Spectrometer Interferogram Perturbation Compensation
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Solution Overview
Problem
Spectrometer systems with scanning Fourier Transform interferometers face issues with temporally periodic perturbations, which introduce false frequency components and artefacts in the intensity spectrum, making it difficult to distinguish real signals from noise without prior knowledge of the perturbations.
Innovation Solution
The system obtains interferograms at multiple scan speeds, allowing for the identification and correction of periodic perturbations by comparing intensity spectra generated from these interferograms, and using a weighted average to generate a corrected intensity spectrum that minimizes the impact of perturbations without degrading the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a scanning FT interferometer is used for optical spectroscopy, then spectral analysis capability is provided, but temporally periodic perturbations introduce false frequency components and artefacts in the intensity spectrum
Solution Approach 1:
The patent applies periodic action by acquiring interferograms at multiple different scan speeds (different periodicities). This allows the system to sample the same spectral information at varying temporal frequencies, causing temporally periodic perturbations to manifest at different positions in the frequency domain for each scan speed. By comparing spectra from multiple scan speeds, the system can identify and eliminate artefacts caused by periodic perturbations while preserving genuine spectral features.
2Measurement precision
If multiple interferograms are acquired at different scan speeds to identify perturbations, then perturbation identification capability is improved, but measurement time increases
Solution Approach 1:
The patent implements partial action by acquiring interferograms at a small number of different scan speeds (typically 2-3 different speeds) rather than continuously varying the scan speed. This limited set of measurements is sufficient to identify temporally periodic perturbations through comparison, achieving perturbation identification without requiring excessive measurement time. The method finds an optimal balance between perturbation detection capability and measurement efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces the effect of periodic perturbations on the intensity spectrum, allowing for accurate signal recovery without degrading the signal-to-noise ratio in unaffected spectral regions.
Implementation Method 1
an observation beam consisting of relatively broad band radiation in a wavelength region of interest enters the interferometer, typically after it having interacted with a sample under observation, and strikes the beamsplitter. This observation beam is split into essentially two parts of equal intensity at the beamsplitter. A first beam is reflected by the beamsplitter and travels along a first 'arm' of the interferometer to the first reflector from where it is reflected back to the beamsplitter. A second beam is transmitted through the beamsplitter
Implementation Method 2
A first beam is reflected by the beamsplitter and travels along a first 'arm' of the interferometer to the first reflector from where it is reflected back to the beamsplitter. A second beam is transmitted through the beamsplitter and travels along a second 'arm' to the second reflector from where it is also reflected back to the beamsplitter
Implementation Method 3
The retardation, δ, is the difference between the optical path lengths of the two arms and depending on the retardation each wavelength of the spectral source may interfere destructively or constructively when the back-reflected light in the two arms overlap on the beamsplitter. The intensity pattern of the overlapping, interfering light as a function of retardation is hereinafter referred to as an observation interferogram.
Implementation Method 4
The observation interferogram is recorded by a detector as one or more of the reflectors (commonly a one of the reflectors) is/are moved at a constant speed to create cyclic excursions of the related optical path and hence a cyclic optical path length difference between the first and the second beams.
Data Source
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AI summary
A Spectrometer System and a Method for Compensating for Time Periodic Perturbations of an Interferogram generated by the Spectrometer System A spectrometer system (2) comprises a scanning interferometer (4); a drive system (6) mechanically coupled to a movable reflector element (14) of the scanning interferometer (4) and operable to effect reciprocation of the movable reflector element (14)at a plurality, preferably more than two, for example three, different scan speeds; a detector arrangement (8) configured to sample at equidistant time intervals an interferogram formed by the scanning interferometer (2) to generate a sampled interferogram; and a data processor (10) is adapted to acquire a sampled interferogram at each of the plurality of different scan speeds and to perform a relative comparison of the content of the so acquired plurality of sampled interferograms.