Laser damage threshold measurement method and device

Abstract

The present application discloses a measuring device and method for measuring the laser damage threshold of a material. The measuring method comprises: adjusting the attenuation coefficient of an energy attenuator to gradually increase the energy of the pump beam, continuously recording the energy of the pump beam, monitoring beam, and detection beam until the sample is damaged by the pump beam, and obtaining energy information of the pump beam, monitoring beam, and detection beam; a data processing module processes the obtained energy information of the pump beam, monitoring beam, and detection beam to obtain the laser damage threshold of the sample to be measured. The method utilizes the fact that the detection beam is shorter than the pump beam in the optical path, and is first focused onto the sample through a lens to perform a detection function. Before the sample is damaged, the transmittance of the detection beam remains unchanged and is a straight line. When the sample is permanently damaged, the energy of the detection beam changes suddenly, thereby accurately determining the damage threshold of the sample.

Description

Technical Field

[0001] The present application belongs to the field of measuring instruments and equipment, and specifically relates to a method and device for accurately measuring the laser damage threshold of a material. Background Art

[0002] Laser limiter is a passive laser protection device and an important application of nonlinear optics. The ideal optical limiting material has a high linear transmittance for low-intensity incident light. When the incident light intensity increases, the nonlinear effect weakens and the transmittance decreases accordingly. The laser is limited to a certain energy limit E. on Next, where E on Defined as the optical limiting threshold, it is the incident light energy flux corresponding to a transmittance of 50% linear transmittance. The optical limiting experiment sample is fixed near the lens focal point. During measurement, the laser power is continuously adjusted, and the detector monitors the input and output energies. Finally, the relationship between input and output energies is plotted to obtain the optical limiting curve.

[0003] High-power lasers can cause irreversible damage to some components and observers. Optical limiters made using nonlinear optical effects can provide excellent laser protection. Therefore, research on optical limiting materials has always been a hot topic.

[0004] The laser-induced damage threshold (LDT) refers to the maximum energy density or power density that an optical component can withstand. Exceeding this critical value will damage the material. However, optical limiting systems can only determine the damage threshold of optical thin films within a rough range and cannot accurately measure it. Summary of the Invention

[0005] In order to overcome the above shortcomings, the present application makes improvements based on the optical limiting technology and proposes a measurement method and device that can accurately measure the laser damage threshold of the material used for measurement.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions:

[0007] A measuring device for measuring the laser damage threshold of a material, comprising:

[0008] The laser light emitted by the laser light source is divided into a reflected light path and a transmitted light path by the first beam splitter, wherein the reflected light path is the pump beam and the transmitted light path is the detection beam.

[0009] The detection beam is converged by the second convex lens and irradiated onto the sample to be tested, and is converged by the third convex lens to the third energy probe.

[0010] The pump beam passes through the energy attenuator and is incident on the second beam splitter.

[0011] The pump beam reflected by the second beam splitter is converged by the first convex lens and then incident on the sample to be tested. After penetrating the sample to be tested, the pump beam is converged by the second convex lens to the second energy probe;

[0012] The light beam passing through the second beam splitter serves as a monitoring beam of the pump beam, and the monitoring beam is incident on the first energy probe;

[0013] The ratio of the pump beam energy captured by the second energy sensor to the monitoring beam energy captured by the first energy sensor is used to determine the ratio between the pump beam and the monitoring beam acting on the sample. This measurement device enables precise measurement of the laser damage threshold of the material being measured.

[0014] In one embodiment, the laser damage threshold measurement device further includes: a beam expansion and collimation module, which is disposed in front of the laser light source and is used to collimate the laser light emitted by the laser light source and transmit it to the first beam splitter.

[0015] In one embodiment, the laser damage threshold measurement device further includes:

[0016] The first energy probe, the second energy probe and the third energy probe are respectively connected to the data processing module.

[0017] In one embodiment, the laser damage threshold measurement device further includes:

[0018] During measurement, the optical path of the probe beam is shorter than the optical path of the pump beam. The probe beam is converged onto the sample to be measured through a second convex lens. Before the sample to be measured is damaged, the transmittance of the probe beam remains unchanged. When the sample is damaged, the energy of the probe beam changes suddenly to determine the damage threshold of the sample.

[0019] In one embodiment, the laser damage threshold measurement device further includes:

[0020] A first reflector and a second reflector are set on the detection beam, and a third reflector is set on the pump beam; by adjusting the positions of the first reflector and the second reflector, and modulating the position of the third reflector, the detection beam and the pump beam are respectively incident on the sample to be measured.

[0021] In one embodiment, the first spot size of the probe beam falling on the sample to be tested is smaller than the second spot size of the pump beam falling on the sample to be tested, so as to ensure that damage changes of the sample to be tested can be detected.

[0022] In one embodiment, a first light spot of the probe beam falling on the sample to be measured partially overlaps with a second light spot of the pump beam falling on the sample to be measured.

[0023] The present application provides a method for measuring the laser damage threshold of a material using the above-mentioned device for measuring the laser damage threshold. The method comprises the following steps:

[0024] S1. Adjust the attenuation coefficient of the energy attenuator to gradually increase the energy of the pump beam incident on the sample to be tested, continuously monitor the energy value of the third energy probe, and maintain the transmittance of the probe beam until the sample to be tested is damaged. When a sudden change in the energy value of the third energy probe is detected, the sample to be tested is determined to have been damaged by the pump beam. Record the energy values ​​of the first, second, and third energy probes to obtain energy information of the pump beam, monitoring beam, and probe beam at the laser damage threshold of the sample to be tested.

[0025] S2. The data processing module processes the energy information of the pump beam, monitoring beam, and detection beam to obtain the laser damage threshold of the sample to be tested.

[0026] In one embodiment, before step S2, the method further includes:

[0027] Obtain a ratio curve of the pump beam and the monitoring beam acting on the sample to be measured.

[0028] In one embodiment, step S2 includes:

[0029] The energy of the pump beam incident on the sample to be measured is obtained by multiplying the obtained ratio curve by the energy of the measured probe beam.

[0030] Divide the energy of the pump beam by the waist area of ​​the pump beam to obtain the energy flux of the pump beam and use it as the horizontal axis.

[0031] The energy of the probe beam is normalized and used as the vertical coordinate to obtain the energy flux of the pump beam at the mutation position of the normalized probe beam, which is the laser damage threshold of the material.

[0032] Beneficial effects

[0033] Compared with the prior art, the measurement device proposed in this application realizes the precise measurement of the laser damage threshold used to measure materials. In this device, the optical path of the probe beam is shorter than that of the pump beam. It is first focused on the sample through a lens to play a detection role. Before the sample is damaged, the transmittance of the probe beam remains unchanged and is a straight line. When the sample is permanently damaged, the energy of the probe beam will suddenly change, so that the damage threshold of the sample can be accurately determined. On the sample surface, the probe beam and the pump beam overlap on the sample, and the spot size of the probe beam is smaller than the spot size of the pump beam to ensure that the detection area can detect the damage changes of the sample. The position where the energy of the probe beam suddenly changes is the damage threshold of the material.

[0034] Compared with other measurement technologies, it has the following advantages:

[0035] The laser damage threshold of a material can be accurately determined in real time, eliminating the need to determine whether the material has been damaged after the laser exposure. This significantly improves the sensitivity and accuracy of the measurement parameters. The measurement device is simple in structure, easy to operate, and provides intuitive and clear results. It also avoids the influence of the material's inherent nonlinear effects on the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are intended to facilitate understanding of the technical solutions of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the technical solutions of the present disclosure and do not constitute a limitation of the technical solutions of the present disclosure. The shapes and sizes of the components in the accompanying drawings do not reflect the actual scale and are intended only to illustrate the contents of this application.

[0037] Figure 1 Schematic diagram of the structure of the measuring device for measuring the laser damage threshold of a material in Example 1;

[0038] Figure 2 Schematic diagram of the structure of a measuring device for measuring the laser damage threshold of a material in Example 2;

[0039] Figure 3 This is the relationship between the output energy and input energy of the first point of ZnSe material under laser action;

[0040] Figure 4 This is the relationship between the output energy and input energy of the second point of the ZnSe material under laser action;

[0041] Figure 5 This is the relationship between the output energy and input energy of the third point of the ZnSe material under laser action;

[0042] Among them: 1-laser light source, 2-beam expansion and collimation module, 3-first beam splitter, 4-energy attenuator, 5-second beam splitter, 6-first energy probe, 7-third reflector, 8-first convex lens, 9-sample to be tested, 10-second convex lens, 11-second energy probe, 12-first reflector, 13-second reflector, 14-second convex lens, 15-third convex lens, 16-third energy probe, 17-data processing module. DETAILED DESCRIPTION

[0043] The above solution is further described below with reference to specific embodiments.

[0044] Unless otherwise defined, the technical or scientific terms used in the embodiments of the present disclosure should have the ordinary meaning understood by a person of ordinary skill in the art to which this application belongs. The terms "first," "second," and similar terms used in the embodiments of the present disclosure do not indicate any order, quantity, or importance, but are simply used to distinguish different components. The terms "include" or "comprises" and similar terms mean that the elements or objects preceding the term include the elements or objects listed after the term and their equivalents, without excluding other elements or objects. The terms "connected" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. In this document, "electrically connected" includes situations where components are connected together through an element with some electrical function. There is no special limitation on "element with some electrical function" as long as it can transmit and receive electrical signals between the connected components. The terms "upper," "lower," "left," "right," etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0045] In this application, terms such as "upper," "lower," "inner," and "middle" indicate positions or locations based on those shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to specific positions, or to their construction or operation in a specific position.

[0046] Example 1

[0047] A measuring device for measuring the laser damage threshold of a material, such as Figure 1 Shown include:

[0048] The laser light source 1 emits a laser beam which is incident on the first beam splitter 3 after passing through the beam expansion and collimation module. The laser light is then divided into a reflected light path and a transmitted light path by the first beam splitter. The reflected light path is the pump beam, and the transmitted light path is the detection beam.

[0049] The pump beam passes through the energy attenuator 4 and is incident on the second beam splitter 5. The pump beam reflected by the second beam splitter is converged by the first convex lens 8 and is incident on the sample to be tested. The pump beam penetrates the sample to be tested 9 and is converged by the second convex lens 10 to the second energy probe 11. The beam passing through the second beam splitter serves as the monitoring beam of the pump beam, and the monitoring beam is incident on the first energy probe 6.

[0050] The ratio between the pump beam acting on the sample to be tested and its monitoring beam is obtained by the ratio of the pump beam energy collected by the second energy probe and the monitoring beam energy collected by the first energy probe.

[0051] The detection beam is converged by the second convex lens 14 and irradiated onto the sample to be tested, and is then converged by the third convex lens 15 to the third energy probe 16 .

[0052] Example 2

[0053] On the basis of the first embodiment, in order to more conveniently deflect the probe beam and the pump beam to the sample to be tested, and modulate the angle between the probe beam and the pump beam incident on the sample to be tested, a measuring device for measuring the laser damage threshold of a material, such as Figure 2 As shown, a first reflector 12 and a second reflector 13 are arranged on the detection beam, and a third reflector 7 is arranged on the pump beam; by adjusting the positions of the first reflector and the second reflector, and modulating the position of the third reflector, the detection beam and the pump beam are respectively made incident on the sample to be measured; the first energy probe, the second energy probe and the third energy probe are respectively connected to the data processing module 17.

[0054] Before the experiment, without placing the sample 9 in place, the ratio between the pump beam acting on the sample and its monitoring beam is measured using the second energy probe 11 and the first energy probe 6. During the measurement, this ratio is multiplied by the energy detected by the first energy probe 6 of the monitoring beam to obtain the energy of the pump beam acting on the sample.

[0055] In the optical path, after the detection beam passes through the first beam splitter 3, it is reflected by the first reflector 12 and the second reflector 13 and reaches the sample to be tested 9. The optical path is shorter than the optical path of the pump beam to reach the sample to be tested, which plays a detection role. Before the sample is damaged, the transmittance of the detection beam remains unchanged. When the sample is damaged, the energy of the detection beam will suddenly change, so that the damage threshold of the sample can be accurately determined. On the surface of the sample, the detection beam and the pump beam need to coincide on the sample. The angle between the pump beam and the detection beam is controlled to be very small by the third reflector 7 and the second reflector 13. The spot size of the detection beam is smaller than the spot size of the pump beam to ensure that the detection area can detect the damage changes of the sample. The position where the energy of the detection beam suddenly changes is the damage threshold of the material. This method can be widely used to accurately measure the laser damage threshold of materials.

[0056] In one embodiment, the experiment was conducted at room temperature using a wavelength of 532 nm, a pulse width of 6 ns, and a pulse repetition frequency of 10 Hz. Using an energy attenuator, the incident laser energy density was increased by the same amount. Energy pulses were then applied to the same test point at the same time intervals. The laser energy density (laser energy per unit area at the test point) at which damage occurred was recorded. The corresponding laser energy density value was the damage threshold at that point.

[0057] In the experiment, the pump beam incident on the front surface of the sample has a beam waist of 17.7 microns at the focal point. The pump beam reaching the sample deviates from the focal position by about 10 mm, and the beam waist radius of the pump beam on the sample is about 101 microns. The spot size of the probe light on the sample surface is consistent with the spot size at the lens focal point, and the input flux is constant at 0.1 J / cm 2 .

[0058] The effectiveness of this method was verified using ZnSe with a thickness of 3 mm. Due to the increased optical path difference (2 m, a delay of about 6.6 ns), the pump beam arrived at the sample later than the probe beam. The first pulse of the probe beam reached the sample without causing damage; after a delay of 6.6 ns, the first pulse of the pump beam reached the sample and caused damage. Next, when the second probe pulse reached the sample, damage was detected. This time interval is equal to one pulse interval (pulse repetition frequency is 10 Hz) minus the corresponding optical path difference, that is, 0.1 s - 6.6 ns. This time interval (about 0.1 s) is sufficient for the relaxation and recovery of some ultrafast dynamic processes, such as two-photon absorption or carrier absorption in ZnSe samples. Figures 3 to 5 The results of measuring the damage threshold at three different points of the ZnSe sample are shown. The curve of the change of the energy flux after passing through the ZnSe sample with the increase of the energy flux of the pump light before incident on the sample clearly shows that there is no sudden change in the pump beam curve. This is because ZnSe has a certain nonlinear effect. In the range near LIDT, the output energy does not increase with the increase of input energy, which makes it impossible for the pump beam to determine the specific location of the damage. In addition, the optical limiting effect of ZnSe causes the transmittance to decrease with the increase of input energy. After the damage occurs, with the increase of energy and the expansion of the damage area, the light passing through the sample is scattered, and the transmittance is further reduced, and can even be reduced to below 10%. Because the specific location of the damage is not determined, the downward trend of the transmittance may be mistaken for the optical limiting effect of the sample. The detection beam can effectively detect the damage location, Figures 3 to 5The probe beam initially maintains a constant initial energy value. Then, as damage occurs, the probe beam experiences a sharp decline at an inflection point. This sudden inflection point is defined as the sample's damage threshold. Because the transmitted light is scattered after sample damage, the energy detected by the detector decreases, while the input flux of the probe beam remains constant. Its change can explain the change in scattered light passing through the sample, that is, the change in the sample's transmittance, further indicating that the sample has suffered irreversible damage. In the experiment, we measured nine damage points, S1 to S9, on the same plane and compared the damage thresholds (FLIDT) at different locations. The measurement results are shown in Table 1, with an error range of approximately 12%. When the beam reaches the first surface, it causes a certain amount of energy accumulation, and the continuous accumulation of heat leads to sample damage. In a sense, damage can be roughly regarded as the sample reaching a certain thermal ablation threshold, which is consistent with reported assessments of damage thresholds.

[0059] Table 1. Damage threshold of ZnSe at different points under experimental conditions of 10 Hz, 532 nm, and 6 ns

[0060]

[0061] Laser damage to optical components is a complex process, which is determined by the laser parameters and the performance of the device. Due to accidental factors such as manufacturing methods and processing technology, the damage effect of the components will also vary greatly. In addition, due to external factors and the presence of impurities and scratches, defects in the material will absorb energy, causing temperature increases in the form of heat and force, resulting in material damage. In our experiment, the random distribution of ZnSe impurities and their physical and chemical properties lead to uncertainty in the degree of damage, and the thermal absorption of impurities is the direct cause of damage to the front surface of the ZnSe sample. Therefore, as shown in Table 1, the damage threshold measured at different positions of the same ZnSe sample will also be different. The damage threshold at 532nm (repetition frequency of 10Hz) is about 2.439J / cm 2 ,

[0062] This application proposes a measurement method using the above-mentioned measurement device, which comprises the following steps:

[0063] S1. Adjust the attenuation coefficient of the energy attenuator to gradually increase the energy of the pump beam. Continuously record the energies of the pump beam, monitoring beam, and probe beam until the sample is damaged by the pump beam. Obtain energy information for the pump beam, monitoring beam, and probe beam.

[0064] S2. The data processing module processes the energy information of the pump beam, monitoring beam, and detection beam to obtain the laser damage threshold of the sample to be tested.

[0065] This measurement method can obtain the laser damage threshold of the material (sample to be tested) in real time and accurately, without having to determine whether the material is damaged after the laser is applied. This greatly improves the sensitivity and accuracy of the measurement-related parameters and can avoid the influence of the nonlinear effect of the material itself on the measurement. Preferably, in S2, a ratio curve of the pump beam and the monitoring beam acting on the sample to be tested is obtained. This step S2 includes: multiplying the obtained ratio curve by the energy of the measured detection beam to obtain the energy of the pump beam incident on the sample to be tested, dividing the energy of the pump beam by the waist area of ​​the pump beam to obtain the energy flux of the pump beam and use it as the horizontal coordinate, normalizing the energy of the detection beam and using it as the vertical coordinate to obtain the energy flux of the pump beam at the mutation position of the normalized detection beam, which is the laser damage threshold of the material.

[0066] The above embodiments are intended only to illustrate the technical concepts and features of this application. Their purpose is to enable those familiar with the art to understand the content of this application and implement it accordingly. They are not intended to limit the scope of protection of this application. Any equivalent changes or modifications made in accordance with the spirit of this application shall be included in the scope of protection of this application.

Claims

1. A device for measuring laser damage threshold, characterized in that: include: The laser light emitted by the laser light source is divided into a reflected light path and a transmitted light path by the first beam splitter, wherein the reflected light path is the pump beam and the transmitted light path is the detection beam. The detection beam is converged by the second convex lens and irradiated onto the sample to be tested, and is converged by the third convex lens to the third energy probe. The pump beam passes through the energy attenuator and is incident on the second beam splitter. The pump beam reflected by the second beam splitter is converged by the first convex lens and then incident on the sample to be tested. After penetrating the sample to be tested, the pump beam is converged by the second convex lens to the second energy probe; The light beam passing through the second beam splitter serves as a monitoring beam of the pump beam, and the monitoring beam is incident on the first energy probe; The ratio of the pump beam energy collected by the second energy probe to the monitoring beam energy collected by the first energy probe is used to obtain the ratio between the pump beam acting on the sample to be tested and the monitoring beam; The system further comprises: a beam expansion and collimation module, which is arranged in front of the laser light source and is used to collimate the laser light emitted by the laser light source and transmit it to the first beam splitter; The first energy probe, the second energy probe and the third energy probe are respectively connected to the data processing module.

2. The laser damage threshold measuring device according to claim 1, wherein: Also includes: a first reflector and a second reflector, The detection light beam after passing through the first beam splitter is reflected by the first reflector and the second reflector in sequence, converged by the second convex lens and irradiated onto the sample to be measured, and converged to the third energy probe by the third convex lens.

3. The laser damage threshold measuring device according to claim 2, wherein: Also includes: The third reflector, the pump beam reflected by the second beam splitter is reflected by the third reflector, converged by the first convex lens, and then incident on the sample to be measured. After penetrating the sample to be measured, the pump beam is converged by the second convex lens to the second energy probe.

4. The laser damage threshold measuring device according to claim 3, characterized in that: Also includes: The first reflector, the second reflector and the third reflector are respectively provided with adjustment components, and the adjustment components are adjusted to adjust the postures of the first reflector, the second reflector and the third reflector so that the detection beam and the pump beam are respectively incident on the sample to be measured.

5. The laser damage threshold measuring device according to any one of claims 1 to 4, characterized in that: The first spot size of the detection beam falling on the sample to be measured is smaller than the second spot size of the pump beam falling on the sample to be measured, or, The first light spot where the detection light beam falls on the sample to be tested partially overlaps with the second light spot where the pump light beam falls on the sample to be tested, so as to ensure that the damage change of the sample to be tested can be detected.

6. A laser damage threshold measurement method, characterized in that: Measuring the laser damage threshold using the device for measuring the laser damage threshold according to any one of claims 1 to 5 comprises the following steps: S1. Adjust the attenuation coefficient of the energy attenuator to gradually increase the energy of the pump beam incident on the sample to be tested, continuously monitor the energy value of the third energy probe, and maintain the transmittance of the probe beam until the sample to be tested is damaged. When a sudden change in the energy value of the third energy probe is detected, the sample to be tested is determined to have been damaged by the pump beam. Record the energy values ​​of the first, second, and third energy probes to obtain energy information of the pump beam, monitoring beam, and probe beam at the laser damage threshold of the sample to be tested. S2. The data processing module processes the energy information of the pump beam, monitoring beam, and detection beam to obtain the laser damage threshold of the sample to be tested.

7. The laser damage threshold measurement method according to claim 6, characterized in that: Also includes: Before step S2, the following steps are also included: Obtain a ratio curve of the pump beam and the monitoring beam acting on the sample to be measured.

8. The laser damage threshold measurement method according to claim 7, characterized in that: Step S2 includes: The energy of the pump beam incident on the sample to be measured is obtained by multiplying the obtained ratio curve by the energy of the measured probe beam. Divide the energy of the pump beam by the waist area of ​​the pump beam to obtain the energy flux of the pump beam and use it as the horizontal axis. The energy of the probe beam is normalized and used as the vertical coordinate to obtain the energy flux of the pump beam at the mutation position of the normalized probe beam, which is the laser damage threshold of the material.

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