Digitisation of interferograms in Fourier transform spectroscopy
First Claim
1. Apparatus for processing the output signals of a Michelson type interferometer used in Fourier Transform spectroscopy, which outputs include a waveform comprising an interferogram and a waveform representing reference interference fringes, said apparatus comprising an analogue-to-digital converter for providing a digital representation of the interferogram waveform, means for providing a fixed frequency clock signal to said analogue-to-digital converter and processing means arranged to receive the digital representation of the interferogram waveform and a digital representation of the reference fringe waveform and to process said inputs to provide a digital output representing the interferogram, wherein the waveform representing the reference fringes is applied to an input of a second fixed frequency analogue-to-digital converter to produce the digital representation of said waveform.
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Abstract
Interferograms produced by a Michelson type interferometer used in Fourier Transform spectroscopy are processed by an arrangement which includes an analogue-to-digital converter (12) which is sampled by a fixed frequency clock signal to provide a digital representation of the interferogram. This signal is processed by a digital data processor (18) which also receives a digital representation of the reference fringe waveform to provide a digital output representing the interferogram. The digital representation of the reference fringe waveform may be produced by a second analogue-to-digital converter or by a timer. The analogue-to-digital converter may be arranged to produce oversampled representations of the interferogram or reference fringe waveforms. In one form of the invention the analogue-to-digital converter or converters include a delta sigma modulator.
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Citations
26 Claims
- 1. Apparatus for processing the output signals of a Michelson type interferometer used in Fourier Transform spectroscopy, which outputs include a waveform comprising an interferogram and a waveform representing reference interference fringes, said apparatus comprising an analogue-to-digital converter for providing a digital representation of the interferogram waveform, means for providing a fixed frequency clock signal to said analogue-to-digital converter and processing means arranged to receive the digital representation of the interferogram waveform and a digital representation of the reference fringe waveform and to process said inputs to provide a digital output representing the interferogram, wherein the waveform representing the reference fringes is applied to an input of a second fixed frequency analogue-to-digital converter to produce the digital representation of said waveform.
- 15. Apparatus for processing the output signals of a Michelson type interferometer used in Fourier Transform spectroscopy, which outputs include a waveform comprising an interferogram and a waveform representing reference interference fringes, said apparatus comprising an analogue-to-digital converter for providing a digital representation of the interferogram waveform, means for providing a fixed frequency clock signal to said analogue-to-digital converter and processing means arranged to receive the digital representation of the interferogram waveform and a digital representation of the reference fringe waveform and to process said inputs to provide a digital output representing the interferogram, wherein the digital representation of the reference waveform is generated by a timer which identifies datum points of the fringes, and wherein the output of the timer is fed through a low pass digital filter.
Specification