Ultra-compact imaging Fourier transform spectrometer for the measurement of atmospheric trace gases

Ultra-compact imaging Fourier transform spectrometer for the measurement of atmospheric trace gases.

 

A novel, ultra-compact (<1 in³) Static Imaging Fourier Transform Spectrometer, SIFTS, with no moving parts has been developed for the detection of atmospheric gases. The instrument has been shown to have high spectral resolution (4 cm^-1) and temporal resolution (10kHz) resolution in both the mid and near infrared and moderate spectral resolution (14cm^-1) in the visible.

This instrument has been developed for the remote sensing and in-situ measurements of atmospheric gases. It has been identified that due to the low mass and compact size of the instrument system, that the SIFTS could be deployed as a remote sensing instrument onboard a Earth Observation satellite or Unmanned Aerial Vehicle (UAV), or conversely as a radiosonde instrument for in-situ measurements of atmospheric gases.

The technique is based on a static optical configuration whereby light is split into two paths and made to recombine along a focal plane producing an interference pattern. The spectral information is returned using a detector array to digitally capture the interferogram which can then be processed into a spectrum by applying a Fourier transform.

As there are no moving components, the speed of measurement is determined by the frame rate of the detector array. Thus, this instrument has a temporal advantage over common Michelson FTIR instruments. Using a high speed Toshiba CCD line array, sensitive over the spectral region of 400 – 1100nm, spectra have been recorded at a rate of one every 100 microseconds.

Using a SELEX infrared detector array, sensitive over the spectral region of 7 to 10μm, the gases NH₃, O₃ and CH₄ have been used to demonstrate the sensitivity of the SIFTS instrument. It has been shown that the Signal to Noise of the SIFTS_MIR is 524 using an integration time of 77msec.

The novel optical design has reduced the optics to only 3 optical components, and the detector array, to generate and measure the interferogram. The experimental performance of the SIFTS instrument has verified the theoretical models, and it has been shown that the spectral resolution in both the Visible and MIR instruments is 4cm^-1 and 14cm^-1 respectively. These verification measurements were determined by measuring the instrument line shape of the instrument using HeNe laser (632.816 nm) for the SIFTS_VIS instrument and a reference CH₄ gas cell for the SIFTS_MIR.