CN221686205U - Permeation enhancement type off-axis integral cavity structure - Google Patents

Abstract

The utility model discloses a transmission-enhanced off-axis integrating cavity structure, including a mechanical cavity, a proximal cavity mirror, a distal cavity mirror and an infrared laser; the proximal cavity mirror and the distal cavity mirror are both plano-concave mirrors, and the planes of the proximal cavity mirror and the distal cavity mirror are both set as incident surfaces and coated with anti-reflection films, and the concave surfaces are both set as reflection surfaces and coated with anti-reflection films; the concave surfaces of the proximal cavity mirror and the distal cavity mirror are parallel to each other and together with the mechanical cavity form an optical resonant cavity; the spacing between the proximal cavity mirror and the distal cavity mirror and the curvature of the concave surface are taken so that the off-axis incident light beam breaks the paraxial approximation condition. The utility model adopts a transmission-through off-axis integrating cavity design, which reduces the excessive light intensity fluctuation noise and baseline fluctuation caused by the F-P cavity interference effect, and at the same time, the resonant cavity is easy to adjust, improves immunity to mechanical vibration, and has a simple device; this method excites a large number of cavity modes, reduces the free spectrum range, effectively suppresses cavity mode noise, and improves sensitivity.

Description

A transmission-enhanced off-axis integrating cavity structure

Technical Field

The utility model relates to the technical field of cavity-enhanced integral output spectrum detection, in particular to a transmission-enhanced off-axis integral cavity structure.

Background Art

Absorption spectroscopy detection technology is widely used in the detection and research of trace gases, isotopes, free radicals and molecular spectra in the atmosphere. Increasing the effective absorption path and improving the transmitted light intensity are two key factors to improve its detection sensitivity.

In terms of improving the effective absorption optical path, optical multi-pass absorption cell technology, cavity ring-down absorption spectroscopy technology ("Cavity Ring-down Optical Spectrometer for Absorption Measurements Using Pulsed Laser Sources", Review of Scientific Instruments, 1988, 59 (12): 2544-2511), integrated cavity output spectroscopy cavity or enhanced absorption spectroscopy ("Integrated Cavity Output Analysis of Ultra-Weak Absorption", Chemical Physics Letter, 1998, 293 (5-6): 331-336) and off-axis integrated cavity output spectroscopy technology ("Sensitive Absorption Measurements In The Near-infrared Region Using Off-axis Integrated Cavity-output Spectroscopy", Applied Physics B, 2002, 75 (2-3): 261-265; U.S. Pat. No. 6,795,190 and "Wavelength Modulated Off-axis Integrated Cavity Output Spectroscopy In The Near Infrared”, Applied Physics B, 2007, 86(2): 353-359) have been proposed to increase the absorption path and improve the detection sensitivity.

Optical multi-pass cells (such as Herriot type, White type and Chernin type, cylindrical mirror type, astigmatic mirror type, etc.) reflect the incident light beam multiple times between two reflectors before emitting it, so that the optical path is increased by dozens of times of the basic length of the measuring cell, but it is still limited to the range of tens of meters to more than two hundred meters. Cavity ring-down absorption spectroscopy is similar to cavity enhanced absorption spectroscopy technology devices. Both use a high-precision optical resonant cavity composed of two ultra-high reflective mirrors (reflectivity>99.99%) to make the incident light infinitely reflect back and forth in the resonant cavity. It can achieve an optical path of several kilometers with a short base length and has a high detection sensitivity. The difference is that cavity ring-down spectroscopy detects the ring-down time, while cavity enhanced spectroscopy detects the intensity of the transmitted light. The device is simpler than cavity ring-down spectroscopy, but due to the inevitable interference effect of the optical resonant cavity, the detection light intensity fluctuates, and the detection sensitivity is slightly lower than that of cavity ring-down spectroscopy.

The off-axis integrated cavity output spectrum technology is to make the incident light off-axis based on the traditional coaxial integrated cavity, forming an optical multi-pass cell similar to the infinite circular reflection of the light beam in the cavity, forming a Herriott-type circular/elliptical spot or a cylindrical mirror/astigmatic mirror-type Lissajous spot on the mirror surface. The required device is simpler, the system stability requirement is low, and it can effectively avoid the interference effect of the resonant cavity, effectively improving the detection sensitivity. At present, it has been reported that this method can achieve a detection sensitivity higher than CRDS ("Design Considerations In High Sensitivity Off-axis Integrated Cavity Output Spectroscopy", Applied Physics B, 2008, 92: 467-474). The basic principle of the coaxial/off-axis integrated cavity output spectrum is: if the incident light intensity is I0, the cavity mirror reflectivity is the same, R=R1=R2, the cavity length is d, and the single-pass absorption is α, then the achievable absorption path length is:

If there is no absorption in the cavity, that is, when the cavity is empty, α=0, and the absorption path length formula becomes L=d/(1-R), where 1/(1-R) is the optical path gain factor. For example, for a cavity length of 0.5m, the effective path length corresponding to a reflectivity of R=99.95% is about 2km, while that corresponding to R=99.96% is 2.5km. Although the difference in reflectivity is small, the difference in path length is large. We use imported layertec high-reflectivity mirrors with a reflectivity of R=99.9986% and an effective optical path of 25km.

If the absorption of light by the cavity mirror is ignored, the transmitted light intensity can be expressed as: It can be seen from the absorption path length formula and the transmitted light intensity formula that the higher the cavity mirror reflectivity R, the greater the optical path gain, and the corresponding lower the transmitted light intensity. There is a balance between R and the transmitted light intensity. Increasing R does not necessarily improve the detection sensitivity. When the transmitted light intensity is weak to a certain extent, increasing R will reduce the sensitivity. The contradictory relationship between the reflectivity R and the transmitted light intensity limits the further improvement of the off-axis integrating cavity detection sensitivity.

The traditional off-axis integrating cavity has a complex structure, high manufacturing and use costs, and cannot avoid the fact that the incident light is directly sharply reduced after passing through the first cavity mirror of the sample cavity. The intensity of the detection light transmitted by the integrating cavity is low.

Utility Model Content

The purpose of the utility model is to provide a transmission-enhanced off-axis integrating cavity structure to solve the problems proposed in the above-mentioned background technology that the off-axis integrating cavity structure is complex, the manufacturing and use costs are high, and the fact that the incident light is directly sharply reduced after passing through the first cavity mirror in the sample cavity cannot be avoided, and the light intensity of the detection light transmitted by the integrating cavity is low.

To achieve the above-mentioned purpose, the utility model provides the following technical solutions: a transmission-enhanced off-axis integrating cavity structure, comprising a mechanical cavity, a proximal cavity mirror, a distal cavity mirror and an infrared laser; the proximal cavity mirror and the distal cavity mirror are both plano-concave mirrors, and the planes of the proximal cavity mirror and the distal cavity mirror are both set as incident surfaces and coated with anti-reflection films, and the concave surfaces are both set as reflection surfaces and coated with anti-reflection films;

The concave surfaces of the proximal cavity mirror and the distal cavity mirror are parallel to each other and together with the mechanical cavity form a sealed optical resonant cavity;

The infrared laser is a near-infrared wavelength tunable laser, and the infrared laser is arranged in front of the proximal cavity mirror so that the laser beam is incident on the optical resonant cavity at an off-axis angle of 0.1 to 0.8° to the X-axis and 1 to 2° to the Y-axis;

A focusing lens and a detector are also arranged outside the mechanical cavity, and the focusing lens is arranged close to a side of the mechanical cavity where a distal end mirror is arranged; the detector is arranged close to the focusing lens;

The laser beam emitted by the infrared laser passes through the proximal cavity mirror into the optical resonant cavity, contacts the gas component to be measured, and then reaches the concave surface of the distal cavity mirror. It is then reflected back to the concave surface of the proximal cavity mirror, and then reflected back to the concave surface of the distal cavity mirror. It is thus reflected back and forth, and forms a light spot on the concave surfaces of the proximal cavity mirror and the distal cavity mirror. At the same time, a large number of weak light beams are transmitted through the reflection enhancement film of the distal cavity mirror to form the required detection light beam. The focusing lens focuses all the detection light beams onto the detection chip of the detector.

The distance between the proximal cavity mirror and the distal cavity mirror and the curvature of the concave surface are set so that the off-axis incident light beam breaks the paraxial approximation condition.

Preferably, the proximal cavity mirror is mounted on the mechanical cavity through four proximal PZT piezoelectric ceramics; the other end of the proximal PZT piezoelectric ceramic is mounted on the mechanical cavity, and the proximal cavity mirror is driven to move by controlling the deformation amount through voltage to destroy the cavity mode matching.

Preferably, the distal laparoscope is mounted on the mechanical cavity through four distal PZT piezoelectric ceramics; the other end of the distal PZT piezoelectric ceramic is mounted on the mechanical cavity, and the deformation amount is controlled by voltage to drive the distal laparoscope to move so as to destroy the cavity mode matching.

Preferably, the concave surface of the proximal cavity mirror is coated with a reflection-enhancing film with a reflectivity of >99.99%, and the transmittance of the reflection-enhancing film is 6 _to 40 ppm.

Preferably, the concave surface of the distal cavity mirror is coated with a reflection enhancement film with a reflectivity of >99.99%, and the transmittance of the reflection enhancement film is 6 _to 40 ppm.

Preferably, the mechanical cavity is connected to and includes the proximal cavity mirror and the distal cavity mirror to form an optical resonant cavity, and the mechanical cavity is provided with an air outlet and an air inlet communicated with the optical resonant cavity.

Preferably, the proximal cavity mirror, the distal cavity mirror and the focusing lens are all made of fused quartz.

Preferably, the detector is a high-bandwidth detector in the near-infrared band.

Compared with the prior art, the advantages and benefits of this utility model are:

1. The utility model adopts a transmission-enhanced off-axis integrating cavity structure, which reduces the excessive light intensity fluctuation noise and baseline fluctuation caused by the F-P cavity interference effect. At the same time, the resonant cavity is easy to adjust, which improves the immunity to mechanical vibration. The device is simple and the requirements for the data acquisition system are not high. This method excites a large number of cavity modes, which reduces the free spectrum range, effectively suppresses the cavity mode noise, and improves the sensitivity.

2. The utility model uses PZT piezoelectric ceramics to drive the periodic movement of the front and rear cavity mirrors through the enhanced off-axis integrating cavity structure to destroy the cavity mode matching, thereby avoiding the problem that the transmission spectrum may not be detected or the accuracy is very low when the resonant cavity is in a stable state, thereby improving the detection accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of a transmission-enhanced off-axis integrating cavity structure according to an embodiment of the present invention.

In the figure: 1. Infrared laser; 2. Proximal cavity mirror; 3. Proximal PZT piezoelectric ceramic; 4. Mechanical cavity; 5. Distal cavity mirror; 6. Distal PZT piezoelectric ceramic; 7. Focusing lens; 8. Detector; 9. Air outlet; 10. Air inlet.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

Example 1

As shown in FIG1 , a technical solution is provided in this embodiment: a transmission-enhanced off-axis integrating cavity structure, comprising a mechanical cavity 4, a proximal cavity mirror 2, a distal cavity mirror 5 and an infrared laser 1; the proximal cavity mirror 2 and the distal cavity mirror 5 are both plano-concave mirrors, and the planes of the proximal cavity mirror 2 and the distal cavity mirror 5 are both set as incident surfaces and coated with anti-reflection films, and the concave surfaces are both set as reflection surfaces and coated with anti-reflection films;

The concave surfaces of the proximal cavity mirror 2 and the distal cavity mirror 5 are parallel and opposite to each other and together with the mechanical cavity 4 form a sealed optical resonant cavity;

The infrared laser 1 is a near-infrared wavelength tunable laser, and the infrared laser 1 is arranged in front of the proximal cavity mirror 2 so that the laser beam is incident on the optical resonant cavity at an off-axis angle of 0.1 to 0.8° to the X-axis and 1 to 2° to the Y-axis (the specific off-axis angle depends on the cavity mirror distance and the interference condition);

A focusing lens 7 and a detector 8 are also provided outside the mechanical cavity 4, and the focusing lens 7 is provided close to a side of the mechanical cavity 4 where the distal cavity mirror 5 is provided; the detector 8 is provided close to the focusing lens 7;

The laser beam emitted by the infrared laser 1 passes through the proximal cavity mirror 2 into the optical resonant cavity and contacts the gas component to be measured. After reaching the concave surface of the distal cavity mirror 5, it is reflected back to the concave surface of the proximal cavity mirror 2, and then reflected back to the concave surface of the distal cavity mirror 5. It is reflected back and forth and forms a light spot on the concave surface of the proximal cavity mirror 2 and the concave surface of the distal cavity mirror 5. At the same time, a large number of weak light beams are transmitted through the reflection enhancement film of the distal cavity mirror 5 to form the required detection beam. The focusing lens 7 focuses all the detection beams onto the detection chip of the detector 8. The near-infrared laser 1 is a near-infrared wavelength tunable laser. After the laser is collimated by the optical fiber, it is incident off-axis at a certain angle into the optical resonant cavity to form "re-incident". When the "re-incident" condition is met, it can be used with a near-infrared ultra-high reflection mirror with a reflectivity of >99.99%, and the maximum measurement optical distance can reach about 25km;

In this embodiment, a transmission-through off-axis integrating cavity design is used to reduce the excessive light intensity fluctuation noise and baseline fluctuation caused by the F-P cavity interference effect. At the same time, the resonant cavity is easy to adjust, which improves immunity to mechanical vibration. The device is simple and does not require a high data acquisition system. This method excites a large number of cavity modes to reduce the free spectrum range, effectively suppress the cavity mode noise, and improve sensitivity. At the same time, PZT piezoelectric ceramics are used to drive the periodic movement of the front and rear cavity mirrors to destroy the cavity mode matching, avoiding the problem that the transmission spectrum may not be detected or the accuracy is very low when the resonant cavity is in a stable state, thereby improving the detection accuracy;

The distance between the proximal cavity mirror 2 and the distal cavity mirror 6 and the curvature of the concave surface are set so that the off-axis incident light beam breaks the paraxial approximation condition.

The utility model adopts a transmission-enhanced off-axis integrating cavity structure, which adopts a transmission-through off-axis integrating cavity design, reduces the excessive light intensity fluctuation noise and baseline fluctuation caused by the F-P cavity interference effect, and at the same time, the resonant cavity is easy to adjust, which improves the immunity to mechanical vibration, the device is simple, and the requirements for the data acquisition system are not high; this method excites a large number of cavity modes, so that the free spectrum range becomes smaller, the cavity mode noise is effectively suppressed, and the sensitivity is improved.

Furthermore, the proximal cavity mirror 2 is installed on the mechanical cavity 4 through four proximal PZT piezoelectric ceramics 3; the other end of the proximal PZT piezoelectric ceramic 3 is installed on the mechanical cavity 4, and the proximal cavity mirror 2 is driven to move by controlling the deformation amount through voltage to destroy the cavity mode matching, thereby increasing the detection light intensity and detection accuracy.

Furthermore, the distal cavity mirror 5 is installed on the mechanical cavity 4 through four distal PZT piezoelectric ceramics 6; the other end of the distal PZT piezoelectric ceramic 6 is installed on the mechanical cavity 4, and the distal cavity mirror 5 is driven to move by controlling the deformation through voltage to destroy the cavity mode matching, thereby increasing the detection light intensity and detection accuracy, avoiding the problem that the transmission spectrum may not be detected or the accuracy is very low when the resonant cavity is in a stable state, thereby improving the sensitivity.

Furthermore, the concave surface of the proximal cavity mirror 2 is coated with a reflection-enhancing film with a reflectivity of >99.99%, and the transmittance of the reflection-enhancing film is 6 _to 40ppm. The concave surface of the distal cavity mirror 5 is coated with a reflection-enhancing film with a reflectivity of >99.99%, and the transmittance of the reflection-enhancing film is 6 _to 40ppm. The curvature radius of the concave surfaces of the proximal cavity mirror 2 and the distal cavity mirror 5 is 1m, and the diameter of the proximal cavity mirror 2 and the distal cavity mirror 5 is 25mm. The concave surfaces of the proximal cavity mirror and the distal cavity mirror are high-precision polished spherical surfaces with the same curvature radius of 1m, and are coated with an ultra-high reflectivity film layer with a reflectivity of R=99.9986%. The theoretical effective optical path can reach 25km.

Furthermore, the mechanical cavity 4 connects and includes the proximal laparoscope 2 and the distal laparoscope 5 to form an optical resonant cavity. The mechanical cavity 4 is provided with an air outlet 9 and an air inlet 10 which are connected to the optical resonant cavity. The front and rear ends of the mechanical cavity 4 are respectively connected to the proximal laparoscope 2 and the distal laparoscope 5 through the proximal PZT piezoelectric ceramic 3 and the distal PZT piezoelectric ceramic 6. The proximal laparoscope 2 is installed at the front end of the mechanical cavity 4 and is connected through the proximal PZT piezoelectric ceramic 3, and the distal laparoscope 5 is installed at the rear end of the mechanical cavity 4 and is connected through the distal PZT piezoelectric ceramic 6.

Furthermore, the materials of the proximal cavity mirror 2, the distal cavity mirror 5 and the focusing lens 7 are all fused quartz.

Furthermore, the detector 8 is a high-bandwidth detector in the near-infrared band.

Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims (8)

1. The utility model provides a pass through enhancement mode off-axis integration chamber structure which characterized in that: comprises a mechanical cavity (4), a near-end endoscope (2), a far-end endoscope (5) and an infrared laser (1); the near-end endoscope (2) and the far-end endoscope (5) are plano-concave mirrors, the planes of the near-end endoscope (2) and the far-end endoscope (5) are both arranged as incident surfaces and are plated with antireflection films, and the concave surfaces are both arranged as reflecting surfaces and are plated with antireflection films;

the concave surfaces of the near-end endoscope (2) and the far-end endoscope (5) are parallel and opposite and form a sealed optical resonant cavity together with the mechanical cavity (4);

The infrared laser (1) is a near infrared wavelength tunable laser, and the infrared laser (1) is arranged in front of the near-end cavity mirror (2) to enable laser beams to be incident into the optical resonant cavity in an off-axis mode at an angle of 0.1-0.8 degrees towards the X axis and 1-2 degrees towards the Y axis;

A focusing lens (7) and a detector (8) are arranged outside the mechanical cavity (4), and the focusing lens (7) is arranged close to one side of the mechanical cavity (4) where the far-end cavity mirror (5) is arranged; the detector (8) is arranged close to the focusing lens (7);

The laser beam emitted by the infrared laser (1) passes through the near-end cavity mirror (2) to reach the concave surface of the far-end cavity mirror (5) after contacting with the gas component to be detected in the optical resonant cavity, and then is reflected back to the concave surface of the near-end cavity mirror (2) and then is reflected back to the concave surface of the far-end cavity mirror (5), so that light spots are formed on the concave surface of the near-end cavity mirror (2) and the concave surface of the far-end cavity mirror (5), a large number of weak beams are transmitted out through the reflection enhancing film of the far-end cavity mirror (5) to form required detection beams, and the focusing lens (7) focuses all the detection beams on the detection chip of the detector (8);

The distance between the near-end endoscope (2) and the far-end endoscope (5) and the curvature of the concave surface take values so that the off-axis incident light beam breaks the paraxial approximate condition.

2. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the near-end cavity mirror (2) is arranged on the mechanical cavity (4) through four near-end PZT piezoelectric ceramics (3); the other end of the near-end PZT piezoelectric ceramic (3) is arranged on the mechanical cavity (4), and the near-end cavity mirror (2) is pushed to move by voltage control deformation so as to destroy cavity mode matching.

3. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the distal cavity mirror (5) is arranged on the mechanical cavity (4) through four distal PZT piezoelectric ceramics (6); the other end of the distal PZT piezoelectric ceramic (6) is arranged on the mechanical cavity (4), and the distal cavity mirror (5) is pushed to move by voltage control deformation so as to destroy cavity mode matching.

4. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the concave surface of the near-end endoscope (2) is plated with a reflection enhancing film with the reflectivity of more than 99.99 percent, and the transmittance of the reflection enhancing film is 6 _～ ppm.

5. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the concave surface of the far-end endoscope (5) is plated with a reflection enhancing film with the reflectivity of more than 99.99 percent, and the transmittance of the reflection enhancing film is 6 _～ ppm.

6. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the mechanical cavity (4) is connected with the near-end cavity mirror (2) and the far-end cavity mirror (5) and comprises an optical resonant cavity, and an air outlet (9) and an air inlet (10) which are communicated with the optical resonant cavity are arranged on the mechanical cavity (4).

7. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the materials of the near-end endoscope (2), the far-end endoscope (5) and the focusing lens (7) are all fused silica.

8. The transmission enhanced off-axis integrating cavity structure of claim 1, wherein: the detector (8) is a high bandwidth detector in the near infrared band.