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Understanding Infrared Thermography Reading 3

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Optomechanical Scanning<br />

To scan optomechanically in two dimensions generally requires two scanning<br />

elements. Although an almost infinite variety of scanning patterns can be<br />

generated using two moving elements. the most common pattern is rectilinear.<br />

This scanning pattern is most often accomplished by two elements, each<br />

scanning a line normal to the other. A representative rectilinear scanner is<br />

illustrated in the schematic of Figure 3.5. Its scanning mechanism comprises<br />

two oscillating mirrors behind the primary lens, a high speed horizontal<br />

scanning mirror and a slower speed vertical scanning mirror. One<br />

performance limitation of single-detector optomechanical scanners is a trade<br />

off between speed of response and signal-to-noise ratio of the detector.<br />

These instruments require high speed cooled photodetectors that are pushed<br />

to their performance limits as the desired real time scanning rate is increased.<br />

Multidetector scanners reduce the constraints on detector performance by<br />

adding detector elements that share the temporal spatial burden, allowing for<br />

faster frame rales with no reduction in signal-to-noise ratio or improving the<br />

signal-to-noise ratio with no decrease in frame rate.<br />

Charlie Chong/ Fion Zhang

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