CN113447497A - Method and device for identifying laser damage of thin film material - Google Patents
Method and device for identifying laser damage of thin film material Download PDFInfo
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- CN113447497A CN113447497A CN202110677862.8A CN202110677862A CN113447497A CN 113447497 A CN113447497 A CN 113447497A CN 202110677862 A CN202110677862 A CN 202110677862A CN 113447497 A CN113447497 A CN 113447497A
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- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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Abstract
The invention belongs to the technical field of advanced optical manufacturing and optical detection, and relates to a method and a device for identifying laser damage of a thin film material. The method comprises the steps of applying strong laser to a film, measuring the oscillation period (or frequency) of the wafer before and after laser irradiation to determine whether the film is damaged once the film is damaged and the equivalent thickness of the quartz wafer is changed, and completing the method by adopting a specific device. The method has high discrimination sensitivity, and takes whether the film material is lost as a direct judgment basis, so that the phenomenon of 'misjudgment' does not exist; the device adopted by the invention has simple structure and high integration, can realize online judgment, and can judge the laser damage within milliseconds.
Description
Technical Field
The invention belongs to the technical field of advanced optical manufacturing and optical detection, and relates to a method and a device for identifying laser damage of a thin film material.
Technical Field
In high power, high energy laser systems, there are tens of thousands of optical thin film elements whose laser damage resistance is indistinguishable from the normal, efficient operation of the optical system. Such films are typically multilayer dielectric film structures prepared by alternating two or more materials of different high and low refractive indices. In addition to optimizing the film structure, it is most important to select a film material with a high damage threshold for preparing a film element with a high damage threshold.
Unfortunately, the current laser damage threshold (LIDT) test also has the problems of complex operation, low test accuracy, poor repeatability, high test cost, and the like. The main reason for these problems is the lack of an effective real-time online lesion identification method. As for the identification method of the damage, the International organization for standardization recommends the phase contrast microscopy as the method for identifying the damage of the thin film (ISO21254), and the method adopts a Normask microscope with the magnification of 100-150 times to observe the surface after laser irradiation so as to identify whether the thin film is damaged or not. The method has the main problems that the working distance of the microscope meeting the magnification of 100-fold-150 is generally short, and the microscope is arranged in a laser damage threshold tester and can shield high-energy irradiation laser beams, so that automatic testing is difficult to realize, and therefore, a sample needs to be repeatedly moved out of an irradiation light path to be tested, so that the testing efficiency is reduced, and the requirement of industrial production is difficult to meet.
At present, other damage identification methods at home and abroad mainly comprise a scattered light intensity method, a plasma flash method, a photoacoustic measurement method, a photothermal method and the like, and the methods respectively have advantages and disadvantages.
The scattering light intensity method judges whether the film material is damaged by detecting whether the photoelectric receiver outputs a non-electric signal or not and actually detecting the change of scattering rate before and after laser radiation.
The plasma flash method judges whether the film is damaged by detecting plasma flash when the laser interacts with the optical surface through a photocell, the detection laser is generally monochromatic light (such as the wavelength of 632.8nm of helium neon laser), and the plasma flash is polychromatic light, so the plasma flash can be accurately detected only by eliminating the spectrum corresponding to the action laser. In the conventional plasma flash method, a photoelectric receiving device is arranged near an optical surface, and when flash exists, the photoelectric receiving device outputs a high-level signal, namely, the change of light intensity is used as a criterion for damage or not. However, when the intensity of the laser is sufficiently high, the atmosphere also breaks down to cause plasma flash. When strong laser acts on the surface of the film and generates plasma flash, in most cases, composite plasma of the film and the atmosphere is obtained, or only atmospheric plasma flash is obtained, so that whether the film is damaged or not is judged by adopting a conventional light intensity detection mode, and a phenomenon of 'misjudgment' is often caused.
The photoacoustic discrimination method discriminates whether the film is damaged or not by collecting audio signals when the film is damaged under strong laser, has a great relationship with the material and the type of the film, and is difficult to discriminate the acoustic spectrum information of atmospheric breakdown and film damage.
The photothermal method judges that the thin film is damaged according to the principle that the light path is turned due to the fact that the thin film material absorbs heat under strong laser to cause the refractive index to deflect, and the judgment accuracy of the dielectric film with extremely small absorption is very low.
Disclosure of Invention
The invention aims to solve the problems of difficulty in real-time online discrimination and low discrimination efficiency in the prior art, and provides a method and a device for identifying laser damage of a thin film material.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for identifying the laser damage of film material features that strong laser is applied to the film to change the equivalent thickness once the film is damaged, and the oscillation period (or frequency) of sample before and after laser irradiation is measured to determine if the film is damaged.
A method for identifying laser damage of film material includes testing initial oscillation frequency or period of quartz crystal sample plated with film, testing variation of oscillation frequency or period after sample surface is irradiated by high-energy laser, judging variation of oscillation frequency or period before and after high-energy laser pulse action to determine whether test sample is damaged or not.
The identification device comprises a laser and a data processing component, wherein an emergent light path of the laser is sequentially provided with a beam expanding and collimating system, an attenuator, a focusing mirror and a two-dimensional sample table, a test sample perpendicular to the light path is arranged on the two-dimensional sample table, the test sample is a thin film material plated on a quartz crystal, an upper electrode and a lower electrode are prepared on the upper surface and the lower surface of the quartz crystal in advance, the lower surface plated electrode completely covers the surface of the whole crystal plate, the center of the upper surface is plated with the thin film material, and the annular electrode is plated at the maximum caliber of the quartz crystal plate.
The width of the electrode on the upper surface of the quartz crystal is 1-3 mm.
The high-energy laser is a high-energy pulse laser with the wavelength of 532nm or 1064nm and the pulse width of 10ns, and has a beam spot
The single pulse energy was 400 mJ.
The attenuator consists of 4 groups of 5 pieces of neutral density absorption glass, and two sides of the glass surface of the attenuator are plated with 1064nm antireflection films.
The electrode on the surface of the quartz wafer is connected with a data processing component, and the data processing component comprises a processing circuit, an analog-to-digital A/D converter and a computer which are connected in sequence.
The attenuator, the two-dimensional workbench and the like are driven by a servo motor. The pulse firing instructions of the laser are controlled by a computer program.
The focal length of the convergent lens is 120-150 mm.
Compared with the prior art, the invention has the advantages that:
1. the method has high discrimination sensitivity, and takes whether the film material is lost as a direct judgment basis, so that the phenomenon of 'misjudgment' does not exist;
2. the device has simple structure and high integration, can realize on-line judgment, and can judge the laser damage within milliseconds;
3. the method and the device are suitable for online discrimination of surface damage of various optical coating elements in laser damage threshold measurement, the discrimination range of the thin film is wide, and high-precision discrimination can be realized for reflective films, antireflection films, thin films and thick films.
Drawings
FIG. 1 is a schematic structural diagram of a measuring device for laser damage identification of an optical film according to the present invention;
wherein, 1 is a laser, and 2 is a beam expanding collimator; 3 is an attenuator; 4 is a focusing lens; 5 is a test sample; 6 is a two-dimensional workbench; 7 is a processing circuit; 8 is an analog-to-digital A/D converter; and 9 is an industrial control computer.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the invention provides a method for identifying laser damage of a film material, which is characterized in that strong laser is applied to a film, once the film is damaged, the equivalent thickness of a quartz wafer is changed, and whether the film is damaged or not is determined by measuring the oscillation period (or frequency) of the wafer before and after laser irradiation.
The specific method can be realized by the following means. The utility model provides a recognition device of thin film material laser damage, includes laser instrument and data processing subassembly, and the outgoing light path of laser instrument sets gradually and expands beam collimation system, attenuator, focusing mirror and two-dimentional sample platform, set up the test sample of perpendicular to light path on the two-dimentional sample platform, the test sample is for plating the thin film material of system on quartz crystal, and two surfaces are prepared in advance about the quartz crystal have upper and lower electrode, and wherein the electrode that the lower surface was plated covers whole wafer surface completely, and upper surface central point puts and plates thin film material, and annular electrode plates at quartz crystal maximum bore department, electrode linewidth 2 mm.
The high-energy laser is a high-energy pulse laser with the wavelength of 532nm or 1064nm and the pulse width of 10ns, and has a beam spot
The single pulse energy was 400 mJ.
The attenuator consists of 4 groups of 5 pieces of neutral density absorption glass, and two sides of the glass surface of the attenuator are plated with 1064nm antireflection films.
The electrode on the surface of the quartz wafer is connected with a data processing component, and the data processing component comprises a processing circuit, an analog-to-digital A/D converter and a computer which are connected in sequence.
The attenuator, the two-dimensional workbench and the like are driven by a servo motor. The pulse firing instructions of the laser are controlled by a computer program.
The focal length of the convergent lens is 120-150 mm.
In the method provided by the invention, the quartz crystal is used as the substrate of the film coating sample, and whether the surface of the sample is damaged or not is judged by detecting whether the oscillation frequency of the quartz crystal changes or not before and after the high-energy laser pulse irradiation. During the test, the high-power and high-energy laser emitted from the laser 1 has the spot size of
After passing through the beam expanding and collimating system 2, the light spot range of the laser beam is expanded to
And is transmitted in the form of parallel light. At this time, the laser energy required by the system is obtained after passing through the attenuator 3. Due to excitation directly after the attenuatorThe light energy density is low, and laser-induced damage cannot be carried out, so that the light beam is converged by the focusing mirror 4, and the laser energy density reaching the surface of the sample is improved. The test sample 5 is a film sample to be tested, which is plated on a substrate material in advance and has a thickness of 0.5mm and a caliber of
On a quartz crystal wafer plated with electrodes. The processing circuit 6 is used for denoising and filtering the received frequency or periodic signal and obtaining accurate numerical information. The action laser 1 is high-energy pulse laser, and can be any laser capable of damaging the thin film, and is not limited to 1064nm or 532nm wavelength. The sample 5 is clamped on the two-dimensional worktable 6, and when the surface of the film is damaged by strong laser irradiation, the surface state of the film changes, which affects the quality of the whole film substrate system, so that the equivalent thickness changes, and the oscillation frequency of the wafer system changes.
When the specific method provided by the invention is realized based on the device, the specific method specifically comprises the following steps:
1) firstly, the laser emitting end of a high-energy laser is opposite to the upper surface of a test sample (plated with a film material to be tested) clamped on a two-dimensional workbench, and a beam expanding collimation system, an attenuator, a focusing mirror, the test sample, the two-dimensional workbench, a processing circuit, an A/D converter and the like are sequentially arranged in the laser pulse output direction of the high-energy laser. Wherein the two-dimensional workbench, the high-energy laser, the attenuator and the like are all connected to an industrial control computer.
2) Secondly, after the sample is clamped on a workbench, the initial oscillation frequency or period of the test sample (the quartz crystal plated with the thin film material) is obtained through the processing of an external circuit, and after the initial oscillation frequency or period is subjected to analog-to-digital conversion, the initial oscillation frequency or period is uploaded to a computer for recording and storing. The main purpose of this step is to calibrate the initial oscillation frequency of the system.
3) Then, the attenuation ratio of the attenuator is adjusted, the energy of the laser pulse is set, and the high-energy laser is triggered to emit 1 laser pulse to act on the surface of the sample.
4) And then repeating the test process in the step 2), so that the change of the oscillation frequency or period of the surface of the test sample after being irradiated by the high-energy laser can be obtained.
5) Finally, a computer is adopted to judge the change of the oscillation frequency or the period of the test sample (the quartz crystal coated with the film material) before and after the action of the high-energy laser pulse (the change of the frequency is determined to be the film damage, namely the damage criterion is determined), so that whether the test sample is damaged or not can be determined.
Specifically, the method for judging whether the test sample is damaged or not specifically comprises the following steps: comparing the crystal oscillator frequency or period obtained in the step 2) with the result obtained in the step 4), and if the numerical value of the oscillation frequency or period changes (is not equal to the numerical value initially calibrated by the system), determining that the surface of the sample is damaged after the high-energy laser is irradiated. Otherwise, the surface of the film is intact, and the sample is not damaged by laser.
The discrimination principle of the present invention is specifically explained as follows:
the invention utilizes the piezoelectric effect of the quartz crystal to measure the variation of the vibration frequency or period of the quartz crystal along with the thickness (equivalent thickness) of the quartz crystal, and finally achieves the purpose of measuring the thickness of the film layer deposited on the quartz crystal. Oscillation frequency f of quartz wafer and thickness d of waferqIn an inverse relationship: f is N/dqWhere N is a constant determined by the quartz wafer. If one surface of the wafer is coated with a film layer with a thickness deltadfAssuming that the corresponding equivalent quartz wafer thickness is Δ dqIf using f0And d0The fundamental frequency and the initial thickness of the quartz wafer are respectively represented by f0＝N/d0To obtain
f＝f0+Δf＝N/(d0+Δdq)
Therefore, d0+Δdq＝N/(f0+Δf)
Relating film thickness to crystal equivalent thickness
Substituting into the formula and finishing to obtain
In the formula, 1/f0＝T01/(f) is the vibration period of the uncoated quartz wafer0And + Δ f) ═ T is the oscillation period of the coated quartz wafer. The variation of the vibration period of the quartz wafer caused by the increment of the thickness of the film layer is obtained as follows:
in summary, the variation of the equivalent film thickness causes the oscillation period of the quartz crystal to vary. When the film is damaged by strong laser, the equivalent thickness of the film is changed, so that the oscillation frequency is changed, and whether the film is damaged can be determined by measuring the oscillation period (or frequency) before and after laser irradiation.
The method is mainly used for judging whether the film is damaged under strong laser, laser damage threshold data of the film are not directly obtained, but the method is the basis for measuring the damage threshold. According to the definition of the damage threshold value by ISO, the laser damage threshold value of the film is finally fitted by testing the damage probability of 10 laser energy levels. The damage probability of each energy level is calculated by testing whether the surface of the sample wafer is damaged or not at 10 different positions, and the method judges whether the surface of the sample wafer is damaged or not at each position. Whether damage occurs is traditionally seen by a microscope, and the method does not need to observe by the microscope, but judges whether damage occurs at a single point or not according to the frequency change of the wafer. By using the method, the data fitting the damage threshold can be calculated after judging 100 points.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (9)
1. A method for identifying laser damage of a thin film material is characterized by comprising the following steps: the method is characterized in that strong laser is applied to a thin film, once the thin film is damaged, the equivalent thickness is changed, and whether the thin film is damaged or not is determined by measuring the oscillation period (or frequency) of a sample before and after laser irradiation.
2. The method for identifying the laser damage of the thin film material as claimed in claim 1, wherein: the method comprises the following steps: the method comprises the steps of firstly testing the initial oscillation frequency or period of a quartz crystal sample coated with a thin film, then testing the change of the oscillation frequency or period of the sample surface after the sample surface is irradiated by high-energy laser, and finally judging the change of the oscillation frequency or period of the sample before and after the high-energy laser pulse action to determine whether the test sample is damaged.
3. A recognition device adopted by a recognition method for laser damage of a thin film material is characterized in that: the device comprises a laser and a data processing component, wherein an emergent light path of the laser is sequentially provided with a beam expanding collimation system, an attenuator, a focusing mirror and a two-dimensional sample table, a test sample perpendicular to the light path is arranged on the two-dimensional sample table, the test sample is a thin film material plated on a quartz crystal, an upper electrode and a lower electrode are prepared on the upper surface and the lower surface of the quartz crystal in advance, the electrode plated on the lower surface completely covers the surface of the whole crystal plate, the thin film material is plated at the central position of the upper surface, and an annular electrode is plated at the position of the maximum caliber of the quartz crystal plate.
4. The identification device adopted by the identification method of the laser damage of the thin film material according to claim 3, is characterized in that: the electrode width of the upper surface of the quartz crystal is 1-3 mm.
5. The identification device adopted by the identification method of the laser damage of the thin film material according to the claim 3 or 4, is characterized in that: the high-energy laser is a high-energy pulse laser with the wavelength of 532nm or 1064nm and the pulse width of 10ns, and the beam spot is formed
The single pulse energy was 400 mJ.
6. The identification device adopted by the identification method of the laser damage of the thin film material according to claim 5, is characterized in that: the attenuator consists of 4 groups of 5 pieces of neutral density absorption glass, and two sides of the glass surface of the attenuator are plated with 1064nm antireflection films.
7. The identification device adopted by the identification method of the laser damage of the thin film material according to claim 6, wherein: the electrode on the surface of the quartz wafer is connected with a data processing assembly, and the data processing assembly comprises a processing circuit, an analog-to-digital A/D converter and a computer which are connected in sequence.
8. The identification device adopted by the identification method of the laser damage of the thin film material according to claim 3, is characterized in that: the attenuator, the two-dimensional workbench and the like are driven by a servo motor. The pulse firing instructions of the laser are controlled by a computer program.
9. The identification device adopted by the identification method of the laser damage of the thin film material according to claim 7 is characterized in that: the focal length of the convergent lens is 120-150 mm.
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| CN202110677862.8A CN113447497A (en) | 2021-06-18 | 2021-06-18 | Method and device for identifying laser damage of thin film material |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103196774A (en) * | 2013-04-03 | 2013-07-10 | 大连理工大学 | Device for measuring ablation resistance of material |
| CN111474182A (en) * | 2020-04-26 | 2020-07-31 | 西安工业大学 | Method and device for identifying laser damage of optical film based on polarization parameters |
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- 2021-06-18 CN CN202110677862.8A patent/CN113447497A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103196774A (en) * | 2013-04-03 | 2013-07-10 | 大连理工大学 | Device for measuring ablation resistance of material |
| CN111474182A (en) * | 2020-04-26 | 2020-07-31 | 西安工业大学 | Method and device for identifying laser damage of optical film based on polarization parameters |
Non-Patent Citations (1)
| Title |
|---|
| 王璐璐: "激光烧蚀聚合物损伤阈值行为的理论研究", 《中国优秀博硕士学位论文全文数据库(硕士) 信息科技辑》 * |
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