Coaxial collection laser-induced breakdown spectroscopy device

Abstract

The invention provides a coaxial collection laser-induced breakdown spectroscopy device. The coaxial collection laser-induced breakdown spectroscopy device comprises a computer, a laser, a 9-to-1 spectroscope, a photoelectric external trigger unit, a reflector, a dichroscope, a galvanometer group, a field lens, a double-focusing lens group, a spectrograph optical fiber probe and a spectrograph, a laser beam passes through the 9-to-1 spectroscope and the reflector, is deflected, then enters the dichroscope, penetrates through the dichroscope, enters the galvanometer group, is reflected by the X reflector and the Y reflector for multiple times and then enters the field lens, and parallel light is focused to a test sample. A laser induced plasma emission spectrum generated in the laser cleaning process serves as a point light source and is converted into parallel light through a field lens, and then the parallel light enters a dichroscope through an original path of a galvanometer set, deflects to enter a double-focusing lens set and is stably focused to a spectrograph optical fiber probe to be processed and analyzed by the spectrograph. The coaxial collection light path is applied to the galvanometer laser head, plasma emission light can be directly collected in the laser cleaning process, and more efficient signal collection and processing are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of laser-induced plasma emission spectroscopy detection, and particularly relates to a coaxial collection laser-induced breakdown spectroscopy device for laser cleaning. Background Art

[0002] When using laser-induced breakdown spectroscopy (LIBS) to detect elements, it is usually the case that the plasma emission light returns from the original optical path and is introduced into the fiber optic port of the spectrometer by a dichroic mirror for detection, which is called coaxial collection of plasma emission light. When using the LIBS technology to detect the types of elements in a sample, a direct writing type optical path design is usually adopted, and its core component is a focusing mirror. The characteristic of this system is to keep the relative position of the laser focus and the optical mirror group fixed, and to achieve an accurate detection effect through this stable structural design. However, in the coaxial collection method, when dealing with complex optical paths such as galvanometers and field lenses, focus shift is likely to occur, thus affecting the quality of spectral data. The high-speed swing of the galvanometer will also cause the angle of the copper sheet to change, making it possible for the plasma emission light to have a focus shift when reaching the spectrometer, resulting in poor signal effects.

[0003] Laser cleaning usually uses laser parameters with high repetition rate and narrow pulse width, and such parameters can just excite plasma. As a damage-type element detection method, LIBS is a very effective and suitable solution for laser cleaning. Laser cleaning usually requires the use of galvanometers and field lenses. The existing technical solutions mainly rely on the method of collecting plasma emission light paraxially, and this method has many deficiencies. For example, an additional collection mirror needs to be set beside the laser processing head, and placing and fixing the collection mirror will increase a large amount of workload and the operation is cumbersome. In addition, during laser cleaning, due to the action of the galvanometer, the laser action point is constantly changing, which makes it difficult for the paraxial collection mirror to collect the defocused plasma emission light. This makes the spectral signal fluctuate greatly and is extremely unstable. Since the angle and position of the paraxial collection method are important parameters, it is very difficult to make them consistent in each experiment, resulting in poor repeatability of multiple measurement results under the same experimental conditions and affecting the reliability of the experimental results. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, the present invention provides a coaxial collection laser-induced breakdown spectroscopy device for laser cleaning, which improves the collection efficiency, quality and stability of spectral signals.

[0005] The present invention is realized through the following technical solutions:

[0006] A coaxial collection laser-induced breakdown spectroscopy device includes a computer, a laser, a 9:1 beam splitter, an electro-optical external trigger unit, a reflecting mirror, a dichroic mirror, a galvanometer group, a field lens, a double focusing lens group, a spectrometer fiber optic probe and a spectrometer;

[0007] The computer is connected to both the laser and the spectrometer and is used to control the laser and the spectrometer; the laser is used to generate a pulse laser of the laser-induced plasma emission spectrum; a 9:1 beam splitter is arranged between the laser and the photoelectric external trigger unit and is used to split the pulse laser beam into 10% of the light incident on the photoelectric external trigger unit and the other 90% of the light incident on the reflector; the photoelectric external trigger unit is connected to the spectrometer and is used to synchronize the laser light emission and the spectrum collection time of the spectrometer;

[0008] The dichroic mirror is used to transmit infrared laser and reflect plasma emission light; the dichroic mirror is arranged between the reflector and the galvanometer group; the reflector is used to change the direction of the light path, and the laser beam incident on the reflector is reflected by the reflector and changed in direction, and then incident on the dichroic mirror, and then passes through the dichroic mirror and incident on the galvanometer group; the field mirror is arranged on the light output side of the galvanometer group;

[0009] The double focusing lens group is arranged between the dichroic mirror and the optical fiber probe of the spectrometer; the double focusing lens group is used to focus the plasma emission spot multiple times, and through double focusing, the original light path is focused to half of the original spot size, and then focused to the optical fiber probe of the spectrometer;

[0010] The galvanometer group includes a control card and X-axis and Y-axis lenses. The control card can control the movement of the two-axis lenses to achieve a predetermined motion trajectory and control the emission direction of the laser beam. The field lens is used to focus the parallel light and expand the laser beam to the entire working area.

[0011] The laser induced plasma emission spectrum generated during the laser cleaning process is used as a point light source, which is incident on the field mirror from bottom to top, converted into parallel light by the field mirror, and then shot into the dichroic mirror through the original path of the galvanometer group. After being reflected by the dichroic mirror, it is deflected 90° to the left and enters the double focusing lens group, and is stably focused on the optical fiber probe of the spectrometer; the spectrometer is used to process the laser induced breakdown spectrum, monitor the element changes in the paint removal process in real time, and monitor the paint removal progress.

[0012] Furthermore, the dichroic mirror can transmit light in the 800-1100 nm band and reflect light in the 350-700 nm band.

[0013] Furthermore, the laser used is a 1064nm infrared nanosecond pulse laser with a frequency of 10-100kHz.

[0014] This aspect has the following beneficial effects:

[0015] (1) Based on the reversibility of light, the present invention applies a coaxial collection optical path to a galvanometer laser head, breaking through the traditional direct writing spectral detection method and replacing the off-axis collection optical path beside the galvanometer. Through the coaxial design, it can directly collect the plasma emission light during the laser cleaning process and introduce it into the spectrometer for on-line monitoring, thus achieving more efficient signal collection and processing, and the overall signal intensity has been greatly improved.

[0016] (2) The coaxial collection method adopted by the present invention can better maintain the optical path alignment, reduce the signal instability problem caused by the optical path deviation, and improve the stability.

[0017] (3) The present invention can provide more consistent spectral data through the coaxial collection method, improving the repeatability of the experiment and the reliability of the results.

[0018] (4) The present invention introduces a dual-lens design in the coaxial collection system to address the problem of focus shift caused by the high-speed swinging of the galvanometer. By precisely adjusting the relative positions of the two lenses, effective double focusing of the plasma emission light is achieved, ensuring the quality and stability of the spectral signal. This dual-lens design can maintain good performance under various laser parameters and cleaning conditions, improving the adaptability and versatility of the system. Description of the Drawings

[0019] Figure 1 is a schematic diagram of the optical path of the coaxial collection laser-induced breakdown spectroscopy device for laser cleaning of the present invention;

[0020] Figure 2 is a schematic diagram of the process of coaxial collection laser-induced breakdown spectroscopy;

[0021] Figure 3 is a comparison diagram of the effect of processing the composite paint layer by this device;

[0022] Figure 4 is a comparison diagram of the signal intensity values of the spectral data obtained by processing the device of the present invention 10 times;

[0023] Figure 5 is a comparison diagram of the spectral intensities corresponding to the signal characteristic spectral peaks of three elements Ca, Fe, and Na and the minimum relative standard deviation RSD in 10 groups of experiments.

[0024] The reference numerals are as follows: 101 - computer; 102 - laser; 103 - 9:1 beam splitter; 104 - photoelectric external trigger unit; 105 - mirror; 106 - dichroic mirror; 107 - galvanometer group; 108 - field lens; 109 - processed paint layer sample; 110 - first focusing lens, 111 - second focusing lens, 112 - spectrometer optical fiber probe; 113 - spectrometer; 114 - timing signal output line, 115 - optical fiber, 301 - surface after paint removal; 302 - surface of the paint layer before paint removal. Detailed implementation manners

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0026] As Figure 1 shown, the present invention provides a device for coaxially collecting laser-induced breakdown spectroscopy for laser cleaning, including a computer 101, a laser 102, a 9:1 beam splitter 103, a photoelectric external trigger unit 104, a mirror 105, a dichroic mirror 106, a galvanometer group 107, a field lens 108, a double focusing lens group, a spectrometer optical fiber probe 112, and a spectrometer 113.

[0027] The computer 101 is connected to both the laser 102 and the spectrometer 113, and is used to control the laser 102 and the spectrometer 113.

[0028] The laser 102 is used to generate pulsed laser for laser-induced plasma emission spectroscopy. The laser 102 in this example uses a 1064 nm infrared nanosecond pulsed laser with a frequency of 10 - 100 kHz, which can obtain a good laser cleaning effect.

[0029] The 9:1 beam splitter 103 is arranged between the laser 102 and the photoelectric external trigger unit 104, and is used to split 10% of the pulsed laser beam and make it incident on the photoelectric external trigger unit 104, and the other 90% of the light is incident on the mirror 105.

[0030] The photoelectric external trigger unit 104 is connected to the spectrometer 113 through a timing signal output line 114, and is used to synchronize the laser light output and the spectral collection time of the spectrometer 113. When the laser 102 emits light, the spectrometer 113 (external trigger mode) synchronously collects spectral signals, enhancing the accuracy of the spectral signals.

[0031] The dichroic mirror 106 is arranged between the mirror 105 and the galvanometer group 107. The mirror 105 is used to change the optical path direction. After the laser beam incident on the mirror 105 is reflected by it and changes the direction, it is incident on the dichroic mirror 106, and then passes through the dichroic mirror 106 and is incident on the galvanometer group 107; the field lens 108 is arranged on the light output side of the galvanometer group 107.

[0032] The dichroic mirror 106 is used to transmit light in the 800 - 1100 nm band and reflect light in the 350 - 700 nm band, that is, it can transmit infrared laser and reflect plasma emission light. The dichroic mirror 106 is an important part of the coaxial optical path. As a kind of visible light, the plasma emission light is reflected by the dichroic mirror 106 when returning along the original optical path, changing the optical path.

[0033] The double-focusing lens group is arranged between the dichroic mirror 106 and the spectrometer fiber optic probe 112. The double-focusing lens group includes a first focusing lens 110 and a second focusing lens 111, which are used to focus the plasma emission spot multiple times. Through double focusing, the original optical path is focused to one-half of the original spot size and then focused to the spectrometer fiber optic probe 112, solving the problem of spot offset when the plasma enters the spectrometer fiber optic probe.

[0034] The galvanometer group 107 includes a control card and X and Y axis lenses. The movement of the two-axis lenses can be controlled through the control card to achieve a predetermined movement trajectory and quickly and accurately control the emission direction of the laser beam.

[0035] The field lens 108 is used to focus parallel light and expand the laser beam to the entire working area to ensure that the laser can evenly cover the target area.

[0036] The galvanometer group 107 and the field lens 108 are used in cooperation. The galvanometer group 107 adjusts the scanning path of the laser beam to ensure accurate reflection of the beam and focuses it on the surface of the processed paint layer sample 109 through the field lens 108. At the same time, by setting an appropriate scanning mode, frequency, and focal length, the laser can evenly cover the target area to achieve a good cleaning effect.

[0037] At the same time, the laser-induced plasma emission spectrum generated during the laser cleaning process acts as a point light source and is incident on the field lens 108 from bottom to top. After being transformed into parallel light by the field lens 108, it enters the dichroic mirror 106 along the original path through the galvanometer group 107. After being reflected by the dichroic mirror 106, it deflects 90° to the left and enters the double-focusing lens group, where it is stably focused on the spectrometer fiber optic probe 112. The spectrometer fiber optic probe 112 is connected to the spectrometer 113 through the optical fiber 115.

[0038] The spectrometer 113 is used to process the laser-induced breakdown spectrum, monitor the elemental changes during the paint removal process in real time, and monitor the paint removal process.

[0039] Based on the existing technology, the present invention has achieved a significant improvement in the on-line in-situ monitoring of LIBS during the laser cleaning process by introducing a coaxial collection optical path and a double-lens system. As Figure 2As shown in the figure, the working process of the above-mentioned device for coaxial collection of laser-induced breakdown spectroscopy for laser cleaning is as follows: The laser is emitted from the laser 102, with the initial direction being forward, and enters the 9:1 beam splitter 103. 10% of the laser triggers the photoelectric external trigger unit 104, sets the spectrometer 113 to the external trigger mode, and starts synchronous acquisition. 90% of the laser deflects upward by 90° after passing through the 9:1 beam splitter 103 and enters the mirror 105, changing the optical path direction and deflecting forward. The laser continues to enter the dichroic mirror 106. After the infrared laser penetrates the dichroic mirror 106, it enters the galvanometer group 107. The path is drawn through the control card, and after multiple reflections by the X and Y mirrors, it enters the field lens 108, focusing the parallel light onto the test sample. The laser-induced plasma emission spectrum generated during the laser cleaning process serves as a point light source, is transformed into parallel light by the field lens 108, and then enters the dichroic mirror 106 along the original path through the galvanometer group 107, and finally deflects left by 90° and enters the double focusing lens group, stably focusing onto the spectrometer fiber probe 112, and is further processed and analyzed by the spectrometer 113.

[0040] Example:

[0041] (1) Prepare a simulated paint layer to be cleaned:

[0042] 1) Select an aluminum sheet with a thickness of 2 mm as the substrate;

[0043] 2) Ultrasonically clean the Al sheet with absolute ethanol and deionized water for 10 minutes and dry it to ensure the surface is clean and pollution-free;

[0044] 3) Uniformly spray the treated aluminum plate with polyurethane topcoat to obtain a paint layer sample;

[0045] (2) Place the sample on the device for coaxial collection of laser-induced breakdown spectroscopy for laser cleaning provided by the present invention, perform laser cleaning, and conduct 10 groups of processing experiments respectively;

[0046] The sample thickness is about 90.6 μm; an infrared nanosecond pulsed laser is used; the pulse frequency is set to 20 KHz; the galvanometer scanning speed is set to 750 mm / s; the laser power is set to 16 W; the number of scans is 2 times.

[0047] (3) According to the principle of reversibility of light, during laser processing, the plasma emission light will be refracted into parallel light after passing through the field lens 108, return along the original path when passing through the galvanometer group 107, pass through the dichroic mirror 106, and the plasma emission light between 400 - 800 nm will be reflected to change the optical path direction, enter the double focusing lens group and be coupled into the optical fiber of the spectrometer 113. The NA of the optical fiber and the lens match, and the distance parameter between the two focusing lenses of the double focusing mirror can be calculated as follows:

[0048] The parallel light with a diameter of about 10 mm obtained from the plasma-emitted light passing through the field lens 108; the focal length of the first focusing lens is 30 mm, and the lens diameter of the second small focusing lens is 6 mm.

[0049] When the plasma-emitted light enters the first focusing lens of the double focusing lens group, the focused size of the obtained light spot should be controlled within 6 mm. At the same time, the second focusing lens cannot be placed at the focal point of the first focusing lens. Therefore, the diameter of the light spot reaching the second focusing lens:

[0050]

[0051] For safety, to avoid extreme conditions,

[0052]

[0053] From the focal length of the first lens and the diameter of the incident light beam, the maximum distance and the minimum distance between the two lenses are calculated proportionally:

[0054]

[0055] Combined to get:

[0056]

[0057] Among them, s is the distance between the two lenses, D is the diameter of the plasma-emitted light, d is the diameter of the light spot focused on the second focusing lens, and f is the focal length of the first focusing lens.

[0058] Substitute the data of the focusing lens into Equation (2) and round up to obtain that the maximum distance between the two focusing lenses is 24 mm and the minimum distance is 15 mm.

[0059] (4) The present invention performs spectral monitoring in real time by coaxially collecting the plasma light generated during laser cleaning, can monitor the change of the spectrum while cleaning, achieves monitoring of the change of the elements being cleaned currently, and uses methods such as machine learning to further judge whether the current cleaning process is completed;

[0060] (5) As Figure 3 shown, the area within the dashed box is the cleaning area (the surface 301 after paint removal); it is significantly different from the non-cleaned area (the surface 302 of the paint layer before paint removal). The white polyurethane topcoat has been basically removed, proving that the device can better achieve the function of laser cleaning;

[0061] (6) The spectral data obtained by using the device of the present invention is as Figure 4 shown. After multiple experiments, multiple groups of data are obtained. By monitoring the three elements of Ca, Fe, and Na, the effect of online monitoring of whether the cleaning is completed can be achieved. Figure 4It can be seen that after 10 tests, the LIBS signal is relatively stable with little change.

[0062] (7) The spectral intensity results corresponding to the signal characteristic spectral peaks of the three elements Ca, Fe, and Na in 10 groups of experiments are as Figure 5 shown. The average signal intensities of the three elements Ca, Fe, and Na in the LIBS of 10 groups of data are 3285, 2162, and 1833, respectively. The minimum relative standard deviation RSD is 5.38%. If the signals collected by paraxial are used, the RSD is usually greater than 10%. This shows that the present invention has better stability compared with the traditional methods.

[0063] Although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields. The above specific embodiments are merely illustrative and guiding, rather than restrictive. Those of ordinary skill in the art can also make many forms under the inspiration of this specification and without departing from the scope protected by the claims of the present invention. All of these fall within the scope of protection of the present invention.

Claims

1. A coaxial collection laser induced breakdown spectroscopy device, characterized in that: It includes a computer, a laser, a 9:1 beam splitter, an optoelectronic external trigger unit, a reflector, a dichroic mirror, a galvanometer group, a field mirror, a double focusing lens group, a spectrometer fiber probe and a spectrometer; The computer is connected to both the laser and the spectrometer and is used to control the laser and the spectrometer; the laser is used to generate a pulse laser of the laser-induced plasma emission spectrum, and a 9:1 beam splitter is arranged between the laser and the photoelectric external trigger unit and is used to split the pulse laser beam into 10% of the light incident on the photoelectric external trigger unit and the other 90% of the light incident on the reflector; the photoelectric external trigger unit is connected to the spectrometer and is used to synchronize the laser light emission and the spectrum collection time of the spectrometer; The dichroic mirror is used to transmit infrared laser and reflect plasma emission light; the dichroic mirror is arranged between the reflector and the galvanometer group; the reflector is used to change the direction of the light path, and the laser beam incident on the reflector is reflected by the reflector and changed in direction, and then incident on the dichroic mirror, and then passes through the dichroic mirror and incident on the galvanometer group; the field mirror is arranged on the light output side of the galvanometer group; The double focusing lens group is arranged between the dichroic mirror and the optical fiber probe of the spectrometer; the double focusing lens group is used to focus the plasma emission spot multiple times, focus the original light path to half of the original spot size through double focusing, and then focus to the optical fiber probe of the spectrometer; The galvanometer group includes a control card and X-axis and Y-axis lenses. The control card can control the movement of the two-axis lenses to achieve a predetermined motion trajectory and control the emission direction of the laser beam. The field lens is used to focus the parallel light and expand the laser beam to the entire working area. The laser induced plasma emission spectrum generated during the laser cleaning process is used as a point light source, which is incident on the field mirror from bottom to top, converted into parallel light by the field mirror, and then shot into the dichroic mirror through the original path of the galvanometer group. After being reflected by the dichroic mirror, it is deflected 90° to the left and enters the double focusing lens group, and is stably focused on the optical fiber probe of the spectrometer; the spectrometer is used to process the laser induced breakdown spectrum, monitor the element changes in the paint removal process in real time, and monitor the paint removal progress.

2. The coaxial laser induced breakdown spectroscopy device according to claim 1, characterized in that: The dichroic mirror can transmit light in the 800-1100nm band and reflect light in the 350-700nm band.

3. The coaxial laser induced breakdown spectroscopy device according to claim 1, characterized in that: The laser used is a 1064nm infrared nanosecond pulse laser with a frequency of 10-100kHz.

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