CN117607099A - CRDS system and method with metalon effect influence eliminating function - Google Patents
CRDS system and method with metalon effect influence eliminating function Download PDFInfo
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- CN117607099A CN117607099A CN202311586994.5A CN202311586994A CN117607099A CN 117607099 A CN117607099 A CN 117607099A CN 202311586994 A CN202311586994 A CN 202311586994A CN 117607099 A CN117607099 A CN 117607099A
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- 230000000694 effects Effects 0.000 title claims abstract description 44
- 238000000180 cavity ring-down spectroscopy Methods 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 title claims abstract description 19
- 230000003287 optical effect Effects 0.000 claims abstract description 27
- 238000004458 analytical method Methods 0.000 claims abstract description 10
- 230000008030 elimination Effects 0.000 claims abstract description 8
- 238000003379 elimination reaction Methods 0.000 claims abstract description 8
- 230000010287 polarization Effects 0.000 claims description 18
- 238000005259 measurement Methods 0.000 claims description 6
- 238000010586 diagram Methods 0.000 description 3
- 229920005560 fluorosilicone rubber Polymers 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000002310 reflectometry Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 238000001579 optical reflectometry Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
- G01N2021/392—Measuring reradiation, e.g. fluorescence, backscatter
Abstract
The invention provides a CRDS system and a CRDS method with an effect elimination function, wherein the CRDS system comprises a light source, an optical switch, an optical reflection cavity and a first detector; the beam splitting unit is used for splitting the measuring light emitted by the light source into a first light beam and a second light beam with the same light intensity; the first light beam passes through the first reflecting mirror, is reflected on the second reflecting mirror, the third reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the first detector; the second light beam passes through the first reflecting mirror, is reflected on the third reflecting mirror, the second reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the second detector; the analysis unit is used for summing the first ring-down signal output by the first detector and the second ring-down signal output by the second detector. The invention has the advantages of high resolution, small volume and the like.
Description
Technical Field
The present invention relates to cavity ring-down techniques, and more particularly to CRDS systems and methods having a metalon effect cancellation function.
Background
Currently, in a system for measuring trace gases by CRDS, the drift of concentration is one of the important indicators affecting the system performance, and the metalon effect of the CRDS optical cavity is a main factor affecting the drift. Because the reflector of the CRDS optical cavity has higher reflectivity, the multiple reflection of the light beam in the optical cavity between the high-reflectivity lenses can cause the metalon effect, and finally, sine modulation is formed at the ring-down time of signals generated by different optical cavity longitudinal modes, which has great influence on a system for obtaining the gas concentration by calculating the integral area of the absorption peak, and is reflected as sine modulation for measuring the concentration.
To mitigate and eliminate this effect of metalon, the prior art employs the following methods:
1. the method is widely used in many researches and products at present, but the traveling wave cavity cannot completely eliminate the influence of the metalon effect.
2. Typical CRDS systems only use optical cavity transmitted (forward) signals because the forward signal to noise ratio is high, the signal strength is high, and there are reflected (backward) signals that are generated by the optical components in the optical cavity due to imperfections in the optical cavity. Researches show that the effect of the metalon effect can be weakened by simultaneously collecting the forward signal and the backward beam, but in practical application, the backward signal is very weak, the signal to noise ratio is low, and the effect is not obvious in a system.
Disclosure of Invention
In order to solve the defects in the prior art scheme, the invention provides a CRDS system with an effect elimination function of the metalon.
The invention aims at realizing the following technical scheme:
the CRDS system with the effect elimination function comprises a light source, an optical switch, an optical reflection cavity and a first detector; the CRDS system with the effect of metalon effect influence elimination function further comprises:
the beam splitting unit is used for splitting the measuring light emitted by the light source into a first light beam and a second light beam with the same light intensity, and the first light beam and the second light beam are linearly polarized light with the same polarization state;
the first reflector, the second reflector and the third reflector are arranged in the light reflecting cavity; the first light beam passes through the first reflecting mirror, is reflected on the second reflecting mirror, the third reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the first detector; the second light beam passes through the first reflecting mirror, is reflected on the third reflecting mirror, the second reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the second detector;
and the analysis unit is used for summing the first ring-down signal output by the first detector and the second ring-down signal output by the second detector.
The invention also aims to provide a method for removing the influence of the metalon effect in the CRDS system, which is realized by the following technical scheme:
a method for eliminating the effect of metalon in a CRDS system comprises the following steps:
after passing through a beam splitting unit, measuring light emitted by a light source is split into a first light beam and a second light beam with the same light intensity, wherein the first light beam and the second light beam are both S or P linearly polarized light;
the first light beam and the second light beam enter the light reflecting cavity at different angles, pass through the first reflecting mirror, then are reflected on the second reflecting mirror, the third reflecting mirror and the first reflecting mirror in sequence, are reflected for a plurality of times according to the sequence, finally are emitted from the second reflecting mirror and are received by the first detector; simultaneously, the second light beam passes through the first reflecting mirror, is reflected on the third reflecting mirror, the second reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the second detector;
turning off a first light beam and a second light beam entering the light reflection cavity, wherein the first detector and the second detector respectively output ring-down signals;
the analysis unit sums the two ring down signals to eliminate the effect of the metalon.
Compared with the prior art, the invention has the following beneficial effects:
the effect of eliminating the effect of the metalon is good;
the first light beam and the second light beam with the same intensity and polarization state enter the first reflecting mirror of the light reflecting cavity at different angles, then the opposite directions are reflected on the three reflecting mirrors, the light is respectively emitted from the second reflecting mirror after being reflected for a plurality of times, after the light is turned off, ring-down signals with the same intensity and pi phase difference are output by the first detector and the second detector, and the influence of the metalon effect is removed through summation;
the signal-to-noise ratio for eliminating the influence of the metalon effect is high, and the detection limit of trace gas is lower;
2. the structure is simple;
the beam splitting unit, the optical switch, the detector, the analysis unit and the like adopted in the CRDS system are all conventional components, and the device has a simple structure and good reliability.
Drawings
The present disclosure will become more readily understood with reference to the accompanying drawings. As will be readily appreciated by those skilled in the art: the drawings are only for illustrating the technical scheme of the present invention and are not intended to limit the scope of the present invention. In the figure:
FIG. 1 is a schematic diagram of a CRDS system with an effect of metalon cancellation function according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of two ring down signal summation in accordance with an embodiment of the present invention;
fig. 3 is a schematic diagram of the effect of eliminating the effect of the metalon effect according to an embodiment of the present invention.
Detailed Description
Figures 1-3 and the following description depict alternative embodiments of the invention to teach those skilled in the art how to make and reproduce the invention. In order to teach the technical solution of the present invention, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations or alternatives derived from these specific embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. Thus, the invention is not limited to the following alternative embodiments, but only by the claims and their equivalents.
Example 1
The embodiment of the invention provides a CRDS system with an effect elimination function, as shown in FIG. 1, the CRDS system with an effect elimination function comprises:
the light source 11, the optical switch 21 and the first detector 51, all of which are known in the art in the field of CRDS;
a beam splitting unit 31, where the beam splitting unit 31 is configured to split the measurement light emitted by the light source 11 into a first light beam 39 and a second light beam 38 with the same light intensity, and the first light beam 39 and the second light beam 38 are linearly polarized light with the same polarization state;
a first mirror 41, a second mirror 42 and a third mirror 43, said first mirror 41, second mirror 42 and third mirror 43 being arranged within said light reflecting cavity 40; the first light beam 39 passes through the first reflecting mirror 41, is reflected on the second reflecting mirror 42, the third reflecting mirror 43 and the first reflecting mirror 41 in this order, is reflected for a plurality of times in this order, and finally exits from the second reflecting mirror 42 to be received by the first detector 51; the second light beam 38 passes through the first mirror 41, is reflected on the third mirror 43, the second mirror 42 and the first mirror 41 in this order, is reflected a plurality of times in this order, and finally exits the second mirror 42 to be received by the second detector 52;
an analysis unit 61, the analysis unit 61 is configured to sum the first ring-down signal output by the first detector 51 and the second ring-down signal output by the second detector 52, as shown in fig. 2.
In order to obtain a first light beam 39 and a second light beam 38 having the same light intensity and polarization, the beam splitting unit 31 further comprises:
a first half-wave plate 32 and a polarization beam splitter prism 33, the measurement light passing through the first half-wave plate 32, and then a first light beam 39 and a second light beam 38 being split on the polarization beam splitter prism 33;
the second beam 38 passes through the second half-wave plate 34 and then enters the light reflecting cavity.
In order to obtain a first light beam 39 and a second light beam 38 with the same light intensity and polarization, further, the measuring light is S or P linearly polarized light, and the beam splitting unit 31 comprises a half mirror.
In order to obtain a greater number of reflections between the three mirrors, further, the first mirror 41 and the second mirror 42 are symmetrically arranged with respect to a normal on the third mirror 43, the third mirror 43 being a concave mirror.
In order to control whether light enters the light reflecting cavity, further, the optical switch 21 is disposed on the optical path between the light source 11 and the beam splitting unit 31.
The method for eliminating the effect influence of the metalon in the CRDS system comprises the following steps:
after the measuring light emitted by the light source 11 passes through the beam splitting unit 31, a first light beam 39 and a second light beam 38 with the same light intensity are split, and the first light beam 39 and the second light beam 38 are both linearly polarized light of S or P;
the first light beam 39 and the second light beam 38 enter the light reflecting cavity 40 at different angles, the first light beam 39 passes through the first reflecting mirror 41, then is reflected on the second reflecting mirror 42, the third reflecting mirror 43 and the first reflecting mirror 41 in sequence, and is reflected for a plurality of times in sequence, and finally is emitted from the second reflecting mirror 42 and is received by the first detector 51; meanwhile, the second light beam 38 passes through the first reflecting mirror 41, is reflected on the third reflecting mirror 43, the second reflecting mirror 42 and the first reflecting mirror 41 in sequence, is reflected for a plurality of times in this sequence, and finally is emitted from the second reflecting mirror 42 and received by the second detector 52;
turning off the first light beam 39 and the second light beam 38 entering the light reflection cavity 40, and the first detector 51 and the second detector 52 output ring-down signals, respectively;
the analysis unit 61 sums the two ring down signals as shown in fig. 2, thereby eliminating the effect of the metalon.
In order to obtain a first light beam 39 and a second light beam 38 with the same light intensity and polarization state, further, the linearly polarized light emitted by the light source 11 sequentially passes through the first half-wave plate 32 and the polarization splitting prism 33, the split second light beam 38 passes through the second half-wave plate 34 and then enters the light reflecting cavity, and the split first light beam 39 enters the light reflecting cavity 40;
the first half wave plate 32 is rotated such that the light intensities of the first light beam 39 and the second light beam 38 entering the light reflecting cavity 40 are the same.
In order to obtain the first light beam 39 and the second light beam 38 with the same light intensity and polarization state, further, the linearly polarized light emitted by the light source 11 passes through the half mirror, and the intensities of the split first light beam 39 and the split second light beam 38 are the same.
In order to control whether light enters the light reflecting cavity, further, an optical switch 21 is provided between the light source 11 and the beam splitting unit 31 to control whether light enters the light reflecting cavity 40.
In order to obtain a greater number of reflections between the three mirrors, further, the first mirror 41 and the second mirror 42 are symmetrically arranged with respect to a normal on the third mirror 43, the third mirror 43 being a concave mirror.
Example 2
Application examples of CRDS systems and methods with an effect of metalon cancellation function according to embodiments of the present invention.
In this application example, as shown in fig. 1, a light source 11, an optical switch 21, and a beam splitting unit 31 are sequentially provided, the light source 11 is a semiconductor laser, S linearly polarized light is output, and the optical switch 21 is an acousto-optic crystal, and controls whether or not light passes through. In the beam splitting unit 31, the first half-wave plate 32, the polarization splitting prism 33 and the second half-wave plate 34 are sequentially arranged, the polarization splitting prism 33 splits the first light beam 39 into S-polarized light and the second light beam 38 into P-polarized light, but the S-polarized light is converted after passing through the second half-wave plate 34, and the first half-wave plate 32 is rotated to make the light intensities of the first light beam 39 and the second light beam 38, which is the S-polarized light, identical, and the polarization states are also identical. The second light beam is reflected by the fourth mirror 35 and the fifth mirror 36 in order and then is incident into the light reflecting cavity 40.
In the light reflecting cavity 40, the first reflecting mirror 41 and the second reflecting mirror 42 are symmetrical with respect to the third reflecting mirror 43, the inner surface is coated with a film, the light reflectivity of the 1603nm wave band is 99.995%, and the outer surface is coated with a high-transmittance film; the included angle between the first mirror 41 and the second mirror 42 is 44.4 degrees; the first mirror 41 and the second mirror 42 are plane mirrors, the third mirror 43 is a concave mirror, and the radius of curvature of the concave surface is 1m. The optical path of the first beam 39 and the second beam 38 traveling one revolution between the three mirrors is 480mm.
The first detector 51 and the second detector 52 employ PD, respectively.
The method for eliminating the effect of the metalon in the CRDS, namely the working method of the CRDS with the effect eliminating function of the metalon, comprises the following steps:
the measuring light (linearly polarized light) emitted from the light source 11 passes through the optical switch 21 and then enters the beam splitting unit 31;
in the beam splitting unit 31, the measurement light passes through the first half-wave plate 32 and then enters the polarization splitting prism 33, the split first light beam 39 is S polarized light, and the second light beam 38 is P polarized light, but the measurement light passes through the second half-wave plate 34 and then is converted into S polarized light, and then is reflected by the fourth reflecting mirror 35 and the fifth reflecting mirror 36 in sequence and then enters the light reflecting cavity 40. By rotating the first half wave plate 32, the light intensity of the first light beam 39 and the second light beam 38, which becomes S-polarized light, is made the same.
The first light beam 39 and the second light beam 38 enter the light reflecting cavity 40 at different angles, the first light beam 39 passes through the first reflecting mirror 41, then is reflected on the second reflecting mirror 42, the third reflecting mirror 43 and the first reflecting mirror 41 in sequence, is reflected for a plurality of times in this sequence, finally passes through the second reflecting mirror 42 and is received by the first detector 51; meanwhile, the second light beam 38 passes through the first reflecting mirror 41, then sequentially reflects on the third reflecting mirror 43, the second reflecting mirror 42 and the first reflecting mirror 41, and then passes through the second reflecting mirror 42 and is received by the second detector 52 after being reflected multiple times in this order;
with the optical switch 21 turned off the measurement light, no light enters the light reflecting cavity 40, and the first detector 51 receives the first ring down signal, and the ring down time Tau for the continuous 50 FSRs exhibits a sinusoidal distribution of phase k by scanning the current point.
At the same time, second detector 52 receives the second ring down signal and, by scanning the current point, the ring down time Tau for the successive 50 FSRs assumes a sinusoidal distribution with a phase (k + pi).
The analysis unit 61 sums the first ring-down signal and the second ring-down signal, the sinusoidal distribution of the ring-down time Tau of the two ring-down signals has exactly equal signal strength, phase difference pi, and the two ring-down signals are cancelled after the addition, so that the effect of the metalon can be basically eliminated, as shown in fig. 2.
In fig. 2, the abscissa is the laser current point corresponding to every other FSR ring down signal, the ordinate is the processed Loss (inversely related to Tau), the sinusoidal phases of the first ring down signal and the second ring down signal are exactly opposite, and a flatter curve that eliminates metalon can be obtained after the signals are added together at the same light intensities of the first beam 39 and the second beam 38. Sinusoidal irregular protrusions are derived from single-point fluctuations, uneven coating of the endoscope, unremoved absorption, and other factors.
As shown in fig. 3, the upper curve is the allen variance of only the data corresponding to the second ring-down signal, and the lower curve is the allen variance of the two superimposed ring-down signals, so that it can be concluded that not only the starting position of the single point precision is optimized, but also the average time is optimized.
Example 3
An application example of the CRDS system and method with the effect of metalon influence cancellation function according to the embodiment of the present invention is different from embodiment 2 in that:
the beam splitting unit is internally provided with a half-mirror to replace the first half-wave plate 32, the polarization beam splitting prism 33 and the second half-wave plate 34, and after the linearly polarized light emitted by the light source 11 passes through the half-mirror, the reflected first light beam 39 and the transmitted second light beam 38 are split, and the light intensities are the same.
Claims (10)
1. The CRDS system with the effect elimination function comprises a light source, an optical switch, an optical reflection cavity and a first detector; the CRDS system with the effect elimination function of the metalon is characterized by further comprising:
the beam splitting unit is used for splitting the measuring light emitted by the light source into a first light beam and a second light beam with the same light intensity, and the first light beam and the second light beam are linearly polarized light with the same polarization state;
the first reflector, the second reflector and the third reflector are arranged in the light reflecting cavity; the first light beam passes through the first reflecting mirror, is reflected on the second reflecting mirror, the third reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the first detector; the second light beam passes through the first reflecting mirror, is reflected on the third reflecting mirror, the second reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the second detector;
and the analysis unit is used for summing the first ring-down signal output by the first detector and the second ring-down signal output by the second detector.
2. The CRDS system with the metalon effect influence eliminating function according to claim 1, wherein the beam splitting unit comprises:
the measuring light passes through the first half wave plate and then is split into a first light beam and a second light beam on the polarization beam splitting prism;
and the second light beam passes through the second half-wave plate and then enters the light reflection cavity.
3. The CRDS system with the effect-on-effect cancellation function according to claim 1, wherein the measurement light is S or P linearly polarized light, and the beam splitting unit comprises a half mirror.
4. The CRDS system with the metalon effect cancellation function according to claim 1, wherein the first and second mirrors are symmetrically disposed about a normal on the third mirror, which is a concave mirror.
5. The CRDS system with the metalon effect influence eliminating function according to claim 1, wherein the optical switch is provided on an optical path between the light source and the beam splitting unit.
6. A method for eliminating the effect of metalon in a CRDS system comprises the following steps:
after passing through a beam splitting unit, measuring light emitted by a light source is split into a first light beam and a second light beam with the same light intensity, wherein the first light beam and the second light beam are both S or P linearly polarized light;
the first light beam and the second light beam enter the light reflecting cavity at different angles, pass through the first reflecting mirror, then are reflected on the second reflecting mirror, the third reflecting mirror and the first reflecting mirror in sequence, are reflected for a plurality of times according to the sequence, finally are emitted from the second reflecting mirror and are received by the first detector; simultaneously, the second light beam passes through the first reflecting mirror, is reflected on the third reflecting mirror, the second reflecting mirror and the first reflecting mirror in sequence, is reflected for a plurality of times according to the sequence, and finally is emitted from the second reflecting mirror to be received by the second detector;
turning off a first light beam and a second light beam entering the light reflection cavity, wherein the first detector and the second detector respectively output ring-down signals;
the analysis unit sums the two ring down signals to eliminate the effect of the metalon.
7. The method of eliminating the effect of metalon in a CRDS system according to claim 6, wherein the linearly polarized light from the light source passes through the first half-wave plate and the polarization splitting prism in sequence, the split first light beam passes through the second half-wave plate and then enters the light reflecting cavity, and the split second light beam enters the light reflecting cavity;
the first half-wave plate is rotated so that the light intensities of the first and second light beams entering the light reflecting cavity are the same.
8. The method of claim 6, wherein the first and second light beams are split to have the same intensity after the linearly polarized light from the light source passes through the half mirror.
9. The method of claim 6, wherein an optical switch is disposed between the light source and the beam splitting unit to control whether light enters the light reflecting cavity.
10. The method of eliminating the effect of metalon in a CRDS system according to claim 6, wherein the first mirror and the second mirror are symmetrically disposed about a normal on the third mirror, the third mirror being a concave mirror.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311586994.5A CN117607099A (en) | 2023-11-27 | 2023-11-27 | CRDS system and method with metalon effect influence eliminating function |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311586994.5A CN117607099A (en) | 2023-11-27 | 2023-11-27 | CRDS system and method with metalon effect influence eliminating function |
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| CN117607099A true CN117607099A (en) | 2024-02-27 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202311586994.5A Pending CN117607099A (en) | 2023-11-27 | 2023-11-27 | CRDS system and method with metalon effect influence eliminating function |
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| CN (1) | CN117607099A (en) |
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- 2023-11-27 CN CN202311586994.5A patent/CN117607099A/en active Pending
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