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Development of Electrical Substitution Fourier Transform Spectrometry for Absolute Optical Power Measurements



Jorge Neira, Solomon I. Woods, James E. Proctor, Joseph P. Rice


We have demonstrated the first continuous-scan Electrical Substitution Fourier Transform Spectrometer (ES-FTS), which serves initially as an apparatus for absolute spectral responsivity calibrations of detectors over the wavelength range from 1.5 µm to 11 µm. The goal is to develop a spectral-comparator system for high accuracy, high dynamic range, high spectral resolution and fast measurement in the infrared region which can be tied directly to an absolute power scale through electrical substitution. The ES-FTS apparatus employs a commercial Fourier transform spectrometer and a custom electrical substitution bolometer detector to enable spectrally-resolved absolute optical power measurements. A generalization of electrical substitution techniques enables determination of the voltage waveform which must be applied to the bolometer's electrical heater to cancel the optical signal from a Michelson interferometer, in order to quantify the time-dependent optical power incident on the bolometer. The noise floor of the electrical substitution bolometer is on the order of 10 pW/Hz½ and its response is expected to be linear from the noise floor to 1 mW. A direct comparison between a pyroelectric standard detector and the Electrical Substitution Fourier Transform Spectrometer has been performed, and experimental results reported here show the great potential for this technique.
Optics Express


FTIR, electrical substitution, bolometer, ACR, infrared spectrometer


Neira, J. , Woods, S. , Proctor, J. and Rice, J. (2021), Development of Electrical Substitution Fourier Transform Spectrometry for Absolute Optical Power Measurements, Optics Express, [online],, (Accessed June 22, 2024)


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Created October 27, 2021, Updated November 29, 2022