Understanding Infrared Thermography Reading 7 Part 2 of 2.pdf

Opto-mechanical Scanner
A typical commercial rectilinear opto-mechanical scanner is shown
schematically in Figure A-17. It employs two oscillating mirrors (reflective
scanning) behind the primary lens and is commonly used in commercially
available scanners. This approach has the advantage of a broad spectral
response limited only by the spectral characteristics of the detector and the
primary lens system. The main disadvantage is that the elements and their
associated drive mechanisms must be arranged so that there is no optical or
mechanical interference. This makes compact design more difficult. An
alternate approach to scanning employs two rotating prisms behind the
primary lens system. This instrument, using refractive scanning elements, has
the advantage of compact design, because all of the scanning elements can
be arranged in a line. It has the disadvantage of spectral limitation in that
each element must transmit the entire portion of the infrared spectrum for
which the instrument was designed. Some energy is absorbed by each
refractive element, reducing the throughput somewhat, and the rather high
cost of infrared transmitting materials add to the instrument cost. It should be
pointed out that opto-mechanical scanners can employ refractive or reflective
scanning elements or even combinations of both elements.
Charlie Chong/ Fion Zhang