Abstract

HgCdTe photoconductive detectors can display a nonlinear response when illuminated. In interferometric applications, this behavior must be accounted for in the data transformation process to avoid errors in the measurement of the spectral distribution of the incident radiation. A model for the distortion of the interferogram is proposed and applied to solar observations made by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier-transform spectrometer during orbital sunrise and sunset from the Space Shuttle. Empirical estimation of the dc current level is necessary for this instrument, and satisfactory nonlinearity correction is obtained for several of the primary ATMOS optical filters. For ATMOS broadband optical filters that cover more than one half the alias bandwidth, the model is inadequate because of the presence of antialiasing electronic filters within the instrument, and it is necessary to resort to estimation and subtraction of the residual baseline offset. In either case the remaining baseline offsets are typically smaller than 1%, which is satisfactory, although offset remains a significant systematic source of error in the estimation of the abundance of telluric and solar constituents from the spectra.

© 1994 Optical Society of America

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References

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  1. F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
    [CrossRef]
  2. M. A. Kinch, S. R. Borrello, “0.1 eV HgCdTe photoconductors,” Infrared Phys. 15, 111–124 (1975).
    [CrossRef]
  3. S. R. Borrello, M. Kinch, D. Lamont, “Photoconductive HgCdTe detector performance with background variations,” Infrared Phys. 17, 121–125 (1977).
    [CrossRef]
  4. R. A. Schindler, “Nonlinearity correction circuit for photoconductive detector,” NASA Tech. Brief 10, 47 (1986).
  5. D. B. Chase, “Nonlinear detector response in FT-IR,” Appl. Spectrosc. 38, 491–494 (1984).
    [CrossRef]
  6. G. Guelachvili, “Distortion free interferograms in Fourier transform spectroscopy with nonlinear detectors,” Appl. Opt. 25, 4644–4648 (1986).
    [CrossRef] [PubMed]
  7. R. O. Carter, N. E. Lindsay, D. Beduhn, “A solution to baseline uncertainty due to MCT detector nonlinearity in FT-IR,” Appl. Spectrosc. 44, 1147–1151 (1990).
    [CrossRef]
  8. C. B. Farmer, “High resolution infrared spectroscopy of the Sun and the Earth’s atmosphere from space,” Mikrochim. Acta 3, 189–214 (1987).
    [CrossRef]

1990 (1)

1987 (1)

C. B. Farmer, “High resolution infrared spectroscopy of the Sun and the Earth’s atmosphere from space,” Mikrochim. Acta 3, 189–214 (1987).
[CrossRef]

1986 (2)

G. Guelachvili, “Distortion free interferograms in Fourier transform spectroscopy with nonlinear detectors,” Appl. Opt. 25, 4644–4648 (1986).
[CrossRef] [PubMed]

R. A. Schindler, “Nonlinearity correction circuit for photoconductive detector,” NASA Tech. Brief 10, 47 (1986).

1984 (1)

1977 (1)

S. R. Borrello, M. Kinch, D. Lamont, “Photoconductive HgCdTe detector performance with background variations,” Infrared Phys. 17, 121–125 (1977).
[CrossRef]

1975 (1)

M. A. Kinch, S. R. Borrello, “0.1 eV HgCdTe photoconductors,” Infrared Phys. 15, 111–124 (1975).
[CrossRef]

1974 (1)

F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
[CrossRef]

Allen, R.

F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
[CrossRef]

Bartoli, F.

F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
[CrossRef]

Beduhn, D.

Borrello, S. R.

S. R. Borrello, M. Kinch, D. Lamont, “Photoconductive HgCdTe detector performance with background variations,” Infrared Phys. 17, 121–125 (1977).
[CrossRef]

M. A. Kinch, S. R. Borrello, “0.1 eV HgCdTe photoconductors,” Infrared Phys. 15, 111–124 (1975).
[CrossRef]

Carter, R. O.

Chase, D. B.

Esterowitz, L.

F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
[CrossRef]

Farmer, C. B.

C. B. Farmer, “High resolution infrared spectroscopy of the Sun and the Earth’s atmosphere from space,” Mikrochim. Acta 3, 189–214 (1987).
[CrossRef]

Guelachvili, G.

Kinch, M.

S. R. Borrello, M. Kinch, D. Lamont, “Photoconductive HgCdTe detector performance with background variations,” Infrared Phys. 17, 121–125 (1977).
[CrossRef]

Kinch, M. A.

M. A. Kinch, S. R. Borrello, “0.1 eV HgCdTe photoconductors,” Infrared Phys. 15, 111–124 (1975).
[CrossRef]

Kruer, M.

F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
[CrossRef]

Lamont, D.

S. R. Borrello, M. Kinch, D. Lamont, “Photoconductive HgCdTe detector performance with background variations,” Infrared Phys. 17, 121–125 (1977).
[CrossRef]

Lindsay, N. E.

Schindler, R. A.

R. A. Schindler, “Nonlinearity correction circuit for photoconductive detector,” NASA Tech. Brief 10, 47 (1986).

Appl. Opt. (1)

Appl. Spectrosc. (2)

Infrared Phys. (2)

M. A. Kinch, S. R. Borrello, “0.1 eV HgCdTe photoconductors,” Infrared Phys. 15, 111–124 (1975).
[CrossRef]

S. R. Borrello, M. Kinch, D. Lamont, “Photoconductive HgCdTe detector performance with background variations,” Infrared Phys. 17, 121–125 (1977).
[CrossRef]

J. Appl. Phys. (1)

F. Bartoli, R. Allen, L. Esterowitz, M. Kruer, “Auger-limited carrier lifetimes in HgCdTe at high excess carrier concentrations,” J. Appl. Phys. 45, 2150–2154 (1974).
[CrossRef]

Mikrochim. Acta (1)

C. B. Farmer, “High resolution infrared spectroscopy of the Sun and the Earth’s atmosphere from space,” Mikrochim. Acta 3, 189–214 (1987).
[CrossRef]

NASA Tech. Brief (1)

R. A. Schindler, “Nonlinearity correction circuit for photoconductive detector,” NASA Tech. Brief 10, 47 (1986).

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Figures (8)

Fig. 1
Fig. 1

Fractional error in retrieved concentration as a function of the zero-level intensity offset for a well-resolved and isolated CO2 line at 957.78 cm−1 observed at air masses corresponding to weak (10%), intermediate (20%), and strong (50%) absorptions in the transmission spectra. The error is a near-linear function of the intensity offset. Intensity offsets between 1 and 10% are commonly observed and need to be corrected to the 1% level to minimize any systematic biasing because of residual zero-level intensity offsets.

Fig. 2
Fig. 2

Uncorrected low-resolution solar spectra obtained with ATMOS filters 1, 2, and 3. Each frame contains two traces, with the upper trace enlarged in the vertical by a factor of 10 to enhance the out-of-band spectral artifacts.

Fig. 3
Fig. 3

Hypothetical detector-response curve exhibiting nonlinearity. The horizontal axis represents the absolute magnitude of the photon flux and the vertical axis represents the measured dc signal. The stylized representations of the interferograms illustrate the relative distortion of the central fringe compared with the rest of the interferogram under the assumption of 70% modulation efficiency.

Fig. 4
Fig. 4

(a) One-eighth alias-bandwidth model of ATMOS filter 1, (b) autocorrelation of (a), (c) cubic correlation of (a). Notice the spectral artifacts near zero frequency and twice the central frequency in (b) and the feature at 3 times the central frequency of the filter in (c). Additionally, the largest cubic-correlation term lies within the bandpass of the filter.

Fig. 5
Fig. 5

(a) One-quarter alias-bandwidth model of ATMOS filter 2, (b) autocorrelation of(a), (c) cubic correlation of (a). Notice the spectral artifacts near zero frequency and twice the central frequency in (b). The sum frequency artifact in (b) occupies most of the upper half of the alias bandwidth. Aliasing is apparent in (c) as the cube frequency artifact is centered at a frequency above the alias cutoff and the hence folded back into the spectrum.

Fig. 6
Fig. 6

(a) One-half alias-bandwidth model of ATMOS filter 3, (b) autocorrelation of (a), (c) cubic correlation of (a). The spectral artifact near zero frequency in (b) is distorted relative to that in Figs. 4 and 5, and the sum frequency artifact is largely aliased into the bandpass of the filter. Aliasing is evident in (b) and (c).

Fig. 7
Fig. 7

ATMOS filters 1 and 2 high-Sun spectra after nonlinearity correction. Each frame contains two traces, one enlarged in the vertical by a factor of 10 to enhance the out-of-band spectral artifacts.

Fig. 8
Fig. 8

ATMOS filter 1 low-Sun spectra: in-band comparison (a) before and (b) after nonlinearity correction.

Equations (7)

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Δ V = K 1 Φ ( 1 + K 2 Φ )
I ( x ) = a Φ ( x ) 1 / 3
[ I ( x ) - I 0 ] TRUE = [ Φ ( x ) - Φ 0 ( x ) ] / [ Φ ( x ) I ( x ) ] I 0 .
[ I ( x ) - I 0 ] TRUE = I AC ( x ) { 1 + I AC ( x ) I 0 + 1 3 [ I AC ( x ) I 0 ] 2 } .
I OBS ( x ) = I ( x ) + α I 2 ( x ) + β I 3 ( x ) ,
S OBS ( σ ) = - + I OBS ( x ) exp ( - i 2 π σ x ) d x = - + I ( x ) exp ( - i 2 π σ x ) d x + α - + I 2 ( x ) exp ( - i 2 π σ x ) d x + β - + I 3 ( x ) exp ( - i 2 π σ x ) d x + ,
S ( σ ) * S ( σ ) = - - I 2 ( x ) exp ( - i 2 π σ x ) d x .

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