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Surfaces
Macken Instruments' Model 24 makes use of three different
types of IR-sensitive surfaces to cover the varied near IR
laser display requirements.
Surface #1 is primarily designed for use with YAG Lasers.
When illuminated by an ultraviolet lamp, this surface
fluoresces a bright green. Striking the fluorescing surface
with near IR light induces a transition which results in a
quenching of the fluorescence. Therefore, the IR beam is
displayed as a dark image on a bright fluorescent
background. The sensitivity of this surface can be varied
over a wide range by changing the intensity of the UV
illumination; i.e, the distance of the UV lamp from the
surface. The response time also depends on the UV
illumination but is typically less than 10 milliseconds.
This fast a response time is well suited for viewing rapidly
changing YAG mode patterns; however, such a recovery time is
too rapid to view a single pulsed laser.
Surface #2 is designed to be used with pulsed neodymium and
other pulsed IR lasers. This surface fluoresces a bright
green. Like surface #1, IR quenching produces a dark image
display on a bright background. However, this surface has a
much longer decay time which is ideally suited for viewing
pulsed lasers. Depending on the illumination conditions, the
image retention time can be varied from one tenth of a
second to several minutes. The more intense the UV
illumination, the shorter the persistence. When no UV
illumination is used, and when the background illumination
is dimmed, the phosphorescence of the surface will retain
the laser beam pattern for several minutes.
Surface #3 is used primarily for viewing gallium arsenide
light-emitting diodes and for probing CW YAG laser beams.
This surface operates on a different principle than
previously described. Energy is stored in the phosphor
surface when it is exposed to fluorescent room lights or UV
light. Near IR radiation stimulates the release of this
energy as yell-orange light. Consequently, the beam appears
as a bright image on a dark background. After the phosphors
have absorbed a given amount of IR energy, the surface can
become depleted. The beam must then be moved to a new area
of the surface or the surfaced recharged.
All plate and imaging surfaces have a matte finish for safe
beam displays.
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