Optical interference low vacuum measuring device based on cavity-enhanced raman reference

Abstract

The application relates to the technical field of vacuum metering, in particular to an optical interference low-vacuum measuring device based on cavity-enhanced Raman reference, which comprises a measuring reference light path system, a measuring detection light path system, a cavity-enhanced Raman detection light path system and a frequency meter, wherein the measuring reference light path system is composed of a reference light path component and a first frequency-locked circuit; the measuring detection light path system comprises a detection light path component and a second frequency-locked circuit; the cavity-enhanced Raman detection light path system shares a set of detection light path components with the measuring detection light path system, and further comprises a Raman spectrum detection component; and the frequency meter is arranged between the measuring reference light path system and the measuring detection light path system. The cavity-enhanced Raman detection technology is introduced into the optical interference low-vacuum measuring device, so that qualitative detection of unknown gas types and detection of the pressure of polar gas can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum metrology, in particular to an optical interference low vacuum measuring device based on cavity-enhanced Raman reference. BACKGROUND

[0002] As a key technology for supporting the progress of national defense science and technology industry and the development of national economy, breaking through the technical blockade in the fields of semiconductor manufacturing and new energy storage and transportation, and as a technology foundation, vacuum metrology technology is in the process of transforming from classical physical standards to quantum standards. Therefore, establishing quantum vacuum metrology standards and developing quantum vacuum measuring instruments are the most important strategic goals and research directions in the field of vacuum metrology.

[0003] At present, various metrology technology institutions and research institutes at home and abroad have proposed different quantum metrology technologies for different parameters and ranges of vacuum values, mainly including: low vacuum measurement technology based on optical interference method, ultra-high / ultra-high vacuum measurement technology based on cold atoms, and vacuum partial pressure measurement technology based on atomic absorption spectrum.

[0004] 5 Among them, in the medium-low vacuum range of (1-10 The principle of the low vacuum measurement method based on optical interference is to accurately measure the resonance laser frequency shift caused by pressure change using a Fabry-Perot cavity structure, and to accurately measure the gas refractive index and to inverse the vacuum value by combining high-precision constant temperature control. However, it is difficult to determine the type of unknown gas by relying solely on the optical interference method, and it is also difficult to accurately measure the pressure of polar gas due to the precision limitations of the calculation theory of the method itself. SUMMARY

[0005] The present application provides an optical interference low vacuum measuring device based on cavity-enhanced Raman reference, which introduces a cavity-enhanced Raman reference into the optical interference low vacuum measurement method, and uses its qualitative measurement of unknown gas types and pressure measurement of non-polar gas to compensate for the shortcomings of existing low vacuum measurement devices based on optical interference method.

[0006] In order to achieve the above object, the application provides an optical interference low vacuum measuring device based on cavity enhanced Raman reference, comprising a measuring reference light path system, a measuring detection light path system, a cavity enhanced Raman detection light path system and a frequency meter, wherein the measuring reference light path system is composed of a reference light path component and a first frequency locking circuit, the reference light path component comprises a first laser, a first beam splitter, a first optical isolator, a first polarization beam splitting prism and a reference cavity; the first frequency locking circuit is used for keeping the reference laser emitted by the first laser in a resonant state in the reference cavity; the measuring detection light path system comprises a detection light path component and a second frequency locking circuit, the detection light path component comprises a second laser, a second beam splitter, a second optical isolator, a second polarization beam splitting prism and a detection cavity; the second frequency locking circuit is used for keeping the detection laser emitted by the second laser in a resonant state before and after the detection cavity is filled with gas; the cavity enhanced Raman detection light path system shares a set of detection light path components with the measuring detection light path system, and further comprises a Raman spectrum detection component, the Raman spectrum detection component comprises a third beam splitter and a spectrometer; the frequency meter is arranged between the measuring reference light path system and the measuring detection light path system and is used for receiving the reference laser passing through the first beam splitter and the detection laser passing through the second beam splitter.

[0007] Further, a first 1 / 2 glass, a first collimator and a second 1 / 2 glass are sequentially arranged between the first laser and the first beam splitter; a first Taylor prism, a first mode adjusting lens group and a third 1 / 2 glass are sequentially arranged between the first beam splitter and the first optical isolator; a fourth 1 / 2 glass is arranged between the first optical isolator and the first polarization beam splitting prism; a first reflector, a fifth 1 / 2 glass and a second reflector are sequentially arranged between the first polarization beam splitting prism and the reference cavity.

[0008] Further, the first frequency locking circuit comprises a first photoelectric detector and a first frequency locking device, wherein the first photoelectric detector is arranged at the back of the reference cavity and is used for receiving a transmission signal of the reference cavity; the first frequency locking device is used for receiving the first photoelectric detector signal and the laser beam split by the first polarization beam splitting prism, so as to keep the reference laser in a resonant state in the reference cavity.

[0009] Further, a sixth 1 / 2 glass, a second collimator and a seventh 1 / 2 glass are sequentially arranged between the second laser and the second beam splitter; a second Taylor prism, a second mode adjusting lens group and an eighth 1 / 2 glass are sequentially arranged between the second beam splitter and the second optical isolator; a ninth 1 / 2 glass is arranged between the second optical isolator and the second polarization beam splitting prism; a third reflector, a tenth 1 / 2 glass and a fourth reflector are sequentially arranged between the second polarization beam splitting prism and the detection cavity.

[0010] Further, the second frequency locking circuit comprises a second photodetector and a second frequency locking device, wherein the second photodetector is arranged at the rear of the detection cavity and is used for receiving the transmission signal of the detection cavity; and the second frequency locking device is used for receiving the second photodetector signal and the laser light split by the second polarization beam splitting prism, so that the detection laser detection cavity maintains the resonant state before and after the cavity is filled with gas.

[0011] Further, a third beam splitter is arranged between the second polarization beam splitting prism and the second frequency locking device.

[0012] Further, the third beam splitter is sequentially provided with a first dichroic plate, a second dichroic plate, a band-pass filter, a long-pass filter, a fifth mirror and a converging lens between the third beam splitter and the spectrometer.

[0013] Further, the reference cavity is always kept in a high vacuum state with a vacuum degree of less than or equal to 10-5Pa; the detection cavity is initially in a high vacuum state with a vacuum degree of less than or equal to 10-5Pa, and during the measurement, the test gas is filled into the detection cavity.

[0014] The optical interference low vacuum measurement device based on the cavity enhanced Raman reference provided in the application has the following beneficial effects:

[0015] The cavity enhanced Raman detection technology is introduced into the optical interference low vacuum measurement device, so that the unknown gas type can be qualitatively detected and the pressure of the polar gas can be detected; the cavity enhanced Raman detection light path and the optical interference low vacuum measurement detection light path share a set of laser resonant frequency locking light path, so that the structure is simple and the cost is saved. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments illustrated in the drawings provide for explanation of the present application and do not constitute an undue limitation on the present application. In the drawings:

[0017] Figure 1 is a schematic diagram of the optical interference low vacuum measurement device based on the cavity enhanced Raman reference provided according to an embodiment of the application;

[0018] In the figure: a-measurement reference light path system, b-measurement detection light path system, c-cavity enhanced Raman detection light path system, 1-first laser, 2-first 1 / 2 glass, 3-first collimator, 4-second 1 / 2 glass, 5-first beam splitter, 6-first Taylor prism, 7, 8-first mode adjustment lens group, 9-third 1 / 2 glass, 10-first optical isolator, 11-fourth 1 / 2 glass, 12-first frequency locking device, 13-first polarization beam splitting prism, 14-first mirror, 15-fifth 1 / 2 glass, 16-second mirror, 17-reference cavity, 19-first photodetector, 19-frequency meter, 20-second laser, 21-sixth 1 / 2 glass, 22-second collimator, 23-seventh 1 / 2 glass, 24-second beam splitter, 25-second Taylor prism, 26, 27-second mode adjustment lens group, 28-eighth 1 / 2 glass, 29-second optical isolator, 30-ninth 1 / 2 glass, 31-second polarization beam splitting prism, 32-third mirror, 33-tenth 1 / 2 glass, 34-fourth mirror, 35-detection cavity, 36-second photodetector, 37-third beam splitter, 38-first dichroic plate, 39-second dichroic plate, 40-band pass filter, 41-long pass filter, 42-mirror, 43-converging lens, 44-spectrometer, 45-second frequency locking device. DETAILED DESCRIPTION

[0019] In order to make the personnel in the technical field better understand the scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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 the person of ordinary skill in the art without making creative labor should belong to the protection scope of the present application.

[0020] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0021] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "transverse", "longitudinal" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0022] In addition, in addition to indicating the orientation or positional relationship, the above-mentioned partial terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the present application can be understood according to the specific situation.

[0023] In addition, the meaning of the term "a plurality of" should be two and more than two.

[0024] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0025] As shown in Figure 1 The present application provides an optical interference low vacuum measurement device based on cavity enhanced Raman reference, which comprises a measurement reference light path system a, a measurement detection light path system b, a cavity enhanced Raman detection light path system c and a frequency meter 19, wherein: the measurement reference light path system a is composed of a reference light path assembly and a first frequency locking circuit, the reference light path assembly comprises a first laser 1, a first beam splitter 5, a first optical isolator 10, a first polarization beam splitting prism 13 and a reference cavity 17; the first frequency locking circuit is used to keep the reference laser emitted by the first laser 1 in a resonant state in the reference cavity 17; the measurement detection light path system b comprises a detection light path assembly and a second frequency locking circuit, the detection light path assembly comprises a second laser 20, a second beam splitter 24, a second optical isolator 29, a second polarization beam splitting prism 31 and a detection cavity 35; the second frequency locking circuit is used to keep the detection laser emitted by the second laser 20 in a resonant state before and after being filled with gas in the detection cavity 35; the cavity enhanced Raman detection light path system c shares a set of detection light path assembly with the measurement detection light path system b, and the cavity enhanced Raman detection light path system c further comprises a Raman spectrum detection assembly, the Raman spectrum detection assembly comprises a third beam splitter 37 and a spectrometer 44; the frequency meter 19 is arranged between the measurement reference light path system a and the measurement detection light path system b, and is used to receive the reference laser passing through the first beam splitter 5 and the detection laser passing through the second beam splitter 24.

[0026] Specifically, the optical interference low-vacuum measuring device based on cavity-enhanced Raman reference provided by the embodiments of the present application uses a cage structure modular design for each part of the optical path, each module is independent of each other, has high stability and coaxiality, is convenient to replace damaged components, and is divided into three parts of the optical path: the first part of the optical path is an optical interference low-vacuum measurement reference optical path system a, which is used to keep the reference cavity 17 in a resonant state in a high-vacuum environment, and provide a stable resonant laser frequency signal in a high-vacuum state for a detection optical path; the second part of the optical path is an optical interference low-vacuum measurement detection optical path system b, which is used to resonate in a detection cavity 35, and keep the resonant state before and after the detection cavity 35 is filled with gas; the third part is a cavity-enhanced Raman detection optical path system c, which is used to accumulate and enhance the cavity Raman excitation laser, and realize the detection of the Raman signal of the gas in the cavity; and the frequency meter 19 is used to measure the difference between the beat frequencies of the reference laser and the detection laser.

[0027] More specifically, the cavity-enhanced Raman detection optical path system c and the measurement detection optical path system b share a set of detection optical path components, so that when the detection laser resonates in the detection cavity 35, not only the laser frequency change measurement can be realized, but also the accumulation of the cavity Raman excitation light signal can be realized, and the Raman signal of the measured gas in the cavity can be enhanced. Therefore, when measuring the pressure of the gas in the cavity, the resonant laser in the detection cavity 35 and the resonant laser in the reference cavity 17 always keep the beat frequency, and the change amount of the resonant laser frequency in the detection cavity 35 before and after being filled with gas can be calculated by the change amount of the beat frequency, so as to realize the inversion of the standard pressure; and the type of the gas in the detection cavity 35 can be qualitatively determined according to the Raman spectrum fingerprint characteristics, the gas concentration can be inverted according to the relationship between the gas concentration and the Raman intensity, and the gas pressure in the detection cavity 35 can be calculated according to the inverted gas concentration.

[0028] Further, the first laser 1 and the first beam splitter 5 are sequentially provided with a first 1 / 2 glass 2, a first collimator 3 and a second 1 / 2 glass 4; the first beam splitter 5 and the first optical isolator 10 are sequentially provided with a first Taylor prism 6, a first mode adjusting lens group (7, 8) and a third 1 / 2 glass 9; the first optical isolator 10 and the first polarization beam splitting prism 13 are provided with a fourth 1 / 2 glass 11; the first polarization beam splitting prism 13 and the reference cavity 17 are sequentially provided with a first mirror 14, a fifth 1 / 2 glass 15 and a second mirror 16.

[0029] Further, the first frequency locking circuit includes a first photodetector 18 and a first frequency locking device 12, wherein: the first photodetector 18 is arranged behind the reference cavity 17 and is used to receive the transmission signal of the reference cavity 17; and the first frequency locking device 12 is used to receive the signal of the first photodetector 18 and the laser beam split by the first polarization beam splitting prism 13, so that the reference laser keeps a resonant state in the reference cavity 17.

[0030] Specifically, the optical interference low vacuum measurement reference light path system a adjusts the reference laser emitted by the first laser 1 through the reference light path component, and then introduces the reference laser into the reference cavity 17 in the horizontal direction, and uses the first frequency locking circuit to keep the reference laser in the reference cavity 17 in a resonant state.

[0031] Further, the sixth 1 / 2 glass 21, the second collimator 22 and the seventh 1 / 2 glass 23 are sequentially arranged between the second laser 20 and the second beam splitter 24; the second Taylor prism 25, the second mode adjustment lens group (26, 27) and the eighth 1 / 2 glass 28 are sequentially arranged between the second beam splitter 24 and the second optical isolator 29; the ninth 1 / 2 glass 30 is arranged between the second optical isolator 29 and the second polarization beam splitting prism 31; the third mirror 32, the tenth 1 / 2 glass 33 and the fourth mirror 34 are sequentially arranged between the second polarization beam splitting prism 31 and the detection cavity 35.

[0032] Further, the second frequency locking circuit includes a second photodetector 36 and a second frequency locking device 45, wherein: the second photodetector 36 is arranged behind the detection cavity 35 and is used to receive the transmission signal of the detection cavity 35; and the second frequency locking device is used to receive the signal of the second photodetector 36 and the laser beam split by the second polarization beam splitting prism 31, so that the detection laser in the detection cavity 35 keeps a resonant state before and after the detection cavity 35 is filled with gas.

[0033] Specifically, the optical interference low vacuum measurement detection light path system b adjusts the detection laser emitted by the second laser 20 through the detection light path component, and then introduces the detection laser into the detection cavity 35 in the horizontal direction, and uses the second frequency locking circuit to keep the detection laser in the detection cavity 35 in a resonant state before and after the detection cavity 35 is filled with gas.

[0034] Further, the third beam splitter 37 is arranged between the second polarization beam splitting prism 31 and the second frequency locking device 45.

[0035] Further, the first dichroic plate 38, the second dichroic plate 39, the band-pass filter 40, the long-pass filter 41, the fifth mirror 42 and the converging lens 43 are sequentially arranged between the third beam splitter 37 and the spectrometer 44.

[0036] Specifically, the Raman spectrum detection assembly uses the third beam splitter 37 to split the reflected signal for frequency locking in the detection light path assembly, and uses the first dichroic filter 38, the second dichroic filter 39, the band-pass filter 40, and the long-pass filter 41 to filter out the Raman spectrum signal that can be used for gas pressure detection, and the signal is collected by the fifth mirror 42 and the converging lens 43, and the spectrum analyzer is used to analyze the gas Raman detection signal, so that the laser frequency change measurement can be realized, and the accumulation of the in-cavity Raman excitation light signal can be realized, and the Raman signal of the in-cavity measured gas is enhanced.

[0037] Further, the reference cavity 17 is always kept in a high vacuum state, and the vacuum degree is ≤10-5Pa; the detection cavity 35 is initially in a high vacuum state, and the vacuum degree is ≤10-5Pa, and the inside of the detection cavity 35 is filled with test gas during measurement.

[0038] Specifically, when the gas pressure is measured by using the embodiment of the application:

[0039] First, the reference cavity 17 is pumped to a high vacuum state by using the air pump set (a mechanical pump and a molecular pump), the vacuum degree is ≤10-5Pa, the polarization state and mode of each detection light path assembly are adjusted, the detection laser emitted by the second laser 20 is introduced into the detection cavity 35 along the horizontal direction, the transmission signal of the detection laser is detected by using the second photodetector 36, the frequency locking of the resonant laser is performed by using the second frequency locking device 45, the initial beat frequency v - 5 Pa, the polarization state and mode of each detection light path assembly are adjusted, the detection laser emitted by the second laser 20 is introduced into the detection cavity 35 along the horizontal direction, the transmission signal of the detection laser is detected by using the second photodetector 36, the frequency locking of the resonant laser is performed by using the second frequency locking device 45, the initial beat frequency v

[0040] Second, the detection cavity 35 is pumped to a high vacuum state by using the air pump set (a mechanical pump and a molecular pump), the vacuum degree is ≤10-5Pa, the polarization state and mode of each detection light path assembly are adjusted, the detection laser emitted by the second laser 20 is introduced into the detection cavity 35 along the horizontal direction, the transmission signal of the detection laser is detected by using the second photodetector 36, the frequency locking of the resonant laser is performed by using the second frequency locking device 45, the initial beat frequency v - 5 Pa, the polarization state and mode of each detection light path assembly are adjusted, the detection laser emitted by the second laser 20 is introduced into the detection cavity 35 along the horizontal direction, the transmission signal of the detection laser is detected by using the second photodetector 36, the frequency locking of the resonant laser is performed by using the second frequency locking device 45, the initial beat frequency v i is measured by using the frequency meter 19, and the record is made; then the detection cavity 35 is filled with gas, and the laser in the detection cavity 35 is kept in a resonant state, after the filling is completed, the initial beat frequency v f is measured by using the frequency meter 19, and the record is made, and then the calculation of the gas refractive index is performed by using the following formula:

[0041]

[0042] In the formula, Ω is a function correction quantity related to the temperature change ΔT and the cavity length change ΔL; then, the inversion of the standard pressure can be realized by combining the virial relationship between the pressure and the refractive index:

[0043] p = c1 · (n-1) + c2 · (n-1) 2 + c3 · (n-1) 3 + c4 · (n-1) 4 + O((n-1) 5 )

[0044] In the formula,

[0045] wherein Aε is the molar polarizability, Aμ is the molar magnetizability, and Bε(T) is the second dielectric Virial coefficient.

[0046] Finally, the laser in the cavity-enhanced Raman detection optical path is resonantly enhanced for Raman excitation light in the detection cavity 35, and the reflected laser out of the cavity is split by the third beam splitter 37, one of the split beams is filtered by the optical filtering assembly to obtain the Raman spectrum signal for gas pressure detection, and is collected by the converging lens 43, and the spectral analyzer is used to analyze the gas Raman detection signal, the type of the gas in the cavity is qualitatively determined according to the Raman spectrum fingerprint characteristics, the gas concentration is inversely calculated according to the relationship between the gas concentration and the Raman intensity, and the gas pressure in the cavity is calculated according to the calculated gas concentration.

[0047] The above only describes the preferred embodiments of the present application and is not used to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An optical interferometric low vacuum measuring device based on a cavity-enhanced Raman reference, characterized in that, The application relates to a frequency counter, a measurement reference light path system, a measurement detection light path system, a cavity-enhanced Raman detection light path system and a frequency counter, wherein: The measurement reference light path system is composed of a reference light path component and a first frequency locking circuit, the reference light path component comprises a first laser, a first beam splitter, a first optical isolator, a first polarization beam splitter prism and a reference cavity; the first frequency locking circuit is used for keeping the reference laser emitted by the first laser in a resonant state in the reference cavity; The measurement detection light path system comprises a detection light path component and a second frequency locking circuit, the detection light path component comprises a second laser, a second beam splitter, a second optical isolator, a second polarization beam splitter prism and a detection cavity; the second frequency locking circuit is used for keeping the detection laser emitted by the second laser in a resonant state before and after the detection cavity is filled with air; The cavity-enhanced Raman detection light path system shares a set of detection light path components with the measurement detection light path system, and the cavity-enhanced Raman detection light path system further comprises a Raman spectrum detection component, the Raman spectrum detection component comprises a third beam splitter and a spectrometer; The frequency counter is arranged between the measurement reference light path system and the measurement detection light path system and is used for receiving the reference laser passing through the first beam splitter and the detection laser passing through the second beam splitter; The second frequency locking circuit comprises a second photodetector and a second frequency locking device, wherein: The second photodetector is arranged behind the detection cavity and is used for receiving the transmission signal of the detection cavity; The second frequency locking device is used for receiving the second photodetector signal and the laser beam split by the second polarization beam splitter prism, so that the detection laser keeps in a resonant state before and after the detection cavity is filled with air; The third beam splitter is arranged between the second polarization beam splitter prism and the second frequency locking device.

2. The cavity-enhanced Raman reference based optical interferometry low vacuum measurement device of claim 1, wherein, A first 1 / 2 glass, a first collimator and a second 1 / 2 glass are sequentially arranged between the first laser and the first beam splitter; a first Taylor prism, a first mode adjusting lens group and a third 1 / 2 glass are sequentially arranged between the first beam splitter and the first optical isolator; a fourth 1 / 2 glass is arranged between the first optical isolator and the first polarization beam splitter prism; a first reflector, a fifth 1 / 2 glass and a second reflector are sequentially arranged between the first polarization beam splitter prism and the reference cavity.

3. The cavity-enhanced Raman reference based optical interferometry low vacuum measurement device of claim 2, wherein, The first frequency locking circuit comprises a first photodetector and a first frequency locking device, wherein: The first photodetector is arranged behind the reference cavity and is used for receiving the transmission signal of the reference cavity; The first frequency locking device is used for receiving the first photodetector signal and the laser beam split by the first polarization beam splitter prism, so that the reference laser keeps in a resonant state in the reference cavity.

4. The cavity-enhanced Raman reference based optical interferometry low vacuum measurement device of claim 3, wherein, The sixth 1 / 2 glass, the second collimator and the seventh 1 / 2 glass are sequentially arranged between the second laser and the second beam splitter; the second Taylor prism, the second mode adjusting lens group and the eighth 1 / 2 glass are sequentially arranged between the second beam splitter and the second optical isolator; the ninth 1 / 2 glass is arranged between the second optical isolator and the second polarization beam splitting prism; the third mirror, the tenth 1 / 2 glass and the fourth mirror are sequentially arranged between the second polarization beam splitting prism and the detection cavity.

5. The cavity-enhanced Raman reference based optical interferometry low vacuum measurement device of claim 4, wherein, The first dichroic plate, the second dichroic plate, the band-pass filter plate, the long-pass filter plate, the fifth mirror and the converging lens are sequentially arranged between the third beam splitter and the spectrometer.

6. The cavity-enhanced Raman reference based optical interferometry low vacuum measurement device of claim 5, wherein, The reference cavity is always kept in high vacuum state, vacuum degree ≤10 -5 Pa; the initial state of the detection cavity is high vacuum state, vacuum degree ≤10 -5 Pa, when measuring, the test gas is filled into the inside of the detection cavity.

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