Teledyne Princeton Instruments PI-MAX 3, Системное руководство

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Chapter 13: MCP Gating
MCP gating (not to be confused with MCP bracket pulsing) provides a unique
combination of nanosecond-scale gating speed and high ultraviolet QE. Normally, such
high UV QE is only available in so-called slow gate intensifiers (i.e., those without a
nickel underlay.) The PI-MAX3 applies the primary gating pulse to the MCP portion of
the tube and applies the bracket pulse to the photocathode. Consequently, it provides
the full benefit of bracket pulsing along with enhanced QE.
The main limitations with this option are that there is a somewhat larger propagation
delay and larger optical FWHM than a standard fast gate PI-MAX3. Insertion delay
between trigger and T
0
is ~12 ns. Insertion delay to the photocathode gate is
≥
30 ns.
Insertion delay to MCP gate is 75-225 ns (dependent on the individual intensifier): this
delay allows the photocathode to be fully on before the MCP is gated. Pulse repetition
rate is limited to 10 kHz.
13.1 Setup and Operation
The PI-MAX3 must have an installed MCP Gating board.
1. Make all of the required cable connections for your experiment.
2. Switch on the equipment and start the application software.
3. Set up the gating parameters. You may want to start with a relatively long gate to
acquire the phenomenon of interest.
4. Begin running the experiment.
5. Finally, narrow down the gate to the desired operation.
NOTE:
Pulse repetition rate is limited to 10 kHz.
13.2 Gain Variation
MCP gain approximately doubles for each 50 V increase in voltage. Therefore, small
ripples in the MCP voltage as a result of the gating waveform will cause gain changes
that vary with time after the rising edge of the gate pulse. A gain overshoot of 20% to
30% during the first 20 ns of a gate pulse is typical, with smaller variations later in time if
a wider gate pulse is used. For a given gain setting and pulse width, these variations are
reasonably repeatable, and may be calibrated.
13.3 Fluorescence Experiment
A typical laser-induced fluorescence experiment might incorporate a pulsed laser that
excites a sample with the laser beam and that additionally provides a trigger to the
PI-MAX3. When the laser pulse hits the sample, some atoms are raised to a higher
energy state and then spontaneously relax to the ground state, emitting photons as
they do to generate the fluorescence signal. This signal can be applied to a
spectrograph that spreads the fluorescence spectrum across the photocathode of the
PI-MAX3. The spectrum would then be intensified and applied to the PI-MAX3's CCD
array.