Biomedical Engineering Reference
In-Depth Information
Rise
time
Irradiance λ 0
625 MHz
Clock
Strat channel
Si PD
Stop channel
Si PD
Fiber delay lines
AOA
Quad
detector
70 mm F/I
Holographic grating
40 nm mm -1 dispersion
Linear
PD
FIGURE 4.31
LWR schematic.
General baseline capabilities might be the following: low false alarm rate,
large field of coverage, early warning time (high sensitivity), low visible pro-
file, low radar and optical cross sections, low or zero emissions, ruggedness,
and mounting configuration flexibility. Nonimaging LWR systems may have
panoramic coverage, but offer only limited directional resolution (typically
between 15° and 90°). Interferometric configurations have the ability to test
temporal and/or spatial coherence, and potentially to provide both bearing
and wavelength data at medium resolution over a reasonable field of view.
Difficulties with these systems include the analysis of complex fringe patterns,
which may be of poor visibility, particularly under high ambient lighting
conditions.
In an imaging LWR, incident laser radiation on the field of view is focused
to a spot in an image. The bearing of a detected threat laser can be obtained
directly from the location of the spot in the image of the scene. Note that
because of the short laser pulse durations, the use of essentially staring rather
than scanned sensors is necessary. Such systems do not provide any wave-
length output, and temporal information is usually lost with conventional
 
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