CN110736721B - Glass plate refractive index uniformity detection device and detection method based on diffraction grating - Google Patents

Abstract

The invention relates to a diffraction grating-based glass plate refractive index uniformity detection device and a detection method. The device comprises a wavelength-tunable light source, and a beam expander, a pinhole diaphragm, a collimator, Mirror, adjustable slit and reflective plane diffraction grating, the working surface of reflective plane diffraction grating 6 forms an incident angle of 20-45° with the optical axis of the outgoing light, and is vertically positioned below the reflective plane diffraction grating. An optical imaging lens and a CCD image acquisition system are set up in sequence, and the CCD image acquisition system is connected to the computer; the object to be tested is set between the reflective plane diffraction grating and the optical imaging lens. The optical path system of the invention realizes the non-contact measurement of the uniform distribution of the spatial refractive index of the optical glass with large thickness and large refractive index change.

Description

Glass plate refractive index uniformity detection device and detection method based on diffraction grating

technical field

The invention belongs to the field of optical detection, relates to light diffraction technology, spectral analysis technology and computer image and data processing technology, in particular to a diffraction grating-based glass plate refractive index uniformity detection device and detection method.

Background technique

Optical glass is the main material for making optical lenses, optical prisms, optical mirrors, beam splitters, optical fibers, lasers and other optical devices. The uniformity of the refractive index of optical glass directly affects the performance of optical devices. Therefore, optical glass uniformity measurement is a research hotspot in the field of optics.

The traditional methods of detecting the refractive index of optical glass mainly include: (1) pin-pin method; (2) spectrometer. It is mainly to measure the angle of incidence and the angle of refraction, and then obtain the refractive index of the glass brick according to the law of refraction of the glass. The advantages of these two methods are direct measurement, simple measurement instrument and convenient operation. The disadvantage is that the contact measurement, the wear of the test piece, the measurement accuracy is low, and the average refractive index of the optical glass is detected.

The methods of non-contact measurement are: mainly interferometric measurement. Interferometric measurement is to use a Michelson interferometer to measure the interference fringes formed by the reflection of the upper and lower surfaces of the optical glass, and perform image and data processing on the interference fringes to obtain the spatial refractive index distribution of the optical flat glass. The advantage of this method is that the non-contact measurement, the detection is the spatial refractive index distribution, and the measurement accuracy is high. The disadvantage is that due to the limitation of interference conditions, the measurement range is small, and it is generally suitable for the measurement of optical glass materials with small thickness of optical glass and small refractive index change.

There are two main optical detection methods based on diffraction gratings: (1) using a transmissive diffraction grating; (2) using a reflective diffraction grating. These two methods mainly use the spectroscopic properties of the diffraction grating to measure the average refractive index of the liquid, with a large measurement range and a simple measurement method. The disadvantage is that the measurement is the average refractive index of the liquid, and the measurement accuracy is low.

SUMMARY OF THE INVENTION

The present application provides a diffraction grating-based glass plate refractive index uniformity detection device and detection method, which solve the problem of low refractive index detection accuracy for optical glass with large thickness and large refractive index change in the prior art.

In order to achieve the above object, technical scheme of the present invention is as follows:

A glass plate refractive index uniformity detection device based on a diffraction grating includes a wavelength-tunable light source, and a beam expander, a pinhole aperture, a collimating mirror, an adjustable slit and a reflector are sequentially arranged along the optical axis direction of the emitted light from the wavelength-tunable light source. The reflective plane diffraction grating forms an incident angle of 20-45° between the working surface of the reflective plane diffraction grating 6 and the optical axis of the outgoing light, and an optical imaging lens is vertically and sequentially arranged below the reflective plane diffraction grating. and a CCD image acquisition system, the CCD image acquisition system is connected to a computer; a piece to be tested is arranged between the reflective plane diffraction grating and the optical imaging lens.

Further, the focal length of the collimating mirror is equal to the distance from the collimating mirror to the pinhole diaphragm.

Further, the slit width of the adjustable slit can be adjusted in the range of 0-10 mm.

The method for detecting the uniformity of refractive index of glass plate based on diffraction grating includes the following steps:

Step 1: Adjust the position of the beam expander to make the light beam emitted by the adjustable wavelength light source converge to a point, and add a pinhole diaphragm at the convergence point to filter out the stray light, so that the emitted light wave is a spherical wave;

Step 2: Adjust the position of the collimating mirror so that the incident spherical wave becomes a plane light wave after passing through;

Step 3: Adjust the slit width of the adjustable slit so that the plane light wave passes through the slit and emits a suitable linear plane light wave;

Step 4, adjust the reflective plane diffraction grating so that the suitable linear plane light wave is obliquely incident, and the reflected light wave is the diffracted light wave;

Step 5: Adjust the reflective plane diffraction grating to make the +1st order diffracted waves converge through the optical imaging lens, obtain the diffraction pattern A on the image plane of the optical imaging lens, and adjust the CCD image acquisition system to receive the diffraction pattern A;

Step 6: In order to evenly project the +1-order diffracted wave with the wavelength of 400nm-800nm onto the receiving surface of the CCD, select the center wavelength of the adjustable light source at 600nm to calibrate the beam incident angle, and adjust the beam incident angle to make the 600nm wavelength diffracted wave perpendicular. Incident to the CCD receiving surface, as the center coordinate of the CCD receiving;

Step 7, adding the DUT between the reflective plane diffraction grating and the optical imaging lens, obtaining the diffracted light wave B refracted by the DUT on the image plane of the optical imaging lens, and adjusting the CCD image acquisition system to receive the diffraction pattern B;

In step 8, the computer compares and processes the diffraction pattern B and the diffraction pattern A to obtain the spatial distribution information of the refractive index of the test piece.

Beneficial effects of the present invention:

The optical path system of the invention realizes the non-contact measurement of the uniform distribution of the spatial refractive index of the optical glass with large thickness and large refractive index change. It combines the superior spectral performance of the reflective diffraction grating with the data processing technology of the computer, which can not only measure the average refractive index of optical glass, but also measure the uniformity of the spatial refractive index, with high measurement accuracy, wide measurement range, and easy operation. Simple.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the device of the present invention;

Fig. 2 is the measurement light path schematic diagram of diffraction pattern A of the present invention;

Fig. 3 is the measurement light path schematic diagram of diffraction pattern B of the present invention;

In the figure, 1-wavelength tunable light source, 2-beam expander, 3-pinhole diaphragm, 4-collimating mirror, 5-adjustable slit, 6-reflection plane diffraction grating, 7-test piece, 8-optical imaging lens, 9-CCD image acquisition system, 10-computer, 11-plane monochromatic light wave, 12-normal, 13-0th order diffracted beam, 14-+1st order diffracted beam, 15-600mm+1st order Diffracted beam, 16-+1st order diffraction angle, 17-standard glass plate, 18-incidence angle, 19-light without DUT, 20-light with DUT.

Detailed ways

The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. Wherein similar elements in different embodiments have used associated similar element numbers. In the following embodiments, many details are described so that the present application can be better understood. However, those skilled in the art will readily recognize that some of the features may be omitted under different circumstances, or may be replaced by other elements, materials, and methods. In some cases, some operations related to the present application are not shown or described in the specification, in order to avoid the core part of the present application being overwhelmed by excessive descriptions, and for those skilled in the art, these are described in detail. The relevant operations are not necessary, and they can fully understand the relevant operations according to the descriptions in the specification and general technical knowledge in the field.

Referring to Fig. 1, a glass plate refractive index uniformity detection device based on a diffraction grating includes a wavelength-tunable light source 1, and a beam expander 2, a pinhole aperture 3, a collimator, and The mirror 4, the adjustable slit 5 and the reflective plane diffraction grating 6 form an incident angle of 20-45° between the working surface of the reflective plane diffraction grating 6 and the optical axis of the outgoing light. Below the diffraction grating 6, an optical imaging lens 8 and a CCD image acquisition system 9 are arranged vertically in sequence, and the CCD image acquisition system 9 is connected to the computer 10; item 7.

The wavelength adjustable light source 1 is a xenon lamp light source, and the wavelength adjustment range of the xenon lamp light source is 400nm-800nm.

The number of line pairs of the reflective plane diffraction grating 6 is 600/mm, and the aperture is 50 mm×50 mm.

The diameter of the pinhole diaphragm 3 is 1.5 mm.

The focal length of the collimating mirror 4 is equal to the distance from the collimating mirror 4 to the pinhole aperture 3 .

The adjustable slit width of the adjustable slit 5 is 0-10mm, and the slit length is 30mm.

The focal length of the optical imaging lens 8 is 25 mm, the diameter is 30 mm, and the distance between the reflective plane diffraction grating 6 and the optical imaging lens 8 is 100 mm.

The method for detecting the uniformity of refractive index of glass plate based on diffraction grating includes the following steps:

Step 1, the wavelength adjustable light source 1 selects a xenon lamp light source (400nm-800nm), selects a certain wavelength of the adjustable wavelength light source to emit, and the emitted beam enters the beam expander 2, and adjusts the distance along the optical axis of the beam expander 2 to make the wavelength adjustable. The light beam emitted by the light source 1 converges to a point, and a small aperture diaphragm 3 (a diameter of 1.5mm) is added at the convergence point to filter out the stray light, so that the emitted light wave is a spherical light wave;

Step 2, the focal length of the collimating mirror 4 is f, and the distance between the optical axis of the collimating mirror 4 and the aperture diaphragm 3 is adjusted to be f, so that the incident spherical wave passes through the collimating mirror 4 and becomes a plane light wave;

Step 3: Adjustable slit 5 (adjustable range 0-10mm), adjust the slit width of adjustable slit 5 to 1mm, and the slit length to 30mm, so that the plane light wave passes through the slit and then emits the ray plane light wave;

Step 4, reflective plane diffraction grating 6, line logarithm 600/mm, aperture 50mm×50mm, adjust reflective plane diffraction grating 6, make the line plane light wave obliquely incident, the incident angle is α (20°-45°), reflect The light wave is the +1st order diffracted light wave;

Step 5, adjust the diffracted light wave + first-order diffracted wave of the reflective plane diffraction grating 6 to converge through the optical imaging lens 8, the focal length of the optical imaging lens 8 is 25mm, the aperture is 30mm, and the distance between the reflective plane diffraction grating 6 and the optical imaging lens 8 It is 100mm, and the photoelectric fixed focus processing system is used to fix the focus of the image surface behind the optical imaging lens 8, so that a clear diffraction pattern A is obtained on the image surface behind the optical imaging lens 8, and the CCD image acquisition system 9 is used to receive the diffraction pattern A. ;

Step 6, select the light source wavelength of 600nm for calibration; as shown in Figure 2, the selected light source wavelength is 600nm, according to the method of step 5, adjust the +1 order diffraction wave of the reflective plane diffraction grating 6 to irradiate the CCD image acquisition system 9 Receive the diffraction pattern M; because the plane monochromatic light wave 11 is incident on the reflective plane diffraction grating 6, the normal line 12 of the reflective plane diffraction grating 6 is defined, the 0th order diffracted beam 13, and the +1st order diffracted beam 14 are still line beams , the diffraction pattern M is a linear light spot, and the position P1 of the linear light spot is recorded. A standard glass plate 17 with a thickness of 10 mm and a refractive index of K9 is added, and the position P2 of the linear light spot is recorded. The principle used is that when the light beam enters the standard glass plate 17 at the vertical interface, the refraction angle and the incident angle are both 0 degrees, so there is no separation. Adjust the incident angle 18 of the plane light wave obliquely incident on the reflective plane diffraction grating 6 so that the position P1 and the position P2 of the recorded linear light spot are completely coincident. The monochromatic plane light wave with a calibrated wavelength of 600 nm is incident on the reflective plane diffraction grating 6 at the incident angle α, and the +1-order diffracted beam 15 corresponding to the wavelength of 600 mm is perpendicular to the plane monochromatic light wave 11, on the CCD image acquisition system 9 The formed line spot is used as the x coordinate during measurement, the geometric center of the line spot is the origin of the coordinate, and the vertical direction to the line spot is the z coordinate.

Step 7: Add the object to be tested 7 in front of the reflective plane diffraction grating 6 (without contact), obtain the variable diffracted light wave on the image plane of the optical imaging lens 8, and adjust the CCD image acquisition system 9 to receive the diffraction pattern B.

Test principle: As shown in Figure 3, for the optical system calibrated in step 6, the line logarithm of the diffraction grating is 600/mm, and the diffraction grating equation is brought into:

d(sinα±sinθ)=mλ

为入射光波波长，m为衍射级次。Where: α is the incident angle, θ is the diffraction angle,

is the wavelength of the incident light wave, and m is the diffraction order.

The selected diffraction order m is the +1 order, and the incident angle is the incident angle calibrated in step 6. When the wavelength of the tunable wavelength light source 1 changes from the visible light range of 400nm-800nm, the diffraction grating equation can be substituted to calculate the +1 order diffraction angle. The range is 14°-29°, and the divergence angle is 15°. If the distance from the diffraction grating 6 to the optical lens 9 is 100mm, the focal length of the optical lens is 25mm, and the general aperture is 30mm (larger than the projected spot size). According to the knowledge of geometric optics, the position of the image plane and the magnification β of the optical lens can be calculated.

As shown in Figure 3, from the formula of the law of refraction:

n ₁ sinθ ₁ =n ₂ sinθ ₂

Where: n ₁ is the refractive index of the incident medium, n ₂ is the refractive index of the refracting medium, θ ₁ is the incident angle, and θ ₂ is the refraction angle.

It can be seen that the refraction angle of adding the DUT 7 is smaller than the angle without the DUT 7. As shown in Figure 3, the light 19 without the DUT 7 and the light 20 adding the DUT 7 are separated to a certain extent. The distance d, the distance d can be collected and calculated by the CCD image acquisition system 9. If the thickness h of the DUT 7 is known, the incident angle θ ₁ is formed through the geometric relationship formed by the law of refraction and the law of linear propagation of the light beam to establish the refraction of the DUT. Mathematical model of rate n and related parameters:

Wherein: n is the refractive index of the DUT 7, θ ₁ is the incident angle, h is the thickness of the DUT, and d is the distance between the light 19 without the DUT and the light 20 with the DUT.

Mathematical model of the refractive index change Δn of the test piece and related parameters:

Wherein: n is the refractive index of the DUT, _θ1 is the incident angle, h is the thickness of the DUT, and Δd is the change in the distance between the light 19 without the DUT 7 and the light 20 with the DUT 7 added.

Step 8, if the magnification of the CCD front optical lens is β, calculate the distance d that separates the light 19 without the object to be tested and the light 20 with the object to be tested from the diffraction pattern B and the diffraction pattern A collected by the CCD image acquisition system 9. ' and the change in distance Δd', then the actual parameters:

According to the mathematical model established in step 7, and the measured parameters d' and Δd', calculate the average value n and variation Δn of the refractive index of the DUT.

Step 9, adjust the wavelength of the wavelength-tunable light source 1 to change it from 400nm to 800nm, take the wavelength difference of 5nm as a step, scan and collect more than 7 pairs of diffraction patterns A without adding the DUT, and add more than 7 DUTs. The secondary diffraction patterns B are stored separately, processed by the established model and the written software, and the spatial refractive index distribution information of the DUT is obtained by calculation.

The above specific examples are used to illustrate the present invention, which are only used to help understand the present invention, and are not intended to limit the present invention. For those skilled in the art to which the present invention pertains, according to the idea of the present invention, several simple deductions, modifications or substitutions can also be made.

Claims (1)

1. The method for detecting the uniformity of the refractive index of the glass plate based on the diffraction grating is characterized by comprising the following steps of:

step 1, adjusting the position of a beam expander to converge light beams emitted by a light source with adjustable wavelength to one point, adding a pinhole diaphragm at the convergence point, filtering stray light and enabling the emitted light waves to be spherical waves;

step 2, adjusting the position of the collimating mirror to enable incident spherical waves to become planar light waves after passing through;

step 3, adjusting the width of the adjustable slit to enable the planar light waves to pass through the slit and then emit appropriate linear planar light waves;

step 4, adjusting the reflective plane diffraction grating to enable the appropriate linear plane light waves to be incident obliquely, wherein the reflected light waves are diffraction light waves;

step 5, adjusting the reflective plane diffraction grating to enable + 1-order diffraction waves to be converged through the optical imaging lens, obtaining a diffraction pattern A on an image plane of the optical imaging lens, and adjusting the CCD image acquisition system to receive the diffraction pattern A;

step 6, in order to uniformly project + 1-order diffraction waves with the wavelength of 400nm-800nm onto a receiving surface of the CCD, selecting the central wavelength of 600nm of an adjustable light source to calibrate a light beam incident angle, and adjusting the light beam incident angle to enable the diffraction waves with the wavelength of 600nm to vertically incident on the receiving surface of the CCD to serve as a central coordinate received by the CCD;

step 7, adding a to-be-detected piece between the reflective plane diffraction grating and the optical imaging lens, obtaining diffracted light waves B refracted by the to-be-detected piece on an image plane of the optical imaging lens, and adjusting the CCD image acquisition system to receive the diffraction pattern B;

step 8, comparing the diffraction pattern B with the diffraction pattern A by the computer to obtain the spatial distribution information of the refractive index of the to-be-detected piece;

the detection device adopted by the detection method comprises a wavelength-adjustable light source (1), wherein a beam expander (2), a pinhole diaphragm (3), a collimating lens (4), an adjustable slit (5) and a reflective planar diffraction grating (6) are sequentially arranged along the optical axis direction of emergent light of the wavelength-adjustable light source (1), an incident included angle of 20-45 degrees is formed between the working surface of the reflective planar diffraction grating (6) and the optical axis of the emergent light, an optical imaging lens (8) and a CCD image acquisition system (9) are vertically and sequentially arranged below the reflective planar diffraction grating (6), and the CCD image acquisition system (9) is connected with a computer (10); a to-be-detected piece (7) is arranged between the reflection type plane diffraction grating (6) and the optical imaging lens (8);

the focal length of the collimating mirror (4) is equal to the distance from the collimating mirror (4) to the pinhole diaphragm (3);

the adjustable range of the slit width of the adjustable slit (5) is 0-10 mm.

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