Teledyne Princeton Instruments PI-MAX 3, System Manual

Page: 241 / 250

Appendix H Glossary 241
Intensifier Gating
Speed:
Temporal resolution in a PI-MAX3 is made possible by switching
the intensifier on and off (gating) very rapidly. Typical fast-gate
intensifiers have minimum gate widths (FWHM) of approximately
2 ns. For slow-gated devices the FWHM is about 50 ns. Refer to
FWHM .
Fast-gating is achieved by adding a nickel (Ni) underlayer to
photocathode. However, this layer may produce an effective QE
reduction of as much as 40%. Slow-gate intensifiers have neither
the Ni layer nor its effects on QE.
Intensifier
On/Off Ratio:
The ratio of light output when the intensifier is gated on and off:
The higher the ratio, the better the gating. A high on/off ratio is
necessary to eliminate the background and to faithfully
reproduce transient events. In the visible region on/off ratios
exceeding 10
6
:1 is typically achieved. In the UV region, the on/off
ratio is typically much poorer (10
4
:1) though with MCP Bracket
Pulsing ratios in the UV region can be improved dramatically
(10
7
:1). Refer to Section 8.3, MCP Bracket Pulsing , on page 100.
Intensifier Size:
18 mm diameter and 25 mm diameter. Generally speaking, the
larger diameter gives a larger field of view at the surface of the
CCD array. The coupling of the intensifier to the CCD array is also
a factor in determining the field view. A fiberoptic reducing taper
of 1.27:1 will increase the field of view, while a taper of 1:1 will
have no effect.
Intensifier Types:
Refer to:
• Gen I Intensifier ;
• Gen II Intensifier ;
• Super Gen II Intensifier ;
• Gen III Intensifier ;
• Filmless Gen III Intensifier ;
• Gen IV Intensifier .
lp/mm:
line pairs per millimeter. A measure of resolution based on the
ability of the imaging system to differentiate between two parallel
lines. The higher the value, the finer the resolution.
lux:
The SI unit of illuminance, equal to one lumen per square meter.
MCP:
MicroChannel Plate.
Composed of cylindrical channels through which electrons from
the photocathode travel and generate additional electrons,
resulting in electron gain. At the output of the MCP is a
phosphor-coated fluorescent screen that converts the electrons
to photons that subsequently strike the CCD array and generate
charge in the array pixels.