CN103954680A - Device and method for identifying laser damages to optical film - Google Patents

Abstract

The invention discloses an identification method and device for laser damage to an optical thin film. By collecting the mass-to-charge ratio distribution and using computer software to perform mass spectrometry analysis and element discrimination, the type of elements contained in the damaged material can be determined, thereby accurately, online, and Quickly identify whether the film is damaged. The device adopting the method is composed of a test sample platform, a mass-to-charge ratio acquisition system and a computer operation system. The invention can realize on-line, real-time, fast and accurate judgment of the damage state of the thin film or optical element under strong laser. Applying this method to the laser damage threshold test can realize the integration, automation and intelligence of the test system.

Description

An identification device and identification method for laser damage to an optical thin film

technical field

The invention belongs to the technical field of optical thin film detection, relates to a method for judging optical thin film damage, in particular to a recognition device and method for laser damage to optical thin film.

Background technique

In high-energy laser systems, there are various optical components and thin-film devices. The anti-laser damage performance of these components is inseparable from the normal and effective operation of the optical system. Laser damage threshold (LIDT) is an important index to measure the performance of thin films and optical components, but there are still many problems in the current test of laser damage threshold. In the process of laser damage threshold testing, how to accurately, real-time, fast and online judge film damage has become the core part of the research. Therefore, in order to obtain the laser damage threshold of the thin film, the first condition is to make a fast and accurate judgment on whether the thin film is damaged under the action of strong laser, that is, the change of the thin film is considered to be damaged.

At present, the methods for judging the damage of thin films and optical components mainly include phase contrast microscopy, scattered light intensity detection method, plasma flash method, photoacoustic measurement method, photothermal method, etc., each of which has its own advantages and disadvantages. Among them, phase contrast microscopy is a detection method recommended by the international standard ISO11254. This method uses a Normaski microscope with a magnification of 100-150 times to observe the surface after laser irradiation to determine whether the film is damaged. The subjectivity of the method is very strong, and the work intensity is high, the test efficiency is low, and it is difficult to realize the automation of the whole machine system. The principle of the scattered light intensity detection method is: when the laser is obliquely incident on the sample at a certain angle, if there is no defect at the reflection point on the surface, the reflected light will be reflected according to the law given by geometric optics. If the main ray is not reflected Entering the optoelectronic receiver, there is almost no electrical signal output. When the reflection point on the surface is not smooth, or is damaged after being irradiated by laser light, a considerable part of the energy in the main light cannot be reflected directionally, but will be scattered, and the corresponding photoelectric receiver will have an electrical signal output. By detecting the photoelectric receiver has There is no electrical signal output. In fact, the change of the electrical signal before and after the laser radiation can be used to judge whether the sample is damaged at the laser irradiation point. This method requires high surface finish of the sample to be tested. If damage is caused, the output electrical signal of the detector will not change too much, so the damage judgment cannot be accurately performed.

The plasma flash method is also a commonly used method for judging laser damage. The mechanism of this method is based on the fact that when high-power laser interacts with the optical surface, it will ionize the substances that make up the optical surface, thereby generating free electrons and ions, that is, plasma. Therefore, damage can be determined by detecting the plasma flash when the laser interacts with the optical surface through the photosensitive element. Usually, the detection laser is monochromatic light (for example, the wavelength of the He-Ne laser is 632.8nm), while the plasma flash is polychromatic light. Therefore, it is necessary to eliminate the spectrum corresponding to the active laser in order to accurately detect the plasma flash, and then determine whether it is There is damage to the optical surface. The conventional plasma flash discrimination method is to install a photoelectric receiving device near the optical surface. When there is a flash, the photoelectric receiving device will output a level signal. This is a conventional method at home and abroad based on plasma flash to judge whether the film is damaged. That is, the change of light intensity is used as the criterion of damage or not. However, when the intensity of the laser is high enough, the atmosphere can also break down, resulting in a plasma flash. When a strong laser acts on the surface of a thin film and a plasma flash occurs, in most cases, the compound plasma of the thin film and the atmosphere is obtained, or only the atmospheric plasma flash is obtained. Therefore, the method of detecting light intensity is used to detect It is inevitable to judge whether the film is damaged or not, resulting in "misjudgment" in the actual test.

Contents of the invention

The object of the present invention is to overcome the above-mentioned problems in the prior art, and provide an identification device and identification method for laser damage to optical thin films. , High precision and accurate features.

In order to achieve the above object, the technical solution adopted in the present invention is:

An identification device for laser damage to an optical film, including a laser and a test sample; the test sample is installed on a test sample table, the laser is facing the surface of the test sample to be tested, and one side of the test sample table is provided with a device for accelerating the laser irradiation sample. The sputtered particles form an accelerating electrode that collimates the particle beam, and an electron source for increasing the ion content is set between the test sample stage and the accelerating electrode; a magnetic field that deflects the ion is set at the rear end of the accelerating electrode, and The parallel side of the accelerating electrode is provided with several receiving electrodes for receiving ions with different deflection radii; the output terminals of the receiving electrodes are all connected to the signal input terminals of the A/D converter, and the signal output terminals of the A/D converter are connected to useful A computer that generates mass-to-charge ratio spectra of sputtered particles.

The laser is a high-energy laser that can damage the film on the surface of the test sample.

The laser has a wavelength of 1064 nm, a pulse width of 10 ns, and a single pulse energy of 400 mJ.

The test sample stage is a two-dimensional mobile platform controlled by a stepping motor.

The magnetic field is a uniform magnetic field.

The plurality of receiving electrodes are arranged side by side in parallel.

The standard mass-to-charge ratios of elements are stored in the computer.

A laser damage identification method for an optical thin film, comprising the following steps:

1) Firstly, install the test device, place the laser emitting end of the laser facing the test sample clamped on the test sample table, then set an accelerating electric field on one side of the test sample table, and place the electron source between the test sample table and the accelerating electric field Each receiving electrode is set in parallel with the accelerating electrode, and the accelerating electrode and the receiving electrode are adjacent to the magnetic field, and finally connected to the receiving electrode, A/D converter and computer in sequence;

2) Next, turn on the laser and the computer, and after the film surface of the test sample is damaged by laser irradiation, the particles in the damaged area are sputtered into the space, and the sputtered particles enter the accelerating electrode after passing through the electron source, and pass through the accelerating electric field between the accelerating electrodes. Entering the magnetic field behind the accelerating electrode, the ions are deflected under the action of the magnetic field force and the emitted magnetic field is received by several receiving electrodes. The receiving electrodes convert the received analog signal into a digital signal through the A/D converter and transmit it to the computer. Computer-generated mass-to-charge ratio spectra of sputtered particles;

3) According to the standard mass-to-charge ratio of the elements stored in the computer, determine the elemental composition of the sputtered matter, and finally, by comparing the standard mass-to-charge ratio, it is possible to directly determine whether the test sample has been damaged.

In the described step 3), the method for judging whether the test sample is damaged is specifically:

Compare the mass spectrogram of the sputtered particles obtained in step 2) with the elements in the atmosphere. If there is a new element, that is, the element does not belong to the elements in the atmosphere, the test sample has been damaged; otherwise, the test sample The sample is intact.

Compared with the prior art, the present invention has the following beneficial effects:

The identification device for laser damage to optical thin film of the present invention uses laser irradiation to test the surface of the sample, and the damaged part will gasify or sputter out particles, which will enter the magnetic field after being accelerated by the accelerating electrode, and the ions will be deflected under the action of the magnetic field and ejected from the magnetic field. It is received by the receiving electrode set outside the magnetic field and generates a pulse signal. The pulse signal is converted into a digital signal by the A/D converter and transmitted to the computer, and finally the mass-to-charge ratio spectrum of the sputtered particles is obtained. The present invention does not use the change of optical or electrical signal as the criterion of damage, but uses mass spectrometry to analyze the elemental components contained in the ejecta. The test environment ensures that the interference of the test is small, and the discrimination speed is fast, and the discrimination of the laser damage of the thin film can be completed within 1s; at the same time, the invention distinguishes a wide range of types of films, whether it is a reflective film, an anti-reflection film, a thin film, a thick Films can achieve high-precision discrimination. Finally, since most of the sputtered particles are ions and some of them are neutral atoms, in order to increase the ion content, an electron source is set between the accelerating electrode and the test sample stage to ionize the sputtered neutral atoms, thereby improving The ionization rate of the splash particles.

The method for identifying laser damage to optical thin films of the present invention uses mass spectrum collection and analysis methods to determine the types of elements contained in the damaged materials, instead of using photodetectors to receive light intensity or scattering signals, nor using CCD to collect images, the collected The type of element in the film is compared with the atmospheric element, and then it can be judged whether the film surface is damaged. At the same time, during the test, the position of the sample is fixed, and there is no need to remove the test, but the target is captured online, transmitted to the computer in real time, and analyzed and processed to achieve the purpose of accurately judging whether the film is damaged.

Further, the present invention adopts elemental mass spectrometry analysis of the damaged sample to determine whether the film or optical element is damaged, that is, "determining the element distribution in the damaged body" is used as the criterion for whether the film or optical element is damaged, thereby effectively eliminating impurities, Interference from dust or the surrounding atmosphere.

Description of drawings

FIG. 1 is a schematic structural view of an optical thin film laser damage identification device of the present invention.

Among them, 1 is a laser; 2 is a test sample; 3 is an electron source; 4 is an accelerating electrode; 5 is a magnetic field; 6 is a receiving electrode; 7 is an A/D converter; 8 is a computer.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

Referring to Fig. 1, the identification device of optical film laser damage of the present invention comprises laser 1 and test sample 2, and laser 1 is the high-energy laser that can make test sample 2 surface film damage, and the wavelength of laser is 1064nm, and pulse width is 10ns, The maximum single pulse energy is 400mJ; the test sample 2 is installed on the test sample table 9, which is a two-dimensional mobile platform controlled by a stepping motor; the laser 1 is facing the surface to be tested of the test sample 2, and the test sample table 9 There is an accelerating electrode 4 for accelerating the particles sputtered out of the sample by laser irradiation and forming a collimated particle beam, and an electron source for increasing the ion content is also arranged between the test sample stage 9 and the accelerating electrode 4 3. The rear end of the accelerating electrode 4 is provided with a magnetic field 5 for deflecting ions, wherein the magnetic field 5 is a uniform magnetic field. One side parallel to the accelerating electrode 4 is provided with several parallel receiving electrodes 6 for receiving ions with different deflection radii; the output terminals of the receiving electrodes 6 are all connected to the signal input terminals of the A/D converter 7, A/D The signal output end of the D-converter 7 is connected to a computer 8, and the computer 8 generates a mass spectrum of sputtered particles according to the standard mass-to-charge ratios of elements stored in the computer 8.

The invention also discloses a method for identifying laser damage to an optical thin film, which includes the following steps:

1) Firstly, install the test device, place the laser emitting end of the laser facing the test sample clamped on the test sample table, then set an accelerating electric field on one side of the test sample table, and place the electron source between the test sample table and the accelerating electric field Each receiving electrode is set in parallel with the accelerating electrode, and the accelerating electrode and the receiving electrode are adjacent to the magnetic field, and finally connected to the receiving electrode, A/D converter and computer in sequence;

2) Next, turn on the laser and the computer, and after the film surface of the test sample is damaged by laser irradiation, the particles in the damaged area are sputtered into the space, and the sputtered particles enter the accelerating electrode after passing through the electron source, and pass through the accelerating electric field between the accelerating electrodes. Entering the magnetic field behind the accelerating electrode, the ions are deflected under the action of the magnetic field force, and finally the emitted magnetic field is received by a number of receiving electrodes. The receiving electrodes convert the received pulse analog signal into a digital signal through the A/D converter and transmit it to the computer. , the mass-to-charge ratio spectrum of sputtered particles generated by computer;

3) According to the standard mass-to-charge ratio of the elements stored in the computer, the elemental composition of the sputtered matter is determined, and it is possible to directly determine whether the test sample is damaged. Specifically, the mass-to-charge ratio spectrum of the sputtered particles obtained in step 2) is compared with the elements in the atmosphere. If there are new elements that do not belong to the atmosphere, the test sample has been damaged; otherwise, the test sample The sample is intact.

Principle of the present invention:

The method for judging film damage adopted by the present invention is different from conventional judging methods. The core of this method is that it does not use the change of optical or electrical signal as the criterion of damage, but adopts the method of elemental analysis, collects mass spectrum and analyzes the elemental components contained in the splash, so that it can directly determine whether the sample has occurred or not. damaged. The basic principle of its judgment is: under the radiation of high-power and high-energy laser, extremely high energy (millijoules) is usually accumulated in the micro-region of the surface of the optical element or film in a very short time (on the order of nanoseconds), so that The material is partially vaporized violently, and flashes may be emitted in severe cases. Vaporized or sputtered particles, most of which are ions and some are neutral atoms. After passing through the electron source, the neutral atoms in it are also ionized, thereby increasing the ionization rate of the sputtered particles. The ions form a collimated ion beam after passing through the electric field and enter the uniform magnetic field.

If the charge of the ion is q, the mass is m, and the velocity is V, and it enters the magnetic field with the magnetic induction intensity B vertically, the radius of the rotating circle is:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mV</span>}}{\mathrm{<span\; class="notranslate">\; wxya</span>}}$

The velocity V of ions is determined by the voltage U of the accelerating electrode.

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; mV</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; wxya</span>}$

then

${\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; mV</span>}}{\mathrm{<span\; class="notranslate">\; wxya</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; q</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; wxya</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; B</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; q</span>}}$

Since U and B are constants, the circular motion radius of charged ions in the magnetic field depends on the ratio of ion mass to charge. It can be seen that in a uniform magnetic field, ions with the same mass-to-charge ratio rotate at the same radius, while ions with different mass-to-charge ratios rotate at different radii, so that various ions are separated according to the mass-to-charge ratio and distributed in different positions The receiving electrode will receive ions with different radii of rotation. Therefore, according to the position of the receiving electrode and the magnitude of the current, the mass of the ion can be determined, and the type of element contained in the sputter can also be clarified. The atmosphere is a common external interference, and its elements are most likely to appear in the mass spectrum, but it mainly contains N, O, C, H and other elements, while the chemical composition of thin films or optical components is different from the atmosphere, usually containing Si, Ti, Al , Mg, Zn, Zr and other elements. If the gasification (or spatter) contains elements of thin films or optical components, then it can be concluded that laser damage has occurred to the sample.

The process of testing method of the present invention comprises:

First, high-power, high-energy pulsed lasers are used to irradiate the surface of the film or optical element. Once the sample is damaged, the surface substances that make up the film or optical element will be vaporized or excited, and splashed out in the form of atoms and ions. Secondly, an electron source is used to ionize the atoms in the spatter, and the mass-to-charge ratio distribution of the spattered ions is collected closely. Then, use computer software to analyze the mass spectrum, and determine the specific element types of the collected ions according to the size of the mass-charge number of the ions. Finally, compared with the elements in the atmosphere, if the elements in the collected particles come from other than atmospheric elements, it can be determined that the film has been damaged. By adopting the method and device, the accurate judgment of the damage of the optical thin film can be realized, and finally the computer system can calculate the laser damage threshold of the thin film quickly.

The invention determines the identification method of the elements contained in the particles by collecting the mass spectrum of the spatter, thereby judging whether different types of film samples are damaged. In order to achieve the purpose of distinguishing laser damage, the following device is used. The device is composed of a test sample platform, a mass-to-charge ratio acquisition system and a computer operation system. The present invention irradiates the high-energy laser to the surface of the sample to be tested. The sample to be tested can be a sample such as a thin film or an optical element. The method of mass spectrometry collection and analysis is used to determine the type of elements contained in the damaged material. The identification method is to collect mass The distribution of the charge ratio is carried out by computer software for mass spectrometry and element identification, so as to accurately, online, and quickly determine whether the film is damaged.

Working process of the present invention:

As shown in Figure 1, the active laser is a high-energy laser, which can be any laser that can damage the film. The test sample 2 is clamped on the test bench. When the surface of the film is damaged by strong laser irradiation, the particles in the damaged area are sputtered into the space immediately. The sputtered particles contain ions, electrons and some neutral atoms. In order to increase its ionization rate, after the sputtered matter is ionized by the electrons emitted by the electron source 3, the content of ions is greatly increased. These ions enter the uniform magnetic field after passing through the accelerating electrode 4, and are deflected by the force of the magnetic field. The radius of ion deflection depends on the mass-to-charge ratio of the ion. The receiving electrodes 6 installed at different positions can receive the deflected ions with different radii, and then convert the analog signal into a digital signal through the A/D converter 7 and transmit it to the computer 8 to obtain the mass spectrum of the sputtered matter picture. In the computer, the obtained mass spectrum should be analyzed, and the element composition of the sputter can be determined according to the standard mass-to-charge ratio of the elements stored in the computer. Therefore, as long as the newly emerging elements do not belong to the elements in the atmosphere (mainly N, O, H, C, Ar and other element spectra), it can be concluded that the element comes from the film, thus indicating that the film has been damaged.

The laser damage discrimination device and mass spectrometry analysis method provided by the present invention are applicable to various types of optical elements and film surfaces, and are suitable for various types of film damage discrimination. Fully automated process. Under the action of the high-energy laser, the invention can obtain the damage state of the optical film online, in real time, quickly and accurately, and eliminates the inaccurate judgment of the film damage commonly used at present. Through detailed theoretical calculation and analysis, the present invention proves to be feasible, has good and stable performance, and has wide application prospects in actual industrial production.

When measuring the laser damage threshold of optical thin films, it is the key to obtain correct results to accurately and quickly judge whether the thin film is damaged or not. When testing the sample, the sample is placed on a two-dimensional mobile platform controlled by a stepping motor. The active laser is a high-energy laser with a wavelength of 1064 nm, a pulse width of 10 ns, and a single pulse energy of 400 mJ. The laser is used to irradiate the sample with a single pulse. If the film is not damaged, the atoms and ions that make up the film or optical components will not sputter (gasify), and the receiving electrode will not receive the signal. If the film is damaged, a strong sputtering phenomenon occurs at the moment of damage, and the sputtered particles are further ionized, transported and finally received by the receiving electrode. The computer processing system receives signals collected by electrodes at different positions, converts these signals into mass spectrograms, and compares them with the standard mass-to-charge ratios of elements stored in the system. If new elements (C, H, O, N outside), it is considered that the film has been damaged. For example, for the TiO2/SiO2 membrane stack, the mass-to-charge ratio is collected during the test. When the collected mass-to-charge ratio is 48 (or 24, 16, 12) and 28 (or 14, 9.3, 7), it is considered that the film has been damaged. , because these mass-to-charge ratio values are the mass-to-charge ratios of Ti or Si elements. This method of mass spectrometry is equally applicable to any thin film or optical component.

The above content is only to illustrate the technical ideas of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solutions according to the technical ideas proposed in the present invention shall fall within the scope of the claims of the present invention. within the scope of protection.

Claims (9)

1. An identification device for laser damage to an optical thin film, characterized in that: comprise a laser (1) and a test sample (2); On the surface to be tested of the sample (2), one side of the test sample stage (9) is provided with an accelerating electrode (4) for accelerating particles sputtered out of the sample by laser irradiation and forming a collimated particle beam, and the test sample stage (9) is also provided with the electron source (3) that is used to improve ion content between (9); The rear end of accelerating electrode (4) is provided with the magnetic field (5) that ion deflects, and accelerating electrode (4) The parallel side is provided with some receiving electrodes (6) for receiving ions with different deflection radii; the output terminals of the receiving electrodes (6) are all connected to the signal input terminals of the A/D converter (7), and the A/D conversion The signal output end of the device (7) is connected with a computer (8) for generating the mass-to-charge ratio spectrum of sputtered particles. 2. The identification device for laser damage to optical thin films according to claim 1, characterized in that: said laser (1) is a high-energy laser capable of damaging the surface thin film of the test sample (2). 3. The identification device for laser damage to optical thin films according to claim 1 or 2, characterized in that: the wavelength of the laser is 1064 nm, the pulse width is 10 ns, and the single pulse energy is 400 mJ. 4. The identification device for laser damage to optical thin films according to claim 1, characterized in that: the test sample stage (9) is a two-dimensional moving platform controlled by a stepping motor. 5. The identification device for laser damage to optical thin films according to claim 1, characterized in that: said magnetic field (5) is a uniform magnetic field. 6. The identification device for laser damage to an optical film according to claim 1, characterized in that: the plurality of receiving electrodes (6) are arranged side by side in parallel. 7. The identification device for laser damage to optical thin films according to claim 1, characterized in that: said computer (8) stores standard mass-to-charge ratios of elements. 8. An identification method using the optical film laser damage identification device according to claim 1, characterized in that, comprising the following steps: 1) Firstly, install the test device, place the laser emitting end of the laser facing the test sample clamped on the test sample table, then set an accelerating electric field on one side of the test sample table, and place the electron source between the test sample table and the accelerating electric field Each receiving electrode is set in parallel with the accelerating electrode, and the accelerating electrode and the receiving electrode are adjacent to the magnetic field, and finally connected to the receiving electrode, A/D converter and computer in sequence; 2) Next, turn on the laser and the computer, and after the film surface of the test sample is damaged by laser irradiation, the particles in the damaged area are sputtered into the space, and the sputtered particles enter the accelerating electrode after passing through the electron source, and pass through the accelerating electric field between the accelerating electrodes. Entering the magnetic field behind the accelerating electrode, the ions are deflected under the action of the magnetic field force and the emitted magnetic field is received by several receiving electrodes. The receiving electrodes convert the received analog signal into a digital signal through the A/D converter and transmit it to the computer. Computer-generated mass-to-charge ratio spectra of sputtered particles; 3) According to the standard mass-to-charge ratio of the elements stored in the computer, determine the elemental composition of the sputtered matter, and finally, by comparing the standard mass-to-charge ratio, it is possible to directly determine whether the test sample has been damaged. 9. The optical film laser damage identification method according to claim 8, characterized in that: in the step 3), the method for judging whether the test sample is damaged is specifically: Compare the mass spectrogram of the sputtered particles obtained in step 2) with the elements in the atmosphere. If there is a new element, that is, the element does not belong to the elements in the atmosphere, the test sample has been damaged; otherwise, the test sample The sample is intact.