Laser post-processing device and method for large aperture optical medium thin film nodular defects

Abstract

This invention discloses a laser post-processing device and method for large-aperture optical dielectric thin film nodule defects, relating to the field of laser technology. The laser post-processing device for large-aperture optical dielectric thin film nodule defects includes: an ultraviolet pumped laser, a focusing lens, a femtosecond laser, a scanning galvanometer, a scanning field mirror, a centrally located aperture mirror, an observation camera, an electrically driven displacement platform, and a control computer. The laser post-processing device and method for large-aperture optical dielectric thin film nodule defects provided by this invention utilize the characteristics of small focal spot and small heat-affected zone of femtosecond lasers, and with the assistance of an optical camera, accurately remove nodule defects in localized areas in real time. Furthermore, it can automatically identify and accurately locate nodule defects, achieving rapid removal of nodule defects and reducing the impact of the post-processing process on the surrounding normal film layer. Simultaneously, it reduces manual intervention, improves the degree of automation, and effectively improves the post-processing efficiency of optical dielectric thin film nodule defects.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a laser post-processing device and method for large-aperture optical medium thin film nodule defects. Background Technology

[0002] Nodule defects are a typical type of micro-defect involving inclusions that occur during the fabrication of optical dielectric thin films. They are typically crown-shaped inclusions on the order of micrometers, formed by impurities seeded from various sources during film deposition. The discontinuity at the film interface where nodule defects are located modulates the optical field, increasing the local field strength. Simultaneously, nodule defects act as strong absorption regions, absorbing additional laser energy and becoming weak points for film damage. Nodule defects are a significant contributing factor to thin film damage under laser irradiation and are considered by many researchers to be a micro-defect with a substantial impact on laser-induced thin film damage.

[0003] To improve the laser damage threshold of optical dielectric thin films, it is necessary to control the distribution of nodule defects in the film, minimizing their content or preventing their occurrence altogether. Strictly controlling environmental cleanliness during film preparation to reduce the introduction of impurities into the depositing film can effectively reduce the density of nodule defects. However, this method cannot completely eliminate the presence of nodule defects; remaining defects can still be trigger points for film damage during laser irradiation. Therefore, after the dielectric thin film is prepared, further post-processing is required to eliminate the risk of film damage caused by these defects. Currently, laser pretreatment of thin films using subthreshold energy laser irradiation is considered an effective post-processing method for removing nodule defects and improving the laser damage threshold. The principle is that under laser irradiation, nodule defects absorb light energy and rapidly expand, leading to localized stress concentration. When the accumulated stress reaches a certain level, the nodule defects will burst out of the film to release stress. The nodule is removed, leaving pinhole defects in the film. When irradiated with higher-energy lasers, these pinhole defects will no longer develop, thus increasing the laser damage threshold of the thin film. However, this type of laser pretreatment method still has shortcomings: it cannot precisely target nodule defects, and while eliminating nodule defects, it can also affect the normal film layer. Furthermore, the lack of an effective feedback mechanism during the process leads to unstable selection of process parameters and reliance on manual experience. This results in poor stability, poor process transferability, and low efficiency of the laser pretreatment method. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing laser preprocessing methods in the post-processing of nodule defects in dielectric thin films. This invention proposes a laser post-processing device and method for nodule defects in large-aperture optical dielectric thin films. Utilizing the characteristics of femtosecond lasers—small focal spot and small heat-affected zone—and with the assistance of an optical camera, nodule defects in local areas can be precisely removed in real time.

[0005] The technical solution adopted in this invention is as follows:

[0006] A laser post-processing device for nodule defects in large-aperture optical dielectric thin films, the device comprising: an ultraviolet pumped laser, a focusing lens, a femtosecond laser, a scanning galvanometer, a scanning field mirror, a centrally located aperture mirror, an observation camera, an electric displacement platform, and a control computer.

[0007] On the other hand, the present invention also provides a laser post-processing method for nodule defects in large-aperture optical dielectric thin films, comprising the following steps:

[0008] S1, Determine the characteristic size of the central hole of the centrally perforated mirror;

[0009] S2, Clean the optical medium thin film sample;

[0010] S3, adjust the optical path of the optical medium thin film sample;

[0011] S4 locates and identifies nodule defects and performs post-processing on them.

[0012] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0013] Compared with existing technologies, the laser post-processing device and method for large-aperture optical dielectric thin film nodule defects provided by this invention utilizes the characteristics of small focal spot and small heat-affected zone of femtosecond laser, and performs precise removal of nodule defects in local areas in real time with the assistance of an optical camera. Secondly, the improved laser post-processing scheme of this invention can automatically identify and accurately locate nodule defects, realize rapid removal of nodule defects, reduce the impact of the post-processing process on the normal film layer around the defect, reduce manual intervention, improve the degree of automation, and effectively improve the post-processing efficiency of optical dielectric thin film nodule defects. Attached Figure Description

[0014] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0015] Figure 1 This is a schematic diagram of the laser post-processing device for nodule defects in large-aperture optical dielectric thin films provided by the present invention.

[0016] Figure 2This is a flowchart of the laser post-processing method for nodule defects in large-aperture optical dielectric thin films provided by the present invention;

[0017] In the figure: 1-Ultraviolet pump laser; 2-Focusing lens; 3-Femtosecond laser; 4-Scanning galvanometer; 5-Scanning field mirror; 6-Central aperture mirror; 7-Observation camera; 8-Electrically operated stage; 9-Control computer; 10-Optical dielectric thin film sample. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0019] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] Example 1

[0021] Figure 1 An embodiment of the present invention is shown, which is a laser post-processing device for nodule defects in large-aperture optical dielectric thin films. It mainly includes: an ultraviolet pump laser 1, a focusing lens 2, a femtosecond laser 3, a scanning galvanometer 4, a scanning field mirror 5, a central aperture mirror 6, an observation camera 7, an electric displacement platform 8, and a control computer 9.

[0022] The ultraviolet pump laser 1 provides an ultraviolet pump laser beam; the focusing lens 2 focuses the ultraviolet pump laser beam; the femtosecond laser 3 provides a femtosecond laser beam; the scanning galvanometer 4 controls the movement and positioning of the femtosecond laser beam within the field of view of the observation camera 7; the scanning field mirror 5 focuses the femtosecond laser beam; the central aperture mirror 6 couples the ultraviolet pump laser beam and the femtosecond laser beam; the observation camera 7 observes within the field of view and acquires images, and transmits the acquired images to the control computer 9; the electric displacement platform 8 carries the optical dielectric thin film sample 10 and moves the area outside the field of view into the field of view; the control computer 9 controls the laser post-processing device to perform post-processing operations for nodule defects in the ultraviolet dielectric thin film according to a preset program.

[0023] In a preferred embodiment, the types of ultraviolet pumped laser 1 may include continuous lasers, pulsed lasers, etc.

[0024] Figure 2 Another embodiment of the present invention is shown, which is a method for laser post-processing of nodule defects in large-aperture optical dielectric thin films using the aforementioned laser post-processing device, comprising the following steps:

[0025] S1, Determine the characteristic size of the central hole of the central aperture mirror 6;

[0026] In this step, based on the focusing focal length f1 of the ultraviolet pump laser beam, the focal spot diameter ω1 of the ultraviolet pump laser beam, the focusing focal length f2 of the femtosecond laser beam, the focal spot diameter ω2 of the femtosecond laser beam, and the distance L from the central aperture mirror 6 to the optical medium thin film sample 10, the characteristic size d of the central aperture mirror 6 is determined. The specific calculation formula is as follows: (1)

[0027] ω2×(1+L 2 / f2 2 ) 1 / 2 < d <ω1×(1+L 2 / f1 2 ) 1 / 2 (1);

[0028] S2, Clean the optical medium thin film sample 10;

[0029] The dust particles adhering to the surface of the optical medium film sample 10 were removed by wiping with alcohol, and the cleanliness was checked under an optical microscope.

[0030] S3, adjust the optical path of the optical medium thin film sample 10;

[0031] The optical medium thin film sample 10 is placed on the electric displacement platform 8 and clamped. The optical path is adjusted so that the center of the pump ultraviolet laser focal spot coincides with the center of the femtosecond laser focal spot. At the same time, the observation camera 7 is adjusted so that the center of the field of view coincides with the center of the pump ultraviolet laser focal spot and the center of the femtosecond laser focal spot.

[0032] S4, Locate and identify nodular defects in the acquired images of optical medium thin film sample 10, and perform post-processing on the nodular defects;

[0033] Since the focusing size of the ultraviolet pump light source is larger than the field of view of the industrial camera (≥1mm×1mm), the embodiment of the present invention uses the field of view as the criterion. Within the field of view, the scanning galvanometer 4 is used to control the femtosecond laser beam to remove nodule defects by means of galvanometer scanning. Outside the field of view, a two-dimensional electric displacement platform 8 is used to carry the optical medium thin film sample 10 for movement.

[0034] Specifically, step S4 involves the control computer 9 controlling each step to perform post-processing of ultraviolet dielectric film nodule defects according to a preset program, including the following steps:

[0035] S401, first determine the area to be processed. If the area to be processed is outside the field of view, control the electric displacement platform 8 to move the optical medium thin film sample 10 into the field of view.

[0036] S402, irradiate the current field of view with ultraviolet pump laser;

[0037] S403: The observation camera 7 acquires images of the current field of view and marks nodule defects, and the scanning galvanometer 4 controls the femtosecond laser to scan and remove the marked nodule defects one by one.

[0038] S404, perform ultraviolet pump laser irradiation again, and use the observation camera 7 to collect images of the current field of view to judge and confirm the removal effect of nodule defects; if the nodule defects in the current field of view are not completely removed, repeat steps S403-S404 to remove nodule defects in the current field of view; if the nodule defects in the current field of view have been completely removed, control the electric displacement platform 8 to move the next area to be processed of the optical medium thin film sample 10 into the field of view;

[0039] S405, repeat the above steps until nodules are identified and removed from the entire optical medium thin film sample 10.

[0040] In a preferred embodiment, the aforementioned electric displacement platform 8 moves the optical medium thin film sample 10 through automatic control operation of the control computer 9, and the aforementioned marking of nodule defects is also achieved by the control computer 9 receiving images acquired from the observation camera 7, and using corresponding image recognition algorithms to automatically analyze and locate all nodule defects contained in the images and mark them.

[0041] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

[0042] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

Claims

1. A method for laser post-processing of blemishes in large aperture optical medium thin films, characterized in that, The method includes: Step S1: Determine the characteristic size of the central hole of the central aperture mirror (6), which is used to couple the ultraviolet pump laser beam and the femtosecond laser beam. Step S1 is to determine the characteristic size d of the central hole of the central aperture mirror (6) based on the focusing focal length f1 of the ultraviolet pump laser beam, the focal spot diameter ω1 of the ultraviolet pump laser beam, the focusing focal length f2 of the femtosecond laser beam, the focal spot diameter ω2 of the femtosecond laser beam, and the distance L from the central aperture mirror (6) to the optical medium thin film sample (10). The specific calculation formula is as follows: ω2x(1+L 2 / f2 2 ) 1 / 2 <d<ω1x(1+L 2 / f1 2 ) 1 / 2 ; Step S2: Clean the optical medium thin film sample (10); Step S3, adjust the optical path of the optical medium thin film sample (10), including: placing the optical medium thin film sample (10) on the electric displacement platform (8), adjusting the optical path so that the center of the pump ultraviolet laser focal spot coincides with the center of the femtosecond laser focal spot, and adjusting the observation camera (7) so that the center of the field of view coincides with the center of the pump ultraviolet laser focal spot and the center of the femtosecond laser focal spot. Step S4: Locate and identify nodular defects in the image of the optical medium thin film sample (10), and perform post-processing on the nodular defects; Step S4 includes: Step S401: First, determine the area to be processed. If the area to be processed is outside the field of view, control the electric displacement platform (8) to move the optical medium thin film sample (10) into the field of view. Step S402: Irradiate the current field of view with ultraviolet pump laser; Step S403: Use the observation camera (7) to collect images of the current field of view and mark nodule defects, and use the scanning galvanometer (4) to control the femtosecond laser to scan and remove the marked nodule defects one by one.

2. The laser post-processing method for nodule defects in large-aperture optical dielectric thin films as described in claim 1, characterized in that, Step S4 also includes: Step S404: Perform ultraviolet pump laser irradiation again, and use the observation camera (7) to collect images of the current field of view to judge and confirm the nodule defect removal effect; Step S405: Repeat the above steps until nodules are identified and removed from the entire optical medium thin film sample (10).

3. The laser post-processing method for nodule defects in large-aperture optical dielectric thin films as described in claim 2, characterized in that, Step S404 also includes: If the nodule defects in the current field of view are not completely removed, repeat steps S403-S404 to remove the nodule defects in the current field of view; if the nodule defects in the current field of view have been completely removed, control the electric displacement platform (8) to move the next area to be processed of the optical thin film sample (10) into the field of view.

4. The laser post-processing method for nodule defects in large-aperture optical dielectric thin films as described in claim 1, characterized in that, The method is achieved through the automatic control operation of the control computer (9).

5. A laser post-processing device for nodule defects in large-aperture optical dielectric thin films, characterized in that, The device is used to implement the laser post-processing method for nodule defects in large-aperture optical dielectric thin films as described in any one of claims 1-4. The device includes: an ultraviolet pumped laser (1), a focusing lens (2), a femtosecond laser (3), a scanning galvanometer (4), a scanning field mirror (5), a central aperture mirror (6), an observation camera (7), an electric displacement platform (8), and a control computer (9).

6. The laser post-processing device for nodule defects in large-aperture optical dielectric thin films according to claim 5, characterized in that, The ultraviolet pump laser (1) is used to provide an ultraviolet pump laser beam; the focusing lens (2) is used to converge the ultraviolet pump laser beam; the femtosecond laser (3) is used to provide a femtosecond laser beam; the scanning galvanometer (4) is used to control the movement and positioning of the femtosecond laser beam within the field of view of the observation camera (7); the scanning field mirror (5) is used to converge the femtosecond laser beam; the observation camera (7) is used to observe within the field of view and acquire images, and transmit the acquired images to the control computer (9); the electric displacement platform (8) is used to carry the optical medium thin film sample (10) and to move the area outside the field of view into the field of view; the control computer (9) is used to control the laser post-processing device to carry out the optical medium thin film nodule defect post-processing operation according to the preset program.

7. The laser post-processing device for nodule defects in large-aperture optical dielectric thin films according to claim 6, characterized in that, The ultraviolet pumped laser (1) is a continuous laser or a pulsed laser.

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