Image intensifier: Photocathode

The photo cathode converts the incoming photons to photo electrons by collisional ionization. The photo cathode is, therefore, directly behind the entrance window of any image intensifier. Multiple photo cathodes cover the spectral range from UV or blue, green to red. The photo cathode sensitivity is one important property to choose the most suiting photocathode for your application or the predominant illumination.

Image intensifier: High Quantum efficiency of several photocathode materials.

The upper graph shows the Spectral Response in mAW of available photo cathodes and the lower shows the High Quantum Efficiency of these photo cathodes.

Photo cathode incoming photons to photo electrons.

The specific material composition of the photo cathode enables to cover different spectral ranges. The incoming light first meets the photo cathode of the ICCD cameras image intensifier. The photo cathode converts the incoming photons to photo electrons by collisional ionization. To obtain a maximum signal to noise ratio in the images the spectral sensitivity of the photo cathode should be well fitted to the applications light spectrum. A maximum number of photoelectrons per incoming photon are generated in this way, i.e. the maximum integral quantum efficiency is achieved. The photocathode of the image intensifier will therefore be selected according to the specific requirements of your application. A selection of popular photo cathode materials is shown in the diagram above. Furthermore the sensitivity of these individual photo cathodes can be extended to the UV by using MgF2.

Spectral sensitivity is selected by photo cathode and entrance window

Before the photons hit the photo cathode, they have to pass the entrance window. Quartz is used as standard material for the window. However, for UV applications a MgF2 window may be applied. The ultraviolet transmission factors of both materials are shown in the appropriate diagram below.

ICCD camera: photocathode of the image intensifier.

The entrance window and the photo cathode as sectional drawing.

The graph below shows the transmission of the MgF2 and quartz window in comparison.

Image intensifier: transmission of the photocathode entrance window

Transmission of input windows. The MgF2 window extends UV and VUV.

Please contact our sales team or your local distributor to get assistance and further details to the photo cathode options.