CN105352915A - Refractive index two-dimensional distribution dynamic measurement method - Google Patents

Abstract

The invention relates to a refractive index two-dimensional distribution dynamic measurement method, which combines a digital holographic interferometry and total internal reflection. Phase shift magnitude of reflected light in a total internal reflection process is relative to an incident angle of the incident light and refractive index of mediums at two sides of a total internal reflection prism interface, a double-exposure digital holographic interferometry is used for dynamic measurement of a phase shift difference value of reflected light before and after a sample to-be-detected is placed on a total internal reflection hypotenuse surface, and the two-dimensional refractive index dynamic distribution of the sample can be calculated directly according to a relation of the reflected light phase shift difference value and the refractive index of air and the sample. The method is characterized in that the refractive index of the sample can ensure that incident light generates total internal reflection in the total internal reflection prism interface, so that large scope refractive index distribution measurement can be realized.

Description

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

Technical field

The present invention relates to a kind of dynamic measurement method of refractive index Two dimensional Distribution, particularly relate to a kind of phase-shift characterisitc of reflected light when utilizing total internal reflection and carry out the method for kinetic measurement refractive index Two dimensional Distribution in conjunction with digital holographic interferometry.

Background technology

Refractive index, as a kind of important optical parametric, is accurately measured extremely important in fields such as material analysis, biochemical sensitive, optical component parameter designs to it.At present, the method for measuring refractive index has nature to collimate method, the method for minimum deviation angle etc., and these methods are all based upon on the basis of refraction and reflection law.Traditional refractometry instrument is refractometer, but it needs to correct in advance.In recent years, the multiple index sensor based on special fiber device is widely used with the advantage of its high sensitivity and high measurement accuracy, but its measurement range is less and need complicated manufacture craft.In addition, refractometer and optic fibre refractive index sensor all can only measure the refractive index of homogeneous material.But the measuring object under practical situation is heterogeneous often, existing method is difficult to its index distribution, especially some is in the dynamic index distribution of the measuring object in chemistry, physical process, effectively measures.Also someone proposes a kind of method (Y.Chu that can realize refractive index Two dimensional Distribution kinetic measurement on a large scale, etal. " Full-fieldrefractiveindexmeasurementwithsimultaneousphas e-shiftinterferometry; " Optik125 (13), 3307-3310 (2014) .), but this method needs complicated light channel structure and loaded down with trivial details data processing method, brings very big inconvenience to practical application.

Summary of the invention

The technical matters solved

In order to avoid the deficiencies in the prior art part, the present invention proposes a kind of dynamic measurement method of refractive index Two dimensional Distribution, utilize reflected light during total internal reflection phase-shift characterisitc and in conjunction with digital holographic interferometry, carry out the Two dimensional Distribution of kinetic measurement refractive index, involved light channel structure is simple, and follow-up data disposal route is easy.

Technical scheme

A dynamic measurement method for refractive index Two dimensional Distribution, is characterized in that step is as follows:

Step 1: the directional light of horizontal polarization or vertical polarization is divided into two bundles, wherein a branch of directional light is from a right-angle side incidence of right-angle prism, and then with incidence angle θ in prism hypotenuse and Air Interface place experiences total internal reflection, then after another right-angle side outgoing, arrive image acquisition device target surface as Object light wave;

Another bundle directional light meets as with reference to light wave and above-mentioned Object light wave and interferes on image acquisition device target surface, and obtains reference number hologram H by image acquisition device record ₀;

Step 2: be placed in by testing sample in the reflector space of right-angle prism hypotenuse surface Object light wave, continues record and obtains N width digital hologram H _i, i=1,2,3 ... N;

Step 3: according to Kirchhoff's diffraction theory, utilizes the diffraction propagation process of Computer Numerical Simulation light wave, to hologram H ₀and H _icarry out numerical reconstruction respectively, obtain the COMPLEX AMPLITUDE of original light wave, further will from H _irebuild Object light wave PHASE DISTRIBUTION with from H ₀the PHASE DISTRIBUTION of Object light wave of rebuilding is poor respectively, calculates the phase distribution Δ φ of Object light wave after placement sample _o(x, y);

Step 4: due to the difference of prism hypotenuse surface sample index distribution, it is poor that reflecting light will produce additional phase shift, and the Object light wave phase distribution that step 3 obtains is equal with this reflected light additional phase shift difference cloth, according to the relation of reflected light additional phase shift difference cloth and sample index distribution, obtain the two-dimentional index distribution of sample:

When adopting horizontal polarization directional light, the additional phase shift difference that reflecting light produces is:

With the phase distribution Δ φ of Object light wave after the placement sample calculated _o(x, y) replaces the Δ φ of above-mentioned formula _s(x, y), obtains the two-dimentional index distribution of sample $n_2(x,y)=n_1\sqrt{{\sin }^2\mathrm{\θ}-{\cos }^2{\mathrm{\θtan}}^2\mathrm{\Γ}},$ Wherein:

$\mathrm{\Γ}=arctan\frac{\sqrt{n_1^2{\sin }^2\mathrm{\θ}-1}}{n_1\cos \mathrm{\θ}}-\frac{{\mathrm{\Δ\φ}}_o(x,y)}{2};$

When adopting vertical polarization parallel light, the additional phase shift difference that reflecting light produces is:

To calculate the phase distribution Δ φ placing Object light wave after sample _o(x, y) replaces the Δ φ of above-mentioned formula _p(x, y), obtains the two-dimentional index distribution of sample $n_2(x,y)=\frac{n_1}{\tan \mathrm{\Λ}cos\mathrm{\θ}}\sqrt{\frac{\sqrt{1+{\tan }^2{\mathrm{\Λsin}}^{2}2\mathrm{\θ}}-1}{2}},$ Wherein:

$\mathrm{\Λ}=\arctan \frac{n_1\sqrt{n_1^2{\sin }^2\mathrm{\θ}-1}}{\cos \mathrm{\θ}}-\frac{{\mathrm{\Δ\φ}}_o(x,y)}{2}$

Wherein: n ₁for the refractive index of prism, n ₂the index distribution that (x, y) is testing sample.

Beneficial effect

The dynamic measurement method of a kind of refractive index Two dimensional Distribution that the present invention proposes, a branch of directional light is when prism surface experiences total internal reflection, reflected light can produce additional phase shift (i.e. phase place change), the size of phase-shift value and the refractive index (n of incident angle θ and prism boundary media of both sides ₁, n ₂) relevant, as incidence angle θ and Refractive Index of Glass Prism n ₁when determining, the measurement of re-expose digital holographic interferometry is utilized to obtain the additional phase shift difference cloth of prism-air and prism-example interface reflected light, according to the relation of this additional phase shift difference cloth and sample and air refraction, the two-dimentional index distribution of sample can be obtained.

A kind of dynamic measurement method of refractive index Two dimensional Distribution that the present invention proposes, utilize digital holographic interferometry fast, the advantage of high precision and whole audience kinetic measurement, total internal reflection prism is incorporated into optical path, can the Two dimensional Distribution of kinetic measurement refractive index.Involved a whole set of simple in measurement system structure, follow-up data disposal route are easy.Because air refraction is known, the index distribution of sample directly can be calculated by measured reflected light additional phase shift difference cloth, overcomes the shortcoming utilizing separately digital holographic interferometry refractive Index Distribution Measurement to need sample refractive index initial distribution.The refractive index of sample makes incident light meet total internal reflection at total internal reflection prism interface, and therefore the method can realize the measurement of refractive index on a large scale.

Accompanying drawing explanation

Fig. 1: the index path being kinetic measurement of the present invention two dimension index distribution;

Fig. 2: be the two-dimentional refractive index profile measured in embodiment in liquid mixed process when 9.2s;

In figure: 1-diode pumped solid state laser, 2-fiber coupler, 3-first optical fiber, 4-fiber optic splitter, 5-second optical fiber, 6-the 3rd optical fiber, 7-first collimation lens, 8-second collimation lens, 9-first half-wave plate, 10-second half-wave plate, 11-right-angle prism, 12-catoptron, 13-Amici prism, 14-image acquisition device, 15-sample.

Embodiment

Now in conjunction with the embodiments, the invention will be further described for accompanying drawing:

Embodiment: the light path of the dynamic measurement method of a kind of refractive index Two dimensional Distribution of the present invention's design as shown in Figure 1, comprising: diode pumped solid state laser 1, fiber coupler 2, first optical fiber 3, fiber optic splitter 4, the second optical fiber 5,3rd optical fiber 6, first collimation lens 7, second collimation lens 8, first half-wave plate 9, second half-wave plate 10, right-angle prism 11, catoptron 12, Amici prism 13, image acquisition device 14, sample 15.

The workflow of the dynamic measurement method of refractive index Two dimensional Distribution is as follows:

Step 1: the directional light of a branch of horizontal or vertical polarization is from a right-angle side incidence of right-angle prism, and then with incidence angle θ in prism hypotenuse and Air Interface place experiences total internal reflection, then after another right-angle side outgoing, arrive image acquisition device target surface as Object light wave;

Step 2: another harness from same laser instrument has the directional light of identical polarization direction meet on image acquisition device target surface as with reference to light wave and above-mentioned Object light wave and interfere, and obtains reference number hologram H by image acquisition device record ₀;

Step 3: the reflector space being close to right-angle prism hypotenuse surface Object light wave places testing sample, due to the difference of prism hypotenuse surface sample index distribution, reflecting light will produce additional phase shift difference cloth, the refractive index n of its size and incidence angle θ and prism boundary media of both sides ₁and n ₂relevant:

(1) if original light wave polarization in the horizontal direction, then it is when experiences total internal reflection, and plane of polarization, perpendicular to the plane of incidence, can be designated as s polarization, and additional phase shift difference is now distributed as

(2) if original light wave vertically polarization, then it is when experiences total internal reflection, and plane of polarization is parallel to the plane of incidence, can be designated as p polarization, and additional phase shift difference is now distributed as

Step 4: the additional phase shift difference cloth that above-mentioned reflecting light produces will make Object light wave carry corresponding phase distribution Δ φ _o(x, y), this phase distribution reflects the information of sample two dimension index distribution, keeps reference light wave constant, takes N width digital hologram H in sample variations in refractive index process continuously _i(i=1,2,3 ... N);

Step 5: according to Kirchhoff's diffraction theory, utilizes the diffraction propagation process of Computer Numerical Simulation light wave, to hologram H ₀and H _icarry out numerical reconstruction respectively, obtain the COMPLEX AMPLITUDE of original light wave, further will from H _irebuild Object light wave PHASE DISTRIBUTION with from H ₀the PHASE DISTRIBUTION of Object light wave of rebuilding is poor respectively, calculates the phase distribution Δ φ of Object light wave after placement sample _o(x, y);

Step 6: because the phase distribution of Object light wave is equal with the additional phase shift difference cloth of reflected light, according to the relation of reflected light additional phase shift difference cloth and sample index distribution, finally obtains the two-dimentional index distribution of sample:

(1) if original light wave polarization in the horizontal direction, then n ₂expression formula be

$n_2(x,y)=n_1\sqrt{{\sin }^2\mathrm{\θ}-{\cos }^2{\mathrm{\θtan}}^2\mathrm{\Γ}},---\left(3\right)$

Wherein,

$\mathrm{\Γ}=arctan\frac{\sqrt{n_1^2{\sin }^2\mathrm{\θ}-1}}{n_1\cos \mathrm{\θ}}-\frac{{\mathrm{\Δ\φ}}_o(x,y)}{2};$

(2) if original light wave vertically polarization, then n ₂expression formula be

$n_2(x,y)=\frac{n_1}{\tan \mathrm{\Λ}cos\mathrm{\θ}}\sqrt{\frac{\sqrt{1+{\tan }^2{\mathrm{\Λsin}}^{2}2\mathrm{\θ}}-1}{2}},---\left(4\right)$

Wherein,

$\mathrm{\Λ}=arctan\frac{n_1\sqrt{n_1^2{\sin }^2\mathrm{\θ}-1}}{\cos \mathrm{\θ}}-\frac{{\mathrm{\Δ\φ}}_o(x,y)}{2}.$

Specific embodiment:

The linearly polarized light that diode pumped solid state laser 1 (wavelength is 532nm) sends is coupled into the first optical fiber 3 through fiber coupler 2, and fiber optic splitter 4 is arranged on the end of the first optical fiber 3, and light beam can be divided into the first light beam and the second light beam by it; Wherein the first light beam becomes the directional light of horizontal polarization after the first collimation lens 7, first half-wave plate 9, and it incides right-angle prism 11 (K9 glass, n as Object light wave with 45 ° ₁=1.5195) in a right-angle surface and in its hypotenuse surface center experiences total internal reflection (θ=72.7332 °), reflected by catoptron 12 afterwards and arrive Amici prism 13, the hypotenuse surface of right-angle prism 11 in the horizontal direction upwards and be adjusted to certain altitude with ensure outgoing beam and incident beam coaxial; Second light beam becomes the directional light of horizontal polarization as reference light wave after the second collimation lens 8, second half-wave plate 10; Thing ginseng light wave is split after prism 13 merges and on image acquisition device 14 (pixel count: 1280H × 960V, Pixel Dimensions: 4.4 μm) target surface, interferes formation off-axis digital holography figure with certain angle.

Before the hypotenuse surface of right-angle prism 11 places sample, taking a width hologram is reference number hologram H ₀; After the hypotenuse surface center being close to right-angle prism 11 places 75% glycerine-water mixed liquid and water successively, take 112 width reflection sample two dimension index distribution n continuously with the frame frequency of 7.5fps immediately ₂the serial hologram H of (x, y) dynamic change _i(i=1,2,3 ... 112); Utilize digital hologram numerical reconstruction algorithm and phase place subtractive method to carry out numerical reconstruction respectively to captured digital hologram, obtain the series of phase difference cloth Δ φ of Object light wave in sample dynamic changing process _oi(x, y); According to the relation (formula (3)) of Object light wave phase distribution and reflected light additional phase shift difference cloth, reflected light additional phase shift difference cloth and sample index distribution, finally obtain the dynamic change of sample two dimension index distribution.

This method combines digital holographic interferometry and total internal reflection.In total internal reflection process, the size of reflected light phase shift is relevant with the refractive index of the incident angle of incident light and total internal reflection prism interface media of both sides, re-expose digital holographic interferometry kinetic measurement total internal reflection prism hypotenuse surface is utilized to place the phase shift difference of reflected light before and after sample, according to the relation of reflected light phase shift difference and air and sample refractive index, the two-dimentional refractive index DYNAMIC DISTRIBUTION of sample directly can be calculated.The method only needs the refractive index of sample to guarantee, and incident light is in total internal reflection prism interface experiences total internal reflection, so can realize large-scale profile measurement.

Claims (1)

1. a dynamic measurement method for refractive index Two dimensional Distribution, is characterized in that step is as follows:

Step 1: the directional light of horizontal polarization or vertical polarization is divided into two bundles, wherein a branch of directional light is from a right-angle side incidence of right-angle prism, and then with incidence angle θ in prism hypotenuse and Air Interface place experiences total internal reflection, then after another right-angle side outgoing, arrive image acquisition device target surface as Object light wave;

Another bundle directional light meets as with reference to light wave and above-mentioned Object light wave and interferes on image acquisition device target surface, and obtains reference number hologram H by image acquisition device record ₀;

Step 2: be placed in by testing sample in the reflector space of right-angle prism hypotenuse surface Object light wave, continues record and obtains N width digital hologram H _i, i=1,2,3 ... N;

Step 3: according to Kirchhoff's diffraction theory, utilizes the diffraction propagation process of Computer Numerical Simulation light wave, to hologram H ₀and H _icarry out numerical reconstruction respectively, obtain the COMPLEX AMPLITUDE of original light wave, further will from H _irebuild Object light wave PHASE DISTRIBUTION with from H ₀the PHASE DISTRIBUTION of Object light wave of rebuilding is poor respectively, calculates the phase distribution Δ φ of Object light wave after placement sample _o(x, y);

Step 4: due to the difference of prism hypotenuse surface sample index distribution, it is poor that reflecting light will produce additional phase shift, and the Object light wave phase distribution that step 3 obtains is equal with this reflected light additional phase shift difference cloth, according to the relation of reflected light additional phase shift difference cloth and sample index distribution, obtain the two-dimentional index distribution of sample:

When adopting horizontal polarization directional light, the additional phase shift difference that reflecting light produces is:

With the phase distribution Δ φ of Object light wave after the placement sample calculated _o(x, y) replaces the Δ φ of above-mentioned formula _s(x, y), obtains the two-dimentional index distribution of sample $n_2(x,y)=n_1\sqrt{{\sin }^2\mathrm{\θ}-{\cos }^2{\mathrm{\θtan}}^2\mathrm{\Γ}},$ Wherein:

$r=arctan\frac{\sqrt{n_1^2{\sin }^2\mathrm{\θ}-1}}{n_1\cos \mathrm{\θ}}-\frac{{\mathrm{\Δ\φ}}_o(x,y)}{2};$

When adopting vertical polarization parallel light, the additional phase shift difference that reflecting light produces is:

To calculate the phase distribution Δ φ placing Object light wave after sample _o(x, y) replaces the Δ φ of above-mentioned formula _p(x, y), obtains the two-dimentional index distribution of sample $n_2(x,y)=\frac{n_1}{\tan \mathrm{\Λ}cos\mathrm{\θ}}\sqrt{\frac{\sqrt{1+{\tan }^2{\mathrm{\Λsin}}^{2}2\mathrm{\θ}}-1}{2}},$ Wherein:

$\mathrm{\Λ}=arctan\frac{n_1\sqrt{n_1^2{\sin }^2\mathrm{\θ}-1}}{\cos \mathrm{\θ}}-\frac{{\mathrm{\Δ\φ}}_o(x,y)}{2}$

Wherein: n ₁for the refractive index of prism, n ₂the index distribution that (x, y) is testing sample.