Dynamic phase pneumatic control system for enhancing laser spectrum based on optical feedback cavity

Abstract

The utility model belongs to the technical field of optical feedback cavity enhanced laser absorption spectrum, and particularly relates to a dynamic phase pneumatic control system based on optical feedback cavity enhanced laser spectrum. In order to provide a dynamic phase adjustment pneumatic control system which does not influence light path collimation, a Fabry-Perot (F-P) cavity is adopted, a distributed feedback type diode laser is used as a light source, the laser and the F-P cavity are subjected to mode matching through a matching lens, a feedback phase is controlled through an adjusting element, and the optical path collimation is not influenced. The incident power and the feedback rate are controlled through the lambda / 2 wave plate, the polarization splitting prism and the lambda / 4 wave plate, then the laser is coupled to enter the F-P cavity and finally is driven into the photoelectric detector through the focusing lens, and the amplitude of the transmitted laser signal is detected.

Description

Technical Field

[0001] The utility model belongs to the technical field of optical feedback cavity enhanced laser absorption spectroscopy, and particularly relates to a dynamic phase gas control system based on optical feedback cavity enhanced laser spectroscopy. Background Technique

[0002] Gas detection plays an important role in many aspects such as industry, agriculture, transportation, science and technology, environmental protection, and national defense. Laser spectroscopy technology has the advantages of high sensitivity, fast response speed, in-situ detection, etc. and is widely used. Its principle lies in the interaction between laser and gas molecules. On this basis, the Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) developed is a high-sensitivity spectroscopy technology. It scans the absorption spectrum lines of the gas corresponding to the wavelength by scanning the temperature or current of the semiconductor laser, and uses an optical cavity composed of high-reflection mirrors to enhance the interaction path between the gas to be measured and the laser, so as to achieve high-precision measurement of the gas concentration. At the same time, in order to narrow the laser linewidth and improve the coupling between the laser and the optical cavity, optical feedback is introduced to achieve frequency locking and suppress the laser frequency noise.

[0003] The feedback phase is a key factor in the optical feedback cavity enhanced technology. Only when the phase of the feedback light is the same as that of the laser field in the optical cavity does the optical feedback work. The conventional method uses a piezoelectric ceramic (PZT) to adjust. By sticking the mirror on the PZT, the error signal is obtained through the asymmetry of the transmitted cavity mode, and the corresponding voltage is applied to the PZT to make it expand and contract to adjust the front and rear distance of the mirror to control the feedback phase, so that the transmitted signal shows a cavity mode signal with appropriate left and right symmetry amplitude. However, this adjustment method directly changes the original collimation of the optical path, affects the signal amplitude, and further affects the measurement.

[0004] Therefore, it is of practical significance to study a phase adjustment system that does not affect the collimation of the optical path. Content of the Utility Model

[0005] The utility model provides a dynamic phase gas control system based on optical feedback cavity enhanced laser spectroscopy for the above problems. This gas control system does not affect the collimation of the optical path, and at the same time has a wide phase tuning range and high optical path stability.

[0006] To achieve the above object, the utility model adopts the following technical solutions:

[0007] An adjustment element includes a gas cell made of quartz glass and in a cylindrical shape. Two gas pipes are installed on the gas cell, and micropores are installed in both of the two gas pipes to control the gas flow rate in the gas pipes. An electromagnetic valve and a vacuum pump are sequentially installed on one of the gas pipes, and a fine filter, a ferrule ball valve, a coarse filter, and a nitrogen cylinder are sequentially installed on the other gas pipe. Nitrogen is filled inside to prevent the laser from directly acting on the internal gas and affecting the measurement.

[0008] Further, the two circular end faces of the gas cell are in a wedge-shaped structure, and the selection of the wedge angle is mainly based on the need to reduce the interference effect, and the included angle is between 0.5° and 5°.

[0009] Further, the circular end faces are coated with an antireflection film corresponding to the laser wavelength band to prevent the influence of secondary reflected light on the optical path.

[0010] A dynamic phase gas control system based on optical feedback cavity enhanced laser spectroscopy includes the adjustment element described above, a distributed feedback diode laser, and a Fabry - Perot cavity;

[0011] The distributed feedback diode laser emits laser light, which sequentially passes through a matching lens, a gas cell, a λ / 2 wave plate, and a polarization beam splitter prism and is divided into three laser signals. The first laser signal passes through a λ / 4 wave plate and is coupled into the Fabry - Perot cavity. The transmitted laser signal of the Fabry - Perot cavity enters the first photodetector through a focusing lens, and the signal collected by the first photodetector enters the computer through a data acquisition card; the second laser signal enters the second photodetector, and the signal collected by the second photodetector enters the computer through a data acquisition card; the third laser signal enters the third photodetector, and the signal collected by the third photodetector enters the computer through a data acquisition card.

[0012] Further, the Fabry - Perot cavity consists of a plane mirror and a concave mirror both coated with a high - reflection film, and a Invar - material cavity body. A filter is installed on the Invar - material cavity body, and the Invar - material cavity body is connected to an air pump through a valve with a pipeline.

[0013] The present utility model is based on the Eddington - Ladenburg equation and takes into account the influence of temperature and pressure:

[0014]

[0015] Where: n(λ, T, P) is the refractive index at wavelength λ, temperature T (in Kelvin) and pressure P (in Pascal), P0 and T0 are the reference pressure and reference temperature respectively (generally 101325 Pascal and 273.15 Kelvin), B i (λ) and C i(λ) is a coefficient related to the wavelength, and their values depend on the specific gas. From s = n·l, it can be seen that by controlling the pressure, the refractive index can be changed, thereby controlling the effective optical path to make the optical feedback phase meet the requirement of an integer multiple of 2π.

[0016] Compared with the prior art, the present utility model has the following advantages:

[0017] 1. Ensure measurement accuracy

[0018] In the OF-CEAS system, the light beam needs to be reflected multiple times in the resonant cavity to enhance the interaction between light and gas. The collimated light beam can ensure that the light enters parallel and is correctly reflected in the cavity, minimizing the light intensity loss caused by the optical path deviation due to phase adjustment, thereby improving the stability of the system and the accuracy of measurement.

[0019] 2. Wide adjustment range

[0020] The air pressure control range can be from near vacuum to positive pressure range, with a large change range of the equivalent refractive index and a relatively large phase adjustable range. It can still achieve phase adjustment when the phase fluctuation is large.

[0021] 3. Reduce optical loss

[0022] The design of the wedge-shaped end face and the antireflection film can significantly reduce the interference fringes (Fabry-Perot interference) caused by multiple reflections between the two parallel planes of the adjustment element. This kind of interference may lead to signal fluctuations and inaccurate measurements in spectroscopy. The wedge angle design reduces this effect by destroying the parallelism of the two reflecting surfaces, thereby providing a more stable signal output. Description of the drawings

[0023] Figure 1 It is a cross-sectional view of the wedge-shaped end face of the gas cell;

[0024] Figure 2 It is a schematic diagram of the device of the dynamic phase gas control system based on optical feedback cavity enhanced laser spectroscopy.

[0025] In the figure: 1 - distributed feedback diode laser, 2 - matching lens, 3 - gas cell, 4 - mirror, 5 - λ / 2 wave plate, 6 - polarization beam splitter prism, 7 - second photodetector, 8 - second photodetector, 9 - λ / 4 wave plate, 10 - air pump, 11 - valve, 12 - Fabry-Perot cavity, 13 - filter, 14 - focusing lens, 15 - first photodetector, 16 - vacuum pump, 17 - solenoid valve, 18 - micropore, 19 - fine filter, 20 - ferrule ball valve, 21 - true coarse filter, 22 - nitrogen cylinder. Detailed implementation manners

[0026] To further elaborate on the technical solution of the present utility model, the present utility model will be further described below through embodiments.

[0027] An adjusting element in this embodiment includes a gas cell 3, which is made of quartz glass and has a cylindrical shape. Two gas pipes are installed on the gas cell 3, and micropores 18 are installed in both of the two gas pipes to control the gas flow rate in the gas pipes. An electromagnetic valve 17 and a vacuum pump 16 are sequentially installed on one of the gas pipes, and a fine filter 19, a ferrule ball valve 20, a coarse filter 21, and a nitrogen cylinder 22 are sequentially installed on the other gas pipe. The two circular end faces of the gas cell 3 are wedge-shaped structures (as Figure 1 shown), with an included angle between 0.5° and 5°, and the circular end faces are coated with an antireflection film corresponding to the laser wavelength band.

[0028] Among them, the vacuum pump 16 uses a micro-vortex vacuum pump, the fine filter 19 uses a vacuum negative pressure pipeline type fine filter, and the coarse filter 21 uses a vacuum negative pressure pipeline type coarse filter.

[0029] A dynamic phase gas control system based on optical feedback cavity enhanced laser spectroscopy in this embodiment includes the above-mentioned adjusting element, a distributed feedback diode laser 1, and a Fabry-Perot cavity 12;

[0030] The distributed feedback diode laser 1 emits laser light, makes it emit light by controlling the temperature and current of the laser, applies a scanning signal to its driving current to tune the frequency of the laser. The laser sequentially passes through a matching lens 2, a gas cell 3, a mirror 4, a λ / 2 wave plate 5, and a polarization beam splitter prism 6, and is divided into three laser signals. The first laser signal passes through the mirror 4 and a λ / 4 wave plate 9 and is coupled into the Fabry-Perot cavity 12. The λ / 2 wave plate 5, the polarization beam splitter prism 6, and the λ / 4 wave plate 9 are used to control the incident power and the feedback rate. The transmitted laser signal of the Fabry-Perot cavity 12 enters the first photodetector 15 through a focusing lens 14. The signal collected by the first photodetector 15 enters the computer through a data acquisition card; the second laser signal enters the second photodetector 7, and the signal collected by the second photodetector 7 enters the computer through a data acquisition card; the third laser signal enters the third photodetector 8, and the signal collected by the third photodetector 8 enters the computer through a data acquisition card.

[0031] The Fabry-Perot cavity 12 is composed of a plane mirror and a concave mirror both coated with a high-reflection film, and an invar material cavity body. A filter 13 is installed on the invar material cavity body, and the invar material cavity body is connected to an air pump 10 through a valve 11 with a pipeline.

[0032] The transmission cavity mode signal collected by the first photodetector 15 passes through a data acquisition card. The program selects the range of the band without gas absorption, and then sets a certain interception threshold to prevent the dark current of the detector and the valley value of the cavity mode from affecting data processing. Then, the maximum value of the out-of-cavity mode, that is, the position of the film peak, is selected, and the parts higher than the threshold on both sides of the cavity mode are selected. The error signal is obtained by integrating and taking the difference, and an appropriate proportional operation is performed according to the ability of the regulating element to change the pressure to generate a correction signal, driving the solenoid valve and the vacuum pump to change the air pressure of the regulating element, thereby adjusting the feedback phase.

[0033] The foregoing has shown and described the main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes that fall within the meaning and scope of the equivalent elements of the claims in the present invention.

[0034] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A regulating element, characterized in that: It comprises a gas pool which is made of quartz glass and is cylindrical in shape. Two gas pipes are installed on the gas pool. Micropores are installed in the two gas pipes for controlling the gas flow rate in the gas pipes. A solenoid valve and a vacuum pump are installed in sequence on one of the gas pipes, and a fine filter, a ferrule ball valve, a coarse filter and a nitrogen bottle are installed in sequence on the other gas pipe.

2. An adjusting element according to claim 1, characterized in that: The two circular end surfaces of the gas pool are wedge-shaped structures, and the included angle is between 0.5° and 5°.

3. An adjusting element according to claim 2, characterized in that: The circular end surface is plated with an anti-reflection film corresponding to the laser wavelength band.

4. A dynamic phase gas control system based on optical feedback cavity enhanced laser spectrum, characterized in that: The device comprises the regulating element, distributed feedback diode laser and Fabry-Perot cavity as claimed in claim 3; The distributed feedback diode laser emits laser light, which is divided into three laser signals after passing through a matching lens, a gas cell, a λ / 2 wave plate, and a polarization beam splitter prism in sequence. The first laser signal enters a Fabry-Perot cavity through a λ / 4 wave plate coupling, and the transmitted laser signal of the Fabry-Perot cavity enters a first photodetector through a focusing lens, and the signal collected by the first photodetector enters a computer through a data acquisition card; the second laser signal enters a second photodetector, and the signal collected by the second photodetector enters a computer through a data acquisition card; the third laser signal enters a third photodetector, and the signal collected by the third photodetector enters a computer through a data acquisition card.

5. The dynamic phase gas control system based on optical feedback cavity enhanced laser spectrum according to claim 4, characterized in that: The Fabry-Perot cavity is composed of a plane reflector and a concave reflector both coated with a high-reflection film, and an Invar cavity. A filter is installed on the Invar cavity, and the Invar cavity is connected to an air pump through a valve with a pipeline.

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