Method and apparatus for frequency doubling of a laser based on modular frequency doubling crystals

Abstract

The present application relates to the technical field of laser frequency doubling, and particularly relates to a laser frequency doubling point changing method and device based on a modular frequency doubling crystal, the method comprising: cutting a crystal element based on a multi-source nonlinear optical crystal, and pre-screening the crystal element; grouping the pre-screened crystal element according to frequency doubling efficiency difference, and configuring the crystal element in the same group as a crystal module; performing multi-point position scanning on each crystal element in the crystal module to obtain point position information; generating an optimal point changing path of the crystal module under a target frequency doubling efficiency according to the point position information; and driving the crystal module to move to a target point position according to the optimal point changing path. The purpose is to solve the technical problem of efficiency fluctuation of a traditional point changing method, and to realize accurate and efficient point changing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser frequency doubling, in particular to a laser frequency doubling point changing method and device based on modular frequency doubling crystals. BACKGROUND

[0002] As a key means to expand the wavelength range of laser and improve the application ability of laser, laser frequency doubling technology has been widely used in industrial processing, medical equipment, scientific research and national defense fields. The core principle of laser frequency doubling technology is to convert the fundamental frequency laser into higher frequency laser output by using nonlinear optical crystals such as potassium dihydrogen phosphate (KDP), barium metaborate (BBO) and lithium triborate (LBO). However, in practical application, the long-term effect of high-power density laser will cause thermal effect, color center formation and even permanent optical damage in the local area of the frequency doubling crystal, which seriously restricts the service life and output stability of the crystal. In order to alleviate the local damage and prolong the service life of the crystal, the traditional method generally adopts periodic point changing method, that is, the crystal is translated or rotated to change the laser action point position. The existing typical point changing schemes mainly include single crystal point changing, same source crystal splicing and multi-crystal random splicing point changing strategies. The common feature of these point changing strategies is to change the action position of laser and crystal to disperse energy deposition and delay damage occurrence.

[0003] However, the existing point changing strategies have certain technical limitations in different aspects, and it is difficult to solve the problems of efficiency fluctuation and precision in the point changing process at the same time. Among them, the single crystal point changing technology is limited by the inherent composition fluctuation and uneven defect distribution of single crystal, and the nonlinear coefficient, phase matching characteristics, etc. of different regions are different, which leads to obvious frequency doubling efficiency fluctuation after point changing, and the anisotropy of the crystal will cause the emission direction of the frequency doubled light to deviate or the light spot morphology to be distorted, which needs to frequently calibrate the optical system; the same source splicing technology has strict requirements for the consistency of crystal growth, and needs to rely on large-size crystals, which leads to high growth cost and long growth period, and cannot solve the problem of optical axis alignment of the sub-crystals after splicing, and there is still light spot deviation after point changing; the multi-crystal random splicing technology has significant differences in doping concentration, defect density and other parameters of different source crystals, and the frequency doubling efficiency stability is poor, and the random splicing leads to chaotic emission direction of the light, which needs complex adaptive optical system compensation, and it is difficult to meet the needs of high-precision laser systems. The above problems jointly lead to the deficiencies of traditional point changing methods in frequency doubling efficiency stability and point changing precision and efficiency, which restricts the long-term stable operation of laser equipment. SUMMARY

[0004] In order to solve the technical problem of efficiency fluctuation of traditional point changing method and realize precise and efficient point changing, the present application provides a laser frequency doubling point changing method and device based on modular frequency doubling crystals, and the technical scheme adopted is as follows:

[0005] The technical scheme of the first aspect of the application provides a laser frequency doubling point changing method based on a modular frequency doubling crystal, and the method comprises the following steps:

[0006] The crystal base elements are cut based on multiple source nonlinear optical crystals, and the crystal base elements are pre-screened;

[0007] The crystal base elements pre-screened are grouped according to the difference in frequency doubling efficiency, and the crystal base elements in the same group are configured as a crystal module;

[0008] The crystal base elements in the crystal module are subjected to multi-point scanning to obtain point information;

[0009] An optimal point changing path of the crystal module under a target frequency doubling efficiency is generated according to the point information;

[0010] The crystal module is driven to move to a target point according to the optimal point changing path.

[0011] Further, the crystal base elements are cut based on multiple source nonlinear optical crystals, and the crystal base elements are pre-screened, which comprises the following steps:

[0012] Nonlinear optical crystals grown in different batches are obtained, and the crystal base elements are cut along the phase matching axis direction and preprocessed;

[0013] The crystal base elements preprocessed are subjected to laser performance detection, and the crystal base elements meeting the standards are pre-screened based on a preset optical parameter threshold.

[0014] Further, the crystal base elements preprocessed are subjected to laser performance detection, and the crystal base elements meeting the standards are pre-screened based on a preset optical parameter threshold, which comprises the following steps:

[0015] A plurality of preset points are selected to irradiate the crystal base elements preprocessed with laser, and the frequency doubling efficiency of each point is extracted;

[0016] The average frequency doubling efficiency value of each crystal base element is calculated according to the frequency doubling efficiency;

[0017] The crystal base elements whose average frequency doubling efficiency does not meet the standards are removed according to a preset efficiency threshold.

[0018] Further, the crystal base elements pre-screened are grouped according to the difference in frequency doubling efficiency, which comprises the following steps:

[0019] The average frequency doubling efficiency value of each crystal base element pre-screened is obtained;

[0020] The frequency doubling spot morphology and exit angle of each crystal base element are detected, and secondary screening is performed based on a preset morphology threshold and an angle threshold;

[0021] After the secondary screening, the crystal base elements whose average frequency doubling efficiency value difference fluctuates within a preset group are divided into the same group.

[0022] Further, the same group of crystal base elements is configured as a crystal module, comprising:

[0023] The same group of crystal base elements is embedded in a prefabricated slot of a prefabricated rigid matrix to form a crystal module;

[0024] The crystal module is configured to be coplanar to the light passing surface of each crystal base element, and the angle of each crystal base element is adjusted to ensure that the laser is normally incident on the light passing surface of each crystal base element;

[0025] The crystal base element is fixed with the prefabricated rigid matrix by optical glue, and the surface of the prefabricated rigid matrix is provided with a coordinate scale.

[0026] Further, each crystal base element in the crystal module is subjected to multi-point scanning to obtain point information, comprising:

[0027] According to a preset grid density, each crystal base element in the crystal module is subjected to laser scanning;

[0028] The spatial coordinates of each scanning point and the corresponding frequency doubling efficiency, frequency doubling spot morphology and exit angle are extracted.

[0029] Further, according to the point information, an optimal point switching path of the crystal module under a target frequency doubling efficiency is generated, comprising:

[0030] According to the target frequency doubling efficiency value and the preset efficiency fluctuation range, the point positions that meet the target efficiency value are selected from each crystal base element;

[0031] The point position with the smallest frequency doubling spot morphology change and the lowest exit angle offset is preferentially selected;

[0032] A continuous point switching sequence is generated in the order of spatial distribution of the crystal base element.

[0033] Further, the crystal module is driven to move to the target point position according to the optimal point switching path, comprising:

[0034] According to the target point position coordinates in the optimal point switching path, the displacement table drives the crystal module to move, so that the frequency doubling efficiency fluctuation after point switching is maintained within the preset range.

[0035] The second aspect of the technical scheme of the present application provides a laser frequency doubling point switching device based on a modular frequency doubling crystal, which adopts the laser frequency doubling point switching method based on a modular frequency doubling crystal of the first aspect of the technical scheme of the present application, and the device comprises:

[0036] A pre-screening detection platform is configured to perform crystal base element cutting and laser performance detection;

[0037] A grouping configuration module is configured to group the qualified crystal base elements according to efficiency and fix them on a rigid matrix;

[0038] a scanning calibration module configured to perform point scanning on the crystal module and record spatial coordinates and optical parameters;

[0039] a path planning module configured to generate an optimal point switching path based on the optical parameters;

[0040] a point switching execution module configured to drive the crystal module to move along the path.

[0041] Further, the pre-screening detection platform comprises:

[0042] a clamping unit for clamping the crystal element;

[0043] a laser emitting unit for irradiating detection laser to the crystal element;

[0044] an optical parameter acquisition unit for acquiring the frequency doubling efficiency, frequency doubling spot morphology and exit angle of the crystal element;

[0045] a position calibration unit for adjusting the crystal element to make the laser normally incident to the light passing surface.

[0046] The present application has the following beneficial effects:

[0047] The laser frequency doubling point switching method based on the modular frequency doubling crystal provided by the present application can avoid the performance fluctuation problem of single crystal or homologous crystal caused by inherent non-uniformity by cutting the multi-source nonlinear optical crystal to form a crystal element and pre-screening the crystal element from different sources. Then, the crystal elements in the same group are configured as a crystal module according to the frequency doubling efficiency difference, which can ensure the consistency of the frequency doubling performance of the crystal elements in the same group and guarantee the performance stability during point switching. Then, the crystal elements in the crystal module are subjected to multi-point scanning to obtain point information and accurately extract the frequency doubling characteristics of each point, which provides a reliable basis for subsequent point switching path planning and realizes rapid positioning of point switching. Finally, the optimal point switching path under the target frequency doubling efficiency is generated based on the point information, which guarantees the stability of the frequency doubling efficiency during point switching and avoids the problem of large efficiency fluctuation in the traditional point switching method. The present application realizes accurate point switching and reduces the situation of frequency doubling light exit direction deviation or frequency doubling spot morphology distortion after point switching, thereby reducing the demand for repeated calibration of the subsequent optical system. The present application realizes high stability control of crystal point switching in the laser frequency doubling process through multi-source crystal pre-screening, modular crystal combination and point information cooperation, breaks through the limitations of large efficiency fluctuation and high maintenance cost in the traditional point switching method, and is especially suitable for high-power precision laser processing scenes. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0049] Figure 1 The method flow chart of the laser frequency doubling point changing method based on modular frequency doubling crystal provided by an embodiment of the present application;

[0050] Figure 2 The schematic diagram of each frequency doubling efficiency corresponding point of the frequency doubling efficiency of 44%-46% provided by an embodiment of the present application;

[0051] Figure 3 The schematic diagram of the precise coordinate calibration of the crystal module provided by an embodiment of the present application;

[0052] Figure 4 The structural schematic diagram of the laser frequency doubling point changing device based on modular frequency doubling crystal provided by an embodiment of the present application. DETAILED DESCRIPTION

[0053] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purpose, the following will combine the drawings and the preferred embodiments to specifically describe the laser frequency doubling point changing method and device based on modular frequency doubling crystal according to the present application, the specific implementation, structure, features and effects thereof in detail. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0055] The following will specifically describe the specific scheme of the laser frequency doubling point changing method and device based on modular frequency doubling crystal provided by the present application in combination with the drawings.

[0056] Please refer to Figure 1 which shows the method flow chart of the laser frequency doubling point changing method based on modular frequency doubling crystal provided by an embodiment of the present application, and the method comprises:

[0057] Step S100: cutting a crystal element based on a multi-source nonlinear optical crystal, and pre-screening the crystal element;

[0058] Step S100 specifically comprises:

[0059] Step S110: Obtain nonlinear optical crystals grown in different batches, cut into crystal units along the phase matching axis direction and pretreat the crystal units;

[0060] In some embodiments, 3 to 5 nonlinear optical crystals grown in different batches but with similar processes can be selected, and the size of the crystals is not less than 20*20*10mm³; the diamond wire saw is used for cutting, the cutting accuracy is controlled within ±2 microns, the large crystal is cut into a crystal unit of 10*10*5mm³ along the phase matching axis direction of the crystal, and the initial angles of the crystal units are ensured to be consistent.

[0061] In some embodiments, after the cutting is completed, the crystal units are pretreated, the light transmission surface is polished to a surface roughness of less than 0.5nm and the side surface is polished to a surface roughness of less than 5nm by atomic force microscope detection, so as to reduce the optical loss in subsequent splicing; then the crystal units are ultrasonically cleaned with ethanol and deionized water for 10 minutes respectively to remove impurities on the surface of the crystal units; finally, argon plasma activation treatment is performed at a power of 50W for 5 minutes to enhance the adhesion of the subsequent bonding interface.

[0062] Step S120: Perform laser performance detection on the pretreated crystal units, and pre-screen the qualified crystal units based on a preset optical parameter threshold;

[0063] Step S120 specifically includes:

[0064] Step S121: Select a plurality of preset points to perform laser irradiation on the pretreated crystal units, and extract the frequency doubling efficiency of each point. Specifically, the preset points in this step are used to preliminarily judge whether the crystal units meet the standard, and the number is preferably 5, that is, 5 preset points are tested for each crystal unit, and then the crystal units are pre-screened based on the frequency doubling efficiency of the 5 points;

[0065] In some embodiments, the laser performance detection uses a 1064 nm Nd:YAG laser as a light source, that is, a solid laser with neodymium-doped yttrium aluminum garnet (Nd:YAG) as a gain medium, the output wavelength of which is 1064 nanometers, belonging to the near-infrared band, and the power thereof can be adjusted within the range of 1 to 10W, and the spot diameter is 1mm;

[0066] In some embodiments, the crystal base element to be tested is fixed on a vacuum chuck clamp, with its light transmission surface perpendicular to the laser incidence direction, and the crystal base element is placed at the laser focal point position; a 1W low-power laser is turned on, the center position of the light spot is observed through a CCD camera, the translation stage is adjusted so that the center of the light spot coincides with the geometric center and the four corners of the crystal base element, and the deviation is controlled within a preset range; then the laser power is increased to 5W, the incident laser power is measured without the crystal, and then the frequency-doubled light power is measured by filtering out the fundamental frequency light or using a dichroic mirror to split the light, and the ratio of the frequency-doubled light power to the fundamental frequency light power is taken as the frequency-doubling efficiency at this point; each crystal base element is tested at 5 preset points;

[0067] Step S122: calculating the average frequency-doubling efficiency value of each crystal base element according to the frequency-doubling efficiency;

[0068] In some embodiments, the average frequency-doubling efficiency of each crystal base element at 5 points is taken as the average frequency-doubling efficiency value of the crystal base element;

[0069] Step S123: according to the preset efficiency threshold, eliminating the crystal base element whose average frequency-doubling efficiency does not meet the standard;

[0070] In some embodiments, the 532nm frequency-doubled light efficiency is measured by using an integrating sphere power meter, and the crystal base element with substandard performance is eliminated based on the preset efficiency threshold.

[0071] Step S100 eliminates the initial performance dispersion from the material source by directional cutting and ultra-precision pretreatment of multiple sources of crystals, systematically eliminates the crystal base elements with inherent defects or uneven performance, and provides a basic unit with consistent optical performance and stable mechanical properties for constructing a high-performance modular crystal assembly.

[0072] Step S200: grouping the pre-screened crystal base elements according to the difference in frequency-doubling efficiency, and configuring the crystal base elements in the same group as a crystal module;

[0073] In some embodiments, the crystal base elements with an efficiency difference of ≤3% are reserved as a group based on the average efficiency, such as the 44-46% group, the 46-48% group, and the crystal with a frequency-doubling efficiency of less than 40% is eliminated.

[0074] Step S200 specifically includes:

[0075] Step S210: obtaining the average frequency-doubling efficiency value of each crystal base element after pre-screening;

[0076] Step S211: detecting the frequency-doubled light spot morphology and exit angle of each crystal base element, and performing secondary screening based on the preset morphology threshold and angle threshold; specifically, on the basis of pre-screening, the crystal base element is characterized for full-parameter optical performance;

[0077] In some embodiments, multiple detection points are selected on the light transmission surface of each crystal base unit. The morphology stability of the frequency-doubled light spot is quantified at three different propagation distances by the M2 spot analyzer, and the angular deviation of the exit angle is recorded simultaneously by the four-quadrant detector. The spot ellipticity and angular deviation are calculated and compared with the preset morphology tolerance threshold and angular tolerance threshold. The individual with beam distortion or pointing deviation is eliminated.

[0078] In some embodiments, for the detected crystal base units, clustering grouping is performed according to the average frequency-doubling efficiency value, so as to ensure that the efficiency difference of each crystal base unit in the same group is controlled within the preset fluctuation range.

[0079] Step S212: After the secondary screening, the crystal base units with the average frequency-doubling efficiency value difference within the preset fluctuation range in the same group are divided into the same group. Specifically, for the crystal base units after the secondary screening, grouping is performed according to the average frequency-doubling efficiency value. The crystal base units with the average frequency-doubling efficiency value difference within the preset fluctuation range (such as ≤3%) are divided into the same group. For example, the crystal base units with the average efficiency in the intervals of 44-46%, 46-48%, etc. are classified into different groups, respectively. Please refer to FIG. 4. Figure 2 , Figure 2 FIG. 5 is a schematic diagram of the efficiency corresponding points of the crystal base units in the group with the frequency-doubling efficiency of 44%-46%. In the figure, A1 represents the frequency-doubling efficiency of 44%, B1 represents the frequency-doubling efficiency of 45%, and C1 represents the frequency-doubling efficiency of 46%. At the same time, the crystal base units with the average frequency-doubling efficiency lower than the preset lower limit of 40% are eliminated.

[0080] Step S220: The crystal base units in the same group are embedded into the prefabricated slots of the prefabricated rigid matrix to form a crystal module.

[0081] In some embodiments, the crystal base units in the same group are precisely assembled in the prefabricated slots of the silicon carbide ceramic matrix with ultra-low thermal expansion coefficient to form a crystal module.

[0082] Step S221: The crystal module is configured to be coplanar to the light transmission surfaces of the crystal base units, and the angles of the crystal base units are adjusted to ensure that the laser is normally incident on the light transmission surfaces of the crystal base units. Specifically, the positioning system can be used to ensure that the light transmission surfaces of the crystal base units are in the coplanar state. The laser interferometer is used to assist in adjusting the spatial posture of each crystal base unit, so that the normal directions of all light transmission surfaces are parallel to the preset optical path axis, and the normal incidence condition is ensured.

[0083] Step S222: The crystal base units and the prefabricated rigid matrix are fixed by optical glue, and the surface of the prefabricated rigid matrix is provided with a coordinate scale.

[0084] In some embodiments, the crystal base units and the prefabricated rigid matrix are fixed and solidified by optical glue to enhance the structural stability of the module. At the same time, a precise coordinate scale is etched on the surface of the rigid matrix, and the scale accuracy is controlled within ±100 μm, so as to provide a coordinate reference for subsequent point scanning and point positioning.

[0085] The embodiment eliminates the performance dispersion of individual crystals by secondary screening of multi-parameter optical performance and efficiency matching grouping, provides a material basis for the efficiency stability of the point replacement process; realizes the spatial consistency matching of the optical interfaces of the multi-crystal by super-precision rigid integration and coplanar adjustment, solves the phase mismatch and optical path calibration problems caused by angle deviation in the traditional point replacement technology. Further, the modular crystal combination always maintains stable frequency doubling efficiency, consistent frequency doubling spot morphology and constant emission direction during the point replacement process, without the need for external optical compensation to realize the continuous and stable output of high-power laser, and provides an accurate spatial coordinate reference for subsequent point replacement path planning.

[0086] Step S300: Multi-point scanning is performed on each crystal element in the crystal module to obtain point information;

[0087] Step S300 specifically includes:

[0088] Step S310: Laser scanning is performed on each crystal element in the crystal module according to a preset grid density;

[0089] In some embodiments, a six-axis precision displacement stage is used in cooperation with a laser interference positioning system to perform full-automatic grid scanning on the light transmission surface of each crystal element in the crystal module; the scanning grid density is set to 1 mm interval, the light transmission surface of each crystal element is observed through an optical microscope, and the areas with obvious defects or scratches are identified and avoided to determine the preset scanning points of each crystal element. A 1064 nm laser source with a power stability of 0.1% is used in the scanning process, the spot diameter is controlled to be 1 mm, and the energy density is kept at 20 megawatts per square centimeter. A synchronous acquisition system records the three-dimensional spatial coordinates of each scanning point in real time, and the accuracy reaches ±1 micrometer. A fast-response integrating sphere power meter is used to measure the frequency doubling efficiency, the sampling frequency is 1 kilohertz, and the instantaneous power measurement is accurate. A high-speed M2 spot analyzer is used to synchronously collect frequency doubling spot morphology data at three axial positions, and the ellipticity and beam quality factor are calculated. A four-quadrant detector is used to monitor the emission angle change in real time with a resolution of 0.01 degrees; among them, all optical parameters and spatial coordinates are in one-to-one correspondence, forming a complete spatial-optical parameter mapping data relationship.

[0090] In some embodiments, please refer to Figure 2 and Figure 3, all point positions of each crystal element in the combined crystal are scanned by laser, with a spacing of 1 mm, and the coordinates of each point and the corresponding frequency doubling efficiency are recorded, for example, in a combined crystal with a frequency doubling efficiency of 43%-45%, the first crystal element A1:43%, A2:44%, A3:45%, and the second crystal element B1:43%, B2:44%, B3:45%; the detection points of each crystal element, such as A1-A3 and B1-B3, are corresponded to the grid coordinates one by one and recorded, and the laser energy, focused spot size, and spot energy density of the experiment are also recorded; C1, C2, and C3 represent the point positions on the third crystal element;

[0091] In some embodiments, when each point position is scanned, the long and short axes of the spot are measured at a preset sampling distance by synchronously using the M2 spot analyzer, the ellipticity is calculated, and the exit angle is calibrated by synchronously using the four-quadrant detector; if multiple point positions of the same crystal element have the same frequency doubling efficiency, the point position with the more circular frequency doubling spot morphology and the smaller exit angle offset is preferentially recorded to ensure the effectiveness of the data.

[0092] Step S320: Extract the spatial coordinates of each scanning point and the corresponding frequency doubling efficiency, frequency doubling spot morphology, and exit angle. Specifically, based on the scanning results of S310, the spatial coordinates of each point are extracted, which are directly related to the coordinate scale value of the rigid matrix; the frequency doubling efficiency corresponding to each point is determined by calculating the ratio of the frequency doubling light power to the incident fundamental frequency light power; the detection data of the M2 analyzer and the four-quadrant detector are summarized to obtain the frequency doubling spot morphology parameters and the exit angle parameters of each point; finally, the spatial coordinates, frequency doubling efficiency, frequency doubling spot morphology data, exit angle data, and corresponding laser parameters are associated and stored to form a complete point information library.

[0093] Step S300 realizes comprehensive spatial characterization of the optical performance of each crystal element in the crystal module by establishing a high-precision grid scanning system and a multi-parameter synchronous acquisition mechanism. The 1 mm precision scanning grid ensures the completeness of the detection coverage and avoids the influence of local defects; the multi-parameter real-time synchronous acquisition system obtains complete optical characteristic data such as the frequency doubling efficiency, frequency doubling spot morphology, and exit angle corresponding to each spatial coordinate point; on the one hand, it can accurately reflect the performance differences of each point, and on the other hand, it can ensure the stability of the frequency doubling efficiency and the consistency of the optical parameters through screening of the optimal point under the same efficiency from the data level, thereby reducing the calibration requirements for the optical system after point replacement.

[0094] Step S400: Generating an optimal point replacement path for the crystal module under the target frequency doubling efficiency based on the point information;

[0095] Step S400 specifically includes:

[0096] Step S410: selecting the points meeting the target efficiency value from each crystal element according to the target frequency-doubling efficiency value and the preset efficiency fluctuation range; first, the target frequency-doubling efficiency value and the allowed preset efficiency fluctuation range are determined according to the actual application requirements, and the range needs to be adapted to the efficiency difference range of the crystal elements in the same group in step S213. Based on the point information library obtained in step S300, the frequency-doubling efficiency data of all points of each crystal element is extracted, and the points whose frequency-doubling efficiency falls within the target value and the preset fluctuation range are selected.

[0097] In some embodiments, the required laser parameter configuration requirements such as wavelength, power density, pulse width, and spot size can be combined to match the corresponding modular crystal combination, which needs to be pre-made according to specific laser parameters in step S200; and according to the customer's requirement for the frequency-doubling time length, the array size of the crystal module is determined, for example, 3x3, 4x4, to ensure that the number of points covered by the switching path meets the continuous working time length requirement, and to ensure that the selected points are all from the adapted crystal module.

[0098] Step S420: preferentially selecting the point with the smallest frequency-doubling spot morphology change and the lowest exit angle offset; for the points meeting the efficiency requirement selected in step S410, the frequency-doubling spot morphology data such as ellipticity and exit angle data recorded in step S300 are called. By comparing the deviation degree of the spot ellipticity of each point from the circular shape, the size of the frequency-doubling spot morphology change is evaluated, and the smaller the deviation, the more stable the morphology; by calculating the offset of the exit angle of each point from the reference direction, the angle stability is evaluated, and the lower the offset, the more consistent the direction.

[0099] In some embodiments, the point with the smallest frequency-doubling spot morphology change and the lowest exit angle offset is preferentially selected, and if there are multiple points meeting the condition, the laser parameter adaptability recorded in step S300 is further combined to ensure that the selected point still maintains stable performance under the actual working parameters.

[0100] Step S430: generating a continuous switching point sequence according to the spatial distribution order of the crystal elements; based on the coordinate scale of the rigid substrate surface in step S222, the spatial coordinates of the preferred points in step S420 are extracted, and these points are arranged in sequence according to the spatial distribution order of the points in the crystal module, such as from left to right, from top to bottom, or according to the proximity principle, to form a continuous switching point sequence.

[0101] In some embodiments, the sequence needs to ensure that the displacement table moves smoothly when switching points, avoiding mechanical vibration or positioning errors caused by large jumps, and finally generating the optimal switching point path under the target frequency-doubling efficiency.

[0102] The embodiment filters the points by combining the target efficiency and the preset fluctuation range, ensures the stability of the frequency doubling efficiency in the point switching process, preferentially selects the points with more optimal frequency doubling spot morphology and exit angle, and further ensures the consistency of the optical parameters after the point switching. The continuous point switching sequence is generated according to the spatial distribution, the fluency and accuracy of the point switching operation are improved, and finally the optical system does not need to be repeatedly calibrated in the point switching process, the efficiency fluctuation is effectively reduced, and the long-term stable operation ability and working efficiency of the laser are significantly improved.

[0103] Step S500: driving the crystal module to move to the target point according to the optimal point switching path.

[0104] Step S500 specifically includes:

[0105] Step S510: controlling the displacement table to drive the crystal module to move according to the target point coordinates in the optimal point switching path, so that the frequency doubling efficiency fluctuation after the point switching is maintained within the preset range. Specifically, based on the optimal point switching path generated in step S400, the spatial coordinates of each target point in the path are extracted, which are directly related to the precise coordinate scale on the surface of the rigid base and correspond to the point coordinate information recorded in step S300. Then, the target point coordinates are converted into the driving signals of the displacement table (such as a multi-axis precision translation table) through the numerical control system, and the displacement table is controlled to drive the crystal module to move in the preset direction. During the movement, the position is calibrated in real time by using the coordinate scale on the rigid base and the closed-loop feedback system of the displacement table, so as to ensure that the movement accuracy of the crystal module and the deviation of the target point coordinates are within the preset range. At the same time, combined with the angle setting of the laser normal incidence in step S221, the angle between the light transmission surface of the crystal element and the laser incidence direction is monitored through the angle sensor, so as to ensure that the laser still normally enters the light transmission surface of the crystal element corresponding to the target point after the movement, and avoid the influence of the angle deviation on the frequency doubling efficiency. Finally, the laser action position is accurately switched to the target point, and the frequency doubling efficiency fluctuation after the point switching is maintained within the preset range set in step S410.

[0106] The embodiment can realize the high-precision movement of the crystal module to the target point through the displacement table control based on the precise coordinates, ensures the stability of the laser normal incidence state through the closed-loop feedback and angle monitoring, effectively maintains the preset fluctuation range of the frequency doubling efficiency after the point switching, avoids the sudden change of the efficiency and the distortion of the optical parameters caused by the position or angle deviation in the traditional point switching, and does not need to repeatedly calibrate the subsequent optical system, which significantly improves the convenience of the point switching operation and the continuity of the laser operation.

[0107] In summary, the laser frequency doubling point changing method based on the modular frequency doubling crystal provided by the application proposes a composite technical solution of laser pre-screening, modular combination and accurate point changing. The method first performs laser pre-screening on multiple source crystals, cuts crystal units from large crystals from different sources, removes crystals with low frequency doubling efficiency (less than 40%) through laser detection, and then selects crystals with standard frequency doubling spot ellipticity and frequency doubling beam exit direction, and divides individuals with large frequency doubling efficiency difference into different groups (each group has an efficiency difference of less than or equal to 3%); then, the crystal units in the same group are embedded in a jig with a preformed slot for fixation, and the screened crystals are irradiated with normal incidence laser for adjustment, and the crystal units are moved for point changing under the premise that the frequency doubling spot morphology (ellipticity less than or equal to 5%) and the exit direction (deviation less than or equal to 0.1°) are almost the same, and the positions of each crystal unit with different frequency doubling efficiencies are recorded, thereby generating the best point changing path under the same frequency doubling efficiency, and realizing fast positioning of point changing through the frequency doubling efficiency corresponding to each position recorded by each crystal unit. Through the application, the combined crystal formed can ensure that various optical parameters are consistent when the point is changed, so that recalibration is not required, and the frequency doubling efficiency fluctuation is controlled to be less than or equal to 1%.

[0108] Referring to Figure 4 which shows a structure schematic diagram of a laser frequency doubling point changing device based on a modular frequency doubling crystal provided by an embodiment of the application, the device comprises:

[0109] The pre-screening detection platform is configured to perform crystal unit cutting and laser performance detection; specifically, the pre-screening detection platform comprises a crystal cutting unit and a laser performance detection unit.

[0110] In some embodiments, the crystal cutting unit is equipped with a diamond wire saw precision positioning jig and a phase matching axis alignment mechanism. After selecting nonlinear optical crystals of different batches, the crystal is fixed by the positioning jig, the phase matching axis direction of the crystal is identified by the alignment mechanism, and the diamond wire saw is controlled to cut the crystal into crystal units with consistent sizes along the direction;

[0111] In some embodiments, the crystal units are polished on the light transmission surface and the side surface by using a pretreatment assembly after cutting, atomic force microscopy is used to detect the surface roughness, and the surface treatment is completed in an ultrasonic cleaning tank containing ethanol and deionized water cleaning station and an argon plasma activation device in an argon gas environment;

[0112] In some embodiments, the laser performance detection unit comprises a 1064 nm Nd:YAG laser source power adjustable, a vacuum chuck clamp, an integrating sphere power meter, an M2 spot analyzer and a four-quadrant angle detector; during detection, the pretreated crystal element is fixed on the vacuum chuck clamp, adjusted to the state of normal incidence of laser, the laser source irradiates the crystal element according to the preset point including the center and the four corners, the power meter measures the frequency doubling efficiency in real time, the spot analyzer detects the frequency doubling spot morphology at multiple sampling distances, and the angle detector records the exit angle, and the comprehensive parameters are used to remove the substandard crystal element;

[0113] The grouping configuration module is configured to group the qualified crystal elements by efficiency and fix them on a rigid matrix;

[0114] In some embodiments, the grouping configuration module is composed of a data processing unit, a crystal grouping unit and a module assembly unit;

[0115] In some embodiments, the data processing unit is used to receive the parameters of the pre-screening detection platform, calculate the average frequency doubling efficiency of each crystal element, and conduct secondary screening combined with the frequency doubling spot morphology and exit angle data;

[0116] In some embodiments, the crystal grouping unit is used to divide the crystal elements with efficiency difference within a preset range into the same group according to the screening results, and generate a grouping list;

[0117] In some embodiments, the module assembly unit comprises a rigid matrix such as a silicon carbide ceramic surface engraved with precise coordinate scales, a pre-prepared slot size with precise tolerance control, a precision displacement table and an optical glue curing device; during assembly, the crystal elements in the same group are embedded into the pre-prepared slot of the rigid matrix according to the grouping list, the position of the crystal element is adjusted by the displacement table to make the light transmitting surfaces coplanar, the angle adjustment mechanism ensures the normal incidence of laser, and finally the crystal element and the rigid matrix are fixed by the optical glue curing device such as ultraviolet curing lamp.

[0118] The scanning calibration module is configured to scan the point of the crystal module and record the spatial coordinates and optical parameters;

[0119] In some embodiments, the scanning calibration module comprises a laser scanning unit, a parameter recording unit and a data storage unit;

[0120] In some embodiments, the laser scanning unit is equipped with a laser source and a grid scanning driving mechanism adapted to the crystal element, and based on the coordinate scales of the rigid matrix, the crystal module is scanned at a preset grid density point spacing not less than 1 mm, and the surface defects of the crystal element are identified by an optical microscope and automatically avoided during the scanning process;

[0121] In some embodiments, the parameter recording unit synchronously collects the spatial coordinates of each scanning point, which are associated with the base scale, the frequency doubling efficiency measured by the power meter, the frequency doubling spot morphology M2 analyzer detection, and the four-quadrant detector recording of the exit angle; the data storage unit stores the above parameters in association with corresponding laser parameters such as energy focusing spot size, etc., to form a complete point information library.

[0122] a path planning module configured to generate an optimal point switching path based on the optical parameters;

[0123] In some embodiments, the path planning module includes a target parameter input unit and a path generation unit.

[0124] In some embodiments, the target parameter input unit is used to receive the target frequency doubling efficiency and the allowed fluctuation range set by the user.

[0125] In some embodiments, the path generation unit can be configured to call the point information stored by the scanning calibration module, filter out the points whose efficiency meets the target range, and then select the point with better performance by comparing the deviation of the frequency doubling spot morphology and the exit angle offset, and finally generate a continuous point switching sequence according to the spatial distribution order of the points on the rigid substrate, such as the proximity principle.

[0126] a point switching execution module configured to drive the crystal module to move according to the path;

[0127] In some embodiments, the point switching execution module is composed of a precision displacement stage multi-axis drive type, a closed-loop feedback unit, and a control unit. The control unit is used to receive the point switching sequence generated by the path planning module and convert the target point coordinates into displacement stage driving signals. The precision displacement stage is used to move the crystal module. The closed-loop feedback unit calibrates the position deviation in real time through the grating ruler and realizes closed-loop control through the angle sensor to monitor the included angle between the light transmission surface of the crystal element and the laser incidence direction, so as to ensure that the laser accurately acts on the target point after moving and maintains the normal incidence state.

[0128] In summary, the device ensures the basic performance of the crystal element through pre-screening and detection platform, ensures the consistency and structural stability of the crystal elements in the same group through grouping configuration module, provides high-precision point data through scanning calibration module, optimizes the point switching sequence through path planning module, and realizes accurate movement through point switching execution module. The modules work together to effectively control the frequency doubling efficiency fluctuation and optical parameter distortion in the point switching process, and improve the long-term stable operation ability and working efficiency of the laser.

[0129] Preferably, the pre-screening and detection platform includes:

[0130] a clamping unit for clamping the crystal element;

[0131] a laser emitting unit for irradiating the crystal base element with a detection laser; the laser emitting unit is equipped with a 1064nm Nd:YAG laser, the output power of which can be continuously adjusted in the range of 1 to 10W, and the laser is processed by a beam expansion collimation system to form a parallel light spot with a diameter of 1mm;

[0132] an optical parameter acquisition unit for acquiring the frequency doubling efficiency, frequency doubling light spot morphology and exit angle of the crystal base element;

[0133] a position calibration unit for adjusting the crystal base element to make the laser normally incident on the light passing surface; the position calibration unit comprises a high-resolution CCD camera, a translation adjustment table and a rotation adjustment table; the CCD camera is installed on an auxiliary light path at an angle of 45 degrees to the laser incidence direction, for observing the projection position of the laser light spot on the light passing surface of the crystal base element; the translation adjustment table is connected with the clamping unit and can drive the crystal base element to move along the X and Y axes, so that the center of the light spot coincides with the geometric center of the crystal base element; the rotation adjustment table is nested below the translation adjustment table, and by fine-tuning the pitch angle and yaw angle of the crystal base element, the light spot reflection is observed in cooperation with the CCD camera, until the laser is normally incident on the light passing surface, and the normal incidence calibration is completed;

[0134] In actual detection, after the clamping unit fixes the crystal base element, the position calibration unit monitors the light spot position in real time through the CCD camera, and the translation adjustment table and the rotation adjustment table are linked to adjust the crystal base element to the state of normal incidence of the laser; then the laser emitting unit opens the shutter according to the preset timing, and the laser irradiates the five preset points of the crystal base element in turn; when each point is irradiated, the optical parameter acquisition unit is started synchronously: the integrating sphere power meter records the frequency doubling efficiency, the M2 light spot analyzer acquires the frequency doubling light spot morphology data, the four-quadrant detector measures the exit angle deviation, and the data synchronization module transmits the parameters to the screening module after they are summarized; the screening module automatically determines whether the crystal base element meets the standard according to the preset threshold, such as the lower limit of the frequency doubling efficiency, the deviation range of the frequency doubling light spot morphology and the upper limit of the exit angle deviation, and the crystal base element with parameters not meeting the standard is removed.

[0135] It should be noted that the above-mentioned order of the embodiments of the present application is only for description, and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multi-task processing and parallel processing are also possible or can be advantageous.

[0136] Each embodiment in the specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment mainly describes the differences from other embodiments.

Claims

1. A laser frequency doubling point changing method based on a modular frequency doubling crystal, characterized in that, The method comprises: cutting the crystal base units based on multiple source nonlinear optical crystals, and pre-screening the crystal base units; grouping the pre-screened crystal base units according to the difference in frequency doubling efficiency, and configuring the crystal base units in the same group as a crystal module, comprising: obtaining the average frequency doubling efficiency value of each crystal base unit after pre-screening; detecting the frequency doubling spot morphology and exit angle of each crystal base unit, and performing secondary screening based on the preset morphology threshold and angle threshold; after secondary screening, the crystal base units with an average frequency doubling efficiency value difference within the preset group fluctuation range are divided into the same group; embedding the crystal base units in the same group into the precast slots of the precast rigid matrix to form a crystal module; configuring the crystal module to be coplanar with the light transmission surface of each crystal base unit, and adjusting the angle of each crystal base unit to ensure that the laser is normally incident on the light transmission surface of each crystal base unit; fixing the crystal base units and the precast rigid matrix by optical glue, and the surface of the precast rigid matrix is provided with a coordinate scale; performing multi-point scanning on each crystal base unit in the crystal module to obtain point information, comprising: laser scanning each crystal base unit in the crystal module according to the preset grid density; extracting the spatial coordinates of each scanning point and the corresponding frequency doubling efficiency, frequency doubling spot morphology and exit angle; generating an optimal point switching path of the crystal module under the target frequency doubling efficiency based on the point information, comprising: selecting the point that meets the target efficiency value from each crystal base unit according to the target frequency doubling efficiency value and the preset efficiency fluctuation range; preferentially selecting the point with the smallest frequency doubling spot morphology change and the lowest exit angle offset; generating a continuous point switching sequence in the order of spatial distribution of the crystal base units; driving the crystal module to move to the target point according to the optimal point switching path.

2. The modular frequency-doubled crystal based laser frequency-doubling point- shifting method of claim 1, wherein, Cutting the crystal base units based on multiple source nonlinear optical crystals, and pre-screening the crystal base units, comprising: obtaining nonlinear optical crystals grown in different batches, cutting the crystals into crystal base units along the phase matching axis direction, and pretreating the crystal base units; performing laser performance detection on the pretreated crystal base units, and pre-screening the qualified crystal base units based on the preset optical parameter threshold.

3. The modular frequency-doubled crystal based laser frequency-doubling point- shifting method of claim 2, wherein, Performing laser performance detection on the pretreated crystal base units, and pre-screening the qualified crystal base units based on the preset optical parameter threshold, comprising: selecting multiple preset points to irradiate the pretreated crystal base units with laser, and extracting the frequency doubling efficiency of each point; calculating the average frequency doubling efficiency value of each crystal base unit according to the frequency doubling efficiency; according to the preset efficiency threshold, eliminating the crystal base units with an average frequency doubling efficiency that does not meet the standard.

4. The modular frequency-doubled crystal based laser frequency-doubling point- shifting method of claim 1, wherein, According to the optimal point switching path, driving the crystal module to move to the target point, comprising: controlling the displacement table to drive the crystal module to move according to the target point coordinates in the optimal point switching path, so that the frequency doubling efficiency fluctuation after point switching is maintained within the preset range.

5. Laser frequency doubling point changing device based on modular frequency doubling crystals, characterized in that, The laser frequency doubling point switching method based on the modular frequency doubling crystal of any one of claims 1 to 4, the device comprising: a pre-screening detection platform configured to perform crystal base unit cutting and laser performance detection; a grouping configuration module configured to group the qualified crystal base units by efficiency and fix them on a rigid matrix; a scanning calibration module configured to perform point scanning on the crystal module and record the spatial coordinates and optical parameters. The path planning module is configured to generate an optimal switching point path based on the optical parameters; The switching point execution module is configured to drive the crystal module to move along the path.

6. The laser frequency-doubling point-switching device of claim 5, wherein, The pre-screening detection platform comprises: A clamping unit configured to clamp the crystal element; A laser emitting unit configured to irradiate the crystal element with detection laser; An optical parameter acquisition unit configured to acquire the frequency doubling efficiency, the spot morphology and the exit angle of the crystal element; A position calibration unit configured to adjust the crystal element so that the laser is normally incident to the light entrance surface.

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