CN103645031A - Device for measuring wave plate phase delay through laser frequency method - Google Patents

Abstract

The invention discloses a device for measuring wave plate phase delay through the laser frequency method. According to the device, the principle that the laser frequency splitting condition will occur when a wave plate is placed into a laser resonator is utilized to convert one oscillation frequency of a laser device into two oscillation frequencies, wherein the frequency difference between the two frequencies is proportional to the phase delay of the wave plate. Optical beat extraction is performed on laser output light in a same polarization direction, and the frequency of the optical beat signal is measured, wherein the frequency of the optical beat signal is the frequency difference of the two split frequencies, so that the wave plate phase delay can be obtained accurately. The device of the invention comprises a half external cavity He-Ne laser device, the wave plate to be measured which is placed in the cavity is born by a support frame including a two-dimensional translation stage and a two-dimensional angle adjusting frame, the wave plate support frame is arranged on the laser axis side, the laser cavity length can be shortened, the light output power can be improved, and the wave plate to be measured can be subjected to translation in two-dimensional directions to measure the phase delay at different points.

Description

A kind of laser frequency method is measured the device of Phase Retardation of Wave Plate

Technical field

The present invention relates to fields of measurement, relate in particular to the device of a kind of laser frequency method measurement Phase Retardation of Wave Plate in fields of measurement.

Background technology

Wave plate is a kind of conventional optical element, has the wide application of sending out in a lot of fine measuring instruments and optical system, and its phase delay is most important technical indicator,

In relating to a lot of optical systems of polarized light, all will use, bit phase delay is its topmost technical indicator, affects to a great extent the performance of system in application, therefore accurately measures its bit phase delay extremely important.Current conventional wave plate retardation measuring method measuring accuracy is generally in 0.5 degree left and right, degree～1, and equipment adjustment is more complicated.What have needs high precisive angle gauge or standard quarter-wave plate; What have is only applicable to quarter-wave plate and is not suitable for the detection of half-wave plate etc.In addition existing measuring method can not be traceable to natural reference, and these factors make it be difficult to meet the measurement requirement day by day improving.

The method of measuring wave plate retardation based on laser frequency splitting provides a kind of system architecture simple, easy to adjust, only need to measure frequency difference and without the measuring method of the high precision wave plate retardation of high precisive angle gauge and standard quarter-wave plate: the half external cavity helium neon laser resonator cavity interpolation forming at the individual mirrors by moving along axis and laser gain pipe enters wave plate, can cause laser frequency division, every one-level longitudinal mode becomes mutually orthogonal two in polarization direction, and the difference on the frequency of two split-modes is proportional to wave plate retardation.The frequency difference of division is compared and can be obtained wave plate retardation with longitudinal mode spacing.For the frequency difference aliasing of avoiding multimode oscillation to cause, can measure respectively the frequency difference of split-mode at the same level and the frequency difference of adjacent level split-mode, then add and obtain laser longitudinal module interval.But for half-wave plate and the full-wave plate of approximate test, one of two longitudinal modes that split into are very approaching with the longitudinal mode frequency of other grades times, and latch-up phenomenon will occur laser instrument, and dividing the longitudinal mode can not vibrate simultaneously.While therefore, measuring with the bit phase delay of double/full-wave plate of above-mentioned measuring method, need to take special measure.

Method is to adopt to add a transverse magnetic field in laser gain pipe both sides, utilizes transverse zeeman effect to eliminate laser instrument locking.Adopt the method for similar frequency splitting, measure frequency difference size and the longitudinal mode spacing of split-mode, the two is compared and can obtain wave plate retardation.Due in measuring, must apply transverse magnetic field, and guarantee that magnetic direction follows one of wave plate fast and slow axis parallel, can not on a covering device, measure any wave plate retardation.

Summary of the invention

The object of the invention is to overcome the above-mentioned deficiency of measuring wave plate retardation method based on frequency splitting, propose a kind of method and the implement device thereof that can measure any wave plate retardation that comprises half-wave plate and full-wave plate.

The method of traced to the source the measurements any wave plate retardation that the present invention proposes, for the wave plate of different bit phase delays, proportion disintegrating method, longitudinal mode direct-reading method and measuring respectively with an additional wave plate generation phase offsetting, the method comprises the following steps:

Step a) is put into wave plate to be measured the resonator cavity of helium-neon laser, one of fast and slow axis that makes described wave plate to be measured is parallel to the initial polarization direction of laser, and the face normal of described wave plate to be measured is tilted with respect to laser axis along slow-axis direction, adopt eyes with non-contact method to measure described wave plate face normal along the pitch angle size becoming with described laser axis;

Step b) anisotropy that unrelieved stress causes in not counting described laserresonator is during on the affecting of described wave plate measurement result to be measured, the chamber of tuning described laser instrument is long, if there is not moding phenomenon, measure split-mode frequency difference at the same level and adjacent level split-mode frequency difference, described split-mode frequency difference at the same level and described adjacent level split-mode frequency difference are added, and

Step b-1) if described addition result is about one times of longitudinal mode spacing size, by frequency splitting method, measure described wave plate retardation to be measured, computing formula is:

$\mathrm{\φ}\frac{\mathrm{\Δv}}{\mathrm{\Δv}+\mathrm{\Δ}{v}^{\′}}\mathrm{\π}$

Wherein, the bit phase delay that φ is described wave plate to be measured, Δ ν is described laser instrument split-mode frequency difference at the same level, Δ ν ' is described laser instrument adjacent level split-mode frequency difference;

Step b-2), if described addition result is about twice longitudinal mode spacing size, adopt longitudinal mode direct-reading method to treat described in measuring

Survey wave plate retardation, computing formula is:

$\mathrm{\φ}=\mathrm{\π}*(1\±|\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}\left|\right)$ (half-wave plate)

$\mathrm{\φ}=\mathrm{\π}*(2\±|\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}\left|\right)$ (full-wave plate)

Wherein, the bit phase delay that φ is described wave plate to be measured, Δ ₁for one in the two successive stages longitudinal mode spacing of continuous three longitudinal modes formation of described laser instrument, Δ ₂another in the two successive stages longitudinal mode spacing forming for continuous three longitudinal modes of described laser instrument;

Step c) if step b) in there is moding phenomenon, with additional wave plate, replace described wave plate to be measured to put into described laserresonator by step method a), adopt step b-1) bit phase delay of the described additional wave plate of described frequency splitting method measurement; Again described wave plate to be measured is also put into laserresonator by step method a), and the quick shaft direction that makes described wave plate to be measured is parallel to the fast axle of described additional wave plate, adopting step b-1) described frequency splitting method measures the bit phase delay under described wave plate to be measured and described additional wave plate acting in conjunction; And the bit phase delay under described acting in conjunction deducts the bit phase delay of described additional wave plate, thereby obtain the bit phase delay of described wave plate to be measured;

Step d) is fetched and described wave plate to be measured detect thickness, the pitch angle size becoming with described laser axis along slow-axis direction according to the wave plate face normal described to be measured recording in step a), calculate the measurement result modified value causing after described wave plate to be measured tilts, computing formula is:

$\mathrm{\Δ}{\mathrm{\φ}}_a=\frac{\mathrm{\πd}}{\mathrm{\λ}}[1/\cos {(\mathrm{\θ}/n)}^{-1}](n_e-n_o)$

Δ φ wherein _afor described modified value, the size at the θ pitch angle that to be described wave plate face normal to be measured become with described laser axis along slow-axis direction, n is described wave plate mean refractive index to be measured, n _e, n _ofor two principal refractive indexs of described wave plate to be measured, d is described wave plate thickness to be measured, and λ is optical maser wavelength; Then from step b) or c) deduct the systematic error that described modified value causes to compensate described pitch angle in the measurement result of the described wave plate to be measured that obtains.

For reducing the abnormal impact of the tuning amount of frequency difference, the face normal of described wave plate is at least 15 minutes along slow-axis direction with respect to the pitch angle of laser axis.While considering unrelieved stress causes in described laserresonator anisotropy on the affecting of described wave plate measurement result to be measured simultaneously, the systematic error that need to cause it is revised, method is: when described wave plate to be measured not being put into described laserresonator, adopt described longitudinal mode direct-reading method to measure the measurement result modified value that in described chamber, unrelieved stress causes, computing formula is:

$\mathrm{\Δ}{\mathrm{\φ}}_r=\mathrm{\π}\×\left|{\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}}_{}\right|$

Δ φ wherein _rfor described measurement result modified value, Δ ₁for one in the two successive stages longitudinal mode spacing of continuous three longitudinal modes formation of described laser instrument, Δ ₂another in the two successive stages longitudinal mode spacing forming for continuous three longitudinal modes of described laser instrument deducts described modified value, the systematic error causing with unrelieved stress in compensated cavity from obtain the measurement result of described wave plate to be measured.

The device that a kind of laser frequency disintegrating method that the present invention proposes is measured Phase Retardation of Wave Plate comprises:

Helium-neon laser, this helium-neon laser comprises gain tube and individual mirrors, the two ends of this gain tube are fixed wtih respectively stationary mirror and anti-reflection window, the reflecting surface of this individual mirrors is relative with this anti-reflection window, this stationary mirror and this individual mirrors form the resonator cavity of this helium-neon laser, and the non-reflecting surface of this individual mirrors is connected with piezoelectric ceramics;

Wave plate support, this wave plate support is between this anti-reflection window and this individual mirrors, this wave plate support comprises parallel guide rail and is fixed on the adjusting support that at least two dimension angular on this guide rail regulates, wave plate to be measured and/or additional wave plate are placed on respectively on this adjusting support, and face normal tilts with respect to the laser axis of this helium-neon laser while making this wave plate to be measured and/or additional wave plate be placed on this adjusting support;

Light intensity probe unit, this light intensity probe unit is arranged on a side of this helium-neon laser, relative with the stationary mirror on this gain tube, for two orthogonal polarisation state light intensity of this helium-neon laser output are measured;

Frequency difference probe unit, this frequency difference probe unit is arranged on the opposite side of this helium-neon laser, relative with this individual mirrors, for measuring the difference on the frequency of laser of two orthogonal polarisation state of this helium-neon laser output;

Controller, this controller and this light intensity probe unit, this frequency difference probe unit and this piezoelectric ceramics electricity are connected, for control survey process and export measurement result.

Particularly, this device can comprise:

Helium-neon laser, is comprised of a gain tube and a slice individual mirrors, and the two ends of described gain tube are fixed wtih respectively a slice catoptron and the anti-reflection window of a slice, and described individual mirrors is relative with described anti-reflection window and be connected with piezoelectric ceramics;

Wave plate support, between described anti-reflection window and described individual mirrors, comprise that a parallel guide rail and two two dimension angulars that are fixed on described guide rail regulate support, described wave plate to be measured and/or additional wave plate are placed on respectively described each and regulate on support, and face normal tilts with respect to laser axis while making described wave plate to be measured and/or additional wave plate be placed on described adjusting support;

Light intensity probe unit, relative with the catoptron on described gain tube, for two orthogonal polarisation state light intensity of described laser instrument output are measured, described light intensity probe unit comprises a wollaston prism and two photodetectors, described wollaston prism is divided into two-beam by the output light of described laser instrument by orthogonal polarisation state, described photodetector can adopt such as photoelectric cell etc., surveys described two-beam light intensity;

Frequency difference probe unit, relative with described individual mirrors, for measuring the difference on the frequency of two orthogonal polarisation state of described laser instrument, described frequency difference probe unit comprises a polaroid, a photodetector and a frequency meter, described photodetector can adopt such as avalanche photo diode (APD) etc., survey two orthogonal polarisation state of described laser instrument and by optical direction, become the photo-beat frequency forming after the described polaroid of miter angle placement with described wave plate fast and slow axis direction to be measured, described frequency meter is connected with described photodetector output terminal;

Control device, is connected with described light intensity probe unit, frequency difference probe unit and piezoelectric ceramics, for control survey process and export measurement result.

Wherein, the angle that the anti-reflection window face normal on described laser gain pipe tilts with respect to laser axis is at least 15 minutes, to avoid causing that the tuning amount of frequency difference is abnormal; Near described wave plate, can adopt temperature sensor measurement temperature, described temperature sensor can adopt such as Pt100 etc.

Preferably, this light intensity probe unit comprises wollaston prism and the first photodetector, and this wollaston prism is divided into two-beam by the output light of this laser instrument by orthogonal polarisation state, and this first photodetector is arranged to receive respectively this two-beam.

Preferably, this frequency difference probe unit comprises polaroid, the second photodetector and frequency meter, this polaroid be arranged to optical direction respectively with the fast axle of this wave plate to be measured and slow axis in angle of 45 degrees, frequently, this frequency meter is connected with the output terminal electricity of this second photodetector the photo-beat that two orthogonal polarisation state laser that this second photodetector is arranged to survey this helium-neon laser output form after by this polaroid.

Preferably, the face normal of the anti-reflection window on this gain tube is at least 15 minutes with respect to the angle of inclination of the axis of the laser of this helium-neon laser output.

Preferably, this device also comprises compensating module, and this compensating module, for according to this angle of inclination, compensates processing to the measurement result of this controller output.

Preferably, this device also comprises the temperature sensor being arranged on this wave plate support.

Preferably, this device also comprises the aperture diaphragm being arranged between this anti-reflection window and this wave plate support.

Preferably, the sharp light wavelength of this helium-neon laser output is 632.8nm.

Based on technique scheme, laser frequency disintegrating method of the present invention is measured the method and apparatus of Phase Retardation of Wave Plate, can realize the measurement to any wave plate retardation at a cover system, simple to operate, automatic discrimination wave plate measurement result, and bucking-out system error, its short-term measuring repeatability is better than 0.02 degree, and long-term measuring repeatability is better than 0.04 degree.And owing to adopting laser frequency measurement wave plate retardation, can be traceable to optical maser wavelength, can provide reference data for other wave plate measuring methods, as a kind of tracing to the source, measure the device of any wave plate retardation.

Accompanying drawing explanation

In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, to the accompanying drawing of required use in the embodiment of the present invention be briefly described below, apparently, below described accompanying drawing be only some embodiments of the present invention, for those of ordinary skills, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is the schematic diagram of the half inner chamber helium-neon laser used of the measuring method based on frequency splitting.

Fig. 2 is the schematic diagram that two-stage longitudinal mode respectively splits into two mutually orthogonal longitudinal modes of polarization direction.

Fig. 3 is that the long time split-mode not at the same level of tuning cavity enters Laser output band vibration schematic diagram successively, and wherein (a) is the adjacent level split-mode schematic diagram that simultaneously vibrates; (b) be the two split-modes at the same level schematic diagram that simultaneously vibrate.

Fig. 4 is that half/full-wave plate is put into laserresonator output pairwise orthogonal polarized light intensity tuning curve schematic diagram, light intensity tuning curve schematic diagram when wherein (a) is emergence pattern saltus step; (b) the light intensity tuning curve schematic diagram while being not emergence pattern saltus step.

Fig. 5 is that half/full-wave plate causes longitudinal mode spacing translation schematic diagram on orthogonal directions, and wherein (a) is that interval increases two longitudinal modes and moves into out light belt vibration schematic diagram; (b) be that interval two longitudinal modes that diminish move into out light belt vibration schematic diagram.

Fig. 6 is according to the structural representation of the traced to the source any wave plate retardation measurement mechanism of the embodiment of the present invention.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is a part of embodiment of the present invention, rather than whole embodiment.Embodiment based in the present invention, the every other embodiment that those of ordinary skills obtain under the prerequisite of not making creative work, should belong to the scope of protection of the invention.

The schematic diagram of the half inner chamber helium-neon laser that Fig. 1 uses for measuring method based on frequency splitting.Wherein, half-intracavity laser is by catoptron 2, and gain tube 1 and catoptron 3 form, and wherein stationary mirror 2 and anti-reflection window 4 are distinguished in gain tube 1 two ends, and resonator cavity is formed by catoptron 2 and 3.The adjacent two-stage longitudinal mode of laser instrument ν _q, ν _q+1between difference on the frequency be that longitudinal mode spacing is

$\mathrm{\Δ}=\frac{c}{2L}---\left(1\right)$

Wherein c is the light velocity, and L is that resonance physics chamber is long.

When putting into birefringence element in resonator cavity, the longitudinal mode of laser instrument output will divide, and original every one-level longitudinal mode becomes mutually orthogonal two in polarization direction, and as shown in Figure 2, wherein solid line and dotted line represent different polarization direction, and G is laser gain curve.The difference on the frequency of two split-modes is

$\mathrm{\Δv}=\frac{v}{L}\mathrm{\δ}---\left(2\right)$

Wherein ν is laser frequency, and δ is the o light that causes of birefringence element and the optical path difference of e light.For wave plate, have

$\mathrm{\δ}=\frac{\mathrm{\λ}}{2\mathrm{\π}}\mathrm{\φ}---\left(3\right)$

Wherein λ is optical wavelength, and φ is wave plate retardation, is greater than the multistage wave plate of 2 π for bit phase delay, refer to bit phase delay deduct the size that obtains after the integral multiple of 2 π at 2 π with interior " decimal " part.In fact for bit phase delay, be greater than the multistage wave plate of 2 π, what in application, work is usually the fraction part of bit phase delay, the result measuring is fraction part often also, and the wave plate of making for quartz material, the level of its integral part time can adopt general mircrometer gauge to record as vernier caliper.Therefore the key of measuring any wave plate retardation be measure wave plate at 2 π the bit phase delay with interior fraction part, for sake of convenience, the bit phase delay of mentioning wave plate below all refers to this situation when not specifying.By (1) (2) (3) formula and wavelength frequency relation c=λ ν, obtained

$\mathrm{\φ}=\frac{\mathrm{\Δv}}{\mathrm{\Δ}}\mathrm{\π}---\left(4\right)$

It should be noted that formula (4) and chamber length, without explicit relation, as long as record frequency difference Δ ν and the longitudinal mode spacing Δ that divides, can obtain the bit phase delay amount φ of wave plate.In order to measure frequency difference, can make laser instrument output light through a polaroid, and make the optical direction of polaroid along laser instrument orthogonal polarization orientation folder bisector of angle.The photo-beat that any like this two patterns equal forming frequency on polaroid optical direction the difference of the two frequently also can be received and is converted to electric signal by detector.It should be noted that in laser instrument, there is more than three or three pattern when work simultaneously, comprise the composition of a plurality of beat frequencies in electric signal, if electric signal is transfused to frequency spectrograph, each composition can directly read in frequency spectrograph; But if electric signal is transfused to frequency meter, the reading of frequency meter will be uncertain.For improving measuring accuracy, in measurement, frequency of utilization meter is read frequency difference, therefore can adopt with the following method: make laser works at the bimodulus state as shown in Fig. 3 (a), measure by longitudinal mode ν _qand ν _qthe beat frequency Δ ν of ' formation, then drives piezoelectric ceramics to change chamber long, makes longitudinal mode ν _qshift out and ν _q+1enter bright dipping bandwidth, as shown in Fig. 3 (b), measure ν _q' and ν _q+1the beat frequency Δ ν ' forming.And obtain according to Fig. 2: Δ=Δ ν+Δ ν ', can obtain longitudinal mode spacing Δ thus.Final wave plate retardation can be expressed as:

$\mathrm{\φ}=\frac{\mathrm{\Δv}}{\mathrm{\Δv}+\mathrm{\Δ}{v}^{\′}}\mathrm{\π}---\left(5\right)$

In this application, this measuring method is called frequency splitting method.

Half-wave plate and full-wave plate for approximate test, there are respectively φ ≈ π and φ ≈ 2 π, by formula (4), know that corresponding Δ ν value is approximately respectively Δ and 2 Δs, this means that one of two longitudinal modes of splitting into and the longitudinal mode frequency of other grades times approach that (mono-of two frequency difference Δ ν and Δ ν ' are very little and another approaches Δ very much, for convenience of narration, below suppose that Δ ν ' is one larger in the two), will there is latch-up phenomenon in laser instrument, and dividing the longitudinal mode can not vibrate simultaneously.Therefore, with the bit phase delay that above-mentioned measuring method cannot half-and-half/full-wave plate, measure.A solution, described in technical background, adopts and in laser gain pipe both sides, adds the locking of transverse magnetic field method elimination frequency difference, but can not on a cover system, realize the measurement to any wave plate retardation equally.Therefore when wave plate to be measured is half/full-wave plate, need to adopt specific process.

For HeNe laser instrument, its frequency difference degating region is about 40MHz.When two split-mode frequency differences are less than 40MHz, due to mode competitive effects, a mode oscillation, another pattern is by suppressed and in extinguishing state, two split-modes can not vibrate simultaneously.Illustrate, if laser longitudinal mode interval is about 750MHz, wave plate is inserted to resonator cavity and produce frequency splitting and make the frequency difference value of adjacent pattern equal 40MHz, the phase retardation amount that corresponding wave plate departs from desirable half/full-wave plate is about 10 degree.Simultaneously within the scope of frequency difference locking, tuned resonating cavity is long, make zlasing mode on going out light belt during translation, there will be two kinds may situations: (1) is when frequency difference is during in 20MHz～40MHz, after a pattern starting of oscillation, close on split-mode by suppressed in extinguishing state, tuning cavity length makes oscillation mode move to out light belt position can there is " moding " phenomenon, oscillation mode transfers to and extinguishing, originally the pattern starting oscillation extinguishing, and the polarization state of new starting of oscillation pattern is along the orthogonal directions of original pattern, it is polarization state generation saltus step, now after going out light belt and going forward, two moulds do not have resonance region substantially, as shown in Fig. 4 (a), wherein solid line and dotted line represent respectively pairwise orthogonal polarized light intensity, (2) when frequency splitting is less than about 20MHz, the mould of split-mode and other grades time is very approaching, due to strong mode competitive effects, after one of them pattern starting of oscillation, another mould will be always in extinguishing state in the tuning process of chamber, now the longitudinal mode of vibration go out on light belt translation can emergence pattern saltus step, as shown in Fig. 4 (b).The laser instrument that is 750MHz corresponding to longitudinal mode spacing, while inserting half/full-wave plate tuned resonating cavity length, above-mentioned two situations correspond respectively to the wave plate of different bit phase delays: if emergence pattern saltus step, the bit phase delay that wave plate departs from desirable half/full-wave plate is between 5 degree～10 degree; If all the time mode oscillation another extinguish, there is no moding, the bit phase delay that wave plate departs from desirable half/full-wave plate will be no more than 5 degree.According to both of these case, need to adopt respectively distinct methods to measure the bit phase delay of half/full-wave plate.

First for the first situation as shown in Figure 4 (a), half/full-wave plate is inserted after laserresonator, and two conditions that the split-mode being caused by wave plate phasic difference meets on Laser output band are: (1) split-mode can not vibrate in laser frequency degating region with closing on the frequency difference that longitudinal mode forms simultaneously; (2) can emergence pattern in the long tuning process in chamber saltus step, mode of oscillation transfers to be extinguished, pattern starting oscillation that originally can not starting of oscillation, in saltus step process, two moulds almost do not have coexistence.Because two split-modes in mode competition state do not have coexistence, the frequency difference of measuring two intermodes is impossible, can adopt new method to make laser split-mode get around this region.With reference to frequency splitting method above-mentioned, measure wave plate retardation, can adopt additional wave plate to produce the position method of biasing mutually: wave plate (non-half-wave plate and the full-wave plate of first in resonator cavity, putting into the known optical axis direction of a slice, as being 30 degree, 45 degree, 60 degree, 75 degree or quarter-wave plate etc.), the frequency splitting of its generation, beyond laser frequency difference degating region, can be measured its bit phase delay φ according to the aforementioned method as Fig. 3 ₁; Again half/full-wave plate to be measured is put into chamber and made its quick shaft direction parallel with known wave plate quick shaft direction, with same method, measure the bit phase delay φ under the two acting in conjunction ₂, the bit phase delay that the bit phase delay that bit phase delay under acting in conjunction deducts additional wave plate obtains wave plate to be measured is φ ₂-φ ₁(can whether increase phase differential π according to actual conditions).This biasing means is actual is equivalent to the bit phase delay of measuring two non-half/full-wave plates, thereby can on original frequency splitting method is measured the device of wave plate, not increase new mechanism (as steady magnetic field) and reach measurement object.The additive method that just brings thus the measuring error of wave plate to use compared with this patent is large.Here it is, and additional wave plate produces position phase offsetting.

For the second situation as shown in Figure 4 (b), when half/full-wave plate to be measured, the half/full-wave plate that is near the mark very much, insert after resonator cavity, split-mode meets following two conditions on Laser output band: (1) split-mode can not vibrate in laser frequency degating region with the frequency difference of closing on longitudinal mode formation simultaneously; (2) starting of oscillation pattern will suppress in extinguishing the pattern of state always, not emergence pattern saltus step when chamber length is tuning, and two split-modes do not have coexistence completely.Now according to formula (4) at oscillation mode with extinguish the little frequency difference Δ ν that causes due to wave plate retardation between mould (as described in background, mono-of two frequency difference Δ ν and Δ ν ' are very little and another approaches Δ, for sake of convenience, below be assumed to be Δ ν less one in the two) can not read, be called hidden frequency splitting amount, as shown in Figure 5.Its size is determined by wave plate phasic difference, and causes the translation dislocation of longitudinal mode spacing generation Δ ν in pairwise orthogonal direction.Tuned laser chamber is long, and the longitudinal mode of not at the same level time enters out light belt successively.In laserresonator, due to mould depression effect, adjacent two oscillation modes are cross polarization.In Fig. 5 (a), suppose initial mode of oscillation ν _qfor horizontal polarization state, due to mode competition, the split-mode ν of vertical polarization state _q' by suppressed.Next stage enters out the pattern ν that the polarization direction of light belt is level simultaneously _q+1same ν _qmould belongs to same polarization state, due to the existence of mould depression effect, can not vibrate.ν when vertical polarization state _q+1' mould enters and could vibrate.So at ν _qand ν _q+1it is Δ that ' intermode forms frequency difference size ₁mode spacing, it is Δ ν with the difference of longitudinal mode spacing Δ.As a same reason, can analyze ν _q-1and ν _q-1' enter out the situation of light belt, as shown in Fig. 5 (b), finally at ν _q-1' and ν _qbetween form frequency difference size for Δ ₂mode spacing, it is Δ ν with the difference of longitudinal mode spacing Δ.Here just at hypothesis ν _qthe result of mould gained in oscillatory regime situation, in Fig. 5, solid line represents that pattern can vibrate in resonator cavity, and dotted line represents that pattern is in blocking.Conversely when initial mode of oscillation is ν _qin ' time, in corresponding orthogonal polarization orientation, the oscillatory regime of pattern is same contrary above, but the frequency difference result obtaining is the same, produces respectively two mode spacings of departing from longitudinal mode spacing Δ ν of forward and negative sense.Similarly situation is no longer narrated.Can obtain thus:

Δ ₁=Δ+Δν，Δ ₂=Δ-Δν (6)

Formula (6) substitution formula (5) can be obtained to half-wave plate bit phase delay scale to be shown

$\mathrm{\φ}=\mathrm{\π}*(1\±|\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}\left|\right)---\left(7\right)$

For full-wave plate, its bit phase delay is expressed as

$\mathrm{\φ}=\mathrm{\π}*(2\±|\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}\left|\right)---\left(8\right)$

Now, tuning laser chamber is long, and actual longitudinal mode spacing Δ can not obtain, and the frequency difference of being measured adjacent two longitudinal modes of laser instrument by frequency meter is Δ ₁and Δ ₂, they are equivalent longitudinal mode spacings.When half/full-wave plate to be measured, the half/full-wave plate that is near the mark very much, insert after resonator cavity, tuning cavity is long, measures the size of adjacent two different equivalent longitudinal mode spacings, substitution formula (7) or (8) can obtain the bit phase delay of corresponding half/full-wave plate, and this is that longitudinal mode direct-reading method is measured.

Sum up and can know, wave plate to be measured is put into laserresonator, if wave plate can produce frequency splitting, proportion disintegrating method is measured; If the split-mode that wave plate produces is in laser instrument frequency difference degating region, and when tuning cavity is long, produce moding, adopt additional wave plate to produce a position phase offsetting and measure, otherwise, the measurement of longitudinal mode direct-reading method adopted.Thus, can on a covering device, realize the measurement to any wave plate retardation.

Two, measurement scheme:

According to measuring method recited above, the technical scheme that the present invention proposes, for the wave plate of different bit phase delays, proportion disintegrating method, longitudinal mode direct-reading method and the phase offsetting measurement of additional wave plate generation position respectively.For distinguishing the wave plate of different bit phase delay scopes, correctly provide measurement result, need to be to using the situation of described three kinds of methods to be differentiated respectively.

First judgement is used additional wave plate to produce the situation of position phase offsetting, and this can judge by observing light intensity tuning curve.As shown in Figure 4, in measuring process, adopt the photodetector light intensity magnitude of detecting laser output pairwise orthogonal polarized light respectively, and export computer recording demonstration.When tuning laser chamber is long, if there is " moding " phenomenon as shown in Fig. 4 (a), can think that wave plate to be measured is half/full-wave plate, its bit phase delay that departs from standard half/full-wave plate is larger, directly measurement can not obtain wave plate retardation, can adopt additional wave plate to produce position phase offsetting and measure.

For the situation of distinguishing frequency of utilization disintegrating method and longitudinal mode direct-reading method and measuring, the frequency difference that can obtain by two kinds of situation lower frequency meters is in different size to be differentiated.According to formula (5), can know, during frequency splitting, the frequency difference sum of twice split-mode in front and back is longitudinal mode spacing; And can be obtained by formula (6): Δ ₁+ Δ ₂=2 * Δ, i.e. the twice that during longitudinal mode direct-reading method, the frequency difference sum of twice longitudinal mode in front and back is longitudinal mode spacing.The method of differentiating thus frequency splitting method and longitudinal mode direct-reading method is: wave plate to be measured is put into after laserresonator, tuning cavity is grown and is measured the frequency difference value that successively enters out light belt two-mode, two frequency differences that obtain are added: if sum is one times of longitudinal mode spacing, wave plate to be measured is for producing the non-half/full-wave plate of frequency splitting, and proportion disintegrating method is measured its bit phase delay; If sum is twice longitudinal mode spacing, half/the full-wave plate of wave plate to be measured for approaching very much with standard half/full-wave plate, adopts longitudinal mode direct-reading method to measure its bit phase delay.In fact just passable as long as said one times of longitudinal mode spacing and twice longitudinal mode spacing are carried out to circumscription, one times or twice longitudinal mode spacing that need not be strict.Because wave plate level to be measured time difference, also there is nuance at corresponding laser longitudinal module interval.The HeNe laser instrument that the cavity longitudinal mode spacing of take is 750MHz is example, and one times longitudinal mode spacing can be set between 650MHz～850MHz, and two times of longitudinal mode spacings are set to 1400MHz～1600MHz, and the two differs still very large, can distinguish completely.When chamber length is tuning, measure adjacent two frequency difference value sums in 650MHz～850MHz, think to be about one times of longitudinal mode spacing, proportion disintegrating method is measured; When adjacent two frequency difference value sums are in 1400MHz～1600MHz, think to be about two times of longitudinal mode spacings, adopt longitudinal mode direct-reading method to measure.

The key step that can obtain thus measuring any wave plate retardation is:

Step a) is put into wave plate to be measured the resonator cavity of helium-neon laser, and one of fast and slow axis that makes described wave plate to be measured is parallel to the initial polarization direction of laser, and the face normal of described wave plate to be measured is tilted with respect to laser axis;

Step b) chamber of tuning described laser instrument is long, if there is not moding phenomenon, measures split-mode frequency difference at the same level and adjacent level split-mode frequency difference, described split-mode frequency difference at the same level and described adjacent level split-mode frequency difference are added, and

Step b-1), if described addition result is about one times of longitudinal mode spacing size, by frequency splitting method, measure described to be measured

Wave plate retardation, computing formula is:

the bit phase delay that wherein φ is described wave plate to be measured, Δ ν is described laser instrument split-mode frequency difference at the same level, Δ ν ' is described laser instrument adjacent level split-mode frequency difference;

Step b-2), if described addition result is about twice longitudinal mode spacing size, adopt longitudinal mode direct-reading method to treat described in measuring

Survey wave plate retardation, computing formula: half-wave plate is

full-wave plate is $\mathrm{\φ}=\mathrm{\π}*(2\±|\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}\left|\right),$

The bit phase delay that wherein φ is described wave plate to be measured, Δ ₁for one in the two successive stages longitudinal mode spacing of continuous three longitudinal modes formation of described laser instrument, Δ ₂another in the two successive stages longitudinal mode spacing forming for continuous three longitudinal modes of described laser instrument;

Step c) if step b) in there is moding phenomenon, with additional wave plate, replace described wave plate to be measured to put into described laserresonator by step method a), use step b-1) bit phase delay of the described additional wave plate of described frequency splitting method measurement; Again described wave plate to be measured is also put into laserresonator by step method a), and the quick shaft direction that makes described wave plate to be measured is parallel to the fast axle of described additional wave plate, adopting step b-1) described frequency splitting method measures the bit phase delay under described wave plate to be measured and described additional wave plate acting in conjunction; And the bit phase delay under described acting in conjunction deducts the bit phase delay of described additional wave plate, thereby obtain the bit phase delay of described wave plate to be measured.

Reality can also adopt some bearing calibrations to improve wave plate measuring accuracy in measurement.Wherein mainly for wave plate position is non-, align, laser instrument unrelieved stress causes the wave plate measuring system error that birefringence and temperature variation cause, measurement result is revised and compensated, and they form the supplementary technology scheme that wave plate is measured.

After putting into the wave plate normal to be measured of resonator cavity and overlapping completely with laser axis, it is high one more than the order of magnitude that the frequency difference that frequency splitting produces is understood the tuning amount causing than nonlinear effect in only by chamber in the long tuning process in chamber, and as quarter-wave plate produces the tuning amount of frequency difference that two split-modes produce during translation on laser band, can to arrive 10MHz even higher.Due to the impact of various enchancement factors, this effect can make near the frequency difference value discrete value increase of reading isocandela point, and the bit phase delay that finally obtains wave plate to be measured can change very large, has reduced measuring repeatability and precision.Therefore should avoid wave plate to insert the frequency difference causing after laser instrument tuning abnormal.The present invention proposes to make wave plate when mounted, and the method that the relative laser axis of its face normal is tilted is eliminated this impact.In fact, as long as wave plate is at least 15 minutes with respect to the pitch angle of laser axis, the tuning abnormal phenomenon of frequency difference can be eliminated.Same for used half outside gas laser, it is anti-reflection, and window is adding the certain angle that also can tilt man-hour in order to avoid generation frequency difference is tuning abnormal.But after wave plate slant setting, the optical path difference of its o light and e light, the refractive index of the difference correspondence of o light and e light, and the net thickness of wave plate all will change, and so will bring the non-aligned position error of wave plate.For by this systematic error compensation, when system debug, adjusting wave plate mounting bracket face normal tilts with respect to laser axis, the two pitch angle becoming is at least 15 minutes, with contactless angular instrument, record the size at this pitch angle, by angle of inclination value record, calculate the extra bits of bringing after wave plate tilts by this pitch angle and differ, and as systematic error compensation value (it should be noted that this offset is the function of wave plate thickness).Adopt foregoing measuring process to measure after wave plate retardation, according to the pitch angle of record and wave plate thickness estimated value to be measured, calculate actual error offset, wave plate measurement result is revised and obtained wave plate retardation to be measured.In fact can make wave plate face normal tilt with respect to laser axis along any direction, just will calculate the non-aligned position error of wave plate of introducing thus, in the end in measurement result, be revised.A kind of fairly simple method is to make one of wave plate fast and slow axis to be measured be parallel to the initial polarization direction of laser, its face normal tilts with respect to laser axis along slow axis simultaneously, the non-aligned position error of wave plate causing like this will only have change and the o light of wave plate net thickness, the change of e light two-way optical path difference.When described wave plate to be measured is put into laserresonator, adopt eyes with non-contact method to measure the pitch angle size that described wave plate face normal becomes with laser axis, and calculate according to wave plate thickness the modified value that described wave plate to be measured tilts to introduce, computing formula is:

$\mathrm{\Δ}{\mathrm{\φ}}_a=\frac{\mathrm{\πd}}{\mathrm{\λ}}[1/\cos (\mathrm{\θ}/n{)}^{-1}](n_e-n_o)---\left(9\right)$

Δ φ wherein _afor described modified value, the size at the θ pitch angle that to be described wave plate face normal become with laser axis, n is described wave plate mean refractive index, n _e, n _ofor two principal refractive indexs of described wave plate, wave plate thickness to be measured described in d, deducts the systematic error that described modified value causes to compensate described pitch angle in the measurement result of the described wave plate to be measured then obtaining in step b from above or step c.

For helium-neon laser, in resonator cavity except wave plate other position phase anisotropy factor, comprise the birefringence that unrelieved stress causes (as in the chamber mirror of laser instrument, anti-reflection window and gain media, all may exist by process or unrelieved stress that thermal effect causes and cause stress birefrin), can cause frequency splitting frequency difference to change, to measurement result, bring systematic error.The birefringence that wherein unrelieved stress causes is main extra birefringence source, can take measures to compensate and eliminate its impact.The frequency splitting effect that unrelieved stress is caused can regard that a very little full-wave plate of phasic difference causes as, therefore detects unrelieved stress and just becomes the bit phase delay of measuring a full-wave plate.Because unrelieved stress is very little, the hidden frequency splitting of generation is also very little, and laser instrument is in degating region, can before inserting wave plate to be measured, adopt longitudinal mode direct-reading method to measure, and concrete steps are with described consistent above.Consider may be greater than or less than 0 degree after its equivalent full-wave plate, its absolute value representation is:

$\mathrm{\Δ}{\mathrm{\φ}}_r=\mathrm{\π}\×\left|\frac{\mathrm{\Δ}1-\mathrm{\Δ}2}{\mathrm{\Δ}1+\mathrm{\Δ}2}\right|---\left(10\right)$

Δ φ wherein _rfor the bit phase delay of described equivalent full-wave plate, Δ ₁for one in the two successive stages longitudinal mode spacing of continuous three longitudinal modes formation of described laser instrument, Δ ₂another in the two successive stages longitudinal mode spacing forming for continuous three longitudinal modes of described laser instrument.Wave plate to be measured is inserted after laserresonator, make its fast and slow axis direction consistent with the initial polarization direction of laser, the fast axle of the equivalent full-wave plate causing with unrelieved stress overlaps, and final measurement is equivalent to two effects that wave plate is compound.While adopting measurement above-mentioned half/full-wave plate, additional wave plate carries out the position principle of biasing mutually, deducts the phasic difference of unrelieved stress equivalence wave plate, bucking-out system error in measurement result.Concrete grammar is: when described wave plate to be measured not being put into described laserresonator, adopt longitudinal mode direct-reading method to measure the bit phase delay size of the equivalent full-wave plate that in chamber, unrelieved stress causes, its size is calculated by formula (10), the each bit phase delay that deducts equivalent full-wave plate in the measurement result obtaining in step b from above or step c, systematic error causing with unrelieved stress in compensated cavity measured after wave plate to be measured.The birefringence dispersiveness that unrelieved stress causes is larger, the systematic error of the laser tube that therefore can also select unrelieved stress birefringence minimum to reduce to compensate as far as possible.If phasic difference is less than 0.1 minute, it affects and substantially can ignore measurement result.In fact every sublaser carry out after its unrelieved stress substantially constant, therefore only need one-shot measurement equivalence wave plate phasic difference when system debug, and measured value is stored in process of measurement, each measurement after finishing carried out error compensation, need not all measure at every turn.

In fact the bit phase delay of wave plate changes with temperature, and temperature is embodied in two aspects, the one, the change of Refractive Index of Material, the 2nd, variation in thickness to the impact of wave plate retardation.To quartz crystal, the wave plate phasic difference change amount that temperature variation causes is:

$\mathrm{\Δ}{\mathrm{\φ}}_T=\frac{2\mathrm{\π}}{\mathrm{\λ}}d[(\frac{{\mathrm{dn}}_e}{\mathrm{dT}}-\frac{{\mathrm{dn}}_o}{\mathrm{dT}})+(n_e-n_o)a]\mathrm{\ΔT}---\left(11\right)$

Wherein α is the axial linear expansion coefficient of vertical light.The zero level quartz wave-plate that is about d=0.017mm for thickness, during 1 ℃ of temperature variation, the change amount of phasic difference is about 0.009 degree; And for the multistage wave plate of the about 1.5mm of thickness, during 1 ℃ of temperature variation, phasic difference variable quantity surpasses 0.8 degree.Result of calculation is negative value, shows that the phasic difference of wave plate is contrary with the variation tendency of temperature, and, along with temperature rises, phasic difference reduces.This shows that temperature is very large on the impact of multistage wave plate phasic difference.If the actual systematic error compensation temperature not being caused, will bring the relatively large deviation of measurement result.The method that reduces system temperature impact has two kinds: (1) measures the temperature of wave plate to be measured, and records this temperature value storage, when providing wave plate phasic difference measurement result, provides corresponding temperature simultaneously.If obtain the wave plate phasic difference under nominal temperature, temperature value substitution formula (11) can be obtained to the offset of wave plate retardation, from measured value, deduct this offset and can convert the wave plate retardation under nominal temperature.(2) be strict controlled under a certain isoperibol and measure, its net result i.e. wave plate retardation at temperature for this reason.In fact the measure that reduces the error that wave plate temperature change causes is: can between wave plate to be measured and laser gain pipe, configure aperture diaphragm reduce measuring process in the thermal-radiating impact of laser instrument, can adopt the temperature value of temperature sensor measurement wave plate to be measured and input computing machine to compensate simultaneously.Be subject to the restriction of temperature sensor measurement resolution and precision, the error of its introducing is about 0.02 degree.Because measuring process is very fast, and temperature variation is slow process, and in same one-shot measurement, changing can be very not large, therefore can think constant.It is to be noted that temperature is measured in wave plate methods and all existed at other the impact of result in wave plate measuring process.

In sum, the present invention is according to principle and the supplementary technology scheme of measuring any wave plate retardation, and proposition can be traced to the source and be measured the concrete measuring process of any wave plate retardation and be:

Step a) is put into wave plate to be measured the resonator cavity of helium-neon laser, one of fast and slow axis that makes described wave plate to be measured is parallel to the initial polarization direction of laser, and the face normal of described wave plate to be measured is tilted with respect to laser axis along slow-axis direction, adopt eyes with non-contact method to measure described wave plate face normal along the pitch angle size becoming with described laser axis;

Step b) anisotropy that unrelieved stress causes in not counting described laserresonator is during on the affecting of described wave plate measurement result to be measured, the chamber of tuning described laser instrument is long, if there is not moding phenomenon, measure split-mode frequency difference at the same level and adjacent level split-mode frequency difference, described split-mode frequency difference at the same level and described adjacent level split-mode frequency difference are added, and

Step b-1), if described addition result is about one times of longitudinal mode spacing size, by frequency splitting method, measure described to be measured

Wave plate retardation, computing formula is:

the bit phase delay that wherein φ is described wave plate to be measured, Δ ν is described laser instrument split-mode frequency difference at the same level, Δ ν ' is described laser instrument adjacent level split-mode frequency difference;

Step b-2), if described addition result is about twice longitudinal mode spacing size, adopt longitudinal mode direct-reading method to treat described in measuring

Survey wave plate retardation, computing formula: half-wave plate is

full-wave plate is $\mathrm{\φ}=\mathrm{\π}*(2\±|\frac{{\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2}{{\mathrm{\Δ}}_1+{\mathrm{\Δ}}_2}\left|\right),$

The bit phase delay that wherein φ is described wave plate to be measured, Δ ₁for one in the two successive stages longitudinal mode spacing of continuous three longitudinal modes formation of described laser instrument, Δ ₂another in the two successive stages longitudinal mode spacing forming for continuous three longitudinal modes of described laser instrument;

Step c) if step b) in there is moding phenomenon, with additional wave plate, replace described wave plate to be measured to put into described laserresonator by step method a), adopt step b-1) bit phase delay of the described additional wave plate of described frequency splitting method measurement; Again described wave plate to be measured is also put into laserresonator by step method a), and the quick shaft direction that makes described wave plate to be measured is parallel to the fast axle of described additional wave plate, adopting step b-1) described frequency splitting method measures the bit phase delay under described wave plate to be measured and described additional wave plate acting in conjunction; And the bit phase delay under described acting in conjunction deducts the bit phase delay of described additional wave plate, thereby obtain the bit phase delay of described wave plate to be measured;

Step d) is fetched and described wave plate to be measured detect thickness, and the pitch angle size becoming with described laser axis along slow-axis direction according to the wave plate face normal described to be measured recording in step a) is calculated the measurement result modified value causing after described wave plate to be measured tilts,

Computing formula:

Δ φ wherein _afor described modified value, the size at the θ pitch angle that to be described wave plate face normal to be measured become with described laser axis along slow-axis direction, n is described wave plate mean refractive index to be measured, n _e, n _ofor two principal refractive indexs of described wave plate to be measured, d is described wave plate thickness to be measured, and λ is optical maser wavelength; Then from step b) or c) deduct the systematic error that described modified value causes to compensate described pitch angle in the measurement result of the described wave plate to be measured that obtains.

For reducing the abnormal impact of the tuning amount of frequency difference, the face normal of described wave plate is at least 15 minutes along slow-axis direction with respect to the pitch angle of laser axis.While considering unrelieved stress causes in described laserresonator anisotropy on the affecting of described wave plate measurement result to be measured simultaneously, the systematic error that need to cause it is revised, method is: when described wave plate to be measured not being put into described laserresonator, adopt described longitudinal mode direct-reading method to measure the measurement result modified value that in described chamber, unrelieved stress causes, computing formula is:

Δ φ wherein _rfor described measurement result modified value, Δ 1 is in the two successive stages longitudinal mode spacing that forms of continuous three longitudinal modes of described laser instrument, Δ ₂another in the two successive stages longitudinal mode spacing forming for continuous three longitudinal modes of described laser instrument deducts described modified value, the systematic error causing with unrelieved stress in compensated cavity from obtain the measurement result of described wave plate to be measured.

The apparatus structure of the traced to the source measurement any wave plate retardation proposing is accordingly:

System is vertical unit, adopts half external cavity helium neon laser being comprised of the individual mirrors of Piezoelectric Ceramic a laser gain pipe and a slice to measure; The wave plate placing rack that two wave plate framves are housed is placed between laser gain pipe and individual mirrors, and its face normal tilts with respect to laser axis; Between wave plate to be measured and laser, can configure aperture diaphragm and reduce the impact of laser emission heat on wave plate temperature, and near wave plate, adopt temperature sensor measurement temperature; Laser instrument is divided into two bundles by orthogonal polarisation state from the output light of gain tube upper reflector end after a wollaston prism, by two photodetectors difference receiving light power signals, is input to computer recording different polarization states light intensity variation tendency after treated circuit; After laser becomes miter angle to place from the output light of individual mirrors end with wave plate fast and slow axis direction polaroid through an optical direction, produce photo-beat, by photodetector, received, and incoming frequency meter is read frequency difference value; Finally can calculate wave plate retardation according to the frequency difference value of twice measurement; Measure the treated circuit of Computer output control signal and amplify the piezoelectric ceramics of rear drive fixed laser resonator cavity individual mirrors, change voltage swing can tuned resonating cavity long.

Three, device explanation:

According to measurement mechanism proposed by the invention, it forms as shown in Figure 6, wherein:

Laser mirror 23 forms resonator cavity, gain tube 1 one end sealing-in catoptron 2, and the window 4 of two-sided anti-reflection film is plated in other end sealing-in; Catoptron 3 is arranged on piezoelectric ceramics 5, can be driven and be moved along laser axis direction by piezoelectric ceramics 5; Wave plate 9 to be measured is placed on wave plate placing rack 6 with additional wave plate 10, wave plate placing rack 6 comprises an one dimension translation guide rail and two two-dimensional adjustment framves, the additional wave plate of wave plate to be measured is arranged on respectively on the wave plate frame of two two-dimensional adjustment framves, and translation guide rail can drive wave plate along vertical outwards translation; Aperture diaphragm 8, between wave plate 9 to be measured and laser gain pipe 1, stops that gain tube 1 heat radiation affects 9 temperature; Temperature sensor 7 is measured temperature near being positioned at wave plate 9 to be measured, and its numerical value is input to computing machine 17 records through controlling after electronic box 16 is processed by data communication port.Laser is divided into two bundles through wollaston prism 14 by orthogonal polarisation state from catoptron 2 end output light and is received by photodetector 15, and light intensity signal is input to computing machine 17 records through controlling after electronic box 16 is processed by FPDP; Laser instrument is received by photodetector 12 after polaroid 11 from catoptron 3 end output light, then sends into frequency meter 13, and frequency meter 13 is inputted computing machine 17 by the frequency difference value recording by FPDP and calculated wave plate retardation; At wave plate, measuring the control signal of computer-chronograph 17 outputs extends long with tuning laser chamber through controlling electronic box 16 amplification rear drive piezoelectric ceramics 5; Whole resonator cavity partly covers on the impact that reduces environmental perturbation in outer cover 18.

During measurement, the wave plate to be measured 9 of a unknown bits phase retardation is put on the wave plate placing rack 6 of laser cavity, made one of its fast and slow axis be parallel to the initial polarization direction of laser.Computing machine 17 starts process of measurement and exports control signal long through controlling electronic box 16 rear drive piezoelectric ceramics 5 elongation tuning laser chambeies.By photodetector 15, receive two-way cross polarization light intensity and be transferred to computer program simultaneously and show.If there is not moding phenomenon in the long tuning process in chamber, continue to drive piezoelectric ceramics 5 to extend.When differentiation two-way light reaches isocandela point, program stopped drives piezoelectric ceramics 5 to extend, read the frequency difference size the record that by frequency meter 13, are recorded two split-modes now, by temperature sensor 7, read near current wave plate temperature and be input in computing machine 17 and show current temperature value after 16 processing simultaneously.After repeatedly duplicate measurements is averaged, continue to be extended by driven by program piezoelectric ceramics 5, and receive the light intensity signal that photodetector 15 transmits.When differentiation reaches second isocandela point, program stopped drives piezoelectric ceramics 5, reads two split-modes frequency extent the records on Laser output band that recorded by frequency meter 13, and repeatedly duplicate measurements is averaged.Computer program is differentiated according to the frequency extent of twi-read: if twice frequency difference sum is about one times of longitudinal mode spacing, wave plate to be measured is non-half/full-wave plate, proportion disintegrating method is measured wave plate retardation, and at isocandela point o light and e light light intensity variation tendency, differentiate measurement result according to twice, after the systematic error that last compensate for residual stress and wave plate tilt to cause, provide wave plate actual bit phase retardation, show temperature when wave plate is measured simultaneously; If twice frequency difference sum is about twice longitudinal mode spacing, wave plate to be measured is to depart from the half/full-wave plate that desirable half/full-wave plate is very little, adopt longitudinal mode direct-reading method to measure wave plate retardation to be measured, and differentiate measurement result according to twice variation tendency at isocandela point o light and e light, after the systematic error that last compensate for residual stress and wave plate tilt to cause, provide wave plate actual bit phase retardation, show temperature when wave plate is measured simultaneously.In tuning process as long in fruit caving, there is moding phenomenon, wave plate to be measured is that bit phase delay departs from the half/full-wave plate that desirable half/full-wave plate is larger, first wave plate to be measured is taken out, additional wave plate 10 is placed on wave plate placing rack 6 wave plate frame below, makes one of its fast and slow axis be parallel to the initial polarization direction of laser.Start process of measurement and adopt described frequency method to measure, and carry out that result is differentiated and error compensation obtains adding wave plate phasic difference φ ₁.Then wave plate to be measured is put on wave plate placing rack 6 wave plate frame above, make its quick shaft direction parallel with additional wave plate quick shaft direction, restart routine adopts frequency splitting method as mentioned above to measure the bit phase delay under wave plate to be measured and additional wave plate acting in conjunction, and carries out that result is differentiated and error compensation obtains bit phase delay φ ₂thereby the bit phase delay that obtains described wave plate to be measured is φ ₂-φ ₁.

Laser frequency disintegrating method of the present invention is measured the device of Phase Retardation of Wave Plate, can realize the measurement to any wave plate retardation at a cover system, simple to operate, automatic discrimination wave plate measurement result, and bucking-out system error, its short-term measuring repeatability is better than 0.02 degree, and long-term measuring repeatability is better than 0.04 degree.And owing to adopting laser frequency measurement wave plate retardation, can be traceable to optical maser wavelength, can provide reference data for other wave plate measuring methods, as tracing to the source, measure the device of any wave plate retardation.

In the several embodiment that provide in the application, should be understood that disclosed system, apparatus and method can realize by another way.For example, device embodiment described above is only schematic, for example, the division of described unit, be only that a kind of logic function is divided, during actual realization, can have other dividing mode, for example a plurality of unit or assembly can in conjunction with or can be integrated into another system, or some features can ignore, or do not carry out.In addition, shown or discussed coupling each other or direct-coupling or communication connection can be indirect coupling or the communication connections by some interfaces, device or unit, can be also electric, machinery or other form connect.

The described unit as separating component explanation can or can not be also physically to separate, and the parts that show as unit can be or can not be also physical locations, can be positioned at a place, or also can be distributed in a plurality of network element.Can select according to the actual needs some or all of unit wherein to realize the object of embodiment of the present invention scheme.

In addition, each functional unit in each embodiment of the present invention can be integrated in a processing unit, can be also that the independent physics of unit exists, and can be also that two or more unit are integrated in a unit.Above-mentioned integrated unit both can adopt the form of hardware to realize, and also can adopt the form of SFU software functional unit to realize.

If the form of SFU software functional unit of usining described integrated unit realizes and during as production marketing independently or use, can be stored in a computer read/write memory medium.Understanding based on such, the part that technical scheme of the present invention contributes to prior art in essence in other words, or all or part of of this technical scheme can embody with the form of software product, this computer software product is stored in a storage medium, comprise that some instructions are with so that a computer equipment (can be personal computer, server, or the network equipment etc.) carry out all or part of step of method described in each embodiment of the present invention.And aforesaid storage medium comprises: various media that can be program code stored such as USB flash disk, portable hard drive, ROM (read-only memory) (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disc or CDs.

The above; it is only the specific embodiment of the present invention; but protection scope of the present invention is not limited to this; anyly be familiar with those skilled in the art in the technical scope that the present invention discloses; can expect easily modification or the replacement of various equivalences, within these modifications or replacement all should be encompassed in protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.

Claims (8)

1. laser frequency method is measured a device for Phase Retardation of Wave Plate, it is characterized in that, comprising:

Helium-neon laser, described helium-neon laser comprises gain tube and individual mirrors, the two ends of described gain tube are fixed wtih respectively stationary mirror and anti-reflection window, the reflecting surface of described individual mirrors is relative with described anti-reflection window, described stationary mirror and described individual mirrors form the resonator cavity of described helium-neon laser, and the non-reflecting surface of described individual mirrors is connected with piezoelectric ceramics;

Wave plate support, described wave plate support is between described anti-reflection window and described individual mirrors, described wave plate support comprises parallel guide rail and is fixed on the adjusting support that at least two dimension angular on described guide rail regulates, wave plate to be measured and/or additional wave plate are placed on respectively on described adjusting support, and face normal tilts with respect to the laser axis of described helium-neon laser while making described wave plate to be measured and/or additional wave plate be placed on described adjusting support;

Light intensity probe unit, described light intensity probe unit is arranged on a side of described helium-neon laser, relative with the stationary mirror on described gain tube, for two orthogonal polarisation state light intensity of described helium-neon laser output are measured;

Frequency difference probe unit, described frequency difference probe unit is arranged on the opposite side of described helium-neon laser, relative with described individual mirrors, for measuring the difference on the frequency of laser of two orthogonal polarisation state of described helium-neon laser output;

Controller, described controller and described light intensity probe unit, described frequency difference probe unit and described piezoelectric ceramics electricity are connected, for control survey process and export measurement result.

2. device according to claim 1, it is characterized in that, described light intensity probe unit comprises wollaston prism and the first photodetector, described wollaston prism is divided into two-beam by the output light of described laser instrument by orthogonal polarisation state, and described the first photodetector is arranged to receive respectively described two-beam.

3. device according to claim 1, it is characterized in that, described frequency difference probe unit comprises polaroid, the second photodetector and frequency meter, described polaroid be arranged to optical direction respectively with the fast axle of described wave plate to be measured and slow axis in angle of 45 degrees, frequently, described frequency meter is connected with the output terminal electricity of described the second photodetector the photo-beat that two orthogonal polarisation state laser that described the second photodetector is arranged to survey described helium-neon laser output form after by described polaroid.

4. device according to claim 1, is characterized in that, the face normal of the anti-reflection window on described gain tube is at least 15 minutes with respect to the angle of inclination of the axis of the laser of described helium-neon laser output.

5. device according to claim 4, is characterized in that, described device also comprises compensating module, and described compensating module, for according to described angle of inclination, compensates processing to the measurement result of described controller output.

6. device according to claim 1, is characterized in that, described device also comprises the temperature sensor being arranged on described wave plate support.

7. device according to claim 1, is characterized in that, described device also comprises the aperture diaphragm being arranged between described anti-reflection window and described wave plate support.

8. according to the device described in any one in claim 1 to 7, it is characterized in that, the sharp light wavelength of described helium-neon laser output is 632.8nm.

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