Laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring

Abstract

The invention discloses a laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring, which utilizes a wavelength meter for detection and comprises the following steps: a combined laser beam passes through a collimator and is split by a spectroscope I; part of the laser is reflected by half of the FP etalon and then enters the detector I after being focused by the convex lens I; the other part of laser is split by a spectroscope II after being projected; part of laser after secondary light splitting passes through the other half of the FP etalon, is focused by a convex lens II and then enters a detector II; the other part of laser projection is reflected by a reflector, focused by a convex lens III and then enters a detector III; the detector I, the detector II and the detector III are used for obtaining detection results. According to the invention, the accuracy and long-term stability of the laser wavelength in cavity ring-down spectroscopy monitoring are ensured.

Description

[0001] The present invention belongs to the technical field of spectrum detection, and in particular relates to a laser wavelength detection optimization method for cavity ring-down spectrum monitoring. Background Art

[0002] Cavity Ring-Down Spectroscopy (CRDS) is a highly sensitive spectroscopic method that can be used to measure the absolute optical extinction of a sample, including both light scattering and absorption. It has been widely used to detect the absorption of gaseous samples at specific wavelengths and to determine the mole fraction of a sample at the parts-per-trillion level.

[0003] A typical cavity ring-down spectroscopy setup consists of a laser source illuminating a high-finesse optical resonator and two highly reflective mirrors that frame the cavity. When the laser and cavity modes resonate, the light intensity within the cavity rapidly increases due to constructive interference. The laser is then quickly switched off, allowing the exponential decay of the light escaping the cavity to be detected. During this decay, the light is reflected back and forth between the mirrors thousands of times, resulting in an effective absorption path length of several to tens of kilometers.

[0004] CRDS technology offers advantages such as being unaffected by fluctuations in laser intensity, a long laser-medium interaction path, high detection accuracy, no calibration required, simple setup, and easy operation. However, it also places higher demands on the accuracy and stability of the laser wavelength. Because the laser wavelength is extremely sensitive to ambient temperature, simple temperature control is a semi-closed-loop method that cannot precisely control the wavelength. Furthermore, laser wavelength drifts due to power output fluctuations, all of which affect the accuracy and long-term stability of intensity ring-down spectroscopy monitoring. Summary of the Invention

[0005] In order to solve the above problems, the present invention proposes a laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring, which ensures the accuracy and long-term stability of the laser wavelength in cavity ring-down spectroscopy monitoring.

[0006] To achieve the above object, the present invention adopts a technical solution: a laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring, which uses a wavelength meter for detection, comprising the steps of:

[0007] The combined laser beam passes through the collimator and is split by the beam splitter I;

[0008] Part of the laser light is reflected and passes through half of the FP etalon, then is focused by convex lens I and enters detector I.

[0009] Another part of the laser is projected and split by the spectroscope II. After the second split, the laser passes through the other half of the FP etalon and is focused by the convex lens II before entering the detector II. Another part of the laser is projected and reflected by the reflector, focused by the convex lens III before entering the detector III.

[0010] The detection results are obtained using detectors I, II and III.

[0011] Furthermore, the combined laser beam passes through a collimator and is split by a beam splitter I in a ratio of 70:30; 30% of the laser light is reflected by half of the FP standard device and then focused by a convex lens I before entering a detector I; 70% of the laser light is projected and then split by a beam splitter II in a ratio of 50:50; half of the laser light passes through the other half of the FP standard device and then is focused by a convex lens II before entering a detector II; the other half of the laser light is projected, reflected by a reflector, and then focused by a convex lens III before entering a detector III.

[0012] Furthermore, a temperature measuring resistor is provided on the FP etalon.

[0013] Furthermore, the FP etalon adopts low-expansion glass-ceramics.

[0014] Furthermore, the collimator is embedded in the through hole of the side wall of the housing through a collimator seat.

[0015] Furthermore, the detectors I, II and III are embedded in the opening of the side wall of the housing through a detector seat.

[0016] Furthermore, the beam splitter I, beam splitter II, reflector, FP etalon, convex lens I, convex lens II and convex lens III are all fixed in the housing by using ultraviolet low-stress curing adhesive.

[0017] Furthermore, it also includes:

[0018] The constant temperature control box carrying the wavelength meter includes an upper cover, a bottom cover, a side cover, a front cover and a rear cover which are connected to form a box body; each cover is provided with a heat-insulating layer;

[0019] A semiconductor temperature-controlled air conditioner is provided on the thermal insulation front cover.

[0020] Furthermore, a windshield is provided around the wave meter, and the windshield is provided with three vertical plates and one opening; the windshield is fixed to the electric control board, and the electric control board is fixed to the bottom plate of the constant temperature control box through a support column.

[0021] Furthermore, the wavelength meter is fixed to the wavelength meter base plate through a fixing seat and a clamping head. The fixing seat and the clamping head are made of PEK material with low thermal conductivity, and the wavelength meter base plate is made of 4J29 Kovar alloy steel.

[0022] The beneficial effects of adopting this technical solution are:

[0023] Since the FP etalon has two blind areas, the top and the bottom, when measuring wavelength, the laser wavelength given in the CRDS cavity ring-down system is a given wavelength. The present invention can effectively avoid blind areas by using two wavelength response curves of transmittance. When the laser wavelength falls within the blind area of one curve, the other curve must be within the non-blind area, thereby realizing closed-loop monitoring and adjustment of the wavelength, ensuring continuous and accurate measurement of multiple wavelengths, and ensuring the accuracy and long-term stability of the laser wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the principle of a laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to the present invention;

[0025] Figure 2 Schematic diagram of the structure of a constant temperature control box carrying a wavelength meter in an embodiment of the present invention;

[0026] Figure 3 Schematic diagram of the relationship between the transmittance of the FP etalon and the incident angle and wavelength in an embodiment of the present invention, wherein (a) shows the trend of the transmittance changing with increasing angle, and (b) shows the wavelength response curve of the transmittance;

[0027] Figure 4 This is a curve after spectroscopic processing in an embodiment of the present invention.

[0028] Among them, 1 is a wavelength meter, 11 is a housing, 12 is a collimator, 13 is a spectroscope I, 14 is a spectroscope II, 15 is a reflector, 16 is an FP standard tool, 17 is a convex lens I, 18 is a convex lens II, 19 is a convex lens III, 20 is a detector I, 21 is a detector II, 22 is a detector III, 23 is a temperature measuring resistor, 24 is a collimator seat, 25 is a detector seat; 31 is an upper cover, 32 is a bottom cover, 33 is a side cover, 34 is a front cover, 35 is a rear cover, 36 is a temperature control air conditioner, 37 is an electric control panel, and 38 is a windshield. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described below with reference to the accompanying drawings.

[0030] In this embodiment, see Figure 1 As shown, the present invention proposes a laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring, which uses a wavelength meter for detection, including the steps of:

[0031] The combined laser beam passes through the collimator and is split by the beam splitter I;

[0032] Part of the laser light is reflected and passes through half of the FP etalon, then is focused by convex lens I and enters detector I.

[0033] Another part of the laser is projected and split by the spectroscope II. After the second split, the laser passes through the other half of the FP etalon and is focused by the convex lens II before entering the detector II. Another part of the laser is projected and reflected by the reflector, focused by the convex lens III before entering the detector III.

[0034] The detection results are obtained using detectors I, II and III.

[0035] Among them, such as Figure 1 As shown, the wavelength meter includes a housing, and a collimator, a beam splitter I, a beam splitter II, a reflector, an FP etalon, a convex lens I, a convex lens II, a convex lens III, a detector I, a detector II and a detector III placed in the housing;

[0036] The collimator is placed on the housing, and a beam splitter I, a beam splitter II and a reflector are sequentially arranged on the extension line of the central axis of the collimator, wherein the beam splitter I, the beam splitter II and the reflector are arranged at an oblique angle;

[0037] A beam splitter II is provided on an extension line of the first beam splitting light path of the beam splitter I, and a convex lens I and a detector I are provided on an extension line of the second beam splitting light path of the beam splitter I;

[0038] A reflector is provided on an extension line of the first splitting light path of the beam splitter II, and a convex lens II and a detector II are provided on an extension line of the second splitting light path of the beam splitter II.

[0039] A convex lens III and a detector III are provided on an extension line of the reflection path of the reflector;

[0040] Detector I, detector II and detector III are all arranged on the housing;

[0041] A portion of the FP etalon is placed between the beam splitter I and the convex lens I, and another portion of the FP etalon is placed between the beam splitter II and the convex lens II.

[0042] Preferably, the combined laser beam passes through a collimator and is split by a beam splitter I in a ratio of 70:30; 30% of the laser light is reflected by half of the FP standard device and then focused by a convex lens I before entering a detector I; 70% of the laser light is projected and then split by a beam splitter II in a ratio of 50:50; half of the laser light passes through the other half of the FP standard device and then is focused by a convex lens II before entering a detector II; the other half of the laser light is projected, reflected by a reflector, and then focused by a convex lens III before entering a detector III.

[0043] A beam splitter with a transmission-reflection ratio of 70:30, a beam splitter with a transmission-reflection ratio of 50:50, and a reflector are used to obtain a laser beam splitting ratio of 30:35:35, respectively, thereby obtaining the transmittance wavelength response curves of the two paths passing through the etalon.

[0044] As an optimization solution of the above embodiment, a temperature measuring resistor is provided on the FP etalon to perform real-time temperature measurement.

[0045] Preferably, the FP etalon uses low-expansion glass-ceramics to ensure the stability of wavelength measurement.

[0046] A FP standard was used to obtain the transmittance response curve with a phase difference of π / 2 at different incident angles.

[0047] Preferably, the collimator is embedded in the through hole of the side wall of the housing through a collimator seat.

[0048] The detectors I, II and III are embedded in the openings of the side wall of the housing through detector seats.

[0049] Preferably, the beam splitter I, beam splitter II, reflector, FP etalon, convex lens I, convex lens II and convex lens III are all fixed in the housing by using ultraviolet low-stress curing adhesive to ensure the stability of the optical path.

[0050] As an optimization solution of the above embodiment, in order to ensure the stability of wavelength measurement by the wavelength meter, Figure 2 As shown, it also includes:

[0051] The constant temperature control box carrying the wavelength meter includes an upper cover, a bottom cover, a side cover, a front cover and a rear cover which are connected to form a box body; each cover is provided with a heat-insulating layer;

[0052] The heat preservation front cover is equipped with a semiconductor temperature control air conditioner to ensure that the temperature of the constant temperature box is stable at a temperature control accuracy of ±0.005 degrees Celsius. The semiconductor temperature control air conditioner has a fan to ensure uniform temperature inside the constant temperature box.

[0053] As an optimization of the above embodiment, a windshield is installed around the wavemeter. It features three vertical panels and one open side, ensuring airflow exchange while minimizing airflow interference. The windshield is secured to the electronic control board, which is in turn secured to the bottom plate of the thermostat via support columns. The wavemeter is placed in the center of the thermostat, and a unique windshield ensures temperature stability.

[0054] The wavelength meter is preferably secured to the wavelength meter base plate via a mounting bracket and a chuck. The mounting bracket and chuck are made of low-thermal-conductivity PEK material to reduce thermal interference with the wavelength meter components. The wavelength meter base plate is constructed of 4J29 Kovar alloy steel to ensure optical path stability due to thermal expansion, thereby ensuring the stability of the wavelength meter.

[0055] Design principle:

[0056] According to the angular characteristics of the interference spectrum of the Fabry-Perot etalon (abbreviated as FP etalon), the output light intensity I tThe ratio of the transmittance to the incident light intensity I is the relationship between the transmittance and the incident angle and wavelength: The output graph is Figure 3 .

[0057] according to Figure 3 The graph shows that the transmittance is related to the incident angle of the laser on the FP etalon. The distance between the beam splitter I and II and the collimator and the angle of the beam splitter can be adjusted to control the wavelength of the transmittance. The phase difference of the corresponding curve is π / 2, thus obtaining Figure 4 The curve in

[0058] Since the FP etalon has two blind zones, the top and the bottom, when measuring wavelength, the laser wavelength given in the CRDS cavity ring-down system is a given wavelength. The blind zones can be effectively avoided by using two wavelength response curves of transmittance. When the laser wavelength falls within the blind zone of one curve, the other curve must be within the non-blind zone, thus ensuring continuous and accurate measurement of multiple wavelengths.

[0059] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring, characterized in that: Detection using a wavelength meter includes the following steps: The combined laser beam passes through the collimator and is split by the beam splitter I; Part of the laser light is reflected and passes through half of the FP etalon, then is focused by convex lens I and enters detector I. Another part of the laser is projected and split by the spectroscope II. After the second split, the laser passes through the other half of the FP etalon and is focused by the convex lens II before entering the detector II. Another part of the laser is projected and reflected by the reflector, focused by the convex lens III before entering the detector III. The detection results are obtained using detectors I, II and III.

2. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 1, characterized in that: The combined laser beam passes through the collimator and is split by the beam splitter I in a ratio of 70:30; 30% of the laser is reflected by half of the FP standard and focused by the convex lens I before entering the detector I; 70% of the laser is projected and split 50:50 by the beam splitter II; half of the laser passes through the other half of the FP standard and is focused by the convex lens II before entering the detector II; the other half of the laser is projected, reflected by the reflector, focused by the convex lens III, and then enters the detector III.

3. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 1, characterized in that: A temperature measuring resistor is provided on the FP etalon.

4. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 1, characterized in that: The FP etalon uses low expansion glass-ceramic.

5. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 1, characterized in that: The collimator is embedded in the through hole of the side wall of the shell through a collimator seat.

6. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 1, characterized in that: The detectors I, II and III are embedded in the openings of the side wall of the housing through detector seats.

7. A laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to any one of claims 1 to 6, characterized in that: The beam splitter I, beam splitter II, reflector, FP standard tool, convex lens I, convex lens II and convex lens III are all bonded and fixed in the housing by using ultraviolet low-stress solidifying adhesive.

8. A laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to any one of claims 1 to 6, characterized in that: Also includes: The constant temperature control box carrying the wavelength meter includes an upper cover, a bottom cover, a side cover, a front cover and a rear cover which are connected to form a box body; each cover is provided with a heat-insulating layer; A semiconductor temperature-controlled air conditioner is provided on the thermal insulation front cover.

9. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 8, characterized in that: A windshield is arranged around the wave meter, and the windshield is provided with vertical plates on three sides and an opening on one side; the windshield is fixed on the electric control board, and the electric control board is fixed on the bottom plate of the constant temperature control box through a supporting column.

10. The laser wavelength detection optimization method for cavity ring-down spectroscopy monitoring according to claim 9, characterized in that: The wavelength meter is fixed on the wavelength meter base plate through a fixing seat and a clamp. The fixing seat and the clamp are made of low thermal conductivity PEK material, and the wavelength meter base plate is made of 4J29 Kovar alloy steel.

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