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Smoke and Mirrors: Ultra-Rapid-Scan FT-IR Spectrometry

The maximum force which can be generated by a voice coil is simply the product of the magnetic field strength, the current in the winding, and the length of winding in the magnetic field. Practical values of these parameters lead to forces on the order of one or two Newtons. Given the 30 gram mass of a typical mirror/bearing assembly, the maximum acceleration can be readily derived. Most conventional FT-IR spectrometers are barely capable of reaching amplitudes of a few fringes of the reference laser when 1000 scans per second are required. The situation is somewhat better if bidirectional scanning is used; the scan distance is then increased by a factor of 4 to 8. This is still woefully short of the 4000 fringe scan required for 4 cm-1 resolution. The situation is even worse when coil inductance and eddy-current losses are considered.

 
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