Device and method for detecting subsurface defect of optical component

Patent metadata

Field	Value
Publication number	US-11835472-B2
Application number	US-202217939768-A
Country	US
Kind code	B2
Filing date	Sep 7, 2022
Priority date	Aug 5, 2021
Publication date	Dec 5, 2023
Grant date	Dec 5, 2023

Abstract

Disclosed are a device and method for detecting a subsurface defect of an optical component. According to the device and method, a spectral confocal technology, a laser scattering technology and a laser-induced ultrasonic technology are combined, excitation laser and detection laser are simultaneously focused to different depths of the optical component through a dispersion lens set, the excitation laser generates a transient thermal expansion effect on a subsurface of the optical component, the detection laser is used for observing and analyzing ultrasonic vibration of the subsurface defect under an action of the thermal expansion effect, and spatial distribution information and scattered spectral information of scattered light at a position of the subsurface defect are acquired by the spectral confocal technology. The device and method are suitable for nondestructive testing of a finished product of an ultra-precise optical component with a strict requirement on the subsurface defect.

First claim

The invention claimed is:

1. A device for detecting a subsurface defect of an optical component, comprising a wide-spectrum light source, a near-infrared laser (NIR laser), a detection laser device, a dispersion lens set, a spectrum detector, a laser interferometer, an optical fiber optical path system, a motion platform, and a main control system, wherein:
the wide-spectrum light source is configured for generating white light, the near infrared laser is configured for generating generates excitation laser light, and the detection laser device is configured for generating detection laser light; wherein the detection laser light is a laser light for detection;
the white light, the excitation laser light and the detection laser light are coupled into the dispersion lens set through the optical fiber optical path system;
the dispersion lens set focuses the white light, the excitation laser light and the detection laser light to different depths of the optical component;
the excitation laser light generates a transient thermal expansion effect on a subsurface of the optical component and induces ultrasonic vibration;
the laser interferometer is used for observing and recording the ultrasonic vibration induced by the excitation laser light, and the laser interferometer is composed of a Fabry-Perot resonator, a dichroic lens, an interference photoelectric detector and an interference signal sampler;
the spectrum detector is configured for detecting spectrum distribution information of reflected light and scattered light; the spectrum detector comprises a first lens, a second lens, a grating optical splitter, a photodetector, and a data acquisition and processing module; the first lens collimates light output by the visible light multi-core optical fiber and makes the light incident on the grating optical splitter in a form of a linear array; the grating optical splitter reflects the incident light at different angles according to different wavelengths, makes the reflected light pass through the second lens to form a plurality of light beams, and finally makes the light beams incident on the photodetector; the photodetector is an area array detector, and is a CMOS or CCD image sensor; and the data acquisition and processing module is configured for controlling exposure of the photodetector, acquiring an electrical signal output by the photodetector into a digital signal, and processing and storing the digital signal to obtain spectral information;
the detection laser device is a laser capable of generating continuous detection laser light and a wavelength of the detection laser light ranges from 480 nanometers to 600 nanometers;
the motion platform is capable of driving the optical component to be detected or the dispersion lens set to move in a three-dimensional space of X, Y and Z, and scanning and detecting a surface and a subsurface of a sample to be detected through the main control system;
the optical fiber optical path system comprises a dual-mode optical fiber, a Y-shaped optical fiber coupler, a 1×2 optical switch, a first visible light optical fiber, a second visible light optical fiber, a third visible light optical fiber, a fourth visible light optical fiber and an optical fiber beam collector;
the dual-mode optical fiber is composed of an infrared annular multi-core optical fiber and a visible light multi-core optical fiber, with a cross section in a circular shape; the infrared multi-core optical fiber surrounds on an outer side of the visible light multi-core optical fiber; and the visible light multi-core optical fiber is provided with an odd number of fiber cores, a central fiber core is located in a geometric center of the visible light multi-core optical fiber, and a diameter of the central fiber core is more than three times that of other fiber cores;
the 1×2 optical switch is provided with three ports comprising a port P 1 , a port P 2 and a port P 3 , which are respectively connected with one ends of the first visible light optical fiber, the second visible light optical fiber and the third visible light optical fiber, and the port P 1 is only communicated with one of the port P 2 and the port P 3 at the same time;
the Y-shaped optical fiber coupler is provided with three ports comprising a light inlet, a light outlet and a coupling port; the other end of the first visible light optical fiber is connected to the light inlet of the Y-shaped optical fiber coupler; one end of the fourth visible light optical fiber is connected to the light outlet of the Y-shaped optical fiber coupler, and the other end of the fourth visible light optical fiber is connected to an intermediate node of the optical fiber beam collector; and the central fiber core of the visible light multi-core optical fiber is connected to the coupling port of the Y-shaped optical fiber coupler;
the white light generated by the wide-spectrum light source enters the port P 2 of the 1×2 optical switch through the second visible light optical fiber;
the detection laser light generated by the detection laser device passes through the laser interferometer and then enters the port P 3 of the 1×2 optical switch through the third visible light optical fiber;
the optical fiber beam collector is provided with an odd number of nodes arranged in a linear array, wherein the number of nodes is the same as the number of cores of the visible light multi-core optical fiber, and used for collecting the fiber cores of the visible light multi-core optical fiber into the linear array;
the main control system comprises a display, a bus controller, a communication interface, and a motion controller; the bus controller is connected to the wide-spectrum light source, the near-infrared laser, the detection laser device, the 1×2 optical switch, respectively; the motion controller is connected to the motion platform; the communication interface is connected to the data acquisition and processing module;
the data acquisition and processing comprises a logic control circuit, a digital signal processor, and a data memory; the logic control circuit is configured for acquiring the electrical signal output by the photodetector; the digital signal processor is configured for converting the electrical signal into the digital signal, and processing the digital signal to obtain spectral information; the data memory is configured for storing the digital signal to obtain spectral information.

2. The device for detecting the subsurface defect of the optical component according to claim 1 , wherein:
the dispersion lens set is capable of respectively focusing polychromatic light and generating axial dispersion, with a numerical aperture larger than 0.6; and through the dispersion lens set, the detection laser light and the excitation laser light are respectively focused at different axial positions, and a distance between the axial positions of the detection laser light and the excitation laser light ranges from 90 microns to 150 microns.

3. The device for detecting the subsurface defect of the optical component according to claim 2 , wherein the distance between the axial positions of the detection laser light and the excitation laser light is 120 microns.

4. The device for detecting the subsurface defect of the optical component according to claim 1 , wherein the wide-spectrum light source is a white light LED point light source, which generates continuous wide-spectrum white light; a wavelength of the excitation laser light preferably ranges from 1,000 nanometers to 1,800 nanometers, and a time domain width of a minimum pulse is less than 1,000 picoseconds.

5. The device for detecting the subsurface defect of the optical component according to claim 1 , wherein a detection method of the device specifically comprises the following steps of:
step 1: turning on a system pow

Assignees

• Univ Zhejiang

Inventors

• Sun Anyu
• Ju Bingfeng
• Guan Kaimin
• Zheng Li
• Zhong Haoze
• Chen Yuanliu
• Zhu Wule

Classifications

• G01N21/958 Primary

  Inspecting transparent materials {or objects, e.g. windscreens (for conveyed flat sheet or rod G01N21/896)} · CPC title

• G01N2201/062

  LED's · CPC title

• G01N2201/068

  Optics, miscellaneous · CPC title

• G01N2201/06113

  Coherent sources; lasers · CPC title

• G01N2201/084

  Fibres for remote transmission · CPC title