An Infrared Pickup Tube

The infra-red (IR) pickup tube contains a sensitive target surface in the form of a thin layer of the photoconductor on a transparent window forming one end of the tube. The photoconductor emnployed must have a very high resistance when the material is in darkness. At the other end of the tube, there is an electron gun producing a low velocity beam of electrons. Electrons returning from the target enter a secondary emission multiplier which is coaxial with the gun, and the greatly amplified return current is supplied to the signal lead. The electron beam is focused by an axial magnetic field and deflected by a system of orthogonal deflecting coils producing fields at right angles to the motion of the beam. The operation of this type of pickup tube is discussed in detail.