Laser preprocessing system and method

Abstract

The present invention provides a laser preprocessing system and method, which includes: a laser pulse generating device and a sample stage for placing a target optical element. The laser pulse generating device is used to output a preset shaped laser pulse, irradiate the target optical element placed on the sample stage, and perform laser preprocessing on the surface of the target optical element. The preset shaped laser pulse includes a first sub-pulse in front and a second sub-pulse in the back, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse. By performing laser preprocessing with a preset shaped laser pulse, the laser preprocessing effect on the target optical element can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a laser preprocessing system and method. Background Art

[0002] Since its birth, laser inertial confinement fusion (ICF) drivers have been facing the problem of limiting the system load capacity due to damage to optical materials. During the operation of the laser drive system, optical components are exposed to strong laser irradiation and laser-induced damage will occur. These damages not only reduce the material transmittance, produce wavefront distortion, and affect the beam quality, but also modulate the light intensity, produce local strong areas, and cause damage to downstream components. Over the past few decades, although the laser damage resistance of optical materials has made great progress, people continue to place higher requirements on the output flux of laser drive systems. At present, laser-induced damage to optical components is a major bottleneck restricting the stable operation and sustainable development of high-power laser devices.

[0003] Laser pretreatment of optical components is the only way to improve the damage performance of optical components. The laser pretreatment process is to irradiate the optical components with a laser flux below the damage threshold before the optical components are used, so that the damage threshold of the optical components is increased. Therefore, in order to meet the high-throughput operation requirements of laser drivers, it is urgent to provide a more effective laser pretreatment solution. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a laser preprocessing system and method, which can effectively improve the laser preprocessing effect on optical elements.

[0005] In a first aspect, an embodiment of the present invention provides a laser preprocessing system, comprising: a laser pulse generating device and a sample stage for placing a target optical element. The laser pulse generating device is used to output a preset shaped laser pulse, irradiate the target optical element placed on the sample stage, and perform laser preprocessing on the surface of the target optical element, wherein the preset shaped laser pulse includes a first sub-pulse in front and a second sub-pulse in the back, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse.

[0006] In a second aspect, an embodiment of the present invention provides a laser preprocessing method, the method comprising: controlling a sample stage to move a target optical element placed on the sample stage to a preset position; controlling a laser pulse generating device to output a preset shaped laser pulse to irradiate a target area on the surface of the target optical element, and performing laser preprocessing on the target area, wherein the shaped laser pulse comprises a first sub-pulse in front and a second sub-pulse in the back, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse.

[0007] The laser preprocessing system and method provided by the embodiment of the present invention performs laser preprocessing on the target optical element by outputting a preset shaped laser pulse through a laser pulse generating device, so that the front part of the preset shaped laser pulse, i.e., the first sub-pulse with a relatively wide pulse width and relatively low intensity, can effectively utilize the thermal effect to interact with the damaged precursor in the target optical element, and the rear part of the preset shaped laser pulse, i.e., the second sub-pulse with a relatively narrow pulse width and relatively high intensity, can effectively utilize the multi-photon absorption effect to interact with the damaged precursor in the target optical element, thereby giving full play to the preprocessing role of the above two effects as much as possible, improving the laser preprocessing effect of the target optical element, and further improving the damage resistance of the target optical element.

[0008] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0010] Figure 1 A schematic diagram of the structure of a laser preprocessing system provided by an embodiment of the present invention;

[0011] Figure 2 A schematic diagram of a waveform of an exemplary preset shaped laser pulse provided in an embodiment of the present invention;

[0012] Figure 3 A schematic diagram of an exemplary single pulse waveform provided by an embodiment of the present invention;

[0013] Figure 4 A schematic diagram of the structure of a pulse generating module provided by an embodiment of the present invention;

[0014] Figure 5 A schematic diagram of the structure of a laser pulse generating device provided by an embodiment of the present invention;

[0015] Figure 6 A schematic diagram of the relationship between the laser pretreatment effect and the laser pulse width provided in an embodiment of the present invention;

[0016] Figure 7 A flowchart of a laser preprocessing method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to better understand the technical solutions provided by the embodiments of this specification, the technical solutions of the embodiments of this specification are described in detail below through the drawings and specific embodiments. It should be understood that the embodiments of this specification and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this specification, rather than limitations on the technical solutions of this specification. In the absence of conflicts, the embodiments of this specification and the technical features in the embodiments can be combined with each other. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0018] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0019] In the description of the present application, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting", "connection" and "coupling" should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two components. The coupling between two devices means that the light emitted by one of the devices is incident on the other device. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0020] like Figure 1As shown, an embodiment of the present specification provides a laser preprocessing system, and the laser preprocessing system 10 includes: a laser pulse generating device 110 and a sample stage 120 for placing a target optical element 100. In the embodiment of the present specification, the target optical element 100 can be an element that needs to be laser preprocessed in an optical system application, such as a crystal element in an optical power laser device.

[0021] The laser pulse generating device 110 is used to output a preset shaped laser pulse, irradiate the target optical element 100 placed on the sample stage 120, and perform laser pretreatment on the target optical element 100. The preset shaped laser pulse includes a first sub-pulse in front and a second sub-pulse in the back. In each preset shaped laser pulse, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse. It can be understood that in the specific implementation process, in the preset shaped laser pulse output by the laser pulse generating device 110, the pulse width of the first sub-pulse, the pulse width of the second sub-pulse, the intensity distribution of the first sub-pulse, and the intensity distribution of the second sub-pulse can be set according to the actual application scenario and multiple tests.

[0022] In an optional embodiment, in the preset shaped laser pulse, the pulse width of the first sub-pulse may be in the range of 1-10 nanoseconds, and the pulse width of the second sub-pulse may be in the range of 10-900 picoseconds. For example, in a certain pre-processing scenario, the pulse width of the first sub-pulse of the preset shaped laser pulse is 5 nanoseconds, and the pulse width of the second sub-pulse is 500 picoseconds. For another example, in another pre-processing scenario, the pulse width of the first sub-pulse of the preset shaped laser pulse is 1 nanosecond, and the pulse width of the second sub-pulse is 10 picoseconds, or the pulse width of the first sub-pulse of the preset shaped laser pulse is 10 nanoseconds, and the pulse width of the second sub-pulse is 900 picoseconds, and so on.

[0023] In an optional embodiment, in the preset shaped laser pulse, the maximum intensity of the second sub-pulse may be 2 to 500 times the maximum intensity of the first sub-pulse. For example, the maximum intensity of the second sub-pulse may be 2, 5, 10, 50, 200 or 500 times the maximum intensity of the first sub-pulse, etc., which may be set according to actual application scenarios and multiple tests.

[0024] For example, in a pre-processing application scenario, the maximum intensity of the first sub-pulse of the preset shaped laser pulse can be 1-5 GW / cm 2 The maximum intensity of the second sub-pulse can be in the range of 10-50 GW / cm 2 The specific range can be set according to the actual application scenario and multiple tests. For example, in a certain pre-processing process, the maximum intensity value of the first sub-pulse of the preset shaping laser pulse can be 1GW / cm 2The maximum intensity of the second sub-pulse can be 10 GW / cm 2 For example, in another preprocessing process, the maximum intensity value of the first sub-pulse of the preset shaped laser pulse can be 5 GW / cm 2 The maximum intensity of the second sub-pulse can be 50 GW / cm 2 It is understandable that the energy flux of the entire preset shaping laser pulse changes in a step-by-step increment during the laser preprocessing process, and the maximum value is less than the damage threshold of the target optical element 100 .

[0025] Figure 2 FIG. 4 shows a waveform diagram of an exemplary preset shaped laser pulse, Figure 3 FIG. 2 shows a waveform diagram of an exemplary single pulse (with a FWHM (Full Width at Half Maximum) of 520 ps). Figure 2 As shown, the preset shaped laser pulse can be a "foot-shaped" pulse, compared to Figure 3 The waveform of the single pulse shown is more complex. The front part of the pulse, i.e., the left part of the dotted line, is the first sub-pulse, which is a low-intensity long pulse with a relatively long duration, i.e., a relatively large pulse width, about several ns, but a relatively low intensity. The rear part of the pulse, i.e., the right part of the dotted line, is the second sub-pulse, which is a high-intensity short pulse with a relatively short duration, i.e., a relatively small pulse width, in the order of hundreds of ps, but a relatively high intensity.

[0026] Specifically, the laser pulse generating device 110 may include: a pulse generating module. The pulse generating module is used to generate the above-mentioned preset shaped laser pulse. As an embodiment, the pulse generating module may include: a laser 101, an amplitude modulator 102 and a waveform generator 103, and the amplitude modulator 102 is connected to the waveform generator 103.

[0027] The laser 101 is used to generate a seed laser to be input to the amplitude modulator 102. In the embodiment of this specification, the laser 101 can use a DFB (Distributed Feedback Laser) fiber laser, and the DFB fiber oscillator can generate a single-mode laser, and the full polarization-maintaining transmission technology can be used to achieve the stability of the polarization state of the system output. Of course, in other embodiments of this specification, other applicable lasers can also be used.

[0028] The amplitude modulator 102 is used to modulate the seed laser under the drive of the preset shaped electric pulse generated by the waveform generator 103 to form the required preset shaped laser pulse. As an implementation, the amplitude modulator 102 can use a high-speed waveguide amplitude modulator. Of course, in other embodiments of this specification, other applicable amplitude modulators can also be used.

[0029] In the embodiment of this specification, the waveform generator 103 can be an arbitrary waveform generator, which is used to generate a shaped electrical pulse, and drive the amplitude modulator to perform amplitude modulation on the input seed laser to generate a shaped optical pulse. It can be understood that the shaped electrical pulse generated by the arbitrary waveform generator is composed of a plurality of (the specific number is determined by the required shaped pulse width) sub-pulse stacks, and the shape of the obtained shaped laser pulse can be adjusted by adjusting the amplitude of each stacked pulse.

[0030] In the specific implementation process, the seed laser generated by the laser 101 is input to the amplitude modulator 102, and is modulated by the amplitude modulator 102 under the drive of the preset shaped electrical pulse generated by the waveform generator 103 to form a preset shaped laser pulse, and is irradiated onto the surface of the target optical element 100 placed on the sample stage 120, so as to perform laser pre-processing on the surface of the target optical element.

[0031] In the above process, the waveform control of the shaped laser pulse can be achieved by computer-assisted multiple iterations. Specifically, the waveform of the output pulse can be tested by a photoelectric tube at the end of the system, that is, the end of the pulse generation module or the end of the laser pulse generation device. According to the waveform test results and the required waveform of the specific shaped laser pulse, the intensity of each sub-pulse in the arbitrary waveform generator is controlled, and the output of the specific shaped laser pulse is achieved by multiple iterations.

[0032] It should be noted that the pulse generation module may also include: broadband fiber amplifiers, power fiber amplifiers, and other amplifiers for high-power amplification of small signal pulses generated in the fiber system, as well as electro-optical shutters for isolating stimulated emission amplification noise in the fiber amplification system, etc., to pre-amplify the shaped pulse output by the amplitude modulator, so that the waveform of the shaped pulse output by the pulse generation module meets the preset requirements. Figure 4 As shown, the shaped pulse output by the amplitude modulator passes through a broadband fiber amplifier such as an ytterbium-doped fiber amplifier (YDFA), an electro-optical shutter, and a power fiber amplifier (PFA) in sequence before being output. Figure 4 In the figure, the DFB fiber laser, amplitude modulator, YDFA, electro-optical shutter and PFA are connected through polarization-maintaining optical fiber, and the dotted line represents the spare equipment.

[0033] In an optional embodiment, in order to obtain a preset shaped laser pulse of required energy, the shaped pulse output by the pulse generation module can be used as a seed shaped pulse, and after amplifying the seed shaped pulse, the amplified seed shaped pulse is used as the preset shaped laser pulse for laser preprocessing. At this time, the laser pulse generation device 110 can also include a pulse amplification module, which is used to amplify the seed shaped pulse output by the pulse generation module to form a preset shaped laser pulse of required energy.

[0034] Specifically, the pulse amplification module can adopt an optical transmission amplification system, such as a high-gain pulse fiber amplifier, a power fiber amplifier, and a joule-level energy amplifier. Figure 5 As shown, the pulse amplification module 112 may include: a high-gain pulse fiber amplifier, a beam control module, a power fiber amplifier, a first joule-level energy amplifier (such as a pair of Φ9 glass rods, i.e., a Φ9mm neodymium glass amplifier, and a group of Φ28 glass rods, i.e., a Φ28mm neodymium glass amplifier), and a second joule-level energy amplifier, such as four groups of Φ70 glass rods, i.e., a Φ70mm neodymium glass amplifier. The seed shaped pulse generated by the pulse generation module 111 may first enter the high-gain pulse fiber amplifier for amplification, and then be coupled into the power fiber amplifier through the beam control module after being emitted from the gain pulse fiber amplifier for amplification, and then, pass through the first joule-level energy amplifier and the second joule-level energy amplifier in sequence before being output to obtain a preset shaped laser pulse.

[0035] In the specific implementation process, the working parameters of the pulse amplification module, such as the amplification factor of each amplifier, can be determined through multiple tests. It should be noted that, corresponding to the preset shaped laser pulse, the seed shaped pulse output by the pulse generation module is also composed of two parts, namely, the low-intensity wide pulse in the front part and the high-intensity narrow pulse in the back part. Therefore, the pulse amplification module needs to effectively amplify both parts of the pulse to achieve the maintenance of the shaped pulse shape.

[0036] In an optional embodiment, if the target optical element is a frequency tripling crystal element such as a KDP / DKDP crystal in an optical power laser device, the pretreatment laser is preferably a frequency tripling (3ω) laser. Figure 5As shown, the laser pulse generating device 110 may further include: a frequency doubling module 113. The frequency doubling module 113 is used to perform frequency doubling processing on the seed shaping pulse output by the pulse generating module 111 or the above-mentioned amplified seed shaping pulse. The specific frequency doubling can be set according to actual needs. For example, the seed shaping pulse can be converted into a three-fold frequency shaping laser pulse for output. For example, the frequency doubling module may include a Class I KDP frequency doubling crystal and a Class II triple frequency doubling crystal. For example, a seed shaping pulse with a wavelength of 1053nm can be converted into a shaping laser pulse with a wavelength of 351nm after the above-mentioned triple frequency doubling process.

[0037] It should be noted that the working parameters of the frequency doubling module can be determined through multiple tests. Similar to the aforementioned amplification process, the frequency doubling module needs to effectively perform frequency conversion on the low-intensity wide pulse in the front part and the high-intensity narrow pulse in the back part of the amplified seed shaped pulse to maintain the shape of the shaped pulse and obtain the preset shaped laser pulse.

[0038] During the laser preprocessing process, it is necessary to gradually increase the irradiation flux of the preset shaped laser pulse from low to high, and irradiate the preset area on the surface of the target optical element for a preset number of times in turn to achieve laser preprocessing of the preset area on the surface of the target optical element.

[0039] Therefore, in order to facilitate the adjustment of pretreatment laser energy, such as Figure 1 As shown, the laser preprocessing system 10 provided in the embodiment of the present specification may further include an energy control module 130. The energy control module 130 is disposed on the light propagation path between the laser pulse generating device 110 and the target optical element 100, and is used to adjust the energy of the preset shaped laser pulse irradiated to the surface of the target optical element 100.

[0040] As an implementation mode, the energy control module 130 includes a 1 / 2 wave plate 131 and a polarizer 132. The preset shaped laser pulse output by the laser pulse generating device 110 is incident on the target optical element 100 through the 1 / 2 wave plate 131 and the polarizer 132 in sequence. By adjusting the angle of the 1 / 2 wave plate 131, the polarization state of the preset shaped laser pulse passing through the 1 / 2 wave plate 131 is adjusted, thereby controlling the energy of the preset shaped laser pulse passing through the polarizer 132. Adjusting the laser pretreatment energy in this way is conducive to ensuring that the same waveform output is achieved when laser pretreatment is performed on the target optical element using different energies.

[0041] It is understandable that if Figure 1As shown, the laser preprocessing system 10 may further include a focusing lens 140 disposed between the polarizer 132 and the target optical element 100 , for focusing the preset shaped laser pulse emitted by the polarizer 132 onto the surface of the target optical element 100 , and performing laser preprocessing on the target optical element 100 .

[0042] In the specific implementation process, the position of the target optical element 100 can be adjusted by the sample stage 120 so that the above-mentioned preset shaped laser pulse scans the surface of the target optical element 100 according to the preset trajectory, thereby realizing the laser pretreatment of the target optical element 100. Specifically, the sample stage 120 can be a manually adjusted translation stage or an electric translation stage. In order to ensure that the surface of the target optical element 100 can be uniformly irradiated by the above-mentioned preset shaped laser pulse during the laser pretreatment process, so as to further improve the laser pretreatment effect, the adjustment step length of the sample stage 120 can be set according to the spot diameter of the preset shaped laser pulse incident on the target optical element 100.

[0043] For example, during the laser preprocessing process, there are 8 energy steps of the preprocessing laser beam, and the energy of the preset shaping laser pulse is adjusted to the required energy steps from low to high. Each time an energy step is adjusted, the position of the target optical element is adjusted through the sample stage, and the preset shaping laser pulse of the energy step is used to perform laser preprocessing on the target optical element until the laser preprocessing of all preset energy steps is completed. The specific preprocessing process is similar to the laser preprocessing process in the prior art and will not be described in detail here.

[0044] In order to more clearly understand the technical solutions provided by the embodiments of this specification, the action mechanism of the above-mentioned preset shaped laser pulses and the target optical element is described below.

[0045] When the front part of the preset shaping laser pulse, i.e., the first sub-pulse, interacts with the damaged precursor on the target optical element (i.e., the defect that causes its body damage threshold to be low), the process can be regarded as a pure thermal process. Part of the energy in the first sub-pulse is absorbed by the damaged precursor and heated, and the crystal around the damaged precursor will also be heated by conduction. The absorption of the first sub-pulse by the damaged precursor is obtained according to the Mie scattering theory, and the heating of the surrounding crystal is a Fourier heat conduction process. When the rear part of the preset shaping laser pulse, i.e., the second sub-pulse, interacts with the damaged precursor on the target optical element, the process is a process of combined action of heat and multi-photons. Among them, the thermal process is consistent with the aforementioned thermal process. Since the probability of occurrence of the four-photon absorption process in the crystal is several orders of magnitude lower than that of the three-photon, because the multi-photon action only considers the three-photon absorption process. Due to the presence of the damaged precursor on the target optical element, it will assist in completing the three-photon absorption process. Therefore, the interaction process between the damaged precursor and the second sub-pulse at the rear of the preset shaping laser pulse is a three-photon absorption process under defect-assisted conditions.

[0046] Therefore, compared to a single pulse, when the target optical element is laser pre-processed by the above-mentioned preset shaped laser pulse, the front part of the pulse, i.e., the first sub-pulse, can effectively utilize the thermal effect to interact with the damaged precursor, and the rear part of the pulse, i.e., the second sub-pulse, can effectively utilize the multi-photon absorption effect to interact with the damaged precursor. In this way, the pre-processing role of the above-mentioned two effects can be exerted as much as possible, thereby effectively improving the laser pre-processing effect of the target optical element.

[0047] Moreover, the thermal effect of the first sub-pulse and the defects of the target optical element can not only directly remove some defects, but also increase the temperature of other defects, so that these defects can interact more effectively with the second sub-pulse with relatively high intensity in the latter part, thereby achieving nonlinear removal of these defects. In other words, through the above-mentioned preset shaped laser pulse, the above-mentioned two mechanisms can be comprehensively utilized to fully interact with the damage precursor on the target optical element, thereby more effectively removing the damage precursor, improving the laser pretreatment effect, and further improving the damage resistance of the target optical element.

[0048] It should be further explained that before proposing the laser pretreatment system provided in the embodiments of this specification, the inventor of this application conducted an in-depth study on the mechanism of action between laser and damage precursor during laser pretreatment, and proposed a new laser pretreatment idea, that is, abandoning the commonly used single pulse and applying shaped pulse to laser pretreatment of optical elements, which can effectively improve the laser pretreatment effect, thereby improving the damage resistance of optical elements. Taking KDP / DKDP crystal as an example, the reasons why shaped pulse can achieve the above effect are analyzed below.

[0049] KDP / DKDP crystal is a nonlinear crystal with excellent optical properties, mainly used for frequency conversion, electro-optical modulation, optical switching, etc. in high-power laser devices. KDP / DKDP crystal is the only frequency conversion crystal available in the driver laser system. This is because the laser driver system has a large output beam aperture (greater than 400mm×400mm), and KDP / DKDP crystal is the only high-performance nonlinear crystal that can be used in such a large-aperture optical system. The function of the frequency conversion crystal is to convert the high-flux output fundamental frequency (1ω) light into triple frequency (3ω) light to improve the coupling efficiency of the interaction between the laser beam and the fusion target.

[0050] The defects formed during the growth process of KDP / DKDP crystals are the root cause of their low body damage threshold. These defects are called damage precursors. Crystal laser damage and laser pretreatment are both based on the interaction between light and damage precursors. The changes that occur after the action of light and damage precursors can be reversibly restored after the laser pulse stops. The restored state is better than the initial state, thereby reducing the number of absorption defects in the crystal. This is laser pretreatment; the action of light and damage precursors causes fundamental and irreversible damage to the physical and chemical properties, thus forming laser damage. Therefore, the inventors of this application propose to adopt an optimal pretreatment laser irradiation scheme, which integrates multiple mechanisms to allow the laser and damage precursor to fully interact when the laser flux is lower than the laser damage threshold flux. This is the fundamental to improving the effect of laser pretreatment.

[0051] In laser pretreatment, there are two basic models of damaged precursors and their laser absorption mechanisms: impurity nanoparticles and linear absorption model, intrinsic defect clusters, and multiphoton absorption model. Among them, the pretreatment mechanism in the linear absorption model is as follows: the precursor absorbs the energy of the laser pulse so that its temperature rises to a critical temperature, but it is lower than the temperature at which damage occurs (at this temperature, thermal explosion will occur and plasma will be formed). At this critical temperature, the precursor only melts and enters the lattice, and its density decreases, which eventually leads to reduced absorption. There are two pretreatment pathways in the multiphoton absorption model. One of the pathways is that the precursor is heated to a critical temperature below the damage threshold through the multiphoton absorption mechanism, which is similar to the linear absorption model, but the absorption mechanism is different; the second pathway is that the pretreatment process is an electronic process rather than a thermal process. The pretreatment pulse laser excites electron transitions, and the transition electrons enter the defect energy level, changing the bandwidth of the defect and reducing the probability and sensitivity of the precursor defect being excited.

[0052] The inventors of the present application have found through long-term research that the above two models are not independently contradictory in the laser pretreatment process, but are complexly integrated and work together. Figure 6The relationship between the laser pretreatment effect and the laser pulse width is shown in the figure. The horizontal axis is the pulse width of the laser pretreatment, in nanoseconds (ns), and the vertical axis is the energy flux after pretreatment, in J / cm 2 .from Figure 6 It can be seen that the laser pulse width with the best pretreatment effect is 200ps-900ps. When the pulse width is greater than 900ps or less than 200ps, the pretreatment effect will decrease. If the laser pretreatment mechanism is a simple impurity nanoparticle and linear absorption model, then when the pretreatment laser pulse width is greater than 900ps, the pretreatment effect will not deteriorate. This is because the larger the pretreatment pulse width, the more sufficient the linear absorption of the nanoparticles will be. Under the condition of reasonable control of the total flux, each damage precursor will be more fully pretreated, and the pretreatment effect will not be worse. Therefore, the result that the pretreatment effect deteriorates when the pretreatment laser pulse width is greater than 900ps indicates that the laser pretreatment mechanism is not a simple impurity nanoparticle and linear absorption model.

[0053] In addition, if the laser pretreatment mechanism is a simple intrinsic defect cluster and multiphoton absorption model, then when the pretreatment laser pulse width is less than 200ps, the pretreatment effect will not deteriorate. This is because as the pretreatment pulse width decreases, the pulse peak power density will be greater under the same laser flux conditions, and the multiphoton absorption effect will be stronger. Under reasonable control of the total flux, each damaged precursor will be more fully pretreated, and the pretreatment effect will not be worse. Therefore, the result that the pretreatment effect deteriorates when the pretreatment laser pulse width is less than 200ps indicates that the laser pretreatment mechanism is not a simple intrinsic defect cluster and multiphoton absorption model.

[0054] It is understandable that the realization of a certain total laser pulse energy can use impurity nanoparticles and linear absorption model, that is, thermal effect treatment to remove part of the damaged precursor; the realization of a certain laser pulse peak power can use intrinsic defect clusters and multiphoton absorption model, that is, multiphoton absorption effect treatment to remove part of the damaged precursor. A single pulse is difficult to fully exert the effects of the above two effects, resulting in limited pretreatment effects.

[0055] By shaping the laser pulse, that is, the front part of the pulse has a relatively long duration (such as 1 to 9 ns) and a relatively low intensity, and the back part of the pulse has a relatively short duration (such as in the order of hundreds of ps) and a relatively high intensity, on the one hand, the front part of the pulse can effectively utilize the thermal effect to interact with the damage precursor, and the back part of the pulse can effectively utilize the multi-photon absorption effect to interact with the damage precursor. On the other hand, the thermal effect of the low-intensity laser in the front part of the pulse and the defects can not only directly remove some defects, but also increase the temperature of other defects, so that these defects with increased temperatures can interact more effectively with the high-intensity pulse in the back part, thereby achieving nonlinear removal of these defects. Such a shaped pulse can comprehensively utilize the two mechanisms under certain flux control conditions to fully interact with the damage precursor, thereby more effectively removing the damage precursor and further improving the damage resistance of optical components.

[0056] In addition, the embodiments of this specification also provide a laser preprocessing method, which is applied to the above laser preprocessing system. Figure 7 As shown, the method includes:

[0057] Step S701, controlling the sample stage to move the target optical element placed on the sample stage to a preset position;

[0058] Step S702, control the laser pulse generating device to output a preset shaped laser pulse, irradiate the target area on the surface of the target optical element, and perform laser pre-processing on the target area, wherein the shaped laser pulse includes a first sub-pulse in front and a second sub-pulse in the back, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse.

[0059] The preset position and target area are set according to the laser preprocessing requirements of the target optical element in the actual application scenario. The energy flux of the entire preset shaping laser pulse changes in a step increment during the laser preprocessing process, and the maximum value is less than the damage threshold of the target optical element.

[0060] The laser preprocessing method provided in the embodiments of this specification has the same implementation principle and technical effects as those of the aforementioned system embodiments. For the sake of brief description, for matters not mentioned in the method embodiments, reference may be made to the corresponding contents in the aforementioned system embodiments.

[0061] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A laser preprocessing system, characterized in that: include: Laser pulse generator and sample stage for placing target optical elements, The laser pulse generating device is used to output a preset shaped laser pulse, irradiate the target optical element placed on the sample stage, and perform laser pretreatment on the surface of the target optical element, wherein the preset shaped laser pulse includes a first sub-pulse in front and a second sub-pulse in the back, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse; The laser pulse generating device comprises: a pulse generating module, the pulse generating module comprises a laser, an amplitude modulator and a waveform generator, the amplitude modulator is connected to the waveform generator, the laser is used to generate a seed laser input to the amplitude modulator; the amplitude modulator is used to modulate the seed laser under the drive of the preset shaped electric pulse generated by the waveform generator to form the preset shaped laser pulse; The sample stage is also used to adjust the position of the target optical element so that the preset shaped laser pulse scans the surface of the target optical element according to a preset trajectory to perform laser preprocessing on the target optical element.

2. The system according to claim 1, characterized in that The pulse width of the first sub-pulse is in the range of 1-10 nanoseconds, and the pulse width of the second sub-pulse is in the range of 10-900 picoseconds.

3. The system according to claim 1, characterized in that The maximum intensity of the second sub-pulse is 2 to 500 times the maximum intensity of the first sub-pulse.

4. The system according to claim 1, characterized in that The laser pulse generating device further comprises a pulse amplifying module, and the pulse amplifying module is used to amplify the seed shaped pulse output by the pulse generating module to form the preset shaped laser pulse.

5. The system according to claim 1, characterized in that The laser pulse generating device further comprises: a frequency doubling module, The frequency doubling module is used to perform frequency doubling processing on the seed shaped pulse output by the pulse generating module to form the preset shaped laser pulse.

6. The system according to claim 1, characterized in that The system also includes an energy control module, which is arranged on the light propagation path between the laser pulse generating device and the target optical element and is used to adjust the energy of the preset shaped laser pulse irradiated onto the surface of the target optical element.

7. The system according to claim 6, characterized in that The energy control module comprises a 1 / 2 wave plate and a polarizing plate, and the preset shaped laser pulse output by the laser pulse generating device is incident on the target optical element through the 1 / 2 wave plate and the polarizing plate in sequence.

8. The system according to claim 1, characterized in that The target optical element is a crystal element in an optical power laser device.

9. A laser pretreatment method, characterized in that: The method comprises: Controlling the sample stage to move a target optical element placed on the sample stage to a preset position; Controlling the laser pulse generating device to output a preset shaped laser pulse to irradiate a target area on the surface of the target optical element, and performing laser pretreatment on the target area, wherein the shaped laser pulse includes a first sub-pulse in front and a second sub-pulse in the back, the pulse width of the first sub-pulse is greater than the pulse width of the second sub-pulse, and the maximum intensity of the first sub-pulse is less than the maximum intensity of the second sub-pulse; The position of the target optical element is adjusted by the sample stage so that the preset shaping laser pulse scans the surface of the target optical element according to a preset trajectory, so as to perform laser pretreatment on the target optical element; Among them, the laser pulse generating device includes: a pulse generating module, the pulse generating module includes a laser, an amplitude modulator and a waveform generator, the amplitude modulator is connected to the waveform generator, and the laser pulse generating device is controlled to output a preset shaped laser pulse, including: the laser generates a seed laser and inputs it into the amplitude modulator; the amplitude modulator is driven by the preset shaped electrical pulse generated by the waveform generator, and modulates the seed laser to form the preset shaped laser pulse.

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