CN105352915B - A kind of dynamic measurement method of refractive index Two dimensional Distribution - Google Patents

A kind of dynamic measurement method of refractive index Two dimensional Distribution Download PDF

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CN105352915B
CN105352915B CN201510697450.5A CN201510697450A CN105352915B CN 105352915 B CN105352915 B CN 105352915B CN 201510697450 A CN201510697450 A CN 201510697450A CN 105352915 B CN105352915 B CN 105352915B
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distribution
light wave
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prism
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赵建林
张继巍
邸江磊
席特立
马超杰
李颖
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Northwestern Polytechnical University
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
    • G01N21/453—Holographic interferometry

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Abstract

本发明涉及一种折射率二维分布的动态测量方法，结合了数字全息干涉术与全内反射。全内反射过程中反射光相移的大小与入射光的入射角度和全内反射棱镜界面两侧介质的折射率有关，利用二次曝光数字全息干涉术动态测量全内反射棱镜斜边表面放置被测样品前后反射光的相移差值，根据反射光相移差值与空气和样品折射率的关系，可以直接计算得到样品的二维折射率动态分布。该方法只需要样品的折射率可以确保入射光在全内反射棱镜界面发生全内反射即可，所以可以实现大范围的折射率分布测量。

The invention relates to a dynamic measurement method for two-dimensional distribution of refractive index, which combines digital holographic interferometry and total internal reflection. The phase shift of the reflected light in the process of total internal reflection is related to the incident angle of the incident light and the refractive index of the media on both sides of the interface of the total internal reflection prism. The second exposure digital holographic interferometry is used to dynamically measure the hypotenuse surface of the total internal reflection prism. The phase shift difference of the reflected light before and after the sample is measured, and according to the relationship between the phase shift difference of the reflected light and the refractive index of air and the sample, the two-dimensional refractive index dynamic distribution of the sample can be directly calculated. This method only needs the refractive index of the sample to ensure that the total internal reflection of the incident light occurs at the interface of the total internal reflection prism, so a wide range of refractive index distribution measurement can be realized.

Description

Dynamic measurement method for refractive index two-dimensional distribution
Technical Field
The invention relates to a dynamic measurement method for refractive index two-dimensional distribution, in particular to a method for dynamically measuring the refractive index two-dimensional distribution by utilizing the phase shift characteristic of reflected light during total internal reflection and combining digital holographic interferometry.
Background
The refractive index is an important optical parameter, and the accurate measurement of the refractive index is very important in the fields of material analysis, biochemical sensing, optical element parameter design and the like. At present, methods for measuring refractive index include a natural collimation method, a minimum deviation angle method, and the like, which are based on the laws of refraction and reflection. The conventional refractive index measuring instrument is a refractometer, but it needs to be corrected in advance. In recent years, various refractive index sensors based on special optical fiber devices have been widely used with the advantages of high sensitivity and high measurement accuracy, but the measurement range thereof is small and a complicated manufacturing process is required. In addition, both refractometers and fiber optic refractive index sensors can only measure the refractive index of homogeneous materials. However, in practical situations, the measurement object is often non-uniform, and the existing method is difficult to effectively measure the refractive index distribution, especially the dynamic refractive index distribution of some measurement objects in chemical and physical processes. A method (y.chu, et al, "Full-field reactive index measurement with a single layer output-shift interferometry," Optik 125(13),3307-3310 (2014)) capable of realizing dynamic measurement of a large-range two-dimensional refractive index distribution has also been proposed, but this method requires a complicated optical path structure and a cumbersome data processing method, which brings great inconvenience to practical application.
Disclosure of Invention
Technical problem to be solved
In order to avoid the defects of the prior art, the invention provides a dynamic measurement method of refractive index two-dimensional distribution, which utilizes the phase shift characteristic of reflected light during total internal reflection and combines digital holographic interferometry to dynamically measure the two-dimensional distribution of the refractive index, the related optical path has a simple structure, and the subsequent data processing method is simple and convenient.
Technical scheme
A dynamic measurement method for refractive index two-dimensional distribution is characterized by comprising the following steps:
step 1: dividing parallel light with horizontal polarization or vertical polarization into two beams, wherein one beam of parallel light enters from one right-angle side of a right-angle prism, then is subjected to total internal reflection at the interface between the hypotenuse of the prism and air at an incident angle theta, and then is emitted from the other right-angle side to reach the target surface of an image acquisition device as an object light wave;
the other beam of parallel light as reference light wave meets and interferes with the object light wave on the target surface of the image acquisition device, and the reference digital hologram H is obtained by recording the reference light wave by the image acquisition device0；
Step 2: placing the sample to be measured in the reflection region of object light wave on the surface of the hypotenuse of the right-angle prism, and continuously recording to obtain N digital holograms Hi，i＝1,2,3…N；
And step 3: simulating the diffraction propagation process of light wave by using computer numerical value according to kirchhoff diffraction theory to obtain the hologram H0And HiRespectively carrying out numerical reconstruction to obtain complex amplitude distribution of original object light wave, and further carrying out self-HiPhase distribution and self-H of reconstructed object light wave0The phase distributions of the reconstructed object light waves are respectively subtracted, and the phase difference distribution delta phi of the object light waves after the sample is placed is calculatedo(x,y)；
And 4, step 4: because the refractive index distribution of the sample on the surface of the hypotenuse of the prism is different, the reflected light wave generates additional phase shift difference, the phase difference distribution of the object light wave obtained in the step 3 is equal to the additional phase shift difference distribution of the reflected light, and the two-dimensional refractive index distribution of the sample is obtained according to the relationship between the additional phase shift difference distribution of the reflected light and the refractive index distribution of the sample:
when using horizontally polarized parallel light, the additional phase shift difference produced by the reflected light waves is:
when using vertically polarized parallel light, the additional phase shift difference produced by the reflected light waves is:
wherein: n is1Is the refractive index of the prism, n2And (x, y) is the refractive index distribution of the sample to be measured.
Advantageous effects
According to the dynamic measurement method for the refractive index two-dimensional distribution, when a beam of parallel light is subjected to total internal reflection on the surface of a prism, additional phase shift (namely phase change) can be generated in reflected light, and the phase shift value is largeSmall angle of incidence theta and refractive index (n) of the medium on both sides of the prism interface1,n2) In relation to the angle of incidence θ and the prism refractive index n1When determining, utilizing secondary exposure digital holographic interferometry to measure and obtain additional phase shift difference distribution of prism-air and prism-sample interface reflected light, and according to the relationship of said additional phase shift difference distribution and sample and air refractive index obtaining two-dimensional refractive index distribution of sample.
The dynamic measurement method for the two-dimensional distribution of the refractive index provided by the invention utilizes the advantages of digital holographic interferometry such as high speed, high precision and full-field dynamic measurement to introduce the total internal reflection prism into a measurement light path, so that the two-dimensional distribution of the refractive index can be dynamically measured. The whole set of the related measuring system has a simple structure and a simple and convenient subsequent data processing method. Because the air refractive index is known, the refractive index distribution of the measured sample can be directly calculated by the measured reflected light additional phase shift differential distribution, and the defect that the refractive index distribution of the measured sample needs to be initially distributed by separately utilizing digital holographic interferometry to measure the refractive index distribution is overcome. The refractive index of the tested sample can ensure that the incident light meets the total internal reflection at the interface of the total internal reflection prism, so the method can realize the measurement of the refractive index in a large range.
Drawings
FIG. 1: is a light path diagram for dynamically measuring two-dimensional refractive index distribution;
FIG. 2: the two-dimensional refractive index profile at 9.2s during the mixing of the liquids was measured in the examples;
in the figure: the optical fiber laser comprises a 1-semiconductor pump solid laser, a 2-optical fiber coupler, a 3-first optical fiber, a 4-optical fiber beam splitter, a 5-second optical fiber, a 6-third optical fiber, a 7-first collimating lens, a 8-second collimating lens, a 9-first half wave plate, a 10-second half wave plate, an 11-right-angle prism, a 12-reflector, a 13-beam splitter prism, a 14-image acquisition device and a 15-sample.
Detailed Description
The invention will now be further described with reference to the following examples and drawings:
example (b): the optical path of the dynamic measurement method for refractive index two-dimensional distribution designed by the invention is shown in fig. 1, and comprises the following steps: the optical fiber laser comprises a semiconductor pump solid laser 1, an optical fiber coupler 2, a first optical fiber 3, an optical fiber beam splitter 4, a second optical fiber 5, a third optical fiber 6, a first collimating lens 7, a second collimating lens 8, a first half-wave plate 9, a second half-wave plate 10, a right-angle prism 11, a reflector 12, a beam splitter prism 13, an image acquisition device 14 and a sample 15.
The work flow of the dynamic measurement method of the refractive index two-dimensional distribution is as follows:
step 1: a beam of parallel light with horizontal or vertical polarization enters from one right-angle side of the right-angle prism, then is totally internally reflected at the interface between the hypotenuse of the prism and the air at an incident angle theta, and then is emitted from the other right-angle side to be used as an object light wave to reach the target surface of the image acquisition device;
step 2: the other beam of parallel light with the same polarization direction from the same laser is used as a reference light wave to meet and interfere with the object light wave on the target surface of the image acquisition device, and the reference digital hologram H is recorded by the image acquisition device0；
And step 3: the sample to be measured is placed in the reflecting area of object light wave tightly attached to the surface of the hypotenuse of the right-angle prism, and the reflected light wave generates additional phase shift difference distribution due to different refractive index distributions of the sample on the surface of the hypotenuse of the prism, the size and the incident angle theta of the additional phase shift difference distribution and the refractive index n of media on two sides of the prism interface1And n2The following steps are involved:
(1) if the original light wave is polarized in the horizontal direction, when the original light wave is totally internally reflected, the polarization plane is perpendicular to the incident plane and can be recorded as s-polarization, and the additional phase shift difference distribution at this time is
(2) If the original light wave is polarized in the vertical direction, when the original light wave is totally internally reflected, the polarization plane is parallel to the incident plane and can be recorded as p-polarization, and the additional phase shift difference distribution at this time is
And 4, step 4: the additional phase-shift difference distribution generated by the reflected light wave will make the object light wave carry the corresponding phase difference distribution delta phio(x, y) reflecting the information of the two-dimensional refractive index distribution of the sample, keeping the reference light wave unchanged, and continuously shooting N digital holograms H in the process of changing the refractive index of the samplei(i＝1,2,3…N)；
And 5: simulating the diffraction propagation process of light wave by using computer numerical value according to kirchhoff diffraction theory to obtain the hologram H0And HiRespectively carrying out numerical reconstruction to obtain complex amplitude distribution of original object light wave, and further carrying out self-HiPhase distribution and self-H of reconstructed object light wave0The phase distributions of the reconstructed object light waves are respectively subtracted, and the phase difference distribution delta phi of the object light waves after the sample is placed is calculatedo(x,y)；
Step 6: because the phase difference distribution of the object light wave is equal to the additional phase shift difference distribution of the reflected light, the two-dimensional refractive index distribution of the sample is finally obtained according to the relationship between the additional phase shift difference distribution of the reflected light and the refractive index distribution of the sample:
(1) if the original light wave is polarized in the horizontal direction, n2Is expressed as
Wherein,
(2) if the original light wave is polarized in the vertical direction, then n2Is expressed as
Wherein,
the specific embodiment is as follows:
linearly polarized light emitted by a semiconductor pump solid laser 1 (with the wavelength of 532nm) is coupled into a first optical fiber 3 through an optical fiber coupler 2, and an optical fiber beam splitter 4 is arranged at the tail end of the first optical fiber 3 and can divide a light beam into a first light beam and a second light beam; the first light beam is converted into parallel light with horizontal polarization after passing through the first collimating lens 7 and the first half-wave plate 9, and the parallel light is incident to a right-angle prism 11(K9 glass, n) as object light wave at 45 DEG11.5195) and total internal reflection (θ 72.7332 °) occurs at the center of its hypotenuse surface, and then reflected by the mirror 12 to the beam splitter prism 13, and the hypotenuse surface of the right angle prism 11 is directed upward in the horizontal direction and adjusted to a certain height to ensure that the outgoing light beam is coaxial with the incoming light beam; the second light beam is converted into parallel light of horizontal polarization as a reference light wave after passing through a second collimating lens 8 and a second half-wave plate 10; the object reference light waves are combined by the beam splitter prism 13 and then interfered on a target surface of an image acquisition device 14 (the number of pixels: 1280H is multiplied by 960V, the pixel size: 4.4 mu m) at a certain included angle to form an off-axis digital hologram.
Before a sample is placed on the hypotenuse surface of the right-angle prism 11, a hologram is photographed as a reference numeral hologram H0(ii) a Abutting right-angle prism 11After 75% of glycerin-water mixed solution and water are sequentially placed in the center of the surface of the bevel edge, 112 frames of images reflecting the two-dimensional refractive index distribution n of the sample are continuously shot at a frame frequency of 7.5fps immediately2(x, y) dynamically varying series of holograms Hi(i ═ 1,2,3 … 112); respectively carrying out numerical reconstruction on the shot digital holograms by utilizing a digital holographic numerical reconstruction algorithm and a phase subtraction method to obtain a series of phase difference distributions delta phi of the object light waves in the dynamic change process of the sampleoi(x, y); and finally obtaining the dynamic change of the two-dimensional refractive index distribution of the measured sample according to the relation (expression (3)) between the object light wave phase difference distribution and the reflected light additional phase shift difference distribution and the refractive index distribution of the sample.
The method combines digital holographic interferometry with total internal reflection. The phase shift of the reflected light in the total internal reflection process is related to the incident angle of the incident light and the refractive indexes of media on two sides of the interface of the total internal reflection prism, the phase shift difference of the reflected light before and after the sample to be measured is placed on the hypotenuse surface of the total internal reflection prism is dynamically measured by utilizing the secondary exposure digital holographic interferometry, and the two-dimensional refractive index dynamic distribution of the sample can be directly calculated according to the relationship between the phase shift difference of the reflected light and the refractive indexes of air and. The method only needs the refractive index of the sample to ensure that the incident light is totally internally reflected at the interface of the total internal reflection prism, so that the measurement of the refractive index distribution in a large range can be realized.

Claims (1)

1.一种折射率二维分布的动态测量方法，其特征在于步骤如下：1. A dynamic measurement method of two-dimensional distribution of refractive index, characterized in that the steps are as follows: 步骤1：将竖直偏振的平行光分为两束，其中一束平行光从直角棱镜的一个直角边入射，进而以入射角θ在棱镜斜边与空气界面处发生全内反射，然后从另一直角边出射后作为物光波到达图像采集器件靶面；Step 1: Divide the vertically polarized parallel light into two beams, one of which is incident from one right-angled side of the right-angle prism, and then undergoes total internal reflection at the interface between the hypotenuse of the prism and the air at an incident angle θ, and then passes through the other After exiting from the right-angle side, it reaches the target surface of the image acquisition device as the object light wave; 另一束平行光作为参考光波与上述物光波在图像采集器件靶面上相遇并发生干涉，并由图像采集器件记录得到参考数字全息图H0；Another beam of parallel light as a reference light wave meets and interferes with the object light wave on the target surface of the image acquisition device, and is recorded by the image acquisition device to obtain a reference digital hologram H 0 ; 步骤2：将待测样品置于直角棱镜斜边表面物光波的反射区域内，继续记录得到N幅数字全息图Hi，i＝1,2,3…N；Step 2: Place the sample to be tested in the reflection area of the object light wave on the surface of the hypotenuse of the rectangular prism, and continue recording to obtain N digital holograms H i , i=1, 2, 3...N; 步骤3：根据基尔霍夫衍射理论，利用计算机数值模拟光波的衍射传播过程，对全息图H0和Hi分别进行数值重建，获得原物光波的复振幅分布，进一步将自Hi重建的物光波的相位分布与自H0重建的物光波的相位分布分别作差，计算得到放置样品后物光波的相位差分布Δφo(x,y)；Step 3: According to Kirchhoff's diffraction theory, use the computer to simulate the diffraction propagation process of light waves numerically, and reconstruct the holograms H 0 and H i respectively to obtain the complex amplitude distribution of the original light wave, and further reconstruct the holograms H 0 and H i The phase distribution of the object light wave is different from the phase distribution of the object light wave reconstructed from H 0 , and the phase difference distribution of the object light wave after placing the sample is calculated Δφ o (x, y); 步骤4：由于棱镜斜边表面样品折射率分布的不同，反射光波将产生附加相移差，且步骤3得到的物光波相位差分布与该反射光波附加相移差分布相等，根据反射光波附加相移差分布与样品折射率分布的关系，得到样品的二维折射率分布：Step 4: Due to the difference in the refractive index distribution of samples on the hypotenuse surface of the prism, the reflected light wave will produce an additional phase shift difference, and the phase difference distribution of the object light wave obtained in step 3 is equal to the additional phase shift difference distribution of the reflected light wave. According to the additional phase shift difference distribution of the reflected light wave The relationship between the shift distribution and the refractive index distribution of the sample is obtained to obtain the two-dimensional refractive index distribution of the sample: 当采用竖直偏振平行光时，反射光波产生的附加相移差为：When vertically polarized parallel light is used, the additional phase shift difference generated by the reflected light wave is: 以计算得到放置样品后物光波的相位差分布Δφo(x,y)取代上述公式的Δφp(x,y)，得到样品的二维折射率分布其中：Replace the Δφ p (x, y) of the above formula with the calculated phase difference distribution of the object light wave after placing the sample Δφ o (x, y), and obtain the two-dimensional refractive index distribution of the sample in: 其中：n1为棱镜的折射率，n2(x,y)为待测样品的折射率分布。Where: n 1 is the refractive index of the prism, and n 2 (x, y) is the refractive index distribution of the sample to be measured.
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CN111025876B (en) * 2019-11-08 2021-09-28 桂林电子科技大学 Transmission type phase microscopic imaging measurement system based on piezoelectric ceramics
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