A cavity ring-down cavity mode adjustment method based on plano-convex lens and infrared photosensitive film

Abstract

The present invention discloses a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film, and relates to the technical field of cavity mode signal adjustment. The method is applicable to a cavity ring-down optoelectronic system, and the cavity ring-down optoelectronic system includes: an infrared laser, and a resonant cavity and a photodetector arranged in sequence along the optical path of the output laser of the infrared laser. The method includes: using an infrared photosensitive film to determine the optical path height of the output laser of the infrared laser, and obtaining an infrared photosensitive film marked with the optical path height; using the infrared photosensitive film marked with the optical path height and the plano-convex lens to assist in adjusting the position and angle of the cavity mirror of the resonant cavity in the optical path, so as to achieve transverse mode adjustment of the cavity mode signal. The method of the present invention simplifies the operation of adjusting the cavity mode signal in the cavity ring-down technology, abandons the visible light laser, reduces the cost, improves the stability of the optical path, and reduces the time cost.

Description

Technical Field

[0001] The invention belongs to the technical field of cavity mode signal adjustment, and in particular relates to a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film. Background Art

[0002] In order to accurately detect carbon dioxide emissions and emission sources, gas detection technology has been vigorously developed. Traditional gas detection methods include electrochemical method, gas chromatography, contact combustion method, etc. These methods all require sampling and analysis, which is time-consuming and labor-intensive, slow to respond, inefficient, and difficult to reflect relevant information in real time.

[0003] In recent years, new laser absorption spectroscopy technology has been increasingly widely used in the field of gas detection. Currently, the more mature ones include direct absorption spectroscopy technology, wavelength modulation technology, photoacoustic spectroscopy technology, etc. However, these methods have low detection accuracy due to noise or short absorption paths. Cavity ring-down gas detection technology measures time and is immune to laser intensity fluctuation noise. The laser and the medium to be measured act in the resonant cavity, which gives it a very long absorption path. These advantages make the detection accuracy of cavity ring-down gas detection technology very high, reaching the ppb level, and it is very popular.

[0004] Mode matching is to match the laser spatial mode with the fundamental mode of the resonant cavity, which mainly includes transverse mode matching and longitudinal mode matching. Longitudinal mode matching is to couple the laser that meets the standing wave condition into the resonant cavity, and transverse mode matching is to instruct the laser coupled into the resonant cavity to have the same curvature radius of the equal phase surface of the laser at the mirror surface of the cavity mirror as the curvature radius of the cavity mirror. Only when the cavity transverse mode and the cavity mirror fundamental mode match can a clear cavity mode signal be generated. In the cavity ring-down gas detection technology, the quality of mode matching will directly affect the detection accuracy of the device.

[0005] Since the active spectral bands of most gases are in the infrared band, the light in the infrared band cannot be observed by the human eye, so lasers in the visible light band are generally used for adjustment. The resonant cavity is composed of two high-reflection mirrors. The reflectivity of the cavity mirrors is higher in the infrared band and lower in the visible light band. When adjusting the cavity mode signal, adjust the rear cavity mirror first, and then adjust the front cavity mirror. The thickness of the high-reflection mirror is about 3-5 mm. When the visible laser is incident perpendicular to the cavity mirror, the front and rear faces of the cavity mirror will reflect part of the laser to produce an interference ring. Fine-tune the cavity mirror until the interference ring state is optimal, and the center of the interference ring coincides with the laser output end. After adjusting the rear cavity mirror, repeat the above operation to adjust the front cavity mirror. After adjusting both cavity mirrors, keep the cavity mirror state unchanged, replace the visible light laser with the infrared laser, observe the oscilloscope and fine-tune the cavity mirror until a better cavity mode signal appears.

[0006] However, the above-mentioned resonant cavity mode adjustment method is relatively expensive. Since the visible light laser is not necessary in the cavity ring-down gas detection technology, it is only used to assist in adjusting the optical path, which increases the cost of the system. In addition, the resonant cavity mode adjustment method is unstable. After the optical path is adjusted using the visible light laser, it is difficult to ensure that the optical path remains unchanged when the visible light laser is replaced by an infrared laser, and a good cavity mode signal may not be obtained. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0008] The present invention provides a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film, which is applicable to a cavity ring-down photoelectric system. The cavity ring-down photoelectric system comprises: an infrared laser, and a resonant cavity and a photodetector sequentially arranged along the optical path of the output laser of the infrared laser; the cavity ring-down cavity mode adjustment method comprises:

[0009] Step 1: using an infrared photosensitive sheet, determining the optical path height of the output laser of the infrared laser, and obtaining an infrared photosensitive sheet marked with the optical path height;

[0010] Step 2: Using the infrared photosensitive sheet and plano-convex lens marked with the optical path height, assist in adjusting the position and angle of the cavity mirror of the resonant cavity in the optical path to achieve transverse mode adjustment of the cavity mode signal.

[0011] In one embodiment of the present invention, the resonant cavity is a plano-concave cavity formed by a planar high-reflection mirror close to the infrared laser and a concave high-reflection mirror close to the photodetector.

[0012] In one embodiment of the present invention, the cavity ring-down cavity mode adjustment method based on the plano-convex lens and the infrared photosensitive film further includes:

[0013] Step 3: Connect the photodetector to an oscilloscope and perform external triangle wave modulation on the infrared laser so that the output laser of the infrared laser is coupled into the resonant cavity to achieve longitudinal mode regulation of the cavity mode signal.

[0014] In one embodiment of the present invention, step 1 comprises:

[0015] Step 1.1: placing the infrared photosensitive sheet in the optical path, wherein the photosensitive surface of the infrared photosensitive sheet is perpendicular to the optical path and faces the infrared laser;

[0016] Step 1.2: The output laser of the infrared laser is irradiated onto the infrared photosensitive sheet to form a light spot on the photosensitive surface of the infrared photosensitive sheet, and the optical path height of the output laser of the infrared laser is determined;

[0017] Step 1.3: A through hole having the same diameter as the light spot is opened at the light spot on the infrared photosensitive sheet to obtain an infrared photosensitive sheet marked with a light path height.

[0018] In one embodiment of the present invention, step 2 comprises:

[0019] Step 2.1: Determine the position of the back cavity mirror of the resonant cavity, and place a plane high-reflection mirror at the position of the back cavity mirror;

[0020] Step 2.2: Using the infrared photosensitive sheet marked with the optical path height, by adjusting the angle of the plane high-reflection mirror, the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam;

[0021] Step 2.3: Replace the plane high-reflection mirror with a plano-convex lens after the angle is determined, and use the infrared photosensitive sheet marked with the optical path height to adjust the position of the plano-convex lens in a plane perpendicular to the optical path so that the output laser of the infrared laser is incident on the plano-convex lens at the center of the plano-convex lens;

[0022] Step 2.4: Replace the plano-convex lens with a concave high-reflection mirror after the position is determined;

[0023] Step 2.5: Determine the position of the front cavity mirror of the resonant cavity according to the preset cavity length of the resonant cavity and the position of the rear cavity mirror of the resonant cavity, and place the planar high-reflection mirror at the position of the front cavity mirror;

[0024] Step 2.6: Repeat steps 2.2 to 2.3, and then replace the plano-convex lens after the position is determined with the planar high-reflection mirror.

[0025] In one embodiment of the present invention, the plane high-reflection mirror, the plano-convex lens and the concave high-reflection mirror have the same radius.

[0026] In one embodiment of the present invention, the step 2.2 comprises:

[0027] Step 2.21: placing the infrared photosensitive sheet marked with the optical path height between the infrared laser and the plane high-reflection mirror, wherein the photosensitive surface of the infrared photosensitive sheet marked with the optical path height is perpendicular to the optical path and faces the plane high-reflection mirror;

[0028] Step 2.22: The output laser of the infrared laser passes through the through hole on the infrared photosensitive sheet marked with the optical path height, irradiates the plane high-reflection mirror, and is reflected by the plane high-reflection mirror to form a reflected light beam;

[0029] Step 2.23: Move the infrared photosensitive sheet marked with the optical path height between the infrared laser and the plane high-reflection mirror along the direction of the optical path, and adjust the angle of the plane high-reflection mirror so that the reflected light beam can pass through the through hole on the infrared photosensitive sheet marked with the optical path height at any position between the infrared laser and the plane high-reflection mirror, so as to ensure that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam.

[0030] In one embodiment of the present invention, step 2.3 comprises:

[0031] Step 2.31: replacing the plane high-reflection mirror with a plane-convex lens after the angle is determined, wherein the plane of the plane-convex lens faces the infrared laser;

[0032] Step 2.32: placing the infrared photosensitive sheet marked with the optical path height between the plano-convex lens and the photoelectric detection device, wherein the photosensitive surface of the infrared photosensitive sheet marked with the optical path height is perpendicular to the optical path and faces the plano-convex lens;

[0033] Step 2.33: The output laser of the infrared laser is irradiated onto the plano-convex lens, and the light beam is deflected;

[0034] Step 2.34: Move the infrared photosensitive sheet marked with the optical path height between the plano-convex lens and the photoelectric detection device along the direction of the optical path to ensure that the position of the plano-convex lens on the optical path remains unchanged, and adjust the position of the plano-convex lens on the plane perpendicular to the optical path so that the infrared photosensitive sheet marked with the optical path height can pass through the through hole on the infrared photosensitive sheet marked with the optical path height at any position between the plano-convex lens and the photoelectric detection device, so as to ensure that the output laser of the infrared laser is at the center of the plano-convex lens at the incident position of the plano-convex lens.

[0035] In one embodiment of the present invention, the cavity ring-down cavity mode adjustment method based on the plano-convex lens and the infrared photosensitive film further includes:

[0036] After step 2.4, the infrared photosensitive sheet marked with the optical path height is used to adjust the angle of the concave high-reflection mirror so that the output laser of the infrared laser is vertically incident on the concave high-reflection mirror, and the incident light beam of the concave high-reflection mirror coincides with its reflected light beam.

[0037] In one embodiment of the present invention, the cavity ring-down cavity mode adjustment method based on the plano-convex lens and the infrared photosensitive film further includes:

[0038] After step 2.6, the infrared photosensitive film marked with the optical path height is used to adjust the angle of the plane high-reflection mirror so that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film of the present invention directly uses an infrared laser, and utilizes the infrared photosensitive film and the plano-convex lens to assist in realizing the lateral mode adjustment of the cavity mode signal, thereby simplifying the operation of adjusting the cavity mode signal in the cavity ring-down technology, abandoning the visible light laser, reducing the cost, and avoiding the destruction of the already adjusted optical path when replacing the visible light laser with an infrared laser in the traditional method, thereby improving the stability of the optical path and reducing the time cost.

[0041] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following specifically cites a preferred embodiment and describes it in detail with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film provided by an embodiment of the present invention;

[0043] Figure 2 is a schematic diagram of a plano-convex lens provided by an embodiment of the present invention;

[0044] Figure 3 is a schematic diagram of positioning an infrared photosensitive sheet provided by an embodiment of the present invention;

[0045] Figure 4 It is a schematic diagram of an output laser provided by an embodiment of the present invention after being reflected by a plane high-reflection mirror;

[0046] Figure 5 This is a schematic diagram of the optical path of an output laser after passing through a plano-convex lens provided by an embodiment of the present invention;

[0047] Figure 6 It is a schematic diagram of another cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film provided by an embodiment of the present invention;

[0048] Figure 7Schematic diagram of a cavity ring-down optoelectronic system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared sensitive film proposed in accordance with the present invention, in combination with the accompanying drawings and specific implementation methods.

[0050] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0051] An embodiment of the present invention provides a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film, which is applicable to a cavity ring-down optoelectronic system. The cavity ring-down optoelectronic system includes: an infrared laser, and a resonant cavity and a photodetector arranged in sequence along the optical path of the output laser of the infrared laser.

[0052] In this embodiment, the resonant cavity is a plano-concave cavity formed by a planar high-reflection mirror close to the infrared laser and a concave high-reflection mirror close to the photodetector.

[0053] When using a cavity ring-down photoelectric system to measure gas concentration, the cavity ring-down time can be measured by setting a threshold circuit. and ring-down time in the presence of an absorbing medium , according to the formula To calculate the absorption coefficient. After obtaining the absorption coefficient, substitute it into the formula , the concentration information of the absorbing medium, i.e. the gas to be measured, can be inverted, where: For strong absorption line, is the concentration, For pressure, is the cavity length of the resonant cavity, is the function value at the center frequency of the absorption line. From the above formula, it can be seen that if you want to obtain a better cavity ring-down time and ring-down time in the presence of an absorbing medium , it is necessary to adjust the cavity mode signal with higher signal amplitude and stability.

[0054] Usually, the adjustment of cavity mode signals is divided into transverse mode adjustment and longitudinal mode adjustment. During longitudinal mode adjustment, the wavelength of the externally tuned laser is used to make the laser incident on the resonant cavity. The laser that meets the standing wave condition will be coupled into the resonant cavity to complete the longitudinal mode adjustment. The transverse mode adjustment process includes two parts. First, the laser light path level is adjusted, and then the position and angle of the resonant cavity mirror are adjusted to achieve transverse mode matching.

[0055] See also Figure 1 , Figure 1 is a schematic diagram of a cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film provided by an embodiment of the present invention, such as Figure 1 As shown, the cavity ring-down cavity mode adjustment method of this embodiment includes:

[0056] Step 1: Use an infrared photosensitive sheet to determine the optical path height of the output laser of the infrared laser, and obtain an infrared photosensitive sheet marked with the optical path height.

[0057] Optionally, step 1 includes:

[0058] Step 1.1: placing an infrared photosensitive sheet in the light path, wherein the photosensitive surface of the infrared photosensitive sheet is perpendicular to the light path and faces the infrared laser;

[0059] Step 1.2: The output laser of the infrared laser is irradiated onto the infrared photosensitive sheet, forming a light spot on the photosensitive surface of the infrared photosensitive sheet, and determining the optical path height of the output laser of the infrared laser;

[0060] Step 1.3: A through hole having the same diameter as the light spot is opened at the light spot on the infrared photosensitive sheet to obtain an infrared photosensitive sheet marked with the light path height.

[0061] See also Figure 3 , Figure 3 is a schematic diagram of positioning an infrared photosensitive sheet provided by an embodiment of the present invention, such as Figure 3 As shown, in this embodiment, an infrared photosensitive sheet is placed in the optical path, and the photosensitive surface of the infrared photosensitive sheet is perpendicular to the optical path, and the photosensitive surface of the infrared photosensitive sheet faces the infrared laser. When the output laser of the infrared laser hits the infrared photosensitive sheet, a light spot will appear. A through hole is punched at the light spot, and the size of the through hole is equal to the light spot, thereby determining the height of the optical path. While ensuring that the infrared photosensitive sheet remains unchanged in the vertical direction, it is moved along the direction of the optical path to one end close to the laser. During the movement, the output laser of the infrared laser can always pass through the through hole on the infrared photosensitive sheet.

[0062] Step 2: Use an infrared photosensitive sheet and a plano-convex lens marked with the optical path height to assist in adjusting the position and angle of the cavity mirror of the resonant cavity in the optical path to achieve transverse mode adjustment of the cavity mode signal.

[0063] Optionally, step 2 includes:

[0064] Step 2.1: Determine the position of the back cavity mirror of the resonant cavity, and place a flat high-reflection mirror at the position of the back cavity mirror.

[0065] The spot size and propagation distance of the laser are known The spot size at the waist position of the laser Gaussian beam is defined as , define the Rayleigh length The spot size is given by Changes to The curvature radius of the Gaussian beam equiphase surface can be expressed as: The Rayleigh length of the resonant cavity is defined as In order to meet the transverse mode matching, it is necessary to make the curvature radius of the equal phase surface of the laser Gaussian beam at the cavity mirror the same as the curvature radius of the concave high reflector. The curvature radius of the laser Gaussian beam at the concave high reflector is defined as , expressed as The position of the resonant cavity and thus the position of the cavity mirror can be determined by combining the ABCD law of beam propagation.

[0066] In this embodiment, after the position of the rear cavity mirror of the resonant cavity is determined by calculation, a three-dimensional displacement platform is installed at the position of the rear cavity mirror, a mirror frame is installed on the three-dimensional displacement platform, and a plane high-reflection mirror is placed on the mirror frame. The output laser of the infrared laser is perpendicular to the end face of the cavity mirror installed on the mirror frame and passes through the mirror frame. The three-dimensional displacement platform is used to adjust the position of the lens, and the mirror frame is used to adjust the angle of the lens.

[0067] Step 2.2: Use an infrared photosensitive sheet marked with the optical path height to adjust the angle of the plane high-reflection mirror so that the output laser of the infrared laser is incident vertically on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam.

[0068] Optionally, step 2.2 includes:

[0069] Step 2.21: Place the infrared photosensitive sheet marked with the optical path height between the infrared laser and the plane high reflective mirror, with the photosensitive surface of the infrared photosensitive sheet marked with the optical path height perpendicular to the optical path and facing the plane high reflective mirror;

[0070] Step 2.22: The output laser of the infrared laser passes through the through hole on the infrared photosensitive sheet marked with the optical path height, and is irradiated onto the plane high-reflection mirror, where it is reflected by the plane high-reflection mirror to form a reflected light beam;

[0071] Step 2.23: Move the infrared photosensitive sheet marked with the optical path height between the infrared laser and the plane high-reflection mirror along the direction of the optical path, and adjust the angle of the plane high-reflection mirror so that the infrared photosensitive sheet marked with the optical path height is at any position between the infrared laser and the plane high-reflection mirror, and the reflected light beam can pass through the through hole on the infrared photosensitive sheet marked with the optical path height, so as to ensure that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam.

[0072] See also Figure 4 , Figure 4 FIG. 1 is a schematic diagram of an output laser after being reflected by a plane high-reflection mirror provided by an embodiment of the present invention. Figure 4 As shown, in this embodiment, the position of the three-dimensional displacement platform in the optical path is ensured to remain unchanged, and the infrared photosensitive sheet marked with the optical path height is placed between the infrared laser and the plane high-reflection mirror. When the output laser of the infrared laser irradiates the plane high-reflection mirror through the small hole on the infrared photosensitive sheet, the output laser will be reflected by the plane high-reflection mirror to form a reflected light beam, and the reflected light beam is irradiated to the infrared photosensitive sheet. Due to the inclination of the frame, the reflected light path and the incident light path have a certain inclination angle, and the reflected light beam will not pass through the through hole on the infrared photosensitive sheet. By adjusting the knob on the frame, the angle of the plane high-reflection mirror is changed so that the reflected light beam can pass through the through hole on the infrared photosensitive sheet. At this time, the end face of the frame is perpendicular to the optical path of the output laser of the infrared laser.

[0073] It should be noted that in this embodiment, for the adjusted angle of the plane high-reflection mirror, it is necessary to ensure that when the infrared sensitive film remains in the vertical position and is moved along the direction of the optical path, the reflected light beam can always pass through the through hole on the infrared sensitive film.

[0074] Step 2.3: Replace the plane high-reflection mirror with a plano-convex lens after the angle is determined. Using an infrared photosensitive film marked with the height of the optical path, adjust the position of the plano-convex lens in a plane perpendicular to the optical path so that the output laser of the infrared laser is incident on the plano-convex lens at the center of the plano-convex lens.

[0075] The law of refraction is known to be defined as when a light wave propagates from one medium to another medium with a different refractive index, refraction occurs, and the relationship between the angle of incidence and the angle of refraction can be expressed as: ,in, , are the refractive indices of the two media, is the angle between the incident light and the interface normal, is the angle between the refracted light and the interface normal, and They are called the incident angle and the refraction angle respectively. After adjusting the optical path of the infrared laser output laser to be horizontal, it is necessary to adjust the position of the cavity mirror to ensure that the contact surface between the laser and the cavity mirror is located at the center of the cavity mirror, and adjust the cavity mirror angle to ensure that the laser incident optical path and the reflected optical path coincide. It is known that the plano-convex lens and air are different media. From the above formula, it can be seen that when the laser is perpendicular to the mirror surface and incident from the center of the plano-convex lens, the optical path will not be deflected.

[0076] In this embodiment, when the cavity mode is adjusted using a plano-convex lens, when the output laser of the infrared laser is incident perpendicular to the plano-convex lens, the optical path of the output laser passing through the plano-convex lens is not deflected. At this time, the contact position between the output laser of the infrared laser and the plano-convex lens is at the center of the plano-convex lens.

[0077] Optionally, step 2.3 includes:

[0078] Step 2.31: Replace the plane high reflective mirror with a plano-convex lens after the angle is determined, with the plane of the plano-convex lens facing the infrared laser;

[0079] In this example, the plano-convex lens and the plano-high-reflectivity mirror have the same radius, see Figure 2 , Figure 2 is a schematic diagram of a plano-convex lens provided by an embodiment of the present invention, such as Figure 2 As shown, one side of the plano-convex lens is a plane and the other side is a convex surface. The thickness of the plano-convex lens in this embodiment is 3 mm, and the two end surfaces at the center of the plano-convex lens are parallel.

[0080] Step 2.32: Place the infrared photosensitive sheet marked with the optical path height between the plano-convex lens and the photoelectric detection device, with the photosensitive surface of the infrared photosensitive sheet marked with the optical path height being perpendicular to the optical path and facing the plano-convex lens;

[0081] Step 2.33: The output laser of the infrared laser is irradiated onto the plano-convex lens, and the beam is deflected;

[0082] Step 2.34: Move the infrared photosensitive sheet marked with the optical path height between the plano-convex lens and the photoelectric detection device along the direction of the optical path, ensure that the position of the plano-convex lens on the optical path remains unchanged, and adjust the position of the plano-convex lens on the plane perpendicular to the optical path so that the infrared photosensitive sheet marked with the optical path height is at any position between the plano-convex lens and the photoelectric detection device, and the deflected light beam can pass through the through hole on the infrared photosensitive sheet marked with the optical path height, so as to ensure that the output laser of the infrared laser is at the center of the plano-convex lens at the incident position of the plano-convex lens.

[0083] See also Figure 5 , Figure 5 FIG. 1 is a schematic diagram of a light path of an output laser after passing through a plano-convex lens provided by an embodiment of the present invention. Figure 5As shown, in this embodiment, the angle in the frame is ensured to remain unchanged, the plane high reflective mirror is replaced with a plano-convex lens, and the infrared photosensitive sheet marked with the optical path height is placed between the plano-convex lens and the photoelectric detection device. The output laser of the infrared laser passes through the plano-convex lens and the infrared photosensitive sheet marked with the optical path height before reaching the photoelectric detector. When the contact position between the output laser of the infrared laser and the plano-convex lens is not at the center of the plano-convex lens, the optical path of the output laser through the plano-convex lens will be deflected due to the law of refraction, and the deflected light beam will no longer pass through the through hole on the infrared photosensitive sheet, and a light spot will be formed on the photosensitive surface of the infrared photosensitive sheet. While observing the light spot, ensure that the position of the three-dimensional displacement platform in the optical path remains unchanged, and by adjusting the displacement of the three-dimensional displacement platform on the plane perpendicular to the optical path, the position of the plano-convex lens on the plane perpendicular to the optical path is changed, so that the light beam passing through the plano-convex lens passes through the through hole on the infrared photosensitive sheet again. At this time, the contact position between the output laser of the infrared laser and the plano-convex lens is located at the center of the plano-convex lens.

[0084] It should be noted that, in this embodiment, for the position of the adjusted plano-convex lens, it is necessary to ensure that when the infrared sensitive film remains in the vertical position and is moved along the direction of the optical path, the light beam passing through the plano-convex lens can always pass through the through hole on the infrared sensitive film.

[0085] Step 2.4: Replace the plano-convex lens with a concave high-reflection mirror after the position is determined.

[0086] In this embodiment, the concave high-reflection mirror and the plano-convex lens have the same radius. The concave high-reflection mirror has a very high reflectivity for the infrared light beam, and most of the infrared laser light is reflected.

[0087] It is worth noting that in order to avoid affecting the angle of the plano-convex lens during the adjustment of the position of the three-dimensional displacement platform, after the plano-convex lens is replaced with a concave high-reflection mirror after the position is determined, the angle of the concave high-reflection mirror needs to be fine-tuned, that is, the mirror frame knob needs to be readjusted so that the output laser of the infrared laser is perpendicular to the concave high-reflection mirror, and the incident light beam of the concave high-reflection mirror coincides with its reflected light beam.

[0088] Specifically, by using an infrared photosensitive sheet marked with the optical path height, the angle of the concave high reflector is adjusted so that the output laser of the infrared laser is incident vertically on the concave high reflector, and the incident beam of the concave high reflector coincides with its reflected beam. After completing the fine adjustment of the angle of the concave high reflector, the rear cavity mirror of the resonant cavity is adjusted.

[0089] In this embodiment, the angle fine-tuning process of the concave high-reflection mirror is similar to the angle adjustment process of the planar high-reflection mirror in step 2.2. Please refer to the detailed adjustment process of step 2.2, which will not be repeated here.

[0090] Step 2.5: According to the preset cavity length of the resonant cavity and the position of the rear cavity mirror of the resonant cavity, determine the position of the front cavity mirror of the resonant cavity, and place a flat high-reflection mirror at the position of the front cavity mirror.

[0091] In this embodiment, after determining the position of the front cavity mirror of the resonant cavity, a three-dimensional displacement platform is installed at the position of the front cavity mirror, a mirror frame is installed on the three-dimensional displacement platform, and a plane high-reflection mirror is placed on the mirror frame. The output laser of the infrared laser is perpendicular to the end face of the cavity mirror installed on the mirror frame and passes through the mirror frame. The three-dimensional displacement platform is used to adjust the position of the lens, and the mirror frame is used to adjust the angle of the lens.

[0092] Step 2.6: Repeat steps 2.2 to 2.3, and then replace the plano-convex lens with a flat high-reflection mirror after the position is determined.

[0093] In this embodiment, first, by using an infrared photosensitive sheet marked with the optical path height, the angle of the plane high reflector is adjusted so that the output laser of the infrared laser is incident on the plane high reflector vertically, and the incident light beam of the plane high reflector coincides with its reflected light beam. The plane high reflector after the angle is determined is replaced with a plano-convex lens, and by using an infrared photosensitive sheet marked with the optical path height, the position of the plano-convex lens in a plane perpendicular to the optical path is adjusted so that the incident position of the output laser of the infrared laser on the plano-convex lens is the center of the plano-convex lens. Finally, the plano-convex lens after the position is determined is replaced with a plane high reflector.

[0094] Specifically, how to use the infrared photosensitive film marked with the optical path height to adjust the angle of the plane high-reflection mirror so that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam, and how to use the infrared photosensitive film marked with the optical path height to adjust the position of the plano-convex lens in the plane perpendicular to the optical path so that the incident position of the output laser of the infrared laser on the plano-convex lens is the center of the plano-convex lens. Please refer to the detailed adjustment process of steps 2.2 and 2.3, which will not be repeated here.

[0095] It is worth noting that in order to avoid affecting the angle of the plano-convex lens during the adjustment of the position of the three-dimensional displacement platform, after the plano-convex lens is replaced with a planar high-reflection mirror after the position is determined, the angle of the planar high-reflection mirror needs to be fine-tuned, that is, the mirror frame knob needs to be readjusted so that the output laser of the infrared laser is perpendicular to the planar high-reflection mirror, and the incident light beam of the planar high-reflection mirror coincides with its reflected light beam.

[0096] Specifically, by using an infrared photosensitive sheet marked with the optical path height, the angle of the plane high reflector is adjusted so that the output laser of the infrared laser is incident vertically on the plane high reflector, and the incident beam of the plane high reflector coincides with its reflected beam. After completing the fine adjustment of the angle of the plane high reflector, the adjustment of the front cavity mirror of the resonant cavity is completed.

[0097] In this embodiment, the angle fine-tuning process of the plane high-reflective mirror is similar to the angle adjustment process of the plane high-reflective mirror in step 2.2. Please refer to the detailed adjustment process of step 2.2, which will not be repeated here.

[0098] In this embodiment, the angle and position of the rear cavity mirror and the front cavity mirror of the resonant cavity are adjusted through the above process, so that the transverse mode adjustment of the cavity mode signal can be achieved. After the transverse mode adjustment of the cavity mode signal is achieved, the longitudinal mode adjustment of the cavity mode signal is required to couple the output laser of the infrared laser into the resonant cavity.

[0099] See also Figure 6 , Figure 6 is a schematic diagram of another cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film provided by an embodiment of the present invention, such as Figure 6 As shown, optionally, the cavity ring-down cavity mode adjustment method based on the plano-convex lens and the infrared photosensitive film further includes:

[0100] Step 3: Connect the photodetector to the oscilloscope and perform external triangle wave modulation on the infrared laser so that the output laser of the infrared laser is coupled into the resonant cavity to achieve longitudinal mode adjustment of the cavity mode signal.

[0101] See also Figure 7 , Figure 7 is a schematic diagram of a cavity ring-down optoelectronic system provided by an embodiment of the present invention, such as Figure 7 As shown, after the two cavity mirrors of the resonant cavity are adjusted, the infrared photosensitive film is removed and the photodetector is connected to the oscilloscope. The laser controller can be used to perform external triangle wave modulation on the infrared laser. At this time, an obvious cavity mode signal can be observed on the oscilloscope. The cavity mode signal on the oscilloscope can be observed and the two cavity mirrors of the resonant cavity can be fine-tuned at the same time until the best cavity mode signal appears on the oscilloscope. Among them, the matching lens is used for transverse mode matching. During transverse mode matching, the beam waist position of the laser needs to be matched to the plane high-reflection mirror. Under normal circumstances, the beam waist position of the laser output is near the laser output end. After the matching lens is transformed, the beam waist close to the laser output end can be transformed to a farther plane high-reflection mirror.

[0102] The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film in an embodiment of the present invention directly uses an infrared laser and utilizes an infrared photosensitive film and a plano-convex lens to assist in realizing the lateral mode adjustment of the cavity mode signal, thereby simplifying the operation of adjusting the cavity mode signal in the cavity ring-down technology, abandoning the visible light laser, reducing the cost, and avoiding the destruction of the already adjusted optical path when replacing the visible light laser with an infrared laser in the traditional method, thereby improving the stability of the optical path and reducing the time cost.

[0103] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant is intended to cover non-exclusive inclusion, so that the article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the article or device including the elements. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The orientation or position relationship indicated by "up", "down", "left", "right", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0104] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film, characterized in that: The invention is applicable to a cavity ring-down optoelectronic system, wherein the cavity ring-down optoelectronic system comprises: an infrared laser, and a resonant cavity and a photodetector arranged in sequence along the optical path of the output laser of the infrared laser; the cavity ring-down cavity mode adjustment method comprises: Step 1: using an infrared photosensitive sheet, determining the optical path height of the output laser of the infrared laser, and obtaining an infrared photosensitive sheet marked with the optical path height; The step 1 comprises: Step 1.1: placing the infrared photosensitive sheet in the optical path, wherein the photosensitive surface of the infrared photosensitive sheet is perpendicular to the optical path and faces the infrared laser; Step 1.2: The output laser of the infrared laser is irradiated onto the infrared photosensitive sheet to form a light spot on the photosensitive surface of the infrared photosensitive sheet, and the optical path height of the output laser of the infrared laser is determined; Step 1.3: A through hole having the same diameter as the light spot is opened at the light spot on the infrared photosensitive sheet to obtain an infrared photosensitive sheet marked with a light path height; Step 2: using the infrared photosensitive sheet and the plano-convex lens marked with the optical path height to assist in adjusting the position and angle of the cavity mirror of the resonant cavity in the optical path, so as to achieve transverse mode adjustment of the cavity mode signal; The step 2 comprises: Step 2.1: Determine the position of the back cavity mirror of the resonant cavity, and place a plane high-reflection mirror at the position of the back cavity mirror; Step 2.2: Using the infrared photosensitive sheet marked with the optical path height, by adjusting the angle of the plane high-reflection mirror, the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam; Step 2.3: Replace the plane high-reflection mirror with a plano-convex lens after the angle is determined, and use the infrared photosensitive sheet marked with the optical path height to adjust the position of the plano-convex lens in a plane perpendicular to the optical path so that the output laser of the infrared laser is incident on the plano-convex lens at the center of the plano-convex lens; The step 2.3 includes: Step 2.31: replacing the plane high-reflection mirror with a plane-convex lens after the angle is determined, wherein the plane of the plane-convex lens faces the infrared laser; Step 2.32: placing the infrared photosensitive sheet marked with the optical path height between the plano-convex lens and the photoelectric detection device, wherein the photosensitive surface of the infrared photosensitive sheet marked with the optical path height is perpendicular to the optical path and faces the plano-convex lens; Step 2.33: The output laser of the infrared laser is irradiated onto the plano-convex lens, and the light beam is deflected; Step 2.34: Move the infrared photosensitive sheet marked with the optical path height between the plano-convex lens and the photoelectric detection device along the direction of the optical path, ensure that the position of the plano-convex lens on the optical path remains unchanged, and adjust the position of the plano-convex lens on the plane perpendicular to the optical path so that the infrared photosensitive sheet marked with the optical path height at any position between the plano-convex lens and the photoelectric detection device, the deflected light beam can pass through the through hole on the infrared photosensitive sheet marked with the optical path height, so as to ensure that the output laser of the infrared laser is incident on the plano-convex lens at the center of the plano-convex lens; Step 2.4: Replace the plano-convex lens with a concave high-reflection mirror after the position is determined; Step 2.5: Determine the position of the front cavity mirror of the resonant cavity according to the preset cavity length of the resonant cavity and the position of the rear cavity mirror of the resonant cavity, and place the planar high-reflection mirror at the position of the front cavity mirror; Step 2.6: Repeat steps 2.2 to 2.3, and then replace the plano-convex lens after the position is determined with the plane high-reflection mirror; use the infrared photosensitive sheet marked with the optical path height to adjust the angle of the plane high-reflection mirror so that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam; The plane high-reflection mirror, the plano-convex lens and the concave high-reflection mirror have the same radius.

2. The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film according to claim 1 is characterized in that: The resonant cavity is a plano-concave cavity formed by a planar high-reflection mirror close to the infrared laser and a concave high-reflection mirror close to the photodetector.

3. The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film according to claim 1 is characterized in that: Also includes: Step 3: Connect the photodetector to an oscilloscope and perform external triangle wave modulation on the infrared laser so that the output laser of the infrared laser is coupled into the resonant cavity to achieve longitudinal mode regulation of the cavity mode signal.

4. The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film according to claim 1 is characterized in that: The step 2.2 comprises: Step 2.21: placing the infrared photosensitive sheet marked with the optical path height between the infrared laser and the plane high-reflection mirror, wherein the photosensitive surface of the infrared photosensitive sheet marked with the optical path height is perpendicular to the optical path and faces the plane high-reflection mirror; Step 2.22: The output laser of the infrared laser passes through the through hole on the infrared photosensitive sheet marked with the optical path height, irradiates the plane high-reflection mirror, and is reflected by the plane high-reflection mirror to form a reflected light beam; Step 2.23: Move the infrared photosensitive sheet marked with the optical path height between the infrared laser and the plane high-reflection mirror along the direction of the optical path, and adjust the angle of the plane high-reflection mirror so that the reflected light beam can pass through the through hole on the infrared photosensitive sheet marked with the optical path height at any position between the infrared laser and the plane high-reflection mirror, so as to ensure that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror, and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam.

5. The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film according to claim 1, characterized in that: Also includes: After step 2.4, the infrared photosensitive sheet marked with the optical path height is used to adjust the angle of the concave high-reflection mirror so that the output laser of the infrared laser is vertically incident on the concave high-reflection mirror, and the incident light beam of the concave high-reflection mirror coincides with its reflected light beam.

6. The cavity ring-down cavity mode adjustment method based on a plano-convex lens and an infrared photosensitive film according to claim 1 is characterized in that: Also includes: After step 2.6, the infrared photosensitive film marked with the optical path height is used to adjust the angle of the plane high-reflection mirror so that the output laser of the infrared laser is vertically incident on the plane high-reflection mirror and the incident light beam of the plane high-reflection mirror coincides with its reflected light beam.

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