CN111122599A - Method for quickly imaging absorption type defects of large-caliber reflective film element - Google Patents
Method for quickly imaging absorption type defects of large-caliber reflective film element Download PDFInfo
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- CN111122599A CN111122599A CN201911352599.4A CN201911352599A CN111122599A CN 111122599 A CN111122599 A CN 111122599A CN 201911352599 A CN201911352599 A CN 201911352599A CN 111122599 A CN111122599 A CN 111122599A
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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
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- 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
- 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
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
- G01N2021/9511—Optical elements other than lenses, e.g. mirrors
Abstract
The invention discloses a method for quickly imaging absorption type defects of a large-caliber reflective film element based on a photo-thermal imbalance technology. Another low-power laser beam with a certain wavelength is adopted to form a large-size detection light spot through collimation and beam expansion, then the large-size detection light spot irradiates the same area of the reflective film element irradiated by the heated laser beam at a certain incident angle, and the light field distribution of the detection laser beam reflected or transmitted by the film is imaged to the CCD target surface for recording through an optical imaging system. And analyzing the light field intensity image recorded by the CCD to determine the absorption type defects of the irradiated area and the corresponding characteristics of the absorption type defects. The method greatly improves the single detection area, and makes the rapid detection of the absorption type defect distribution of the large-caliber reflective film element realized by scanning possible.
Description
Technical Field
The invention relates to the field of laser optical element detection, in particular to a high-resolution, rapid and nondestructive imaging detection method for absorption defects of a large-caliber reflective thin film element.
Background
The light absorption characteristic is an important index for measuring the quality of the laser optical element. For intense laser systems, characterization and control of the absorption loss distribution of the laser optics is particularly important, since absorption can result in laser energy loss, local temperature rise, beam quality degradation, and even laser damage. Among the many causes that cause the above problems, absorption type defects of the laser optical element are one of the main causes. Whereas for intense laser systems, large aperture reflective thin film elements are used in large numbers, their absorption type defects are the most significant factor that ultimately leads to damage to the intense laser system and the limiting factor of the laser system.
Among the technologies for characterizing the absorption characteristics of the reflective thin film element, the photothermal absorption measurement series technology has the advantages of no damage, no contact, high spatial resolution (up to submicron level), high sensitivity (weak absorption measurement is superior to 0.1ppm) and the like, and has become a mainstream nondestructive testing means for characterizing the absorption characteristics of the reflective thin film element. The photothermal absorption measurement series technology comprises a laser calorimetric technology, a photothermal deflection technology based on photothermal surface deformation (thermoelastic effect), a photothermal lens technology based on photothermal refractive index change (thermo-optic effect), a photothermal detuning technology based on temperature drift of a thin film element spectral band, and the like. Taking photo-thermal detuning technique as an example (see chinese patent application No. 200710118694.4, "a method for measuring absorption loss of optical film"), the measurement principle is as follows: irradiating the reflective thin film element with a focused heating laser beam, wherein the light absorption and thermal diffusion of the reflective thin film element can cause a temperature rise distribution with certain characteristics in a certain area of a sample with defects, so that a certain shift of a reflection or transmission spectral band in the area is caused; and irradiating the spectral band shift region with another detection laser beam, wherein the reflected or transmitted light intensity of the detection laser beam changes, and the light absorption characteristic of the reflective thin film element is determined by detecting the change of the reflected or transmitted light field of the detection laser beam.
However, for large aperture reflective film elements (typically 100X 100mm in size)2Above) the requirement of spatial distribution imaging of absorption characteristics, the above photothermal technology based on focused laser excitation and single-point detector measurement takes a very long time to complete imaging covering a full-aperture optical element in a point-by-point scanning mode: assuming that the step length of point-by-point scanning is 50 μm, each measurement point needs 1s of data acquisition, processing,And the time to move to the next measurement point (already fast), then a 400 x 400mm is done without a gap2The detection of the elements of (1) takes about 2 years, obviously lacking in technical realism; if the scanning step length is increased and the number of detection points is reduced in order to increase the scanning speed, the imaging detection can only be regarded as random sampling for the large-aperture reflective thin film element, and the randomness of defect detection can greatly reduce the characterization effect. The Chinese patent application No. 201811470960.9 'a method for rapidly imaging the surface absorption type defect distribution of a large-aperture optical element', proposes that the defect distribution imaging of the large-aperture optical element is realized by adopting large-size pulse excitation light spots and pulse detection light spots and based on CCD area array detection based on the principle of a photothermal thermal lens, but the method has the defects of high cost of a high-energy pulse laser, poor light beam quality, high delay control precision between excitation and detection pulse laser beams and influence on the defect detection sensitivity to a certain extent.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method has the advantages of keeping the advantages of high sensitivity and high spatial resolution of the traditional photothermal technology, simultaneously improving the single detection area by utilizing the large-size heating and detection light spots and the area array detection capability of the CCD, enabling the rapid detection of the absorption type defect distribution of the large-caliber reflective film element to be feasible, reducing the system cost, simplifying the complexity and difficulty of the configuration of a measuring optical system and the adjustment of a light path, and realizing the high-sensitivity detection and imaging of the micro absorption type defect of the micro large-caliber reflective film element.
The technical solution of the invention is characterized in that: a rapid imaging method for absorption type defects of a large-caliber reflective thin film element comprises the following steps:
the method comprises the steps of irradiating and heating a reflective film element after high-power laser beams are collimated and expanded to a certain size, forming certain temperature rise distribution in a defect area on the surface of a sample due to temperature rise and thermal diffusion generated by light absorption of the absorption type defect of the reflective film element, further changing the reflectivity or transmittance of the reflective film in the area by temperature change, irradiating the same area of the reflective film element irradiated by the high-power heating laser beams after another low-power laser beam with a certain wavelength is collimated and expanded to form a large-size detection light spot, imaging the light field distribution of the reflected or transmitted detection light beam to a CCD target surface for recording after passing through an optical imaging system and a narrow-band filter, and determining the absorption type defect of the irradiated area of the reflective film element and corresponding characteristics thereof by analyzing the intensity distribution change of a light field image recorded by the CCD.
Wherein the heating laser is high power: (>500W) continuous laser, the spot size of which is adjusted so that the irradiation power density on the surface of the reflective film element is 1-100kW/cm2The output power is modulated periodically, and the modulation frequency is one half of the frame frequency of the CCD camera.
The detection laser is a low-power (< 100mW) continuous laser with high beam quality (M2<2), the size of the continuous laser is consistent with that of the heating laser beam on the surface of the reflective film element, the wavelength is positioned at the edge of the reflective band of the reflective film element, the incidence angle is determined according to the reflection spectrum or the transmission spectrum of the reflective film element to be detected, and the incidence angle is adjusted within the range of 1-50 degrees, so that the detection light wavelength is at or near the maximum value of the first derivative of the reflection spectrum or the transmission spectrum of a specific incidence angle.
The intensity distribution of the heating light beam and the detection light beam after the collimation and beam expansion is uniform, and the size of the detection light spot in the irradiated area of the reflection film element is larger than that of the excitation light spot.
The optical imaging system images the reflected or transmitted detection light field distribution on the surface of the reflective thin film element to the CCD target surface, so that the reflected or transmitted light field distribution on the surface of the reflective thin film element is accurately measured, and the magnification of the optical imaging system is determined according to the requirement of measurement resolution.
The narrow-band filter placed in front of the CCD completely filters out the heating laser beam and only passes through the detection laser beam.
The CCD frame frequency is 2 times of the power modulation frequency of the heating laser beam, and a certain phase delay exists between the CCD trigger signal and the heating laser beam modulation signal, and is realized and controlled by a delay device.
When the incidence angle of the detection laser beam is larger than 15 degrees, the polarization control device is adopted to adjust the polarization state of the detection laser beam, so that the detection sensitivity is maximized.
And acquiring absorption type defect information from the multi-frame detection laser beam optical field distribution image recorded by the CCD through algorithms such as Fast Fourier Transform (FFT) and the like.
The CCD image reflects the absorption defects and the characteristics of the large-size light spot coverage area, and the full-aperture distribution and the characteristics of the absorption defects of the reflection film element are obtained by placing the reflection film element on a two-dimensional scanning table and scanning the whole detected area of the sample by using the large-size light spot.
Compared with the prior art, the invention has the following advantages:
(1) compared with the photo-thermal offset technology of single-point scanning, the method can realize high-resolution rapid imaging of the absorption type defects of the large-caliber reflective film element;
(2) compared with the surface thermal lens technology based on pulse excitation, pulse detection and CCD area array detection, the high-method configuration is relatively simple in configuration, easy to adjust, low in cost and high in engineering realizability.
Drawings
FIG. 1 is a schematic structural diagram of a reflection-type measuring device for implementing the method of the present invention;
FIG. 2 is a schematic diagram of a transmission-type measuring device for implementing the method of the present invention;
Detailed Description
The following describes a fast imaging method for absorption type defect distribution of a large-aperture reflective thin film element according to the present invention with reference to fig. 1-2. It is to be understood, however, that the drawings are provided for a better understanding of the invention and are not to be construed as limiting the invention.
As shown in fig. 1 and 2, the measuring device for implementing the method of the present invention may be a reflective measuring device or a transmissive measuring device, and mainly comprises a high-power heating laser device and a collimated beam expanding optical system thereof, a low-power detection laser device and a collimated beam expanding optical system thereof, a detection laser beam polarization control device, a function generator, a time delay device, a sample clamp and an electrically controlled two-dimensional scanning translation stage, an optical imaging device, a narrow-band optical filter 9, a CCD area array camera, a diaphragm, an optical trash can, a control and data acquisition and processing computer, and the like, of which the output can be modulated.
The specific implementation of the method of the invention is as follows: high-power laser beams with periodically modulated output power are collimated and expanded to a certain size, then the high-power laser beams irradiate and heat the reflective film element, the output power of a laser is periodically modulated by a function generator, the modulation frequency is generally 1-20Hz, and the modulation frequency is 1/2 of the frame frequency of a CCD imaging array detector. The absorption type defect of the reflective film element absorbs the energy of the heating laser to cause the temperature rise of the defect area and the thermal diffusion to form a certain temperature distribution in the defect area on the surface of the sample, and the temperature rise further changes the reflectivity or the transmittance of the reflective film in the defect area due to the temperature change characteristic of the film material. Selecting low-power laser beams with proper wavelength, collimating and expanding the beams to form large-size detection light spots, irradiating the same area of the reflective film element irradiated by the high-power heating laser beams, correspondingly changing the distribution of light fields of the reflected or transmitted detection light beams due to the change of the reflectivity or the transmittance of a defect area, imaging the light intensity change to a CCD target surface for recording through an optical imaging system, and adjusting the light intensity record time and the irradiation of the heating laser beams by a time delay device, wherein a certain phase (time) delay exists between the light intensity record time and the irradiation of the heating laser beams. And finally determining the absorption type defects and the corresponding characteristics of the irradiated area of the reflective film element by analyzing the intensity distribution change of the multi-frame light field image recorded by the CCD. The narrow-band filter is used for eliminating the influence of the heating laser beam and the stray light on measurement. The incident angle of the detection laser beam should be adjusted within a certain range, so that the sensitivity of the reflectivity/transmittance change caused by the detection temperature change of the detection laser beam is maximized. After the measurement of one area of the reflective film element is completed, the full-aperture two-dimensional imaging of the absorption type defects of the reflective film sample can be realized by transversely scanning the sample along the surface direction of the element.
Claims (10)
1. A method for quickly imaging absorption type defects of a large-caliber reflective film element is characterized by comprising the following steps: the method comprises the steps of irradiating and heating a reflective film element after high-power laser beams are collimated and expanded to a certain size, forming certain temperature distribution on the surface of a sample due to temperature rise and thermal diffusion generated by light absorption of the absorption type defects of the reflective film element, further changing the reflectivity or transmittance of a reflective film in a defect area by temperature change, irradiating the same area of the reflective film element irradiated by the high-power heating laser beams after another low-power laser beam with a certain wavelength is collimated and expanded to form large-size detection light spots, imaging the light field distribution of the reflected or transmitted light beams to a CCD target surface for recording after passing through an optical imaging system and a narrow-band filter, and determining the absorption type defects and the corresponding characteristics of the irradiated area of the reflective film element by analyzing the intensity distribution change of light field images recorded by the CCD.
2. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: heating the laser to high power: (>500W) continuous laser, the spot size of which is adjusted so that the irradiation power density on the surface of the reflective film element is 1-100kW/cm2The output power is modulated periodically, and the modulation frequency is one half of the frame frequency of the CCD camera.
3. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: the detection laser is a low power (< 100mW), high beam quality (M2<2) continuous laser having a dimension at the surface of the reflective film element greater than the size of the heating laser beam, a wavelength at the edge of the reflective strip of the reflective film element, and an angle of incidence determined from the reflection or transmission spectrum of the reflective film element being measured, adjusted in the range of 1-50 degrees, such that the detection wavelength is at or near the maximum of the first derivative of the reflection or transmission spectral band at a particular angle of incidence.
4. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: the intensity distribution of the heating light beam and the detection light beam after collimation and beam expansion is uniform, and the size of the detection light spot in the irradiated area of the reflective film element is larger than that of the excitation light spot.
5. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: the optical imaging system images the reflected or transmitted detection light field distribution on the surface of the reflective thin film element to the CCD target surface to realize accurate measurement of the reflected or transmitted light field distribution on the surface of the reflective thin film element, and the magnification of the optical imaging system is determined according to the measurement resolution requirement.
6. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: a narrow band filter placed in front of the CCD completely filters out the heating laser beam and passes only the detection laser beam.
7. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: the CCD frame frequency is 2 times of the power modulation frequency of the heating laser beam, and a certain phase delay exists between the CCD trigger signal and the heating laser beam modulation signal, and is realized and controlled by a delay device.
8. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: when the incidence angle of the detection laser beam is larger than 15 degrees, the polarization control device is adopted to adjust the polarization state of the detection laser beam, so that the detection sensitivity is maximized.
9. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: and acquiring absorption type defect information from the multi-frame detection laser beam optical field distribution image recorded by the CCD through algorithms such as Fast Fourier Transform (FFT) and the like.
10. The method for rapidly imaging absorption-type defects of a large-aperture reflective thin film element according to claim 1, wherein: a CCD image reflects the absorption defects and the characteristics of a large-size light spot coverage area, and the full-aperture distribution and the characteristics of the absorption defects of the reflection film element are obtained by placing the reflection film element on a two-dimensional scanning table and scanning the whole detected area of the sample by using the large-size light spot.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112388156A (en) * | 2020-11-06 | 2021-02-23 | 电子科技大学 | Combined device for laser pretreatment and absorption type defect imaging detection of large-caliber optical element |
| CN113008529A (en) * | 2021-05-12 | 2021-06-22 | 中国工程物理研究院应用电子学研究所 | Large-caliber optical element measuring system based on ultrafast laser imaging |
| WO2021227134A1 (en) * | 2020-05-11 | 2021-11-18 | 中国科学院上海光学精密机械研究所 | Absorptive defect single-beam photothermal measurement device and measurement method |
| CN116660318A (en) * | 2023-07-25 | 2023-08-29 | 中国科学院长春光学精密机械与物理研究所 | Large-caliber optical element damage positioning device and repairing method |
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| CN101082537A (en) * | 2007-07-12 | 2007-12-05 | 中国科学院光电技术研究所 | Method for measuring optical film absorption loss |
| CN109444166A (en) * | 2018-12-04 | 2019-03-08 | 电子科技大学 | A kind of method of optical elements of large caliber Surface absorption type defect distribution fast imaging |
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2019
- 2019-12-25 CN CN201911352599.4A patent/CN111122599A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101082537A (en) * | 2007-07-12 | 2007-12-05 | 中国科学院光电技术研究所 | Method for measuring optical film absorption loss |
| CN109444166A (en) * | 2018-12-04 | 2019-03-08 | 电子科技大学 | A kind of method of optical elements of large caliber Surface absorption type defect distribution fast imaging |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2021227134A1 (en) * | 2020-05-11 | 2021-11-18 | 中国科学院上海光学精密机械研究所 | Absorptive defect single-beam photothermal measurement device and measurement method |
| CN112388156A (en) * | 2020-11-06 | 2021-02-23 | 电子科技大学 | Combined device for laser pretreatment and absorption type defect imaging detection of large-caliber optical element |
| CN113008529A (en) * | 2021-05-12 | 2021-06-22 | 中国工程物理研究院应用电子学研究所 | Large-caliber optical element measuring system based on ultrafast laser imaging |
| CN116660318A (en) * | 2023-07-25 | 2023-08-29 | 中国科学院长春光学精密机械与物理研究所 | Large-caliber optical element damage positioning device and repairing method |
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