Abstract

Infrared sensitive television-camera tubes have responsivities orders of magnitude higher than scanner cells, yet the latter give better images of terrestrial scenes by their own thermal radiation. It is shown that although the camera tube electron beam reading mechanism saturates to limit maximum signal-to-noise ratio (SNR) to about 100, the large ir photon flux permits SNR up to 105 for typical nonsaturating cells that respond from the visible to 12 μm, despite their lower responsivity. Since ir images have very low contrast, ir sensitive camera tubes would be preferred only for wavelengths shorter than about 2.5 μm where photon flux is small and high responsivity is required.

© 1971 Optical Society of America

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  1. For more typical conditions, see the last two paragraphs of Sec. II.
  2. The alternative of developing the signal from the returning electron beam permits use of an electron multiplier and is used in the image orthicon. Electron beam shot noise then becomes dominant. This system is not discussed here because of its added complexity, but similar arguments will apply.
  3. M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
    [CrossRef]

1963

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Auphan, M.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Boutry, G. A.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Brissot, J. J.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Dormont, H.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Perilhou, J.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Pietri, G.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Infrared Phys.

M. Auphan, G. A. Boutry, J. J. Brissot, H. Dormont, J. Perilhou, G. Pietri, Infrared Phys. 3, 117 (1963).
[CrossRef]

Other

For more typical conditions, see the last two paragraphs of Sec. II.

The alternative of developing the signal from the returning electron beam permits use of an electron multiplier and is used in the image orthicon. Electron beam shot noise then becomes dominant. This system is not discussed here because of its added complexity, but similar arguments will apply.

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Figures (7)

Fig. 1
Fig. 1

Typical television-camera tube uses full frame integration to provide high responsivity.

Fig. 2
Fig. 2

In typical ir scanner system moving mirror provides one- or two-axis scan.

Fig. 3
Fig. 3

In the image dissector the signal represents the instantaneous radiation flux received from a single element of the scene.

Fig. 4
Fig. 4

Effect of responsivity and gamma on small contrast detection.

Fig. 5
Fig. 5

Ir detector evaluation apparatus measures change in input radiant power for signal equal to noise.

Fig. 6
Fig. 6

Sensor transfer characteristics—camera tube vs scanner.

Fig. 7
Fig. 7

Velocity selector structure can be adjusted to discard most of background before image reaches phosphor. (1) transparent electrode, (2) cooled ir sensitive photoconductor, (3) opaque multilead plate, (4) extractor mesh grid, (5) velocity selector mesh grid, (6) light source, (7) phosphor screen, (8) photoemitting islands. Ve—potential of extractor mesh grid, Vk—potential of photoemitter, Vt—potential of velocity selector grid, and Vb—potential of output phosphor.

Tables (1)

Tables Icon

Table I Evaluation of Q 0 - λ c = 0 λ c Q λ d λ = 0 λ c 1 h c / λ 2 π c 2 h λ 5 d λ e h c / λ k t - 1

Equations (2)

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i s max = C A Δ V max / t f ,
i s max = 10 - 8 F × 5 V 1 30 sec = 1.5 × 10 - 6 A .

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