CN105716756B - A kind of device for accurately measuring of optical material microstress spatial distribution - Google Patents

Abstract

The invention discloses an accurate measurement device for the spatial distribution of microscopic stress of optical materials. The device is characterized in that the device adopts a double optical path design of detection light and reference light, which eliminates the error caused by the fluctuation of the laser light source and the temperature difference caused by the silicon photodiode. At the same time, the precision servo motor is used to drive the analyzer to rotate for curve fitting, which eliminates the huge influence of the inaccurate positioning of the servo motor on the phase difference, thus realizing the high-precision measurement of the spatial distribution of microscopic stress. In the whole device, according to laser 1, laser beam splitter 2, chopper 3, polarizer 4, mirror 5, optical shaper 6, sample 7, electric two-dimensional micro-movement translation stage 8, phase retarder 9, The analyzer 10 , the servo motor 11 , the mirror 12 , the silicon photodiode 13 , the dual-channel lock-in amplifier 14 , and the computer 15 form an optical path in sequence, and are sequentially fixed on the steel connecting frame 16 . The present invention can be used for quality control of optical crystal materials and their finished components.

Description

An accurate measurement device for the spatial distribution of microscopic stress in optical materials

technical field

The invention belongs to the technical measurement field, in particular to an accurate measurement technology for the spatial distribution of microscopic stress of optical materials.

Background technique

The primary defects and post-processing of most optical crystal materials will generate non-uniformly distributed microscopic stress inside the material. This microscopic stress usually causes local fluctuations in the birefringence of the material (ie, stress birefringence), which has a negative impact on the optical uniformity of the finished optical device. Sexual adverse effects. The microscopic stress of optical materials is difficult to measure directly, and can only be indirectly characterized by measuring the stress birefringence calculated from the phase retardation. For the spatial fluctuation of the stress birefringence (ie, the spatial distribution of microscopic stress), the measurement method of two-dimensional point-by-point scanning is generally used, which requires the microscopic stress measurement system to have both good accuracy and very high measurement stability. Micro-stress spatial distribution detection technology is of great significance to the quality analysis and control of optical materials such as glass, crystal, polymer film, lens, wafer, etc.

In 2011, Xiao Haosu et al. (Analysis of the accuracy of measuring crystal stress birefringence by polarization interferometry, "Infrared and Laser Engineering", Vol. 40, No. 2, p. 272, 2011) proposed a method for measuring crystal stress birefringence based on polarization interferometry. This method uses a wedge-shaped sample to avoid measurement errors that may be caused by the thickness of the sample, but it uses a single-point measurement at the extinction position, so the measurement accuracy of the analyzer's extinction angle is relatively low; in addition, this solution cannot eliminate laser power fluctuations and optical probes. The influence of temperature drift on the measurement results, the stability is poor.

In 2012, Hou Junfeng (a precision measurement system for the phase delay of a wave plate and its realization method, patent application number: 201210009867.4) proposed to use the phase delay as an unknown parameter on the basis of the ellipsometer of the rotating compensator to set up a simultaneous nonlinear equation Calculate the phase delay of the measured sample. Although the method uses multi-point measurement to improve the accuracy, the light source must be a continuous spectrum light source such as a xenon lamp, and the quality of the light spot is not suitable for shaping, so it cannot be used for the characterization of microscopic stress. In addition, this solution uses a single optical path and a single probe, which cannot eliminate the influence of light source power fluctuations and the temperature drift of the photodetector, and has poor stability. Therefore, this scheme cannot be used to measure the spatial distribution of microscopic stress.

In 2013 and 2014, Gao Hansong et al. (Micro stress testing system for semiconductor materials, patent application number 201310194074.9, Micro stress testing system for materials, patent number: 201410143013.4) proposed the use of photoelastic modulators on the micro stress of optical materials The spatial distribution is tested, and the stress of the material is measured by measuring the difference in the reflection ratio of light intensity and the difference in the ratio of light intensity transmission in two directions perpendicular to each other on the surface of the material. These two methods require the use of expensive imported photoelastic modulators, which greatly increases the cost of the components of the system. In addition, this scheme does not consider the fluctuation of laser power, the temperature drift of the optical probe, the influence of the optical modulator itself and external environmental factors on the measurement results. Impact. In 2014, Fang Jiancheng et al. proposed (a detection device and method based on double beam differential to eliminate photoelastic modulator and environmental influence, patent application number is 201410670079.9) so that two beams of light in the same state pass through the same photoelastic modulator. It is converted into an electrical signal by two photodetectors, and differentially processed by a lock-in amplifier and a signal processing system to eliminate the influence of the photoelastic modulator itself and environmental changes. Although this scheme suppresses the influence of external factors such as lasers and photoelastic modulators on the measurement results to a certain extent, because it still uses two independent photodetectors, it cannot eliminate the influence of the temperature drift of the optical probes and individual differences on the measurement results. impact, poor stability.

In 2015, Tan Yidong et al. (an optical material stress measurement system, patent application number: CN201510409605.0) proposed a scheme to measure the optical material stress using dual detectors. A laser beam is emitted from the external cavity of the laser, After passing through the beam splitting prism, it is divided into two beams and received by the two detectors. The other laser beam is emitted from the second cavity of the laser, irradiated on the sample, and is reflected back to the laser by the reflective film at the bottom of the beam. The laser is modulated to measure the stress in different parts of the crystal. The invention also uses two optical probes to detect the optical signal, which cannot eliminate the influence of the individual differences of the optical probes on the measurement result, and has poor stability.

SUMMARY OF THE INVENTION

The existing micro-stress measurement solutions have shortcomings such as low precision, high cost, and poor stability (susceptible to laser power fluctuations, optical probe temperature drift, and individual differences). In view of the above problems, the present invention provides a low-cost, high-precision, and high-stability microscopic stress spatial distribution measurement device.

The present invention provides an accurate measurement device for the spatial distribution of microscopic stress of optical materials, which is characterized in that: the device adopts a single silicon photodiode to detect signal light and reference light at the same time with a dual-optical path and single-probe design, which greatly reduces the fluctuation of laser power, The influence of the temperature drift of the optical probe and individual differences has extremely high measurement stability; the device uses the servo motor to drive the analyzer to rotate, and indirectly measures and fits the change curve of the normalized transmittance with the compensation angle. To measure the stress birefringence fluctuations in the material micro-region, the multi-point fitting measurement method greatly improves the measurement accuracy of the micro-stress spatial distribution.

The present invention provides an accurate measurement device for the spatial distribution of microscopic stress of optical materials, which is characterized in that: the device is based on laser 1, laser beam splitter 2, chopper 3, polarizer 4, reflector 5, optical shaper 6. Sequential formation of sample 7, electric two-dimensional micro-moving translation stage 8, phase retarder 9, analyzer 10, servo motor 11, mirror 12, silicon photodiode 13, dual-channel lock-in amplifier 14, and computer 15 The optical path is fixed on the steel connecting frame 16 in turn.

Compared with the prior art, the core optical detection components of the device of the present invention all use common optoelectronic components, and the cost is low; the dual-optical path and single-probe design of using a single silicon photodiode to simultaneously detect the signal light and the reference light greatly reduces the laser power. The influence of fluctuation, optical probe temperature drift and individual differences has extremely high measurement stability; the servo motor is used to drive the analyzer to rotate, and by measuring and fitting the change curve of normalized transmittance with the compensation angle, indirectly To measure the stress birefringence fluctuations in the material micro-region, the multi-point fitting measurement method greatly improves the measurement accuracy of the micro-stress spatial distribution.

Description of drawings

FIG. 1 is a schematic structural diagram of the basic principle of the optical material microscopic stress spatial distribution measuring device of the present invention.

FIG. 2 is a data fitting diagram of the optical material microscopic stress spatial distribution measuring device of the present invention.

FIG. 3 is a graph of the stability test of lithium niobate crystal measured by the device of the present invention.

FIG. 4 is a graph showing the detection result of an embodiment (Example 1) of the apparatus for measuring the microscopic stress spatial distribution of optical materials according to the present invention.

FIG. 5 is a diagram showing the detection results of an embodiment (Example 2) of the apparatus for measuring the microscopic stress spatial distribution of optical materials according to the present invention.

FIG. 6 is a diagram showing the detection results of an embodiment (Example 3) of the apparatus for measuring the microscopic stress spatial distribution of optical materials according to the present invention.

Detailed ways

The present invention will be further described below with reference to the embodiments and accompanying drawings.

The invention discloses an accurate measurement device for the spatial distribution of microscopic stress of optical materials. Sample 7, electric two-dimensional micro-movement translation stage 8, phase retarder 9, analyzer 10, servo motor 11, mirror 12, silicon photodiode 13, dual-channel lock-in amplifier 14, computer 15 The order forms an optical path, and They are fixed on the steel connecting frame 16 in turn.

The laser is required to have a wavelength range of 400-700nm, a power of 0.5-5.5mW, and a monochromaticity of less than ±1nm. The material is high quality mica stone, calcite or iceland stone. The test sample must be a transparent optical crystal with birefringence. The extinction ratio of polarizer and analyzer should be greater than 1:500. The stage is an electric two-dimensional micro-movement translation stage, and its precision should be better than 3 μm.

In summary, considering the cost of each component and the measurement accuracy requirements, the preferred range of its components is: the laser uses a laser with a wavelength of 400-700nm, a power of 1-3mW, and the monochromaticity should be less than ±0.1nm, The frequency of the chopper is 150-700Hz, and the material of the polarizer and the analyzer is high-quality Bingzhou stone. The extinction ratio between the polarizer and the analyzer should be greater than 1:1000, the stage is an electric two-dimensional micro-movement translation stage, and its resolution should be between 0.1μm-1μm, all optical components on the optical path And the electronic devices are fixed on the steel connecting frame 16 to ensure the correct propagation of light and measurement accuracy.

The working principle of the device of the present invention is as follows: the present invention measures the spatial distribution of the microscopic stress of the optical material based on the phase compensation technology. In the present invention, the laser light emitted by the light source is divided into two laser beams with the same polarization and equal light intensity through the laser beam splitter, one beam is the reference beam _IR and the other beam is the probe beam _Is . After the two beams of light are modulated into different frequencies by the chopper, the reference light directly enters the optical probe after being reflected, while the probe light is polarized and wavefront adjusted by polarizers, optical shapers, etc., and then enters the sample for detection. The microscopic stress finally enters the optical probe via the phase retarder and analyzer. The optical probe signal extracts the reference light and the probe light signal through the dual-channel lock-in amplifier and gives a normalized light intensity signal (I= _{Is /} IR), which is input to the computer for data processing and recording. According to the principle of phase compensation: normalized transmittance T=1/2[1±sin(δ±2β)] (where T=I/I ₀ , I ₀ is the maximum normalized light intensity signal that can be obtained by the system, δ is the phase delay, β is the rotation radian of the analyzer, that is, the compensation angle) T is the function T(β) of β, and δ is the function parameter. The computer controls the servo motor to rotate the analyzer, and measures the relationship between the normalized transmittance T and the compensation angle β—the function curve T(β), and then the least squares method is performed on the curve to obtain the parameter phase delay. δ, and the birefringence Δn can be obtained from the formula δ=2πdΔn/λ. The computer scans and measures the sample through the electric two-dimensional micro-movement translation stage, and can give the fluctuation of the birefringence Δn of the optical material in the two-dimensional space, that is, the spatial distribution map of the microscopic stress.

Specific embodiments of the detection device of the present invention are given below, and the specific embodiments are only used to describe the present invention in detail, and do not limit the protection scope of the claims of the present application.

Example 1

An accurate measurement device for the spatial distribution of microscopic stress of optical materials is designed. The specific parameters of each component of the device are as follows: laser light source 1 has a wavelength of 632.8 nm, a power of 1 mW, and a monochromaticity of less than ±0.1 nm; chopper 2 is a reference light The modulation frequencies of the polarizer and the probe light are 350 and 700 Hz; the polarizer and the analyzer are made of Bingzhou stone; the sample 7 is lithium niobate crystal; the extinction ratio of the polarizer and the analyzer is 1:1000; The translation resolution of the micro-movement translation stage 8 is 0.1 μm;

Example 2

An accurate measurement device for the spatial distribution of microscopic stress of optical materials is designed. The specific parameters of each component of the device are as follows: laser light source 1 has a wavelength of 514.5 nm, a power of 2 mW, and a monochromaticity of less than ±0.1 nm; chopper 2 is a reference light The modulation frequencies of the polarizer and the probe light are 200 and 400 Hz; the polarizer and the analyzer are made of Bingzhou stone; the sample 7 is sapphire crystal; the extinction ratio of the polarizer and the analyzer is 1:1500; The translation resolution of the translation stage 8 is 0.5 μm

Example 3

An accurate measurement device for the spatial distribution of microscopic stress of optical materials is designed. The specific parameters of each component of the device are as follows: laser light source 1 has a wavelength of 488.0nm, a power of 3mW, and a monochromaticity of less than ±0.1nm; chopper 2 is a reference light and detection light modulation frequencies of 150 and 300 Hz; polarizer and analyzer material are Bingzhou stone; sample 7 is lithium tantalate crystal; the extinction ratio of polarizer and analyzer is 1:2500; The translation resolution of the micro-movement translation stage 8 is 1 μm;

Using the detection device of the present invention to perform microscopic stress detection on the fixed area of the lithium niobate sample (see Example 1), the normalized transmittance T as a function of the compensation angle β as shown in Figure 2 is obtained. The curve T(β) and the minimum The fitting result of the square method curve shows that the R-square value of the fitting similarity is 0.994, and the birefringence is calculated to be 52.35×10 ^-6 . The spatial fluctuation of this value with the two-dimensional scanning represents the spatial distribution of microscopic stress, so the fluctuation (stability) of the birefringence measurement value at the same measurement point with time is very important. Figure 3 shows the single-point birefringence stability test curve of the lithium niobate sample. The fluctuation of the measured refractive index difference is less than 2×10 ^-7 within 3 hours, and the stability is extremely high.

The microscopic stress spatial distribution of the lithium niobate sample was detected by using the detection device of the present invention (see Example 1), and the spatial fluctuation diagram of the stress birefringence as shown in FIG. 4 was obtained.

The microscopic stress spatial distribution was detected on the sapphire sample by using the detection device of the present invention (see Example 2), and the spatial fluctuation diagram of stress birefringence as shown in FIG. 5 was obtained.

The microscopic stress spatial distribution of the lithium tantalate sample was detected by using the detection device of the present invention (see Example 3), and the spatial fluctuation diagram of the stress birefringence as shown in FIG. 6 was obtained.

The above specific examples further describe the technical solutions and implementation methods of the present invention in detail. It should be understood that the above examples are not only used in the present invention, but all equivalent modifications, etc., are carried out within the spirit and principles of the present invention. Effective replacement, improvement, etc. should all fall within the protection scope of the present invention.

Claims (1)

1. an accurate measuring device for the spatial distribution of microscopic stress of optical materials, it is characterized in that: the device adopts a single silicon photodiode to simultaneously detect the double optical path single probe design of signal light and reference light, which greatly weakens laser power fluctuation, optical probe The influence of temperature drift and individual differences has extremely high measurement stability; the device uses a servo motor to drive the analyzer to rotate, and indirectly measures the material by measuring and fitting the curve of normalized transmittance versus compensation angle. The stress birefringence fluctuation of the micro area, the multi-point fitting measurement method greatly improves the measurement accuracy of the microscopic stress spatial distribution. 5. Optical shaper 6, sample 7, electric two-dimensional micro-movement translation stage 8, phase retarder 9, analyzer 10, servo motor 11, mirror 12, silicon photodiode 13, dual-channel lock-in amplifier 14, The optical paths of the computers 15 are formed in sequence, and are sequentially fixed on the steel connecting frame 16 .