5.4.5 - Intelligate
With traditional Image Intensier gating the photocathode of the tube is switched on and off. But even when the
photocathode is switched off, some photons can still pass through it and reach the Microchannel Plate (MCP). UV
photons can be energetic enough to be converted into photoelectrons that are amplied by the MCP in the normal way,
and are then detected by the CCD sensor. The ability of the Image Intensier to reject photons when it is switched off
becomes worse in the UV, so the On/Off ratio of the tube is compromised. The solution to this, as utilized by Andor’s
Intelligate™ function, is to gate the MCP as well as the photocathode.
A checkbox is accessible under the Gating tab of the Setup Acquisition menu allows the user to apply the Intelligate
function.
The gating electronics will output a fast rising edge that is sent to the MCP. After a 100 ns delay, which allows the MCP
voltage to rise and settle, the photocathode will open. The MCP will remain at the gain value (as set by the user in the
software) for the duration of the gate width, and then the MCP will decay rapidly. This method of gating eliminates the
need for a pre-pulse or anticipator circuit and results in photoelectron rejection of better than 10
7
:1, below 200 nm.
MCP Gating in practice
Pre-Acquisition Setup - Image Intensier
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