent with the data on the black coating applied to all surfaces. The analysis makes it possible to compare the photon contributions of each of the internal reflecting areas and to estimate the effective scattering width of the metallic electrode edge.

© 1992 Optical Society of America

History
Original Manuscript: September 27, 1990
Published: September 1, 1992

Citation
Federico A. Herrero, "Light-trap design using multiple reflections and solid-angle attenuation: application to a spaceborne electron spectrometer," Appl. Opt. 31, 5331-5340 (1992)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-31-25-5331


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References

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  14. This ratio is adopted from previous use in practice. Strictly speaking, the ratio measures the photons not rejected by the light trap. Perhaps a more adequate representation of the rejection is given by the reciprocal of the ratio, fo/fi, which corresponds to the efficiency of rejection.
  15. The fraction of the illuminated area is computed with the rays proceeding from one surface to the other, taking into account the presence of the obstacle. The fraction given is the ratio of the intensity received by the illuminated surface with the obstacle in place to the intensity that it would receive without the obstacle.
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  17. D. Milsom, Rep. 1860 (Breault Research Organization, Tucson, Arizona, 1990).
  18. The grazing angle is the complement of the incidence angle used in our calculations in Table 1.

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