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Chapter 7 WinX and Gated Operation 125
7.4.4 Impact of Bracket Pulsing on Delay
If operating in the UV when bracket pulsing is activated (Gen II Intensifier only,) the MCP
gate automatically brackets the photocathode gate pulse to further enhance the on/off ratio.
There is, however, a limitation of bracket pulsing that can complicate the coincidence of the
signal and gate at the camera. Because MCP bracket gating is slower than photocathode
gating (35 ns is required to gate the MCP on and another 1 µs to gate the MCP off at the end
of the photocathode gate.) As a result, MCP bracket pulsing should not be used in experiments
where the delay between the trigger and the photocathode gate is less than 35 ns.
7.4.5 Configuration
MCP Bracket pulse implementation is enabled by selecting Bracket Pulsing ON from
within the host software. Figure 7-2 illustrates the timing diagram for bracket pulsing.
NOTE:
Because Gen III Intensifiers do not respond in the UV, bracket
pulsing is not available for these intensifiers.
Figure 7-2: Timing Diagram: MCP Bracket Pulsing
As shown in Figure 7-2, the insertion delay between Trigger In and T
0
is approximately
12 ns, and the insertion delay between
Trigger In and Photocathode Gating is 35 ns.
NOTE:
The minimum delay between Trigger In and Photocathode
Gating
in bracket mode is 35 ns in order to allow the MCP to
achieve “full gain” before the photocathode is gated on.
Bracket
Aux Out
~12 ns
ŮPU
`PU
Trigger In
T0
T0 remains high for the
duration of the pulse ensemble.
Switches Photocathode OFF
Gates MCP ON and OFF
Delay is programmable.
Switches Photocathode ON
T0
T0
Off Off
Off Off
On
On
Photocathode Gating
Photocathode Gating
MCP Gating
MCP Gating
Gate Start
Gate Stop
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