
56
PI-MAX
®
3 System Manual
Version 1.A
MCP bracket pulsing
**
keeps the MCP biased OFF except for an interval that brackets
the timing of the photocathode gate as shown in Figure 21. For emitted photoelectrons to
be accelerated in the MCP, the MCP must be biased ON. In conventional intensified
cameras, the MCP is biased ON continuously. In the PI-MAX3, however, when bracket
pulsing is ON, the MCP is biased OFF until just before the photocathode is gated ON and
is biased OFF shortly after the photocathode is biased OFF.
Figure 21. Timing: Bracket Pulsing
By bracket pulsing the MCP off (in addition to photocathode gating), the on/off ratio of
the Gen II PI-MAX3
in UV is improved by 2-3 orders of magnitude. The resulting UV
ratio exceeds even the high levels normally achieved in the visible. Applications that
benefit from this new approach include LIF and nanosecond pump-probe experiments.
Note:
Bracket pulsing does not help in the visible region. Under extremely low duty-
factor conditions, the only remedy is to install an external shutter ahead of the camera.
Bracket Pulsing in LIF Measurements
Most experiments using laser-induced fluorescence to probe combustion flows are
performed with UV probe/lasers. Atomic emission from flames also has significant UV
content. If the flame is continuous, the UV background will also be continuous. Even
where a flame is transient (e.g. internal combustion engine), its lifetime can be many
milliseconds, compared to the nanosecond time scale of the laser used. This background
can be a million times as long. If the background is bright, then a UV on/off ratio of
20,000:1 will be overwhelmed by the duty cycle and will not be adequate for extracting a
signal of 10
-5
. In high dynamic range quantitative measurements, backgrounds must be
kept to an absolute minimum. MCP bracket pulse gating dramatically improves the
rejection of CW and even millisecond time-scale background.
An alternative to suppressing background for imaging has been the use of very narrow
spectral bandpass filters. In the UV, these filters are expensive and they can have low
transmission at their central wavelength. An additional filter is required for each
wavelength to be imaged. The use of electronic temporal rejection of CW or quasi-CW
background may make it unnecessary to use these filters, thus increasing the optical
throughput, sensitivity, and quantitative precision of the measurement.
Bracket Pulsing in Nanosecond Pump Probe Experiments
Some nanosecond pump-probe experiments combine a nanosecond or faster pump with a
flashlamp probe. The duration of the probe flash can be 10-50 µs and a gate is used to
select the specific nanosecond-scale time slice to be observed within the much longer
probe flash. In these absorbance experiments, accurate measurement of absorbance
**
Bracket pulsing is not available for cameras having a filmless Gen III Intensifier. Gen III
Intensifiers do not respond in the UV.
Содержание PI-MAX 3 System
Страница 1: ...4411 0129 Version 1 A September 8 2010 4411 0069 ...
Страница 32: ...32 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 52: ...52 PI MAX 3 System Manual Version 1 A Figure 20 Safe Mode and Fast Mode Operation ...
Страница 60: ...60 PI MAX 3 System Manual Version 1 A Figure 24 Experiment is Master Clock Hardware Setup and Timing Diagram ...
Страница 72: ...72 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 90: ...90 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 100: ...100 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 110: ...110 PI MAX 3 System Manual Version 1 A Figure 68 Outline Drawing PI MAX3 with F mount Adapter ...
Страница 111: ...Appendix B Outline Drawings 111 Figure 69 Outline Drawing PI MAX3 with Spectroscopy mount Adapter ...
Страница 112: ...112 PI MAX 3 System Manual Version 1 A PI MAX3 Power Supply Figure 70 Outline Drawing PI MAX3 Power Supply ...
Страница 113: ...Appendix B Outline Drawings 113 CoolCUBEII Circulator Figure 71 Outline Drawing CoolCUBEII Circulator ...
Страница 114: ...114 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 120: ...120 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 140: ...140 PI MAX 3 System Manual Version 1 A This page intentionally left blank ...
Страница 142: ...142 PI MAX 3 System Manual Version 1 A ...