Abstract

By cooling the chopping blade, the recovery time of a thermal detector can be reduced to a negligible fraction of the chopping cycle. The possible gains in chopping frequency and responsivity are analyzed and calculated for the case of square-wave chopping. Disadvantages, such as distortion of the detector output waveform, are also analyzed.

© 1961 Optical Society of America

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References

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  1. R. C. Jones, Advances In Electronics (Academic Press, Inc., New York, 1953) pp. 1–96.
  2. R. C. Jones, Proc. IRE 47, 1481 and 1495 (1959).
    [Crossref]
  3. R. A. Smith, F. E. Jones, and R. P. Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University Press, New York, 1957), especially Chaps. 3 and 7.
  4. M. Jakob, Heat Transfer (John Wiley & Sons, 1957), Vol. II, Chap. 31.

1959 (1)

R. C. Jones, Proc. IRE 47, 1481 and 1495 (1959).
[Crossref]

Chasmar, R. P.

R. A. Smith, F. E. Jones, and R. P. Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University Press, New York, 1957), especially Chaps. 3 and 7.

Jakob, M.

M. Jakob, Heat Transfer (John Wiley & Sons, 1957), Vol. II, Chap. 31.

Jones, F. E.

R. A. Smith, F. E. Jones, and R. P. Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University Press, New York, 1957), especially Chaps. 3 and 7.

Jones, R. C.

R. C. Jones, Proc. IRE 47, 1481 and 1495 (1959).
[Crossref]

R. C. Jones, Advances In Electronics (Academic Press, Inc., New York, 1953) pp. 1–96.

Smith, R. A.

R. A. Smith, F. E. Jones, and R. P. Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University Press, New York, 1957), especially Chaps. 3 and 7.

Proc. IRE (1)

R. C. Jones, Proc. IRE 47, 1481 and 1495 (1959).
[Crossref]

Other (3)

R. A. Smith, F. E. Jones, and R. P. Chasmar, The Detection and Measurement of Infrared Radiation (Oxford University Press, New York, 1957), especially Chaps. 3 and 7.

M. Jakob, Heat Transfer (John Wiley & Sons, 1957), Vol. II, Chap. 31.

R. C. Jones, Advances In Electronics (Academic Press, Inc., New York, 1953) pp. 1–96.

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Figures (4)

Fig. 1
Fig. 1

Detector temperature (or voltage output) and radiation input versus time.

Fig. 2
Fig. 2

Ratio of decay time to rise time versus degrees Centigrade that the chopper blade has been cooled below ambient, for different incident beams.

Fig. 3
Fig. 3

Percentage gain of responsivity versus original fraction of full response, for different arrangements of forced cycled cooling.

Fig. 4
Fig. 4

Fractional amplitude of fundamental component of signal versus various amounts of cycled cooling for two pairs of full-response fractions. Compensatory responsivity gains due to longer rise times are not included.

Equations (29)

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C ( d Δ T / d t ) + G Δ T = W ,
Δ T / Δ T 0 = l 2             at             t = 0.
G r Δ T 4 σ 1 S T 3 A Δ T ,
Δ T = ( W / G ) { 1 - ( 1 - l 2 ) exp [ - ( G / C ) t ] } ,
W / G = Δ T 0 .
J = C / G .
E = P Δ T .
E = P Δ T 0 [ 1 - ( 1 - l 2 ) e - t / J ] .
C ( d Δ T / d t ) + ( G c + G a ) Δ T + σ 1 S A [ ( T A + Δ T ) 4 - T A 4 ] + σ 2 S B [ ( T A + Δ T ) 4 - T B 4 ] = 0 ,
4 σ ( 1 S A + 2 S B ) T A 3 Δ T + σ 2 S B ( T A 4 - T B 4 ) = G r Δ T + Q ,
C ( d Δ T / d t ) + G Δ T = - Q .
E = P Δ T 0 [ ( l 2 + Q / W ) e - t / J - Q / W ] .
t 2 = J ln [ l 2 + Q / W l 1 + Q / W ] .
t 1 = J ln [ ( 1 - l 1 ) / ( 1 - l 2 ) ] = k J ,
k = ln [ ( 1 - l 1 ) / ( 1 - l 2 ) ] .
J D = J ln ( e 1 + Q / W 1 + e Q / W ) .
b t 2 t 1 = ln [ 1 + Δ l / ( l 1 + Q / W ) ] ln [ 1 + Δ l / ( 1 - l 2 ) ] ,
Δ l = l 2 - l 1 .
b ( J W / t 1 Q ) Δ l .
E = F i α R Δ T = K Δ T ,
t 1 + t 2 = J ln [ l 2 ( 1 - l 1 ) / l 1 ( 1 - l 2 ) ] .
t 1 = J ln [ ( 1 - l 1 ) / ( 1 - l 2 ) ] .
Δ l / Δ l = ( 1 - l 1 ) / l 2 ( 1 - l 1 ) .
A 1 = P W G 1 + Q / W π [ 2 { 1 - cos [ 2 π b / ( 1 + b ) ] } 1 + [ 2 π J / t 1 ( 1 + b ) ] 2 ] 1 2 .
r = 2 A 1 / W .
r 0 = 4 P G π ( 1 + ω 1 2 J 2 ) 1 2 = 4 P G π [ 1 + ( π / k ) 2 ] 1 2 .
r r 0 = 1 2 ( 1 + Q / W ) { 2 { 1 - cos [ 2 π b / ( 1 + b ) ] } } 1 2 × [ 1 + ( π / k ) 2 1 + [ 2 π / k ( 1 + b ) ] 2 ] 1 2 .
lim b 0 r r 0 = π b Q W ( 1 + b ) [ 1 + ( π / k ) 2 1 + [ 2 π / k ( 1 + b ) ] 2 ] 1 2 .
( r r 0 ) b = 0 = π Δ l k [ 1 - 3 π 2 k 2 + 4 π 2 ] 1 2 .