Optical resonator and gas absorption spectroscopy detection apparatus

Abstract

An optical resonant cavity (100) and a gas absorption spectrum detection device, comprising a first cavity mirror (101) and a second cavity mirror (102), the first cavity mirror (101) comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror (101) being an input reflection point (103), the reflection surface of the second cavity mirror (102) being arranged at the opposite side of the reflection surface of the first cavity mirror (101) to form the optical resonant cavity (100) with the first cavity mirror (101), the second cavity mirror (102) comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror (101) or the second cavity mirror (102) being an output reflection point (104), a light beam being transmitted into the optical resonant cavity (100) through the input reflection point (103) and after being reflected between the reflection points of the first cavity mirror (101) and the reflection points of the second cavity mirror (102) for at least 4 times, meeting the re-entry condition and entering the next reflection cycle, and so on until the energy of the light beam in the optical resonant cavity (100) is attenuated to 0.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cavity enhance absorption spectroscopy (CEAS), and particularly relates to an optical resonant cavity and a gas absorption spectrum detection device. BACKGROUND

[0002] The lower limit of gas absorption spectrum detection in the fields of environmental protection, safety, industry and the like is required to be higher. In order to meet this requirement, the gas absorption spectrum detection technology adopts the method of increasing the optical path to improve the gas absorption rate and reduce the detection lower limit. However, the optical path cannot be increased indefinitely in a limited volume. In recent years, the CEAS technology developed, such as the cavity ring-down spectroscopy (CRDS) technology, the incoherent broad band (IBB) cavity enhance absorption spectroscopy (IBBCEAS) technology, the off axis integrating cavity output spectroscopy (OA-ICOS) technology and the like, utilizes the characteristics that light is reflected in the optical resonant cavity, so that the effective optical path can be improved by 10 2 -10 4 times in a limited volume, thereby greatly improving the sensitivity of the gas absorption spectrum detection device.

[0003] However, the gas absorption spectrum detection device based on the CEAS technology generally has the problem that the light energy received by the photodetector is low, which limits the improvement of the signal-to-noise ratio and the sensitivity of the gas absorption spectrum detection device.

[0004] TECHNICAL PROBLEM

[0005] One of the purposes of the embodiments of the present application is to provide an optical resonant cavity and a gas absorption spectrum detection device, so as to solve the problem that the light energy received by the photodetector of the existing gas absorption spectrum detection device based on the CEAS technology is low, which limits the improvement of the signal-to-noise ratio and the sensitivity of the gas absorption spectrum detection device.

[0006] TECHNICAL SOLUTION

[0007] The first aspect of the embodiments of the present application provides an optical resonant cavity, comprising:

[0008] A first cavity mirror, the first cavity mirror comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror being an input reflection point;

[0009] a second cavity mirror, a reflective surface of the second cavity mirror is disposed at an opposite side of the reflective surface of the first cavity mirror, the second cavity mirror comprises a plurality of reflective points, at least one of all the reflective points of the first cavity mirror or the second cavity mirror is an output reflective point;

[0010] wherein the light beam is transmitted into the optical resonant cavity through the input reflective point, and after being reflected N times between the reflective points of the first cavity mirror and the second cavity mirror, the light beam satisfies a re-entry condition and enters a next reflection cycle, and the cycle is repeated until the energy of the light beam in the optical resonant cavity is attenuated to 0, N≥4, the re-entry condition is that the reflection position and reflection angle of the light beam in the optical resonant cavity are the same as the transmission position and transmission angle of the light beam when the light beam is first transmitted into the optical resonant cavity;

[0011] At least one of all the input reflective points and all the output reflective points is a target reflective point, the transmittance of the target reflective point is greater than or equal to T, and the transmittance of the remaining reflective points is equal to T0, T>T0>0.

[0012] In one embodiment, T=mT0, m=(N-1) / 2, m>1.

[0013] In one embodiment, the transmittance of one of all the input reflective points and one of all the output reflective points is greater than or equal to T.

[0014] In one embodiment, T=mT0, m=N-2, m>1.

[0015] In one embodiment, the transmittance of one of all the input reflective points or one of all the output reflective points is greater than or equal to T.

[0016] In one embodiment, T=mT0, m=(N-1) / 2, m>1.

[0017] In one embodiment, the transmittance of at least one of all the input reflective points is greater than or equal to T in , the transmittance of at least one of all the output reflective points is greater than or equal to T out , T in ≠T out , T in ≥T, T out ≥T.

[0018] In one embodiment, for a target cavity mirror of the first cavity mirror and the second cavity mirror, a plurality of reflective points with different transmittances are formed on the target cavity mirror based on an integrated coating method or a split coating method, the target cavity mirror comprises a plurality of reflective points with different transmittances.

[0019] In one embodiment, based on the integrated coating method, the method for forming multiple reflection points with different transmittances on the target cavity mirror is: using a mask to generate different film layers on different areas of the target cavity mirror during the integrated coating process.

[0020] Based on the integrated coating method, the method for forming multiple reflection points with different transmittances on the target cavity mirror is: using a mask to generate different film layers on different areas of the target cavity mirror during the integrated coating process.

[0021] In one embodiment, the optical resonant cavity further comprises:

[0022] At least one folding mirror, a reflecting surface of each folding mirror is arranged opposite to a reflecting surface of the first cavity mirror or a reflecting surface of the second cavity mirror, and the folding mirror comprises multiple reflection points.

[0023] The light beam is transmitted into the optical resonant cavity through the input reflection point, and after being reflected M times between the reflection points of the first cavity mirror, the reflection points of the folding mirror and the reflection points of the second cavity mirror, the light beam satisfies the re-entry condition and enters the next reflection cycle, and the cycle is repeated until the energy of the light beam is attenuated to 0, M>N.

[0024] In one embodiment, at least one of all the reflection points of the first cavity mirror or the second cavity mirror is an output reflection point, and the output reflection point is a target reflection point.

[0025] In one embodiment, at least one of the first cavity mirror and the second cavity mirror is a concave mirror.

[0026] The second aspect of the embodiment of the present application provides a gas absorption spectrum detection device, which comprises:

[0027] The optical resonant cavity provided by the first aspect of the embodiment of the present application;

[0028] A photodetector, the photodetector is used to measure the light intensity of the light beam transmitted through the output reflection point, so as to obtain the absorption spectrum information of the gas in the optical resonant cavity according to the light intensity or the decay time of the light intensity.

[0029] In one embodiment, the gas absorption spectrum detection device further comprises a converging lens, and the light beam transmitted through the output reflection point is converged to the photodetector through the converging lens.

[0030] In one embodiment, the gas absorption spectrum detection device further comprises a converging lens and a receiving optical fiber, the light beam is transmitted to the converging lens after being transmitted to the output reflection point, is converged by the converging lens to the receiving optical fiber, and is transmitted to the photodetector.

[0031] In one embodiment, the gas absorption spectrum detection device is implemented based on a cavity ring-down spectrum technology, an incoherent broadband cavity enhanced absorption spectrum technology or an off-axis integrated cavity output spectrum technology.

[0032] Advantages

[0033] The first aspect of the embodiments of the present application provides an optical resonant cavity, comprising a first cavity mirror and a second cavity mirror, the first cavity mirror comprises a plurality of reflection points, at least one of all the reflection points of the first cavity mirror is an input reflection point, a reflection surface of the second cavity mirror is arranged at the opposite side of the reflection surface of the first cavity mirror to form an optical resonant cavity with the first cavity mirror, the second cavity mirror comprises a plurality of reflection points, at least one of all the reflection points of the first cavity mirror or the second cavity mirror is an output reflection point, a light beam is transmitted to the optical resonant cavity through the input reflection point, and after being reflected at least 4 times between the reflection points of the first cavity mirror and the reflection points of the second cavity mirror, the light beam satisfies a re-entry condition and enters a next reflection cycle, and the cycle is repeated until the energy of the light beam in the optical resonant cavity is attenuated to 0, the re-entry condition is that the reflection position and the reflection angle of the light beam in the optical resonant cavity are the same as the transmission position and the transmission angle of the light beam when the light beam is first transmitted to the optical resonant cavity; by making the transmittance of at least one of all the input reflection points and all the output reflection points greater than the transmittance of the remaining reflection points, the light energy output by the output reflection point can be enhanced, so that when the optical resonant cavity is applied to a gas detection device, the light energy coupled to the photodetector by the optical resonant cavity can effectively improve the signal-to-noise ratio and the sensitivity of the gas detection device.

[0034] It can be understood that the advantages of the second aspect described above can be referred to the related description in the first aspect described above, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0036] Figure 1 FIG. 1 is a first structural schematic diagram of an optical resonant cavity and a gas absorption spectrum detection device provided by the embodiments of the present application;

[0037] Figure 2Figure 2 is a second structural schematic diagram of an optical resonant cavity and a gas absorption spectrum detection device provided by an embodiment of the present application;

[0038] Figure 3 Figure 3 is a third structural schematic diagram of an optical resonant cavity and a gas absorption spectrum detection device provided by an embodiment of the present application.

[0039] Embodiments of the present application

[0040] In order to enable persons skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by persons skilled in the art without creative labor should fall within the scope of protection of the present application.

[0041] The terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", "consist", "consisting", "consist of", and any variations thereof in the specification and in the claims and the above-described drawings are intended to cover non-exclusive inclusion. In addition, the terms "first" and "second" and the like are used to distinguish different objects, rather than to describe a specific order.

[0042] As shown in Figure 1 , Figure 2 or Figure 3 An optical resonant cavity 100 provided by an embodiment of the present application comprises:

[0043] A first cavity mirror 101, the first cavity mirror 101 comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror 101 being an input reflection point 103;

[0044] A second cavity mirror 102, the reflection surface of the second cavity mirror 102 being arranged at the opposite side of the reflection surface of the first cavity mirror 101, the second cavity mirror 102 comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror 101 or the second cavity mirror 102 being an output reflection point 104;

[0045] Wherein, the light beam is transmitted to the optical resonant cavity 100 through the input reflection point 103, and after being reflected N times between the reflection points of the first cavity mirror 101 and the reflection points of the second cavity mirror 102, the light beam satisfies the re-entry condition and enters the next reflection cycle, and the cycle is repeated until the energy of the light beam in the optical resonant cavity is attenuated to 0, N≥4, the re-entry condition being that the reflection position and reflection angle of the light beam in the optical resonant cavity 101 are the same as the transmission position (i.e. the position of the input reflection point 103) and transmission angle θ of the light beam when the light beam is first transmitted to the optical resonant cavity 100;

[0046] The transmittance of at least one of all input reflection points 103 and all output reflection points 104 is greater than or equal to T, and the transmittance of the remaining reflection points is less than or equal to T0, T > T0 > 0.

[0047] In applications, the reflection points are position points on the cavity mirror for reflecting the light beam, the input reflection points are position points on the cavity mirror for inputting the light beam from the light source and reflecting the light beam, the output reflection points are position points on the cavity mirror for reflecting the light beam and outputting the light beam to the photodetector, the remaining reflection points other than the input reflection points and the output reflection points are defined as ordinary reflection points, the reflection points with the transmittance greater than or equal to T among all the input reflection points and all the output reflection points are defined as target reflection points, and the remaining reflection points with the transmittance equal to T0 include the input reflection points, the output reflection points and the ordinary reflection points other than the target reflection points.

[0048] In applications, the positions and the number of the input reflection points and the output reflection points of the optical resonant cavity can be set according to actual needs, which is related to the type of the optical resonant cavity. As long as the input reflection point is set on the first cavity mirror, the output reflection point can be set on the first cavity mirror or the second cavity mirror. The input reflection point and the output reflection point can be set on the first cavity mirror at the same time, and in this case, the second cavity mirror is only provided with ordinary reflection points. The input reflection point and the output reflection point can be the same reflection point (defined as an input-output reflection point), and at least one of all the reflection points of the first cavity mirror can be an input-output reflection point for inputting the light beam and outputting the light beam.

[0049] In applications, when the number of the target reflection points is at least two, the transmittance of these target reflection points can be the same or different. Due to the limitation of the modern coating process level, the maximum reflectivity R of the cavity mirror can usually reach 0.99999, and it is difficult and costly to further improve the reflectivity. Correspondingly, the minimum T0 (i.e. 1-R) can be made to be 0.00001, i.e. the minimum of T0 can be made to be 10 -5 orders of magnitude. The size of T is between 10 -5 -10 -3 orders of magnitude, for example, between 0.0009 and 0.005.

[0050] In applications, the transmittance of all the target reflection points greater than or equal to T can specifically include but is not limited to the following cases:

[0051] First, the transmittance of all the target reflection points is equal, for example, the transmittance of all the target reflection points is equal to T;

[0052] Second, the transmittance of all the target reflection points is not equal or partially equal, for example, the transmittance of the target reflection points among all the input reflection points is equal to T in , the transmittance of the target reflection points among all the output reflection points is equal to Tout or, the transmittance of the target reflection point among all the input reflection points is greater than or equal to T in and all are not equal or partially equal, the transmittance of the target reflection point among all the output reflection points is greater than or equal to T out and all are not equal or partially equal, T in ≠ T out , T in ≥ T, T out ≥ T.

[0053] In application, the light beam is transmitted into the optical resonant cavity through the input reflection point, and after being reflected between the reflection points of the first cavity mirror and the second cavity mirror for N times, the re-entry condition is met, and the next reflection cycle is entered to be reflected again between the reflection points of the first cavity mirror and the second cavity mirror along the same reflection path, and the cycle is repeated until the energy of the light beam is attenuated to 0.

[0054] In application, by making the transmittance of the target reflection point greater than the transmittance of the remaining reflection points, the average reflectivity of all the reflection points is slightly lowered, and the effective optical path is slightly lowered, which has a negative impact on the signal-to-noise ratio. However, this technical means greatly increases the output light energy of the output reflection point, thereby increasing the light energy of the optical resonant cavity coupled to the photodetector when the optical resonant cavity is applied to the gas absorption spectrum detection device, which has a positive impact on improving the signal-to-noise ratio of the gas absorption spectrum detection device. Since the positive impact is much greater than the negative impact, the signal-to-noise ratio is also greatly improved, and the greater the number N of single-cycle reflection points, the greater the multiple of the signal-to-noise ratio.

[0055] In one embodiment, the transmittance of at least one of all the input reflection points is greater than or equal to T, and the second cavity mirror includes N / 2 output reflection points; wherein the relationship between T and T0 can be: T=mT0, m=(N-1) / 2, m>1.

[0056] In application, at least one target reflection point for input light beam can be arranged on the first cavity mirror, and N / 2 (i.e. at least two) output reflection points for output light beam can be arranged on the second cavity mirror, and the transmittance of the target reflection point can be greater than or equal to (N-1) / 2 (i.e. at least 1.5) times T0.

[0057] In one embodiment, the transmittance of one of all the input reflection points and one of all the output reflection points is greater than or equal to T, wherein the relationship between T and T0 can be: T=mT0, m=N-2, m>1.

[0058] In applications, one target reflection point for inputting light beams can be arranged in the first cavity mirror, and one target reflection point for outputting light beams can be arranged in the first cavity mirror or the second cavity mirror. When the target reflection point for inputting light beams and the target reflection point for outputting light beams are arranged in the first cavity mirror, the target reflection point for inputting light beams and the target reflection point for outputting light beams can be the same target reflection point. The transmittance of the target reflection point can be greater than or equal to N-2 (i.e., at least 2) times T0.

[0059] In one embodiment, the transmittance of one of all the input reflection points or one of all the output reflection points is greater than or equal to T, where the relationship between T and T0 can be T = mT0, m = (N-1) / 2, and m > 1.

[0060] In applications, one target reflection point for inputting light beams can be arranged in the first cavity mirror, and one target reflection point for outputting light beams can be arranged in the first cavity mirror or the second cavity mirror. When the target reflection point for inputting light beams and the target reflection point for outputting light beams are arranged in the first cavity mirror, the target reflection point for inputting light beams and the target reflection point for outputting light beams can be the same target reflection point. The transmittance of the target reflection point can be greater than or equal to N-2 (i.e., at least 2) times T0.

[0061] In one embodiment, for a target cavity mirror including reflection points with different transmittances in the first cavity mirror and the second cavity mirror, the reflection points with different transmittances are formed in the target cavity mirror based on an integrated coating method or a split coating method.

[0062] In applications, for each of the first cavity mirror and the second cavity mirror, if the cavity mirror includes reflection points with different transmittances, the reflection points with different transmittances can be formed in the cavity mirror based on an integrated coating method or a split coating method; if the cavity mirror includes only reflection points with the same transmittance, the reflection points with the same transmittance can be formed in the cavity mirror based on an integrated coating method; and the cavity mirror including reflection points with different transmittances is defined as a target cavity mirror.

[0063] In one embodiment, the method for forming reflection points with different transmittances in a target cavity mirror based on an integrated coating method is to use a mask to generate different film layers in different regions of the target cavity mirror during the integrated coating process.

[0064] The method for forming reflection points with different transmittances in a target cavity mirror based on a split coating method is to separate different regions of the target cavity mirror into independent elements, and to coat the different elements separately.

[0065] In application, different regions of the target cavity mirror are the positions of the reflection points with different transmittances. The number of the independent elements separated from different regions of the target cavity mirror is determined by the number of the target reflection points and the number of the remaining reflection points, and the value range is between the number of the target reflection points plus 1 and the number of the target reflection points plus the number of the remaining reflection points, that is, each target reflection point is separated into a region, and all the remaining reflection points are separated into one region or each remaining reflection point is separated into a region. In an embodiment, the first cavity mirror is a concave mirror, and the second cavity mirror is a concave mirror or a plane mirror.

[0066] In application, the number and setting position of the input reflection point and the output reflection point, and the type of the first cavity mirror and the second cavity mirror can be adjusted according to actual needs.

[0067] Figure 1 The structure schematic diagram of the first optical resonant cavity based on Herriott Cell is exemplarily shown in FIG. 1;

[0068] In the embodiment, the first cavity mirror 101 is a concave mirror, and one of all the reflection points of the first cavity mirror 101 is an input reflection point 103.

[0069] The second cavity mirror 102 is a concave mirror, and a plurality of all the reflection points of the second cavity mirror 102 are output reflection points 104. The first cavity mirror 101 and the second cavity mirror 102 constitute a Herriott Cell.

[0070] In application, Figure 1 The number of reflections of the light beam in the optical resonant cavity shown in FIG. 1 can generally reach 50-100 times. The first cavity mirror and the second cavity mirror are a pair of high-reflectivity concave mirrors, and the reflectivity can reach more than 99%.

[0071] Figure 2 The structure schematic diagram of the second optical resonant cavity based on Herriott Cell is exemplarily shown in FIG. 2;

[0072] In the embodiment, the first cavity mirror 101 is a concave mirror, and one of all the reflection points of the first cavity mirror 101 is an input reflection point 103, and the other is an output reflection point 104.

[0073] The second cavity mirror 102 is a concave mirror, and the first cavity mirror 101 and the second cavity mirror 102 constitute a Herriott Cell.

[0074] As shown in FIG. 3, in an embodiment, the optical resonant cavity 100 further comprises: Figure 3

[0075] ​at least one folding mirror, a reflecting surface of each folding mirror is arranged opposite to a reflecting surface of the first cavity mirror 101 or a reflecting surface of the second cavity mirror 102, and the folding mirror comprises a plurality of reflecting points;

[0076] The light beam is transmitted into the optical resonant cavity 100 through the input reflecting point 103, and after being reflected M times between the reflecting points of the first cavity mirror 101, the reflecting points of the folding mirror and the reflecting points of the second cavity mirror 102, the light beam satisfies the re-entry condition and enters the next reflecting cycle, and the cycle is repeated until the energy of the light beam in the optical resonant cavity is attenuated to 0, and M>N.

[0077] In the application, at least one folding mirror can be additionally added on the basis of the first cavity mirror and the second cavity mirror to increase the number of reflections of the light beam in the optical resonant cavity. In the case where the straight-line distance between the first cavity mirror and the second cavity mirror is unchanged, the total optical path of the light beam propagating in the optical resonant cavity can be increased by adding the folding mirror. In the case where the total optical path is unchanged, the volume of the optical resonant cavity can be reduced by adding the folding mirror, and the optical path volume ratio of the optical resonant cavity is improved.

[0078] In an embodiment, for the optical resonant cavity comprising the folding mirror, at least one of all the reflecting points of the first cavity mirror or the second cavity mirror is an output reflecting point, and the output reflecting point is the target reflecting point.

[0079] Figure 3 FIG. 3 shows a structural schematic diagram of a third optical resonant cavity 100 comprising a first folding mirror and a second folding mirror;

[0080] In the figure, the first cavity mirror 101 is a plane mirror, one of all the reflecting points of the first cavity mirror 101 is an input reflecting point 103, and the other is an output reflecting point 104.

[0081] The second cavity mirror 102 is a concave mirror.

[0082] A reflecting surface of the first plane folding mirror 105 is arranged opposite to a reflecting surface of the first cavity mirror 101.

[0083] A reflecting surface of the second plane folding mirror 106 is arranged opposite to a reflecting surface of the second cavity mirror 102 and is parallel to the reflecting surface of the first plane folding mirror 105.

[0084] The optical resonant cavity provided by the embodiment of the application has at least the following aspects of characteristics:

[0085] In a first aspect, in the case where the light beam is a non-coherent light beam, the absorption signal of the optical resonant cavity is greatly enhanced. The number of reflections in a single reflecting cycle is N, N≥4, the average transmittance of the optical resonant cavity is T', the average reflectance is R', the cavity length is L, and the transmittance of the input reflecting point is T.in , the reflectivity is R in = 1-T in , the number of output reflection points is n, the transmissivity is T out , the reflectivity is R out = 1-T out , the transmissivity of other reflection points is T0, the reflectivity is R0=1-T0, T in > T0 or T out > T0, the equivalent absorption optical path L eff of the optical resonant cavity is:

[0086] L eff = L / (1-R') = L / T'(Formula 1)

[0087] The average transmissivity T' is:

[0088] T' = [(N-n-1)T0+T in +nT out ] / N(Formula 2)

[0089] While the light beam continuously reflects between the cavity mirrors, a small amount of light is continuously transmitted out of the optical resonant cavity at each of the n output reflection points, and after being converged by the converging lens, it reaches the photodetector. The energy efficiency η is:

[0090] η = nT in T out / [(N-n-1)T0+T in +nT out ](Formula 3)

[0091] Substituting Formula 1 into Formula 3, the relative signal-to-noise ratio SNRr is:

[0092] SNRr = L eff η 1 / 2 / L = (nT in T out ) 1 / 2 / T' [(N-n-1)T0+T in +nT out ] 1 / 2 (Formula 4)

[0093] Further, in order not to lose generality, let T in = m1T0, T out = m2T0, m1≥1, m2≥1, then the relative signal-to-noise ratio SNRr is:

[0094] SNRr = N(2nm1m2) 1 / 2 / (N-n-1+m1+nm2) 3 / 2 (2T0) 1 / 2 = K / (2T0)1 / 2 (Formula 5)

[0095] K = N(2nm1m2) 1 / 2 / (N-n-1+m1+nm2) 3 / 2 (Formula 6)

[0096] According to Formula 6, for the first optical resonant cavity as shown in Figure 1 , when n = N / 2, m1 = m2 = 1, the relative signal-to-noise ratio SNRr of the first optical resonant cavity is 1 / (2T0) 1 / 2 , that is, K = 1. Therefore, for a given N, by reasonably designing the values of n, m1 and m2, K > 1 can be achieved, so that the relative signal-to-noise ratio of the first optical resonant cavity is improved. The value of K represents the multiple of the improvement of the relative signal-to-noise ratio. For example:

[0097] When n = N / 2, m1 = m, m2 = 1, and m > 1, that is, the transmittance of the input reflection point is greater than the transmittance of the remaining reflection points, then:

[0098] K = m 1 / 2 [1+(m-1) / N] -3 / 2 (Formula 7)

[0099] Taking the derivative of K with respect to m in Formula 7, the extreme value K max of K is:

[0100] K max = 2N(N / 3) 1 / 2 / (3N-3), m = (N-1) / 2 (Formula 8)

[0101] When n = 1, m1 = m2 = m, and m > 1, that is, the transmittance of the input reflection point and the transmittance of the output reflection point are greater than the transmittance of the remaining reflection points, then:

[0102] K = (2 / N) 1 / 2 m[1+(2m-2) / N] -3 / 2 (Formula 9)

[0103] Taking the derivative of K with respect to m in Formula 9, the extreme value K max of K is:

[0104] K max = [2 / (3N-6)] 1 / 2 N / 3, m = N-2 (Formula 10).

[0105] In the second aspect, in the case of coherent light beams, the number of output reflection points is n = 1, the number of reflection times in a single reflection cycle is N, and the relative coupling efficiency T rThe optical energy efficiency ratio of the folded cavity (i.e. the optical resonant cavity comprising at least one folded mirror) coupled to the photoelectric detector to the straight cavity (i.e. the optical resonant cavity comprising two plane mirrors arranged oppositely) is analyzed as follows:

[0106] The first case is as follows:

[0107] The transmittance of the input and output reflection points is T1, and the transmittance of the remaining reflection points is T0, T1 = mT0, m > 1.

[0108] Considering the free spectral range FSR, the fineness with the change of N, and the change of the cavity mode peak coupling efficiency, the relative coupling efficiency T r can be expressed as:

[0109] T r = 4m 2 / [N(N+2m-2)] (Formula 11)

[0110] When m = 1 and N = 2, the optical resonant cavity is a straight cavity, and substituting Formula 11 can obtain T r = 1.

[0111] When m = 1 and N ≥ 4, the optical resonant cavity is a folded cavity or an off-axis integral cavity (for example, the first optical resonant cavity as shown in Figure 1 or the second optical resonant cavity as shown in Figure 2 ), and substituting Formula 11 can obtain T r = 4 / N 2 .

[0112] The relative signal-to-noise ratio SNRr is:

[0113] SNRr = L eff T r 1 / 2 / L = 2K / (NT0) (Formula 12)

[0114] K = m[1 + (2m-2) / N] -3 / 2 (Formula 13)

[0115] When m = 1, the optical resonant cavity is a straight cavity or a folded cavity, and K = 1, SNRr = 2 / (NT0).

[0116] When N ≥ 4 and m > 1, K > 1, and the derivative of K with respect to m in Formula 13 can obtain the extreme value K max of K as follows:

[0117] K max = [N / (3N-6)] 1 / 2 N / 3, m = N-2 (Formula 14).

[0118] The second case is as follows:

[0119] Let the transmittance of one of the input or output reflection points be T1, i.e. there is only one target reflection point, and the transmittance of the remaining reflection points be T0, T1 = mT0, m > 1;

[0120] Taking into account the free spectral range FSR, the fineness with the change of N, and the change of the cavity mode peak coupling efficiency, the relative coupling efficiency T r may be expressed as:

[0121] T r = 4m / [N(N+m-1)] (Formula 18)

[0122] When m = 1, N = 2, the optical resonant cavity is a straight cavity, substituting Formula 18, T r = 1;

[0123] When m = 1, N ≥ 4, the optical resonant cavity is a folded cavity or an off-axis integral cavity (for example, the first optical resonant cavity as shown in Figure 1 or the second optical resonant cavity as shown in Figure 2 ), substituting Formula 18, T r = 4 / N 2 ;

[0124] The relative signal-to-noise ratio SNRr is:

[0125] SNRr = L eff T r 1 / 2 / L = 2K / (NT0) (Formula 16)

[0126] K = m 1 / 2 [1+(m-1) / N] -3 / 2 (Formula 17)

[0127] When m = 1, the optical resonant cavity is a straight cavity or a folded cavity, then K = 1, SNRr = 2 / (NT0);

[0128] When N ≥ 4, m > 1, K > 1, taking the derivative of K with respect to m in Formula 13, the extreme value K max of K is:

[0129] K max = 2N(N / 3) 1 / 2 / (3N-3), m = (N-1) / 2 (Formula 18).

[0130] In one embodiment, for the optical resonant cavity as shown in Figure 1The first type of optical resonator shown can be either a coherent beam or an incoherent beam (e.g., an incoherent broadband beam). In the case of a coherent beam, since there are multiple output reflection points, the interference effect is greatly smoothed. Therefore, the coherent beam case can be approximated using the same method as the incoherent beam case.

[0131] When T in =mT0,T out When T > 0 and m > 1, we can obtain the following from formulas 6 and 7:

[0132] K = m 1 / 2 [1+(m-1) / N] -3 / 2 (Formula 19)

[0133] When N≥4, by reasonably designing the value of m, it is possible to make K>1;

[0134] When m = (N-1) / 2, according to Formula 8, the larger the value of N, the more K... max The larger the value, for example:

[0135] When N = 50, K max =2.78;

[0136] When N = 100, K max =3.89;

[0137] For example Figure 1 The first type of optical resonator shown has a relative signal-to-noise ratio improvement factor of 2.78-3.89 when the value of N is between 50 and 100. The larger the value of N, the greater the relative signal-to-noise ratio improvement factor.

[0138] When T0 = 0.01%, R0 = 99.99%, and N = 50, according to Formula 19, the optimal value of m is 24.5. At this point, T... in =24.5×0.01%=0.245%, R in =99.755%.

[0139] In one embodiment, an optical resonator that is an output reflection point for one of the reflection points of the first or second cavity mirror (e.g., Figure 2 The second type of optical resonator shown can be a coherent beam or an incoherent beam (e.g., an incoherent broadband beam).

[0140] When T in =T out When m > 1, since the number of output reflection points is only one, i.e., n = 1, then:

[0141] 1) when the light beam is a non-coherent light beam, K = (2 / N) 1 / 2 m[1+(2m-2) / N] -3 / 2 (Formula 9);

[0142] Correspondingly, K max = [2 / (3N-6)] 1 / 2 N / 3, m = N-2 (Formula 10);

[0143] If N = 50, K max = 1.96;

[0144] If N = 100, K max = 2.75;

[0145] For the second optical resonant cavity as shown in Figure 2 , when the value of N is between 50-100, the relative signal-to-noise ratio is increased by a factor of 1.96-2.75, and the larger the value of N, the greater the relative signal-to-noise ratio is increased;

[0146] 2) when the light beam is a coherent light beam, K = m[1+(2m-2) / N] -3 / 2 (Formula 13);

[0147] Correspondingly, K max = [N / (3N-6)] 1 / 2 N / 3, m = N-2 (Formula 14);

[0148] If N = 50, K max = 9.82;

[0149] If N = 100, K max = 19.4;

[0150] For the second optical resonant cavity as shown in Figure 2 , when the value of N is between 50-100, the relative signal-to-noise ratio is increased by a factor of 9.82-19.4, and the larger the value of N, the greater the relative signal-to-noise ratio is increased;

[0151] 3) when T0=0.01%, R0=99.99%, N=50, the optimal value of m is m=N-2=48, at this time, T in = T out = 48x0.01%=0.48%, R in = R out = 99.52%.

[0152] In an embodiment, for the folded cavity (e.g., the third optical resonant cavity as shown in Figure 3 , the light beam can be a coherent light beam or a non-coherent light beam (e.g., a non-coherent broadband light beam);

[0153] When T in =T out When m > 1, since the number of output reflection points is only one, i.e., n = 1, then:

[0154] 1) When the beam is incoherent, K = (2 / N) 1 / 2 m[1+(2m-2) / N] -3 / 2 (Formula 9);

[0155] Correspondingly, K max =[2 / (3N-6)] 1 / 2 N / 3, m = N-2 (Formula 10);

[0156] If N = 50, then K max =1.96;

[0157] If N = 100, K max =2.75;

[0158] For example Figure 3 The third type of optical resonator shown has a relative signal-to-noise ratio improvement factor of 1.96-2.75 when the value of N is between 50 and 100. The larger the value of N, the greater the relative signal-to-noise ratio improvement factor.

[0159] 2) When the beam is a coherent beam, K = m[1 + (2m - 2) / N] -3 / 2 (Formula 13);

[0160] Correspondingly, K max = [N / (3N-6)] 1 / 2 N / 3, m = N-2 (Formula 14);

[0161] If N = 50, then K max =9.82;

[0162] If N = 100, K max =19.4;

[0163] For example Figure 3 The third type of optical resonator shown has a relative signal-to-noise ratio improvement factor of 9.82-19.4 when the value of N is between 50 and 100. The larger the value of N, the greater the relative signal-to-noise ratio improvement factor.

[0164] 3) When T0 = 0.001%, R0 = 99.999%, and N = 100, the optimal value of m is m = N - 2 = 98. At this time, T in =T out =98×0.001%=0.098%, R in =Rout = 99.902%. It can be seen that the value of N can be further increased by using the folded mirror to form the folded cavity, so as to further increase the multiple K of the relative signal-to-noise ratio, and meanwhile, the free spectral range FSR can be reduced, and the resolution of the gas absorption spectrum detection device can be improved.

[0165] As shown in Figure 1 , Figure 2 or Figure 3 , the embodiment of the present application further provides a gas absorption spectrum detection device comprising:

[0166] an optical resonant cavity 100;

[0167] a photodetector 200, the photodetector 200 being configured to measure the light intensity of the light beam transmitted through the output reflection point 104, so as to obtain the absorption spectrum information of the gas in the optical resonant cavity 100 according to the light intensity or the decay time of the light intensity.

[0168] In application, the light intensity of the light beam coupled to the photodetector can be increased by using the optical resonant cavity provided by the embodiment of the present application, so as to effectively improve the signal-to-noise ratio of the gas absorption spectrum detection device, and further improve the accuracy of the obtained absorption spectrum information of the gas.

[0169] As shown in Figure 1 , Figure 2 or Figure 3 , in one embodiment, the gas absorption spectrum detection device further comprises a converging lens 300, and the light beam transmitted through the output reflection point 104 is converged to the photodetector 200 through the converging lens 300.

[0170] In one embodiment, the gas absorption spectrum detection device can further comprise a receiving optical fiber, and the light beam transmitted through the output reflection point is converged to the receiving optical fiber through the converging lens, and then transmitted to the photodetector.

[0171] In application, the light beam output by the optical resonant cavity can be converged by the converging lens, and then coupled to the photodetector or transmitted to the photodetector through the receiving optical fiber, so as to reduce the area of the receiving surface of the photodetector, thereby effectively reducing the volume of the gas absorption spectrum detection device, and especially suitable for the case that the number of output reflection points is multiple.

[0172] Figure 2 The gas absorption spectrum detection device shown in

[0173] In one embodiment, the gas absorption spectroscopy detection device is implemented based on cavity ring-down spectroscopy technique, incoherent broadband cavity-enhanced absorption spectroscopy technique, or off-axis integrated cavity output spectroscopy technique.

[0174] The above descriptions are only the preferred embodiment of the present application, not intended to limit the present application. Any modification, equivalent replacement and improvement made within the principle and technical scope of the present application shall be included in the protection scope of the present application.

Claims

1. An optical resonator, characterized by, The optical resonant cavity is applied to a gas absorption spectrum detection device, and comprises: a first cavity mirror comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror being an input reflection point; a second cavity mirror, a reflection surface of the second cavity mirror being arranged opposite to a reflection surface of the first cavity mirror, the second cavity mirror comprising a plurality of reflection points, at least one of all the reflection points of the first cavity mirror or the second cavity mirror being an output reflection point; wherein a light beam is transmitted into the optical resonant cavity through the input reflection point, and after being reflected between the reflection points of the first cavity mirror and the reflection points of the second cavity mirror for N times, the light beam satisfies a re-entry condition and enters a next reflection cycle, and the cycle is repeated until the energy of the light beam in the optical resonant cavity is attenuated to 0, N≥4, the re-entry condition being that the reflection position and reflection angle of the light beam in the optical resonant cavity are the same as the transmission position and transmission angle of the light beam when the light beam is first transmitted into the optical resonant cavity; at least one of all the input reflection points and all the output reflection points is a target reflection point, the target reflection point having a transmittance greater than or equal to T, and the remaining reflection points having a transmittance equal to T0, T>T0>0.

2. The optical resonator of claim 1, wherein, at least one of all the input reflection points has a transmittance greater than or equal to T, and the second cavity mirror comprises N / 2 output reflection points.

3. The optical resonator of claim 2, wherein, T=mT0, m=(N-1) / 2, m>1.

4. The optical resonator of claim 1, wherein, one of all the input reflection points and one of all the output reflection points have a transmittance greater than or equal to T.

5. The optical resonator of claim 4, wherein, T=mT0, m=N-2, m>1.

6. The optical resonator of claim 1, wherein, one of all the input reflection points or one of all the output reflection points has a transmittance greater than or equal to T.

7. The optical resonator of claim 6, wherein, T=mT0, m=(N-1) / 2, m>1.

8. The optical resonator of claim 1, wherein, the transmissivity of at least one of the input reflection points is greater than or equal to T in , the transmissivity of at least one of the output reflection points is greater than or equal to T out , T in ≠ T out , T in ≥ T, T out ≥ T.

9. An optical resonator as claimed in any one of claims 1 to 8, characterized in that For a target cavity mirror of the first cavity mirror and the second cavity mirror, a plurality of reflection points with different transmittances are formed on the target cavity mirror based on an integrated coating method or a split coating method.

10. The optical resonator of claim 9, wherein, Based on the integrated coating method, the method for forming the plurality of reflection points with different transmittances on the target cavity mirror is that, during the integrated coating process, a mask is used to generate different film layers in different regions of the target cavity mirror. Based on the split coating method, the method for forming the plurality of reflection points with different transmittances on the target cavity mirror is that, during the split coating process, different regions of the target cavity mirror are separated into independent elements, and different elements are coated separately.

11. An optical resonator as claimed in any one of claims 1 to 8, characterized in that The optical resonant cavity further comprises: at least one folding mirror, a reflection surface of each folding mirror being arranged opposite to a reflection surface of the first cavity mirror or a reflection surface of the second cavity mirror, the folding mirror comprising a plurality of reflection points; a light beam is transmitted into the optical resonant cavity through the input reflection point, and after being reflected between the reflection points of the first cavity mirror, the reflection points of the folding mirror and the reflection points of the second cavity mirror for M times, the light beam satisfies a re-entry condition and enters a next reflection cycle, and the cycle is repeated until the energy of the light beam is attenuated to 0, M>N.

12. The optical resonator of claim 11, wherein, At least one of all the reflection points of the first cavity mirror or the second cavity mirror is an output reflection point, and the output reflection point is a target reflection point.

13. An optical resonator as claimed in any one of claims 1 to 8, characterized in that At least one of the first cavity mirror and the second cavity mirror is a concave mirror.

14. A gas absorption spectroscopic detection apparatus characterized by comprising: The optical resonant cavity comprises: The optical resonant cavity according to any one of claims 1 to 13; The photoelectric detector is used for measuring the light intensity of the light beam transmitted through the output reflection point, so as to obtain the absorption spectrum information of the gas in the optical resonant cavity according to the light intensity or the decay time of the light intensity.

15. The gas absorption spectroscopic detection apparatus as claimed in claim 14, wherein, The light beam transmitted through the output reflection point is further converged to the photoelectric detector through a converging lens.

16. The gas absorption spectroscopic detection apparatus as claimed in claim 14, wherein, The light beam transmitted through the output reflection point is further converged to the photoelectric detector through a converging lens and a receiving optical fiber.

17. A gas absorption spectroscopic detection apparatus as claimed in any one of claims 14 to 16, characterized in that, The gas absorption spectrum detection device is based on a cavity ring-down spectrum technology, a non-coherent broadband cavity-enhanced absorption spectrum technology or an off-axis integrated cavity output spectrum technology.

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