| A novel, ultra-compact Static Imaging Fourier Transform Spectrometer, SIFTS, with no
moving parts has been developed for the remote and in-situ detection of atmospheric gases.
This technique has previously been demonstrated in the visible spectral region (400 to
1100nm) using a CCD detector. This paper the author presents the results of the infrared
version of the SIFTS instrument, which uses an uncooled microbolometer detector array to
measure infrared spectra (7 to 14μm) with a resolution of up 4 cm-1 and temporal resolution
of 30Hz.
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 the application of a Fourier
transform.
The novel optical design has reduced the optics required 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, which has shown that the spectral
resolution is for the infrared instrument is 4cm-1. The Connes advantage, inherent
to the Michelson spectrometer Fourier Transform Spectrometer (FTS), whereby
the spectral wavelength accuracy is referenced to a stabilised laser has also been
demonstrated in the SIFTS instrument. This has been implemented through the use of an
expanded internal laser diode with Distributed Bragg Reflector (DFB) which acts
as the calibration source used to maintain the wavelength stability of the SIFTS
instrument.
As there are no moving components, the instrument is compact, light and insensitive to
mechanical vibration, additionally 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. For example, this technique has shown that by using a high speed Toshiba
CCD line array, sensitive over the spectral region of 400 to 1100nm, spectra can be recorded
at a rate of one every 0.1 milliseconds.
Using an NEC infrared detector array, sensitive over the spectral region of 7 to 14μm,
low pressure gas cells of NH3 and CH4 have been measured to demonstrate the
sensitivity and wavelength accuracy of the SIFTS instrument. It has been shown
that the Signal to Noise of the SIFTS(MIR) is 524 using an integration time of 30
milliseconds.
This instrument has been developed for both remote sensing and in-situ measurements of
atmospheric gases. Due to the low mass and compact size of the instrument system, the
SIFTS instrument could be deployed as a remote sensing instrument onboard Earth
observation satellites, Unmanned Aerial Vehicles (UAV’s), or as an in-situ sensor for the
measurement of atmospheric gases. |