Infrared Fourier Transform Spectrometer Scan Speed
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Solution Overview
Problem
Conventional Fourier transform spectrometers using uncooled microbolometer detectors face challenges in rapidly collecting scans due to their relatively low sample rate, leading to ambiguous data as the scene may change during the scanning process, necessitating a method to reduce scan time without degrading spectral resolution or bandwidth.
Innovation Solution
The implementation of an infrared Fourier transform spectrometer with two detectors and a movable mirror, where pairs of pixels are sampled alternately and their data interleaved to form a higher resolution spectrum, along with the use of a color filter mosaic to suballocate the optical spectrum among pixels, allowing for faster scan completion while maintaining spectral resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the scan time is decreased by using uncooled microbolometer detectors, then the device complexity is reduced and cost is lowered, but the sample rate becomes too low causing ambiguous data when scene changes occur during scanning
Solution Approach 1:
The detector array is divided into multiple independently controllable pixel groups. By sequentially activating and reading out different pixel groups rather than reading the entire array simultaneously, the effective scan speed is increased while using the same uncooled microbolometer detector, thus resolving the contradiction between low cost and high scan speed
Solution Approach 2:
The system implements periodic scanning by alternating between different pixel groups in a cyclic manner. This periodic activation and reading of pixel subsets allows the scan time to be effectively reduced without requiring faster detector technology, maintaining compatibility with uncooled microbolometers while achieving higher productivity
2Speed
If the scan time is reduced by decreasing the optical bandwidth or degrading spectral resolution, then the scan speed increases, but the measurement precision deteriorates
Solution Approach 1:
The system dynamically adjusts the active pixel subset size and scanning parameters based on the required spectral resolution and scan speed. By adaptively controlling which pixels are active and how they are sequenced, the system can achieve high scan speeds without compromising spectral resolution, as the dynamic reconfiguration allows optimal trade-off adjustment
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 enables the collection of at least 50 samples per scan in less than 1 second, effectively doubling the sampling rate and maintaining spectral resolution, thereby reducing the likelihood of scene changes during scanning.
Implementation Method 1
taking the Fourier transform of the autocorrelation, for example using a fast Fourier transform (FFT) algorithm, results in the spectrum of the light
Implementation Method 2
a first detector at a first output, and a second detector at a second output, for detecting the light flux at the first and second outputs respectively
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A Fourier transform infrared spectrometer includes a beam splitter (22), end mirrors (21, 23), one of which may be scanned, and at least one detector (32) detecting the interfered light at one of the two outputs of a beam combiner (22), which may be the same optical element as the beam splitter (22). Time records of detector samples may be transformed by Fourier transform to obtain the corresponding spectra. The pixels of detector (32) may be sampled alternately in time and the samples subsequently interleaved to provide an increased effective sampling rate. The at least one detector (32) is masked by a color filter mosaic so that each pixel is sensitive only to one color of light, and the spectra obtained from pixels detecting different colors may be concatenated.