CN103033478A - Double refraction realtime measuring device and method - Google Patents

Abstract

The invention relates to a double refraction realtime measuring device and method. The device is characterized by comprising an alignment light source, a circular polarizer, a spectroscope, a first Wollaston prism, a second Wollaston prism, a first double quadrant detector, a second double quadrant detector and a signal processing unit. According to the device and the method, double refraction of a sample can be measured in real time, and the measurement result is not affected by light-intensity variation.

Description

Birefringence real-time measurement apparatus and measuring method

Technical field

The present invention relates to the polarimetry technical field, particularly a kind of birefringence real-time measurement apparatus and method for sample.

Technical background

Birefringence is a key property of optical material, and characterizing birefringent parameter mainly is phase-delay quantity and phase retardation.In actual use because the environment for use variation, the phase-delay quantity of birefringence element can produce certain deviation with nominal value, and generally the phase retardation of birefringent material is not indicated, in use needs critically to measure the birefringence of birefringent material.

Formerly technology [1] is (referring to Xiaojun Chen, Lianshan Yan, andX.Steve Yao.Waveplateanalyzer using binary magneto-optic rotators.OPTICS EXPRESS.Vol.15, No.20,12989-12994,2007) a kind of device of measuring retardation of wave plate and phase retardation with the rotary process of magneto-optic polarization has been described, this device is by a laser instrument, a circular polarizer, two magneto-optic polarization rotators, an analyzer and a photodetector form, and testing sample places in the middle of two magneto-optic polarization rotators.Rotary magnetic light polarization spinner obtains different polarization states, and photodetector is measured corresponding different light intensity, can obtain measuring phase-delay quantity and the phase retardation of wave plate to be measured.But this device obtains different polarization states by the magneto-optic polarization rotator, can not measure in real time phase-delay quantity and the phase retardation of testing sample.The measurement result of this device is subjected to the impact of light source intensity fluctuation easily simultaneously.

Summary of the invention

The object of the invention is to overcome above-mentioned the deficiencies in the prior art, propose a kind of birefringence real-time measurement apparatus and measuring method for sample.These apparatus and method can be measured the birefringence of sample in real time, and measurement result is not subjected to the impact of light source intensity fluctuation.

Technical solution of the present invention:

A kind of birefringence real-time measurement apparatus for sample, its characteristics are that this device is comprised of collimated light source, circular polarizer, spectroscope, the first wollaston prism, the second wollaston prism, the first dual quadrant detector, the second dual quadrant detector and signal processing unit.Its position relationship is: along on the light beam working direction of described collimated light source, pass through successively described circular polarizer and spectroscope.Spectroscope is divided into transmission beamlet and reflection beamlet with incident beam, the transmission beamlet by described the first wollaston prism light splitting analyzing after by described the first dual quadrant detector collection and finally be connected to signal processing unit.The reflection beamlet by described the second wollaston prism light splitting analyzing after by described the second dual quadrant detector collection and finally be connected to signal processing unit.The angle that the direction of thoroughly shaking of described the second wollaston prism becomes with the direction of thoroughly shaking of described the first wollaston prism is 45 ° or-45 °.Described the first dual quadrant detector, the second dual quadrant detector and signal processing unit are by electrical connection, and signal processing unit is not in light path.The socket of testing sample is set between described circular polarizer and spectroscope.

Described the first dual quadrant detector and the second dual quadrant detector form by assembly and the signal amplification circuit that two photodetectors form.Described photodetector is photodiode, phototriode, photomultiplier or photoelectric cell.

Described signal processing unit is made of multi-channel high-speed data capture card and computing machine with A/D translation function, or is made of the signal processing circuit with respective handling function and microprocessor.

Utilize above-mentioned birefringence real-time measurement apparatus to measure birefringent method, it is characterized in that comprising the steps:

1. testing sample is inserted the socket between described circular polarizer and the spectroscope and adjust light path, make light beam vertically pass through testing sample.

2. utilize described the first dual quadrant detector record by the light intensity I of two beamlets of the first wollaston prism beam splitting generation ₁And I ₂And changing electric signal into, simultaneously described the second dual quadrant detector record is by the light intensity I of two beamlets of the second wollaston prism beam splitting generation ₃And I ₄And changing electric signal into, these electric signal are inputted described signal processing unit simultaneously.

3. described signal processing unit carries out lower column operations:

$V_1=\sin \left(\mathrm{\δ}\right)\sin \left(2\mathrm{\θ}\right)=\frac{I_1-I_2}{I_1+I_2}$

$V_2=\sin \left(\mathrm{\δ}\right)\cos \left(2\mathrm{\θ}\right)=\frac{I_3-I_4}{I_3+I_4}$

Then can obtain, $\mathrm{\δ}=\arcsin \left(\sqrt{V_1^2+V_2^2}\right);$ Amount and phase retardation

Work as V ₁＜0 and V ₂＜0 o'clock,

Work as V ₁0 o'clock, $\mathrm{\θ}=\frac{1}{2}\arctan \left(\frac{V_2}{V_1}\right),$

Work as V ₁＜0 and V ₂0 o'clock,

Through calculating δ in 0～90 ° of scope and the value of θ in-90 °～90 ° scopes, namely obtained phase-delay quantity δ and the phase retardation θ of testing sample.

Compare with first technology, technique effect of the present invention is as follows:

1. can measure in real time the birefringence of sample.The light intensity signal of four beamlets is birefringent functions, and four beamlets are surveyed and high speed processing simultaneously by two dual quadrant detectors, can obtain in real time birefringence.

2. the reflectivity of the light-intensity variation of light source, beam splitter and transmissivity do not affect measurement result.Calculate in real time the light intensity value of current light source in the computation process, the measurement result of two dual quadrant detectors comprises reflectivity and the transmissivity of beam splitter simultaneously, and the birefringent measurement result of testing sample is not subjected to light source intensity fluctuation, the reflectivity of beam splitter and the impact of transmissivity.

3. two of wollaston prism directions of thoroughly shaking are strictly vertical, do not exist the deflection error of shaking to affect the problem of measuring accuracy.Wollaston prism is simultaneously to light splitting and the analyzing of incident light.

4. measurement mechanism is simple in structure.

Description of drawings

Fig. 1 is the structured flowchart of birefringence real-time measurement apparatus of the present invention

Embodiment

The invention will be further described below in conjunction with accompanying drawing and embodiment, but should not limit protection scope of the present invention with this.

See also first Fig. 1, Fig. 1 is the structured flowchart of birefringence real-time measurement apparatus of the present invention.As seen from the figure, birefringence real-time measurement apparatus of the present invention, this device is comprised of collimated light source 1, circular polarizer 2, spectroscope 4, the first Wollaston 5, the second Wollaston 6, the first dual quadrant detector 7, the second dual quadrant detector 8 and signal processing unit 9, its position relationship is: along on the light beam working direction of described collimated light source 1, pass through successively described circular polarizer 2 and spectroscope 4.Spectroscope 4 is divided into transmission beamlet and reflection beamlet with incident beam, and the transmission beamlet gathers and finally be connected to signal processing unit 9 by described the first dual quadrant detector 7 after by the 5 light splitting analyzings of described the first wollaston prism.The reflection beamlet gathers and finally is connected to signal processing unit 9 by described the second dual quadrant detector 8 after by the 6 light splitting analyzings of described the second wollaston prism.The angle that the direction of thoroughly shaking of described the second wollaston prism becomes with the direction of thoroughly shaking of described the first wollaston prism is 45 ° or-45 °.Described the first dual quadrant detector 7, the second dual quadrant detector 8 pass through electrical connection with signal processing unit 9, and signal processing unit 9 is not in light path.The socket 3 of testing sample is set between described circular polarizer 2 and spectroscope 4.

Described the first dual quadrant detector 7 is comprised of two photodiodes 71 and 72 assemblys that form and signal amplification circuit.The second dual quadrant detector 8 is comprised of two photodiodes 81 and 82 assemblys that form and signal amplification circuit.

Described signal processing unit 9 is made of multi-channel high-speed data capture card and computing machine with A/D translation function.

The structure of most preferred embodiment of the present invention as shown in Figure 1, its concrete structure and parameter are as follows:

Described collimated light source 1 is better than 10 for the described circular polarizer 2 of He-Ne laser instrument for the extinction ratio of utilizing calcite crystal and quartz crystal to be made into ^-3Circular polarizer.Described spectroscope 4 is the spectroscope of transmitance 1:1.The splitting angle of described the first wollaston prism 5 and the second wollaston prism 6 is 5 °, and its extinction ratio all is better than 10 ^-5Described the first dual quadrant detector 7 and the second dual quadrant detector 8 form by two photodiodes and signal amplification circuit.Described signal processing unit 9 is made of multi-channel high-speed data capture card and computing machine with A/D translation function.

Utilize described birefringence real-time measurement apparatus to measure birefringent method, it is characterized in that comprising the following steps:

1. testing sample 3 is inserted the socket between described circular polarizer 2 and the spectroscope 4 and adjusts light path, make light beam vertically by testing sample 3;

2. utilize described the first dual quadrant detector 7 records by the light intensity I of two beamlets of the first wollaston prism 5 beam splitting generation ₁And I ₂And changing electric signal into, simultaneously described the second dual quadrant detector 8 records are by the light intensity I of two beamlets of the second wollaston prism 6 beam splitting generation ₃And I ₄And changing electric signal into, these electric signal are inputted described signal processing unit 9 simultaneously;

3. described signal processing unit 9 carries out lower column operations:

$V_1=\sin \left(\mathrm{\δ}\right)\sin \left(2\mathrm{\θ}\right)=\frac{I_1-I_2}{I_1+I_2}$

$V_2=\sin \left(\mathrm{\δ}\right)\cos \left(2\mathrm{\θ}\right)=\frac{I_3-I_4}{I_3+I_4}$

Obtain $\mathrm{\δ}=\arcsin \left(\sqrt{V_1^2+V_2^2}\right);$

Work as V ₁＜0 and V ₂＜0 o'clock,

Work as V ₁0 o'clock, $\mathrm{\θ}=\frac{1}{2}\arctan \left(\frac{V_2}{V_1}\right),$

Work as V ₁＜0 and V ₂0 o'clock,

Through calculating δ in 0～90 ° of scope and the value of θ in-90 °～90 ° scopes, namely obtained phase-delay quantity and the phase retardation of testing sample 3.

The parallel beam of described collimated light source 1 outgoing forms circularly polarized light through described circular polarizer 2, this circularly polarized light is through being divided into transmission beamlet and reflection beamlet by spectroscope 4 behind the described testing sample 3, and two light intensity that the transmission beamlet produces after by the 5 light splitting analyzings of described the first wollaston prism are I ₁And I ₂Beamlet and received by described the first dual quadrant detector 7, produce two voltage signals.It is I that the reflection beamlet produces two light intensity after by the 6 light splitting analyzings of described the second wollaston prism ₃And I ₄Beamlet and received by described the second dual quadrant detector 8, also produce two voltage signals.Described signal processing unit 9 gathers respectively and processes this four voltage signals, processes in real time phase-delay quantity and the phase retardation that obtains testing sample 3.

The circularly polarized light of described circular polarizer 2 outgoing can be expressed as with Jones vector E

$E=\sqrt{\frac{I_0}{2}}\left[\begin{array}{c}1\\ i\end{array}\right],---\left(1\right)$

Wherein: I ₀Amplitude for circularly polarized light.The Jones matrix J of described testing sample 3 _SCan be expressed as

$J_s=\left[\begin{array}{cc}\cos \frac{\mathrm{\δ}}{2}-i\sin \frac{\mathrm{\δ}}{2}\cos 2\mathrm{\θ}& -i\sin \frac{\mathrm{\δ}}{2}\sin 2\mathrm{\θ}\\ -i\sin \frac{\mathrm{\δ}}{2}\sin 2\mathrm{\θ}& \cos \frac{\mathrm{\δ}}{2}+i\sin \frac{\mathrm{\δ}}{2}\cos 2\mathrm{\θ}\end{array}\right],---\left(2\right)$

Wherein: δ and θ are respectively phase-delay quantity and the phase retardation of described testing sample 3.Described the first wollaston prism 5 and the second wollaston prism 6 can be used Jones matrix J _PBe expressed as

$J_P=\left[\begin{array}{cc}{\cos }^2\mathrm{\α}& \sin \mathrm{\α}\cos \mathrm{\α}\\ \sin \mathrm{\α}\cos \mathrm{\α}& {\sin }^2\mathrm{\α}\end{array}\right],---\left(3\right)$

Wherein α is the direction of principal axis angle that thoroughly shakes of described the first wollaston prism 5 and the second wollaston prism 6.The angle of two thoroughly shake direction and horizontal directions of described the first wollaston prism 5 is respectively 0 ° and 90 °, and the angle of two thoroughly shake direction and horizontal directions of described the second wollaston prism 6 is respectively 45 ° and 135 °.Four beamlets through the first wollaston prism 5 or 6 formation of the second wollaston prism can be expressed as with Jones vector E

E ₁＝K ₁J _αJ _sE ₀| _α＝0,(4)

E ₂＝K ₁J _αJ _sE _0α＝90,(5)

E ₃＝K ₂J _αJ _sE ₀| _α＝45,(6)

E ₄=K ₂J _αJ _sE ₀| _α=135, (7) are K wherein ₁And K ₂Be respectively transmissivity and the reflectivity of beam splitter, with multiplying each other with himself behind the Jones matrix conjugate transpose that obtains, obtain surveying light intensity I ₁, I ₂, I ₃And I ₄Be respectively

$I_1=\frac{1}{2}{K}_1^2{I}_0[1+\sin \left(\mathrm{\δ}\right)\sin \left(2\mathrm{\θ}\right)],---\left(8\right)$

$I_2=\frac{1}{2}{K}_1^2{I}_0[1-\sin \left(\mathrm{\δ}\right)\sin \left(2\mathrm{\θ}\right)],---\left(9\right)$

$I_3=\frac{1}{2}{K}_2^2{I}_0[1-\sin \left(\mathrm{\δ}\right)\cos \left(2\mathrm{\θ}\right)],---\left(10\right)$

$I_4=\frac{1}{2}{K}_2^2{I}_0[1+\sin \left(\mathrm{\δ}\right)\cos \left(2\mathrm{\θ}\right)].---\left(11\right)$

Can be obtained by formula (8)～(11)

$V_1=\sin \left(\mathrm{\δ}\right)\sin \left(2\mathrm{\θ}\right)=\frac{I_1-I_2}{I_1+I_2},---\left(12\right)$

$V_2=\sin \left(\mathrm{\δ}\right)\cos \left(2\mathrm{\θ}\right)=\frac{I_3-I_4}{I_3+I_4}.---\left(13\right)$

Then can obtain

$\mathrm{\δ}=\arcsin \left(\sqrt{V_1^2+V_2^2}\right),---\left(14\right)$

Work as V ₁＜0 and V ₂＜0 o'clock,

Work as V ₁0 o'clock, $\mathrm{\θ}=\frac{1}{2}\arctan \left(\frac{V_2}{V_1}\right),---\left(16\right)$

Work as V ₁＜0 and V ₂0 o'clock,

Utilize formula (14)～(17) can calculate value and θ the value-90 °～90 ° scopes in of δ in 0～90 ° of scope, namely obtained the birefringence of testing sample 3.

Utilize most preferred embodiment that light ball modulator is measured under out of phase retardation and phase retardation, it is 0.74 ° that its phase-delay quantity is measured maximum deviation, and the phase retardation maximum standard deviation is 0.47 °.

Claims (8)

1. birefringence real-time measurement apparatus that is used for sample, it is characterized in that this device is by collimated light source (1), circular polarizer (2), spectroscope (4), the first wollaston prism (5), the second wollaston prism (6), the first dual quadrant detector (7), the second dual quadrant detector (8) and signal processing unit (9) form, its position relationship is: along the light beam working direction of described collimated light source (1), pass through successively described circular polarizer (2) and spectroscope (4), this spectroscope (4) is divided into transmission beamlet and reflection beamlet with incident beam, the transmission beamlet is gathered by described the first dual quadrant detector (7) after by described the first wollaston prism (5) light splitting analyzing, described reflection beamlet is gathered by described the second dual quadrant detector (8) after by described the second wollaston prism (6) light splitting analyzing, the angle that the direction of thoroughly shaking of described the second wollaston prism (6) becomes with the direction of thoroughly shaking of described the first wollaston prism (5) is 45 ° or-45 °, described the first dual quadrant detector (7) be connected the output terminal of dual quadrant detector (8) and be connected with the input end of described signal processing unit, the socket (3) of testing sample is set between described circular polarizer and spectroscope.

2. birefringence real-time measurement apparatus according to claim 1, it is characterized in that described the first dual quadrant detector and the second dual quadrant detector form by assembly and the signal amplification circuit that two photodetectors form, described photodetector is photodiode, phototriode, photomultiplier or photoelectric cell.

3. birefringence real-time measurement apparatus according to claim 1, it is characterized in that described signal processing unit is made of multi-channel high-speed data capture card and computing machine with A/D translation function, or consisted of by the signal processing circuit with respective handling function and microprocessor.

4. birefringence real-time measurement apparatus according to claim 1 is characterized in that described collimated light source (1) is the He-Ne laser instrument.

5. birefringence real-time measurement apparatus according to claim 1 is characterized in that described circular polarizer (2) is to be better than 10 by the extinction ratio that calcite crystal or quartz crystal are made into ^-3Circular polarizer.

6. birefringence real-time measurement apparatus according to claim 1 is characterized in that described spectroscope (4) is the spectroscope of transmitance 1:1.

7. birefringence real-time measurement apparatus according to claim 1 is characterized in that the splitting angle of described the first wollaston prism (5) and the second wollaston prism (6) is 5 °, and its extinction ratio all is better than 10 ^-5

8. utilize birefringence real-time measurement apparatus claimed in claim 1 to measure birefringent method, it is characterized in that comprising that the method comprises the following steps:

1. testing sample is inserted the socket (3) between described circular polarizer (2) and the spectroscope (4) and adjust light path, make light beam vertically pass through testing sample;

2. utilize described the first dual quadrant detector (7) record by light intensity I1 and the I2 of two beamlets of the first wollaston prism (5) beam splitting generation and change electric signal into, simultaneously described the second dual quadrant detector (8) records light intensity I3 and the I4 of two beamlets that produced by the second wollaston prism (6) beam splitting and changes electric signal into, and these electric signal are inputted described signal processing unit (9) simultaneously;

3. described signal processing unit (9) carries out lower column operations:

$V_1=\sin \left(\mathrm{\δ}\right)\sin \left(2\mathrm{\θ}\right)=\frac{I_1-I_2}{I_1+I_2}$

$V_2=\sin \left(\mathrm{\δ}\right)\cos \left(2\mathrm{\θ}\right)=\frac{I_3-I_4}{I_3+I_4}$

Obtain: $\mathrm{\δ}=\arcsin \left(\sqrt{V_1^2+V_2^2}\right);$

Work as V ₁＜0 and V ₂＜0 o'clock,

Work as V ₁0 o'clock, $\mathrm{\θ}=\frac{1}{2}\arctan \left(\frac{V_2}{V_1}\right),$

Work as V ₁＜0 and V ₂0 o'clock,

Through calculating δ in 0～90 ° of scope and the value of θ in-90 °～90 ° scopes, wherein: δ is the phase-delay quantity of described testing sample, and θ is the phase retardation of testing sample.