FT Spectrometer Calibration Detector for Stable Frequency Axis
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Solution Overview
Problem
Existing FT spectrometers face challenges in achieving high measuring accuracy and availability due to wavelength instability of laser diodes and oblique incidence of reference laser light, which distort the spectrum and require interruptions for calibration measurements.
Innovation Solution
The FT spectrometer arrangement employs retro-reflectors and additional detectors to allow simultaneous data acquisition for sample and calibration information without interrupting the measurement, using a calibration substance in the light path to determine a calibration factor that corrects for wavelength instability and oblique incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If laser diodes are used as reference lasers, then the device becomes more compact and durable, but wavelength stability deteriorates
Solution Approach 1:
An additional detector is introduced as an intermediary component to measure a partial beam that has passed through the interferometer but not the measurement position. This detector provides calibration data that mediates between the unstable laser diode wavelength and the required spectral accuracy, enabling continuous wavelength correction without interrupting measurements.
2Measurement precision
If calibration measurements are performed to correct wavelength drift, then measurement accuracy is improved, but measurement availability deteriorates due to interruptions
Solution Approach 1:
The additional detector operates continuously alongside the main measurement detector, enabling calibration measurements to be performed simultaneously with sample measurements. This continuous operation eliminates interruptions and maintains measurement availability while ensuring spectral accuracy through ongoing wavelength calibration.
Solution Approach 2:
The light beam is segmented into two paths: one passing through the measurement position to the main detector for sample analysis, and another partial beam passing through the interferometer but bypassing the measurement position to the additional detector for calibration. This segmentation allows both measurement and calibration to proceed concurrently without interference.
3Ease of operation
If reference laser light enters oblique to the interferometer, then alignment simplicity is improved, but frequency axis accuracy deteriorates
Solution Approach 1:
The additional detector provides continuous feedback on the actual wavelength of the reference laser by measuring the partial beam. This feedback enables real-time detection and correction of frequency axis deviations caused by oblique incidence, maintaining spectral accuracy despite simplified alignment conditions.
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 high-accuracy, continuous calibration without interrupting measurements, maintaining the FT spectrometer's availability and improving the signal-to-noise ratio, allowing for precise spectrum calibration and enhanced measurement accuracy.
Implementation Method 1
the reflectors are designed as retro-reflectors
Implementation Method 2
broadband light, for example infrared (IR) light, is split into two partial beams in an interferometer
Implementation Method 3
The superimposed partial beams cause interference, which, depending on the path difference and the frequency of the light, leads to a reduction or increase in the irradiance on the detector
Implementation Method 4
a detector for the light... with the detector another partial beam of light which has passed the interferometer and the measurement position can be measured
Implementation Method 5
a reference laser with which the reference laser light is passed through the interferometer... To accurately determine the path difference, it is advantageous to know the exact laser wavelength of the reference laser
Implementation Method 6
an additional detector is provided with which a partial beam of light can be measured which has passed the interferometer but not the measurement position... enables high-accuracy, continuous calibration without interrupting measurements
Data Source
Figure 1
Figure 2~3
Figure 4a~5
AI summary
The invention relates to a FT spectrometer assembly (1), comprising: - a light source (2) for light (3), - an interferometer (5) having at least one beam splitter (6) and two interferometer arms (9, 10), by which the light (3) of the light source (2) is guided, each of the interferometer arms (9, 10) having a reflector (7, 8), - a measurement sample (12a) at a measurement position (12), - a detector (13) for the light (3), the measurement position (12) being disposed in the beam path of the light (3) between the interferometer (5) and the detector (13), - a device (11) for changing an optical path difference (GU) between the two interferometers (9, 10), - a reference laser (22), by which reference laser light (23) is guided through the interferometer (5), and - at least one reference detector (26) for measuring the reference laser light (23), the reference detector (26) being disposed in the beam path of the reference laser light (23) behind the interferometer (5). The spectrometer assembly is characterised in that an additional detector (14) is also provided, by means of which it is possible to measure a sub-beam (17) of the light (3) that has passed the interferometer (5) but has not passed the measurement position (12), and in that a further sub-beam (18) of the light (3) that has passed the interferometer (5) and has passed the measurement position (12) can be measured by the detector (13) concurrently with a measurement of the sub-beam (17) at the additional detector (14). The invention allows a high degree of measurement accuracy to be achieved in a simple manner with a high degree of availability of the FR spectrometer assembly.