photocathode sensitivity

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Photocathode sensitivity quantifies the conversion efficiency for photons into photoelectrons; the relationship between photocathode sensitivity and wavelength is called the spectral response.

The terms quantum efficiency, radiant sensitivity, luminous sensitivity are used to specify photocathode sensitivity. The optimum way of quantifying a photocathode depends on the application. The terms used and their inter-relationships are discussed below.

quantum efficiency:  h(l) or QE%
Usually designated by h(l), quantum efficiency is the average percentage of  incident photons that convert to photoelectrons.

radiant sensitivity (responsivity): E(l)
Radiant sensitivity is defined as the photocathode current emitted per watt of incident radiation and is expressed in mA/W.

luminous sensitivity: S
The luminous sensitivity specification has been adopted by all photomultiplier manufacturers and is a traditional unit for spectral response measured in units of mA/lumen. Values of S range from 20 mA/lm to over 400 mA/lm, depending on the photocathode type.

All photocathodes respond to white light and will give the S range described above but with varying sensitivity across the Blue, Red and Infrared areas of the spectrum. To test these variations three filters can be placed in turn between a white-light source and the photocathode. This will enable a more accurate choice of photocathode dependent on the application the photomultiplier is required for. The results are expressed by industry standard Corning Blue (CB), Corning Red (CR) and Infrared (IR) parameters.

For more detailed information, request our brochure "Understanding photomultipliers" via this form.