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

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. W. G. Fastie, “Ultraviolet measurements in planetary atmospheres,” Appl. Opt. 6, 397–402 (1967).
    [CrossRef] [PubMed]
  2. V. M. Vasyliunas, Methods of Experimental Physics, Vol. 9B of Plasma Physics, R. H. Lovberg, ed. (Academic, New York, 1971) p. 49.
    [CrossRef]
  3. E. C. Sittler, Rep. NASA TM-85037 (National Aeronautics and Space Administration, Washington, D.C., 1983).
  4. W. E. McClintock, C. A. Barth, R. E. Steele, G. M. Lawrence, J. G. Timothy, “Rocket-borne instrument with a high-resolution microchannel plate detector for planetary UV spectroscopy,” Appl. Opt. 21, 3071–3079 (1982).
    [CrossRef] [PubMed]
  5. A honeycomb structure of low-reflectance material was considered, because this material has been used successfully in other energy analyzers [e.g., G. L. Wrenn, J. F. E. Johnson, J. J. Sojka, “The supra-thermal plasma analysers on the ESA GEOS satellites,” Space Sci. Instrum. 5, 271–293 (1981)]. However, adequate mechanical mounting of the honeycomb structure would take much more mass than was required with the present approach.
  6. G. R. Carruthers, T. Page, R. R. Meier, “Apollo 16 Lyman alpha imagery of the hydrogen geocorona,” J. Geophys. Res. 81, 1664 (1976).
    [CrossRef]
  7. L. J. Heroux, H. E. Hinteregger, Handbook of Geophysics and the Space Environment, A. S. Jursa, ed. (U.S. Air Force Geophysics Laboratory, Hanscom Field, Mass., 1985) pp. 2-1–2-16.
  8. C. Martin, S. Bowyer, “Quantum efficiency of opaque CsI photocathodes with channel electron multiplier arrays in the extreme and far ultraviolet,” Appl. Opt. 21, 4206–4207 (1982).
    [CrossRef] [PubMed]
  9. J. D. Winningham, Southwest Research Institute, San Antonio, Tex. (personal communication, 1989).
  10. R. G. Johnston, R. P. Madden, “On the use of thermopiles for absolute radiometry in the far ultraviolet,” Appl. Opt. 4, 1574–1580 (1965).
    [CrossRef]
  11. C. E. Johnson, “Black electroless nickel surface morphologies with extremely high light absorption capacity,” Met. Finish. 16, 21–24 (1980); “Ultra-black coating for high absorptance of solar energy,” Dimensions NBS 63, 30–31 (1979).
  12. P. Jelinsky, S. Jelinsky, “Low reflectance EUV materials: a comparative study,” Appl. Opt. 26, 613–615 (1987).
    [CrossRef] [PubMed]
  13. J. Heaney, R. Keski-Kuha, internal memoranda, Code 717 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).
  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.
  16. M. C. Shai, internal memoranda, Code 732.5 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).
  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.

1987 (1)

1982 (2)

1981 (1)

A honeycomb structure of low-reflectance material was considered, because this material has been used successfully in other energy analyzers [e.g., G. L. Wrenn, J. F. E. Johnson, J. J. Sojka, “The supra-thermal plasma analysers on the ESA GEOS satellites,” Space Sci. Instrum. 5, 271–293 (1981)]. However, adequate mechanical mounting of the honeycomb structure would take much more mass than was required with the present approach.

1980 (1)

C. E. Johnson, “Black electroless nickel surface morphologies with extremely high light absorption capacity,” Met. Finish. 16, 21–24 (1980); “Ultra-black coating for high absorptance of solar energy,” Dimensions NBS 63, 30–31 (1979).

1976 (1)

G. R. Carruthers, T. Page, R. R. Meier, “Apollo 16 Lyman alpha imagery of the hydrogen geocorona,” J. Geophys. Res. 81, 1664 (1976).
[CrossRef]

1967 (1)

1965 (1)

Barth, C. A.

Bowyer, S.

Carruthers, G. R.

G. R. Carruthers, T. Page, R. R. Meier, “Apollo 16 Lyman alpha imagery of the hydrogen geocorona,” J. Geophys. Res. 81, 1664 (1976).
[CrossRef]

Fastie, W. G.

Heaney, J.

J. Heaney, R. Keski-Kuha, internal memoranda, Code 717 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).

Heroux, L. J.

L. J. Heroux, H. E. Hinteregger, Handbook of Geophysics and the Space Environment, A. S. Jursa, ed. (U.S. Air Force Geophysics Laboratory, Hanscom Field, Mass., 1985) pp. 2-1–2-16.

Hinteregger, H. E.

L. J. Heroux, H. E. Hinteregger, Handbook of Geophysics and the Space Environment, A. S. Jursa, ed. (U.S. Air Force Geophysics Laboratory, Hanscom Field, Mass., 1985) pp. 2-1–2-16.

Jelinsky, P.

Jelinsky, S.

Johnson, C. E.

C. E. Johnson, “Black electroless nickel surface morphologies with extremely high light absorption capacity,” Met. Finish. 16, 21–24 (1980); “Ultra-black coating for high absorptance of solar energy,” Dimensions NBS 63, 30–31 (1979).

Johnson, J. F. E.

A honeycomb structure of low-reflectance material was considered, because this material has been used successfully in other energy analyzers [e.g., G. L. Wrenn, J. F. E. Johnson, J. J. Sojka, “The supra-thermal plasma analysers on the ESA GEOS satellites,” Space Sci. Instrum. 5, 271–293 (1981)]. However, adequate mechanical mounting of the honeycomb structure would take much more mass than was required with the present approach.

Johnston, R. G.

Keski-Kuha, R.

J. Heaney, R. Keski-Kuha, internal memoranda, Code 717 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).

Lawrence, G. M.

Madden, R. P.

Martin, C.

McClintock, W. E.

Meier, R. R.

G. R. Carruthers, T. Page, R. R. Meier, “Apollo 16 Lyman alpha imagery of the hydrogen geocorona,” J. Geophys. Res. 81, 1664 (1976).
[CrossRef]

Milsom, D.

D. Milsom, Rep. 1860 (Breault Research Organization, Tucson, Arizona, 1990).

Page, T.

G. R. Carruthers, T. Page, R. R. Meier, “Apollo 16 Lyman alpha imagery of the hydrogen geocorona,” J. Geophys. Res. 81, 1664 (1976).
[CrossRef]

Shai, M. C.

M. C. Shai, internal memoranda, Code 732.5 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).

Sittler, E. C.

E. C. Sittler, Rep. NASA TM-85037 (National Aeronautics and Space Administration, Washington, D.C., 1983).

Sojka, J. J.

A honeycomb structure of low-reflectance material was considered, because this material has been used successfully in other energy analyzers [e.g., G. L. Wrenn, J. F. E. Johnson, J. J. Sojka, “The supra-thermal plasma analysers on the ESA GEOS satellites,” Space Sci. Instrum. 5, 271–293 (1981)]. However, adequate mechanical mounting of the honeycomb structure would take much more mass than was required with the present approach.

Steele, R. E.

Timothy, J. G.

Vasyliunas, V. M.

V. M. Vasyliunas, Methods of Experimental Physics, Vol. 9B of Plasma Physics, R. H. Lovberg, ed. (Academic, New York, 1971) p. 49.
[CrossRef]

Winningham, J. D.

J. D. Winningham, Southwest Research Institute, San Antonio, Tex. (personal communication, 1989).

Wrenn, G. L.

A honeycomb structure of low-reflectance material was considered, because this material has been used successfully in other energy analyzers [e.g., G. L. Wrenn, J. F. E. Johnson, J. J. Sojka, “The supra-thermal plasma analysers on the ESA GEOS satellites,” Space Sci. Instrum. 5, 271–293 (1981)]. However, adequate mechanical mounting of the honeycomb structure would take much more mass than was required with the present approach.

Appl. Opt. (5)

J. Geophys. Res. (1)

G. R. Carruthers, T. Page, R. R. Meier, “Apollo 16 Lyman alpha imagery of the hydrogen geocorona,” J. Geophys. Res. 81, 1664 (1976).
[CrossRef]

Met. Finish. (1)

C. E. Johnson, “Black electroless nickel surface morphologies with extremely high light absorption capacity,” Met. Finish. 16, 21–24 (1980); “Ultra-black coating for high absorptance of solar energy,” Dimensions NBS 63, 30–31 (1979).

Space Sci. Instrum. (1)

A honeycomb structure of low-reflectance material was considered, because this material has been used successfully in other energy analyzers [e.g., G. L. Wrenn, J. F. E. Johnson, J. J. Sojka, “The supra-thermal plasma analysers on the ESA GEOS satellites,” Space Sci. Instrum. 5, 271–293 (1981)]. However, adequate mechanical mounting of the honeycomb structure would take much more mass than was required with the present approach.

Other (10)

V. M. Vasyliunas, Methods of Experimental Physics, Vol. 9B of Plasma Physics, R. H. Lovberg, ed. (Academic, New York, 1971) p. 49.
[CrossRef]

E. C. Sittler, Rep. NASA TM-85037 (National Aeronautics and Space Administration, Washington, D.C., 1983).

L. J. Heroux, H. E. Hinteregger, Handbook of Geophysics and the Space Environment, A. S. Jursa, ed. (U.S. Air Force Geophysics Laboratory, Hanscom Field, Mass., 1985) pp. 2-1–2-16.

J. D. Winningham, Southwest Research Institute, San Antonio, Tex. (personal communication, 1989).

J. Heaney, R. Keski-Kuha, internal memoranda, Code 717 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).

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.

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.

M. C. Shai, internal memoranda, Code 732.5 (NASA Goddard Space Flight Center, Greenbelt, Md., 1989).

D. Milsom, Rep. 1860 (Breault Research Organization, Tucson, Arizona, 1990).

The grazing angle is the complement of the incidence angle used in our calculations in Table 1.

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (5)

Fig. 1
Fig. 1

Three-dimensional cutaway view of the PPA electron spectrometer. The parallel plates P1, P2, and P3 establish the electric field that deflects and focuses electrons onto the 32 × 32 pixel PSD. The central electron trajectory ET is shown. Light-trap action is achieved by the blocking of the exit slit SO by the plates P1, P2, and P3, and by the curved back surface SB, which reflects the incident light away from the SO. Mask M eliminates reflections from the SB to the top of the spectrometer housing.

Fig. 2
Fig. 2

Schematic showing the three sources of ultraviolet light entering the field of view (fov) of an instrument on a spinning spacecraft in Earth orbit.

Fig. 3
Fig. 3

The solar spectral irradiance plotted together with the QE of the microchannel plate detector (MCP). Wavelength is in nanometers.

Fig. 4
Fig. 4

(a) Side view of the PPA electron spectrometer showing the limiting rays RL that define the first reflection area A1, located on the curved back surface of the spectrometer housing. Specular reflection on A1 deflects most of the light toward the lower right-hand corner of the spectrometer cavity and away from the exit slit SO, as shown by RL–RS. The edge E3 provides the only double-reflection paths into the PSD, as shown by rays RE. Rays RC reflecting from the mouth of the entrance slit are effectively scattered away by cone BIC. (b) The principal reflecting areas A1, A2, and A3 are highlighted. Here A2 consists of the six components A2(1), A2(2), A2(3), A2(4), A2(5), and A2(6); A3 consists of AP3 and A3′. The baffles BO above the PSD define a pyramidal field of view that admits rays from areas AP3 and A3′. Here AP3 provides the largest flux into the PSD by virtue of the closeness of element A2(4).

Fig. 5
Fig. 5

Plots of Eq. (10) for several values The horizontal of G2. line segments represent the expected range of reflectance based on the surveyed data.

Tables (1)

Tables Icon

Table 1 Geometric Terms for Eqs. (11)(14)a

Equations (16)

Equations on this page are rendered with MathJax. Learn more.

ϕ O = A 3 A O B 3 ( x 3 ) x 3 - x 0 2 e ^ o · d A o e ^ 3 · d A 3 + A E 3 A o B E 3 ( x E 3 ) x E 3 - x 0 2 e ^ o · d A o e ^ E 3 · d A E 3
d ϕ l m = B l d Ω e ^ l · d A l ,
E l m ( x m ) = A l B l ( x l ) cos θ m x m - x l 2 e ^ l · d A l .
M m = Ω B m cos θ m d Ω = r E l m .
B m ( x m ) = ( r π ) E l m = r π A l B l ( x l ) cos θ m x m - x l 2 e ^ l · d A l .
ϕ o = F 2 ( σ 1 ) r 2 + F 3 ( σ 1 ) r 3 ,
F 2 ( σ 1 ) = B i π 2 A o A E 3 σ 1 cos θ E 3 e ^ 1 · d σ 1 x 1 - x E 3 2 e ^ E 3 · d A E 3 x o - x E 3 2 × e ^ o · d A o ,
F 3 ( σ 1 ) = B i π 3 A o A 3 σ 1 cos θ 2 e ^ 1 · d σ 1 x 1 - x 2 2 cos θ 3 e ^ 2 · d A 2 x 2 - x 3 2 × e ^ 3 · d A 3 x 3 - x o 2 e ^ o · d A o .
o = S 2 r 2 + S 3 r 3 ,
G = G 2 r 2 + G 3 r 3 ,
B 2 ( n ) = ( r π ) B 1 σ 1 f 12 ( n ) c 12 ( n ) x 12 ( n ) 2 .
B 3 = ( r π ) n = 1 6 B 2 ( n ) A 2 ( n ) f 23 ( n ) c 23 ( n ) x 23 ( n ) 2 ,
B P 3 = ( r π ) n = 3 5 B 2 ( n ) A 2 ( n ) f 2 P ( n ) c 2 P ( n ) x 2 P ( n ) 2 .
G 3 = a 0 π 3 [ A 3 cos θ 3 x 3 o 2 n = 1 6 T ( n ) + A P 3 cos θ 3 P x P o 2 n = 3 5 T P 3 ( n ) ] .
T ( n ) = f 12 ( n ) c 12 ( n ) x 12 ( n ) 2 A 2 ( n ) f 23 ( n ) c 23 ( n ) x 23 ( n ) 2 ,
T P 3 ( n ) = f 12 ( n ) c 12 ( n ) x 12 ( n ) 2 A 2 ( n ) f 2 P ( n ) c 2 P ( n ) x 2 P ( n ) 2 .

Metrics