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Design and Performance of a Hadamard Transform Infrared Spectrometer with No Moving Parts

Volume 49, Number 9 (Sept. 1995) Page 1338-1346

Tilotta, David C.; Zhou, Zhou

The development of an improved Hadamard transform infrared (HT-IR) spectrometer with no moving optical parts is described. This spectrometer is based on a thermo-optic array for the stationary encoding of radiation (TOASTER) fabricated from Nichrome resistance wire. The TOASTER HT-IR instrument utilizes a reversed Czerny-Turner optical mount and relies on entrance focal plane modulation for operation. This design allows the dedispersion optics to be eliminated while still providing for a multiplex advantage. In addition, a conventional mechanical chopper is not needed in this instrument because the TOASTER is used as a natural modulator. The TOASTER HT-IR spectrometer can acquire an infrared spectrum in the range of 2.5 to 11 μm (4000 to 910 cm-1). Its spectral resolution is 0.07 μm (~7 cm-1 at 1000 cm-1), and, for fifteen spectral resolution elements, the observation window is 0.5 μm (~48 cm-1 at 1000 cm-1). In addition to the design of the instrument, this communication also examines the thermo-optic switching properties of the Nichrome wire used in the prototype TOASTER. Although the maximum switching speed of the Nichrome wire is governed by its thermal decay time, we show that the TOASTER can be operated faster than this limit by employing a preheating step.