A kind of optical maser wavelength amendment type planar reflector laser interference instrument and measuring method thereof
Technical field
The present invention relates to a kind of Precision Inspection and instrument field, particularly a kind of optical maser wavelength amendment type planar reflector laser interference instrument and measuring method thereof.
Background technology
The appearance of laser instrument, makes ancient interference technique be developed rapidly, and laser has that brightness is high, good directionality, monochromaticity and the feature such as coherence is good, and laser interferometry techniques is comparative maturity.Laser interferometry system is applied widely: the measurement of accurate length, angle is as the detection of linear scale, grating, gauge block, precision lead screw; Position detecting system in exact instrument is as the control of precision optical machinery, correction; Position detecting system in large scale integrated circuit specialized equipment and detecting instrument; Minute sized measurement etc.At present, in most of laser interference length-measuring system, all have employed Michelson interferometer or similar light channel structure, such as, single frequency laser interferometer conventional at present.
Single frequency laser interferometer is the light beam sent from laser instrument, after beam-expanding collimation, be divided into two-way by spectroscope, and reflects can be combined in spectroscope from stationary mirror and moving reflector respectively and produce interference fringe.When moving reflector moves, the light intensity change of interference fringe is converted to electric impulse signal by the photo-electric conversion element in receiver and electronic circuit etc., after shaping, amplification, input up-down counter calculate overall pulse number N, calculating formula L=N × λ/2 are pressed again by robot calculator, in formula, λ is optical maser wavelength, calculates the displacement L of moving reflector.
In actual use, present inventor finds, current single frequency laser interferometer only counts the integral part of laser interference ripple, namely, can only when the most capable and experienced relating to, namely the strongest constructive interference time count, and in laser interference process, counting is then difficult to during non-the strongest constructive interference, so make, its measuring accuracy is limited to the wavelength of laser, its precision can only be the integral multiple of half optical maser wavelength, but in actual measurement, the shift value that testee produces is all random usually, it can not be just the integral multiple of half optical maser wavelength, namely, also have the fraction part exceeding half optical maser wavelength, this partial distance can not be reflected by above-mentioned receiver, so also cannot calculate.Simultaneously due to the change of atmospheric environment, as the change of temperature, humidity and air pressure, optical maser wavelength changes in the environment, and the precision that this directly causes laser interference to find range reduces.
Although in conventional arts, the half wavelength of laser has had high precision, but, along with the progress of science and technology, in Technology of Precision Measurement field, the accuracy requirement of precision measurement is more and more higher, the precision of this half optical maser wavelength, day by day can not meet the requirement of people again.
So, based on above-mentioned deficiency, need a kind of laser interferometer that more high measurement accuracy can be provided at present badly.
Summary of the invention
The object of the invention is to be limited to optical maser wavelength for current laser interferometer precision, and the deficiency that measurement environment has a direct impact optical maser wavelength, a kind of laser interferometer and the measuring method thereof with more high measurement accuracy are provided.
In order to realize foregoing invention object, the invention provides following technical scheme:
A kind of optical maser wavelength amendment type planar reflector laser interference instrument, comprise lasing light emitter, fixed pan catoptron, photodetector, measurement plane reflector apparatus and spectroscope, described measurement plane reflector apparatus comprises measurement plane catoptron and accurate displacement device, the laser beam of described lasing light emitter injection is divided into the first laser beam and the second laser beam after described spectroscope, fixed pan catoptron described in first laser beam directive, spectroscope described in directive again after the reflection of described fixed pan catoptron, photodetector described in directive after spectroscope again, measurement plane catoptron described in second laser beam directive, spectroscope described in directive again after the reflection of described measurement plane catoptron, photodetector described in directive after spectroscope, first laser beam and the second laser beam are interfering during photodetector described in directive, described measurement plane catoptron is arranged on described accurate displacement device, described accurate displacement device is arranged on testee, described accurate displacement device for described measurement plane catoptron provide with testee displacement in the same way or reverse displacement.
In the such scheme of the application, due to measurement plane catoptron is arranged on accurate displacement device, and accurate displacement device is arranged on testee, when testee is subjected to displacement, testee drives accurate displacement device, and then drive measurement plane catoptron, so, when testee is subjected to displacement, in displacement process, due to the change of the second laser beam light path, make, the interference state of the first laser beam and the second laser beam also changes thereupon, before starting surveying work, start accurate displacement device, measurement plane catoptron is made to produce displacement, the sense of displacement of described measurement plane catoptron and the sense of displacement of testee are on the same line, when photodetector detects the strongest constructive interference, stop accurate displacement device, and photodetector counting is reset, and then start the displacement of measuring testee, in the first laser beam and the second laser beam interference state change process, the times N of the strongest constructive interference of photodetectors register, when testee mobile end, when remaining static, photodetector stops counting, now, by accurate displacement device, measurement plane catoptron is moved on the sense of displacement of testee, and observe photodetector, when photodetector detects the strongest constructive interference, stop accurate displacement device, and read the shift value △ L that accurate displacement device provides for measurement plane catoptron.
If displacement △ L is identical with the sense of displacement of testee, then, the shift value L=N × λ/2+ (λ/2-△ L) of the actual generation of testee, wherein △ L < λ/2, in formula, λ is optical maser wavelength;
If displacement △ L is contrary with the sense of displacement of testee, then, the shift value L=N × λ/2+ △ L of the actual generation of testee, wherein △ L < λ/2, in formula, λ is optical maser wavelength.
So, pass through said structure, also measure add in displacement detecting result by exceeding half optical maser wavelength fraction part △ L in testee actual displacement, and then make the displacement result that obtains measured by the laser interferometer of the application more accurate, its degree of accuracy, higher than half optical maser wavelength, specifically depends on the displacement accuracy that accurate displacement device can provide.
As the preferred version of the application, described accurate displacement device comprises support platform and is arranged on the drive unit in described support platform, described support platform matches with described testee, and described drive unit is the displacement that described measurement plane catoptron is provided on testee sense of displacement.
As the preferred version of the application, described drive unit is Piezoelectric drive unit.
In this programme, adopt the ceramic material that mechanical energy and electric energy can be changed mutually by Piezoelectric drive unit, its deformation quantity produced under electric field action is very little, be no more than at most the micro-displacement of 1/10000000th of size own, there is good repetitive distortion recovery capability, good stability, precision are high, further increase accuracy and the reliability of the application's accurate displacement device.
As the preferred version of the application, described accurate displacement device also comprises the first displacement piece be arranged in described support platform and the second displacement piece be arranged in described first displacement piece, described drive unit matches with described first displacement piece, for described first displacement piece provides the displacement along described support platform, described first displacement piece has an inclined-plane tilted relative to its sense of displacement, described second displacement piece is slidably arranged on the inclined-plane of described first displacement piece, described second displacement piece can be slided along the inclined-plane of described first displacement piece, snug fit between described first displacement piece and the second displacement piece, described measurement plane catoptron is arranged in described second displacement piece, described support platform is also provided with restraint device, described second displacement piece of described restraint device restriction is along moving on described first displacement piece sense of displacement, make when the first displacement piece is driven by described drive unit and produces displacement, described second displacement piece is driven by described first displacement piece and produces displacement, and, the sense of displacement of described second displacement piece and the sense of displacement of described first displacement piece perpendicular, the inclined-plane of described first displacement piece and the angle of its sense of displacement are A degree, 0<A<45.
In the such scheme of the application, drive unit matches with the first displacement piece, for the first displacement piece provides the displacement along support platform, first displacement piece has an inclined-plane tilted relative to its sense of displacement, second displacement piece is slidably arranged on the inclined-plane of the first displacement piece, second displacement piece can be slided along the inclined-plane of the first displacement piece, when accurate displacement device works, drive unit provides certain displacement to promote the first displacement piece, now, because restraint device limits the second displacement piece along moving on the first displacement piece sense of displacement, make the sense of displacement of the sense of displacement of the second displacement piece and the first displacement piece perpendicular, so, the displacement of the second displacement piece is relevant to the displacement that drive unit provides for the first displacement piece, also relevant with the angle of its sense of displacement to the inclined-plane of the first displacement piece.
Namely, if the inclined-plane of the first displacement piece and the angle of its sense of displacement are A degree, when the displacement that drive unit provides is X, second displacement piece is being Y=Xtan (A) perpendicular to the displacement that drive unit direction of motion produces, so, when included angle A is less than 45 degree, the displacement that one is less than X value will be obtained, when further reducing included angle A, displacement Y also reduces thereupon, so, make in the scheme of the application, accurate displacement device is by changing the mode of precision with stroke, directly enhance the precision of the application's accurate displacement device, also just further improve the measuring accuracy of the application's laser interferometer.
As the preferred version of the application, be also provided with the magnetic magnetic part of tool between described first displacement piece and described support platform, described second displacement piece has magnetic, state that described second displacement piece and described magnetic part are that there is a natural attraction between the sexes.Making the first displacement piece when being pushed, can keep fitting tightly with the second displacement piece, ensure the precision of the application's accurate displacement device, and then ensure the measuring accuracy of the application's laser interferometer.
As the preferred version of the application, described second displacement piece and described measurement plane catoptron are integral type structure.
In such scheme, the second displacement piece and measurement plane catoptron are integral type structure, that is, directly a reflecting surface is set in the second displacement piece, makes itself to form measurement plane catoptron, so, simplify the structure of the application's laser interferometer, convenient debugging and use.
In actual measurement environment, the measuring accuracy of laser interferometer is also by the impact of actual measurement environment, due in actual measurement environment, the change of the temperature of air, humidity and air pressure, capital causes the change of air dielectric, and then the wavelength of laser also can be changed, make final result of calculation there is error;
Although at present, also there is the device measuring air refraction, the atmospheric temperature of single locus, humidity and air pressure are measured, by wavelength compensation formula, optical maser wavelength is revised, but it is merely able to detect local air, and in the displacement measurement field of the application, because its displacement carries out in a region, in this region, each parameter of the air of each position all has difference, particularly there is the situations such as larger thermograde, moist gradient and barometric gradient, comparatively big error will be there is with single-point parameters revision optical maser wavelength.
So, for these reasons, in this application, detect current measurement environment in measuring process under, the environment effective wavelength λ ' of laser, so the problem directly avoiding zones of different air refraction difference and bring, so, reduce the error that environmental factor is brought, and then further improve the measuring accuracy of the application's laser interferometer.
Disclosed herein as well is a kind of measuring method for above-mentioned optical maser wavelength amendment type planar reflector laser interference instrument, it includes following step:
Step one: install planar reflector laser interference instrument of the present invention;
Step 2: measurement plane reflector apparatus is arranged on testee;
Step 3: debug corner reflector laser interferometer of the present invention, makes the satisfactory light path of formation, and, make the first laser beam and the second laser beam be in interference state;
Step 4: before starting surveying work, start accurate displacement device, measurement plane catoptron is made to produce displacement, the sense of displacement of described measurement plane catoptron and the sense of displacement of testee are on the same line, when photodetector detects the strongest constructive interference, stop accurate displacement device, and photodetector counting is reset;
Step 5: start surveying work, testee starts mobile, the times N of photodetectors register first laser beam and the strongest constructive interference of the second laser beam;
Step 6: testee displacement terminates, remain static, again start accurate displacement device, measurement plane catoptron is made to produce displacement, the sense of displacement of described measurement plane catoptron and the sense of displacement of testee are on the same line, when photodetector detects the strongest constructive interference again, stop described accurate displacement device, measurement plane catoptron is stopped;
Step 7: read the shift value △ L that accurate displacement device provides for described measurement plane catoptron;
Step 8: the strongest constructive interference times N and the measurement plane mirror displacements value △ L that record photodetectors register in measuring process.
Step 9: again start accurate displacement device, traverse measurement plane mirror, makes the number of times M of the strongest constructive interference of photodetectors register (M is positive integer), and reads measurement plane mirror displacements value Z corresponding to M constructive interference the strongest.According to Z=M × λ '/2, under drawing current measurement environment, effective wavelength the λ '=2Z/M of laser.
Step 10: the shift value calculating testee.
If displacement △ L is identical with the sense of displacement of testee, then, shift value L=N × λ '/2+ of the actual generation of testee (λ '/2-△ L), wherein △ L < λ '/2, in formula, λ ' is laser effective wavelength;
If displacement △ L is contrary with the sense of displacement of testee, then, shift value L=N × λ '/2+ △ L of the actual generation of testee, wherein △ L < λ '/2, in formula, λ ' is laser effective wavelength.
The measuring method of the application, owing to replenishing in the shift value of testee by measurement plane mirror displacements value △ L, directly enhances the measuring accuracy of testee displacement., by detecting the effective wavelength λ ' in measurement environment, namely the wavelength of laser being revised meanwhile, so reducing the error that environmental factor is brought, and then further improve the measuring accuracy of the application's laser interferometer.
As the preferred version of the application, described step 4 is in step 9, and the strongest described constructive interference can also be the most weak destructive interference.In this programme, carrying out in measuring process, photodetector is the number of times of record first laser beam and the most weak destructive interference of the second laser beam, so still can obtain the shift value L of the higher testee of precision.
Compared with prior art, beneficial effect of the present invention:
1, the fraction part △ L exceeding half optical maser wavelength in testee actual displacement is also measured add in displacement detecting result, and then make the displacement result that obtains measured by the laser interferometer of the application more accurate, its precision, higher than half optical maser wavelength, specifically depends on the displacement accuracy that accurate displacement device can provide;
2, detect the effective wavelength λ ' of laser in measurement environment, optical maser wavelength is revised, so, reduce the error that environmental factor is brought, and then further improve the measuring accuracy of the application's laser interferometer.
Accompanying drawing illustrates:
Fig. 1 is the light path schematic diagram of laser interferometer structure of the present invention;
Fig. 2 is that in the present invention, measurement plane catoptron and the second displacement piece are the schematic diagram of integral type structure,
Mark in figure:
1-lasing light emitter, 2-fixed pan catoptron, 3-photodetector, 4-measurement plane reflector apparatus, 5-spectroscope, 6-measurement plane catoptron, 7-accurate displacement device, 8-first laser beam, 9-second laser beam, 10-testee, 11-support platform, 12-drive unit, 13-first displacement piece, 14-second displacement piece, 15-inclined-plane, 16-restraint device, 17-magnetic part.
Embodiment
Below in conjunction with test example and embodiment, the present invention is described in further detail.But this should be interpreted as that the scope of the above-mentioned theme of the present invention is only limitted to following embodiment, all technology realized based on content of the present invention all belong to scope of the present invention.
Embodiment 1,
As Fig. 1, shown in 2, a kind of optical maser wavelength amendment type planar reflector laser interference instrument, comprise lasing light emitter 1, fixed pan catoptron 2, photodetector 3, measurement plane reflector apparatus 4 and spectroscope 5, described measurement plane reflector apparatus 4 comprises measurement plane catoptron 6 and accurate displacement device 7, the laser beam that described lasing light emitter 1 penetrates is divided into the first laser beam 8 and the second laser beam 9 after described spectroscope 5, fixed pan catoptron 2 described in first laser beam 8 directive, spectroscope 5 described in directive again after described fixed pan catoptron 2 reflects, photodetector 3 described in directive after spectroscope 5 again, measurement plane catoptron 6 described in second laser beam 9 directive, spectroscope 5 described in directive again after described measurement plane catoptron 6 reflects, photodetector 3 described in directive after spectroscope 5, first laser beam 8 and the second laser beam 9 are interfering during photodetector 3 described in directive, described measurement plane catoptron 6 is arranged on described accurate displacement device 7, described accurate displacement device 7 is arranged on testee 10, described accurate displacement device 7 for described measurement plane catoptron 6 provide with testee 10 displacement in the same way or reverse displacement.
In the present embodiment, due to measurement plane catoptron 6 is arranged on accurate displacement device 7, and accurate displacement device 7 is arranged on testee 10, when testee 10 is subjected to displacement, testee 10 drives accurate displacement device 7, and then drive measurement plane catoptron 6, so, when testee 10 is subjected to displacement, in displacement process, due to the change of the second laser beam 9 light path, the interference state of the first laser beam 8 and the second laser beam 9 is also changed thereupon, before starting surveying work, start accurate displacement device 7, measurement plane catoptron 6 is made to produce displacement, the sense of displacement of described measurement plane catoptron 6 and the sense of displacement of testee 10 are on the same line, when photodetector 3 detects the strongest constructive interference, stop accurate displacement device 7, and photodetector 3 is counted clearing, and then start the displacement of measuring testee 10, in the first laser beam 8 and the second laser beam 9 interference state change procedure, photodetector 3 records the times N of the strongest constructive interference, when testee 10 mobile end, when remaining static, photodetector 3 stops counting, now, by accurate displacement device 7, measurement plane catoptron 6 is moved on the sense of displacement of testee 10, and observe photodetector 3, when photodetector 3 detects the strongest constructive interference, stop accurate displacement device 7, and read the shift value △ L that accurate displacement device 7 provides for measurement plane catoptron 6.
If displacement △ L is identical with the sense of displacement of testee 10, then, shift value L=N × λ/2+ (λ/2-△ L) that testee 10 reality produces, wherein △ L < λ/2, in formula, λ is optical maser wavelength;
And if displacement △ L is contrary with the sense of displacement of testee 10, then, shift value L=N × λ/2+ △ L that testee 10 reality produces, wherein △ L < λ/2, in formula, λ is optical maser wavelength.
So, pass through said structure, the fraction part △ L exceeding half optical maser wavelength in testee 10 actual displacement is also measured and adds in displacement detecting result, and then make the displacement result that obtains measured by the laser interferometer of the application more accurate, its precision, higher than half optical maser wavelength, specifically depends on the displacement accuracy that accurate displacement device 7 can provide.
Embodiment 2,
As shown in Figure 1, 2, laser interferometer as described in Example 1, the drive unit 12 that described accurate displacement device 7 comprises support platform 11 and is arranged in described support platform 11, described support platform 11 matches with described testee 10, described drive unit 12 is the displacement that described measurement plane catoptron 6 is provided on testee 10 sense of displacement, and described drive unit 12 is Piezoelectric drive unit.
In the present embodiment, the Piezoelectric drive unit 12 adopted is ceramic material mechanical energy and electric energy can changed mutually, its deformation quantity produced under electric field action is very little, be no more than at most the micro-displacement of 1/10000000th of size own, there is good repetitive distortion recovery capability, good stability, precision are high, further increase the precision of accurate displacement device 7 in the present embodiment.
Embodiment 3,
As Fig. 1, shown in 2, laser interferometer as described in Example 2, described accurate displacement device 7 also comprises the first displacement piece 13 be arranged in described support platform 11 and the second displacement piece 14 be arranged in described first displacement piece 13, described drive unit 12 matches with described first displacement piece 13, for described first displacement piece 13 provides the displacement along described support platform 11, described first displacement piece 13 has an inclined-plane 15 tilted relative to its sense of displacement, described second displacement piece 14 is slidably arranged on the inclined-plane 15 of described first displacement piece 13, described second displacement piece 14 can be slided along the inclined-plane 15 of described first displacement piece 13, snug fit between described first displacement piece 13 and the second displacement piece 14, described measurement plane catoptron 6 is arranged in described second displacement piece 14, described support platform 11 is also provided with restraint device 16, described restraint device 16 limits described second displacement piece 14 along moving on described first displacement piece 13 sense of displacement, make when the first displacement piece 13 is driven by described drive unit 12 and produces displacement, described second displacement piece 14 is driven by described first displacement piece 13 and produces displacement, and, the sense of displacement of described second displacement piece 14 and the sense of displacement of described first displacement piece 13 perpendicular, the inclined-plane 15 of described first displacement piece 13 is A degree with the angle of its sense of displacement, preferred 0<A<45.
In an embodiment, drive unit 12 matches with the first displacement piece 13, for the first displacement piece 13 provides the displacement along support platform 11, first displacement piece 13 has an inclined-plane 15 tilted relative to its sense of displacement, second displacement piece 14 is slidably arranged on the inclined-plane 15 of the first displacement piece 13, second displacement piece 14 can be slided along the inclined-plane 15 of the first displacement piece 13, when accurate displacement device 7 works, drive unit 12 provides certain displacement to promote the first displacement piece 13, now, because restraint device 16 limits the second displacement piece 14 along moving on the first displacement piece 13 sense of displacement, make the sense of displacement of the sense of displacement of the second displacement piece 14 and the first displacement piece 13 perpendicular, so, the displacement of the second displacement piece 14 is relevant to the displacement that drive unit 12 provides for the first displacement piece 13, also relevant with the angle of its sense of displacement to the inclined-plane 15 of the first displacement piece 13.
That is, if the inclined-plane 15 of the first displacement piece 13 is A degree with the angle of its sense of displacement, when the displacement that drive unit 12 provides is X, the second displacement piece 14 is being Y=Xtan (A) perpendicular to the displacement that drive unit 12 direction of motion produces.Preferably, when included angle A is less than 45 degree, the displacement that one is less than X value will be obtained, when further reducing included angle A, displacement Y also reduces thereupon, so, make in the present embodiment, accurate displacement device 7, by changing the mode of precision with stroke, directly enhances the precision of the present embodiment accurate displacement device 7, also just further improves the measuring accuracy of the present embodiment laser interferometer.
Embodiment 4,
As shown in Figure 2, laser interferometer as described in Example 3, the magnetic magnetic part 17 of tool is also provided with between described first displacement piece 13 and described support platform 11, described second displacement piece 14 has magnetic, state that described second displacement piece 14 and described magnetic part 17 be that there is a natural attraction between the sexes, described second displacement piece 14 and described measurement plane catoptron 6 are integral type structure.Make the first displacement piece 13 when being pushed, measurement plane catoptron 6 can keep fitting tightly with the second displacement piece 14, ensure the precision of the application's accurate displacement device 7, and then ensure the measuring accuracy of the application's laser interferometer, second displacement piece 14 is integral type structure with measurement plane catoptron 6, that is, directly a reflecting surface is set in the second displacement piece 14, make itself to form measurement plane catoptron 6, so, simplify the structure of the present embodiment laser interferometer, convenient debugging and use.
Embodiment 5,
As shown in Figure 1, 2, a kind of measuring method for above-mentioned optical maser wavelength amendment type planar reflector laser interference instrument, it includes following step:
Step one: install planar reflector laser interference instrument of the present invention;
Step 2: measurement plane reflector apparatus 4 is arranged on testee 10;
Step 3: debug corner reflector laser interferometer of the present invention, makes the satisfactory light path of formation, and, make the first laser beam 8 and the second laser beam 9 be in interference state;
Step 4: before starting surveying work, start accurate displacement device 7, measurement plane catoptron 6 is made to produce displacement, the sense of displacement of described measurement plane catoptron 6 and the sense of displacement of testee 10 are on the same line, when photodetector 3 detects the strongest constructive interference, stop accurate displacement device 7, and photodetector 3 is counted clearing;
Step 5: start surveying work, testee 10 starts mobile, and photodetector 3 records the times N of the first laser beam 8 and the strongest constructive interference of the second laser beam 9;
Step 6: testee 10 displacement terminates, remain static, again start accurate displacement device 7, measurement plane catoptron 6 is made to produce displacement, the sense of displacement of described measurement plane catoptron 6 and the sense of displacement of testee 10 are on the same line, when photodetector 3 detects the strongest constructive interference again, stop described accurate displacement device 7, measurement plane catoptron 6 is stopped;
Step 7: read the shift value △ L that accurate displacement device 7 provides for described measurement plane catoptron 6;
Step 8: the strongest constructive interference times N that in record measuring process, photodetector 3 records and measurement plane catoptron 6 shift value △ L.
Step 9: again start accurate displacement device 7, traverse measurement plane mirror 6, makes photodetector 3 record the number of times M (M is positive integer) of the strongest constructive interference, and read measurement plane catoptron 6 shift value Z corresponding to M constructive interference the strongest.According to Z=M × λ '/2, under drawing current measurement environment, effective wavelength the λ '=2Z/M of laser.
Step 10: the shift value calculating testee 10.
If displacement △ L is identical with the sense of displacement of testee 10, then, shift value L=N × λ '/2+ (λ '/2-△ L) that testee 10 reality produces, wherein △ L < λ '/2, in formula, λ ' is laser effective wavelength;
If displacement △ L is contrary with the sense of displacement of testee 10, then, shift value L=N × λ '/2+ △ L that testee 10 reality produces, wherein △ L < λ '/2, in formula, λ ' is laser effective wavelength.
The measuring method of the present embodiment, owing to replenishing measurement plane catoptron 6 shift value △ L the measuring accuracy directly enhancing testee 10 displacement in the shift value of testee 10., by detecting the effective wavelength λ ' in measurement environment, namely the wavelength of laser being revised meanwhile, so reducing the error that environmental factor is brought, and then further improve the measuring accuracy of the application's laser interferometer.
Embodiment 6,
As shown in Figure 1, 2, measuring method as described in Example 5, described step 4 is in step 9, and the strongest described constructive interference can also be the most weak destructive interference.In this programme, carrying out in measuring process, photodetector 3 is number of times of record first laser beam 8 and the most weak destructive interference of the second laser beam 9, so still can obtain the shift value L of the higher testee 10 of precision.
Above embodiment only in order to the present invention is described and and unrestricted technical scheme described in the invention, although this instructions with reference to each above-mentioned embodiment to present invention has been detailed description, but the present invention is not limited to above-mentioned embodiment, therefore anyly the present invention is modified or equivalent to replace; And all do not depart from technical scheme and the improvement thereof of the spirit and scope of invention, it all should be encompassed in the middle of right of the present invention.