The
photosensitive target plate converts the variations in the intensity of light
into variation in electrical signals utilising: (i) a photoemissive surface or
(ii) a photoconductive coating or layers.
photosensitive target plate converts the variations in the intensity of light
into variation in electrical signals utilising: (i) a photoemissive surface or
(ii) a photoconductive coating or layers.
(i)
Photoemissive
Surfaces: Light
is in the form of bundles or packets of electromagnetic energy called photons
that have energy inversely proportional to the wavelength. The photons of light
have energy adequate to dislodge electrons from surfaces made of certain metals
like caesium silver, bismuth, lithium, etc, belonging to the alkali group.
Photoemissive surfaces of this type are used in some camera tubes, viz the
iconoscope and the image orthicon. The photoelectric efficiency of such
surfaces expressed as the ratio of the number of photoelectrons emitted to the
number of incident photons is referred to as “quantum efficiency”, a parameter
useful for comparing of photosensitivities of different surfaces.
Photoemissive
Surfaces: Light
is in the form of bundles or packets of electromagnetic energy called photons
that have energy inversely proportional to the wavelength. The photons of light
have energy adequate to dislodge electrons from surfaces made of certain metals
like caesium silver, bismuth, lithium, etc, belonging to the alkali group.
Photoemissive surfaces of this type are used in some camera tubes, viz the
iconoscope and the image orthicon. The photoelectric efficiency of such
surfaces expressed as the ratio of the number of photoelectrons emitted to the
number of incident photons is referred to as “quantum efficiency”, a parameter
useful for comparing of photosensitivities of different surfaces.
(ii)
Photoconductive
Coatings or Layers:
The resistance of semiconducting materials like selenium, antimony trisulphide
and lead oxides is affected by the light incident on it. The photons of light
are absorbed by the semiconducting materials to generate electron-hole pairs as
charge carriers. This reduces the resistance or increases the conductivity of
the material, proportional to the incident light. Photoconductive coatings of
these types are used in targets of camera tubes like vidicon and plumbicon.
Photoconductive
Coatings or Layers:
The resistance of semiconducting materials like selenium, antimony trisulphide
and lead oxides is affected by the light incident on it. The photons of light
are absorbed by the semiconducting materials to generate electron-hole pairs as
charge carriers. This reduces the resistance or increases the conductivity of
the material, proportional to the incident light. Photoconductive coatings of
these types are used in targets of camera tubes like vidicon and plumbicon.
