CN1034763C - Heterodyne frequency-shifting-type twin laser interferometer with common-mode suppressed frequency shift interference - Google Patents

Heterodyne frequency-shifting-type twin laser interferometer with common-mode suppressed frequency shift interference Download PDF

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CN1034763C
CN1034763C CN93109465A CN93109465A CN1034763C CN 1034763 C CN1034763 C CN 1034763C CN 93109465 A CN93109465 A CN 93109465A CN 93109465 A CN93109465 A CN 93109465A CN 1034763 C CN1034763 C CN 1034763C
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interferometer
frequency
reflecting
laser
heterodyne
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CN1085315A (en
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陈赋
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陈赋
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Abstract

The present invention relates to a heterodyne frequency-shifting type twin laser interferometer with common-mode suppressed frequency shift interference, which can be used for manufacturing precise length measuring instruments, velocimeters, etc. In the present invention, a reference optical path is added into a Michelson interferometer, and a laser device of an original interferometer and a reflecting surface are jointly used for forming another interferometer to form a twin interferometer. The common reflecting surface moves back-and-forth to become a heterodyne frequency shift surface to replace the function of double frequencies for reducing low-frequency noise errors. The frequency variation of photoelectric signals caused by the frequency drift of the laser device is totally the same (in a common mode) to the two interferometers, and frequency drift errors can be canceled out by subtracting frequency syntheses. The present invention has the advantages of simple structure and low cost, and a measurement error delta f/f is at most 1*10<-18>.

Description

Common mode inhibition is floated frequently and is disturbed the heterodyne frequency-shifting-type twin laser interferometer
The present invention relates to measurement technology, belong to the Technology of Precision Measurement field of length, speed.
Laser interferometer is because its measuring accuracy height, in the precision measurement of length, angle, velocity of displacement and angular velocity etc., obtained widely using, also available simultaneously it make specialized instrument and equipments such as seismograph, strainmeter, gravity meter and industrial automation supervising device.
The measuring accuracy of laser interferometer depends primarily on the stability of laser frequency (or wavelength).The frequency-selecting effect of laser resonator is the assurance of the good monochromaticity of laser.The length of resonant cavity can change with environmental factors such as temperature, causes the variation of can drifting about in time of laser instrument emitted laser frequency, causes the measuring error of interferometer.The way commonly used that improves measuring accuracy is the frequency stabilization that makes laser instrument.In making the stable various measures of laser frequency, with the best results of servo frequency stabilization system.Wherein the frequency stabilization system that obtains the error signal of servo frequency stabilization system with Zeeman effect simultaneously can also obtain double-frequency laser.The interferometer that makes with two-frequency laser can reduce the error that the low frequency noise of photodetector causes significantly, and it is stronger than the antijamming capability of single frequency laser interferometer, working environment is required also just lower.So modal in the commodity is the two-frequency laser interferometer of Zeeman effect frequency stabilitzation.(consulting " laser technology ", the Hunan science tech publishing house that Huazhong Institute of Technology, University Of Tianjin, Northwest Inst. of Telecommunication Engineering compile in collaboration with publishes).
Though use the laser servo frequency stabilization system can reduce the measuring error of interferometer significantly, make interferometer structure complexity, cost costliness, main is that the world highest frequency degree of stability Δ f/f that laser frequency stabilization reaches is 1 * 10 -14, 1 * 10 -15The still following target (consulting " China's laser development strategy research ", Shanghai scientific and technical literature publishing house 1988) of frequency stability, the Frequency Stabilized Lasers interferometer is not less than 1 * 10 because of the laser frequency measuring error Δ f/f that causes that drifts about at present -14
A kind of acoustooptic modulation formula heterodyne ineterferometer (No. 5061071, United States Patent (USP)) as shown in Figure 4.It comprises: 1, play a two-frequency laser by swashing heterodyne system, this system of forming in device (10), polarization beam apparatus (14) and (18), reflecting surface (16) and (20) and acousto-optic modulator (22) and (24), detect the difference frequency signal Sf of acoustooptic modulation generation by photodetector (30) B2, by first interference system that said heterodyne system, polarization beam apparatus (40), the reflecting surface (34) which is provided with object lens (36), reflecting surface (38) and photodetector array (56) constitute, the interference signal Sf that this system produces WBe used for controlling the flexible of piezoelectric ceramics regulator (70), the focus of object lens (36) is always dropped on the testee surface (34); 3, by second interference system that said heterodyne system, polarization beam apparatus (46), the catoptron (42), stationary mirror (44) and the photodetector (68) that move with object lens (36) constitute, the interference signal SfD and the said difference frequency signal Sf of this system's generation BComparing is used for measuring object lens (36) position and moves frequency displacement and the phase change that is produced, thereby provides the fluctuating situation on testee surface (34).
The antijamming capability that this acoustooptic modulation formula heterodyne ineterferometer had both had a double frequency interferometer can suppress the advantage of low frequency noise by force, again can continuous working under need not the situation of servo frequency stabilization system, so cost can reduce.But it still will thereupon use annexes such as the quarter wave plate and the polarizer again with expensive polarization beam apparatus, and structure is still complicated, and cost still is higher.Its topmost shortcoming is that measuring accuracy is low.Because it does not use laser frequency stabilizing system, independently of one another on its first and second interference system functions, of no usely solve the beat frequency measuring error problem that laser frequency drift causes, this problem can not solve with two interference systems of this no specific symmetry of Fig. 4.And acousto-optic modulator can make the difference frequency signal Sf that modulates again because of the unstable of variation of temperature, power supply and the instability of self BChange in time, that is to say, double-frequency laser Shu Xianhou has different frequency differences when arriving photodetector (30) with (68), though all complete transfixion of all catoptrons, signal Sf DWith Sf BAlso different frequency values will be arranged, by comparing Sf DWith Sf BThe object lens of being tried to achieve (36) move the frequency displacement that is produced and just have error.The shakiness of acoustooptic modulation frequency and the shakiness of laser frequency all can influence the measuring accuracy of interferometer.Take measures such as constant humidity, voltage stabilizing and frequency stabilization if improve precision, incident is the increasing substantially of complicated and cost of interferometer.
The objective of the invention is to substitute traditional frequency-stabilizing method, make laser interferometer be reduced to 1 * 10 because of the measuring error Δ f/f that frequency drift produces with new method -18Below, making the simple in structure of interferometer simultaneously, cost is cheaper.
Essence of the present invention is: by laser instrument [1], part reflecting face [2], in the common interferometer of the Michelson form that reflecting surface [3] and [4] and photodetector [5] are formed, add one by part reflecting face [7], the reference path that reflecting surface [8] and photodetector [6] are formed, laser instrument [1] in the shared above-mentioned Michelson form interferometer of this reference path (to call stellar interferometer in the following text) and reflecting surface [4] constitute another interferometer (to call reference interferometer in the following text).Reference interferometer and stellar interferometer synthesize the twin laser interferometer that common mode inhibition is floated interference frequently, as shown in Figure 1.Because measure and the shared same laser instrument of reference interferometer, the electric signal of the photodetector of two interferometers [5,6] output simultaneously Stimulated Light device frequency drift shadow to, and change (abbreviation common mode variations) in time with identical pattern.Subtract each other two electric signal are synthetic, just can eliminate the influence that laser frequency is drifted about.Equally, the Doppler shift of the random motion of laser instrument [1] and shared reflecting surface [4] generation disturbs and is also eliminated.Remaining instrument is to measure the to be measured phase shifts signal of reflecting surface [3] with respect to static reference reflecting surface [8] motion.So thisly float the method for interference frequently, can eliminate the measuring error that the laser frequency instability causes with the twin laser interferometer common mode inhibition.Further allow the shared reflecting surface [4] of two interferometers with certain speed back and forth movement, make that the light through its reflection produces Doppler shift, this frequency displacement is detected simultaneously by the photodetector [5,6] of two interferometers, eliminates in frequency synthesis is subtracted each other again.Even this frequency displacement less stable can not cause measuring error yet, because it no longer appears in the synthesized output signal to be measured.Method with this heterodyne shift frequency, make common single frequency laser interferometer originally based on the measurement of change in optical path length with direct current method counting interference fringe, become to changing based on laser frequency with beat frequency method survey frequency difference Δ f, this is the same with the double frequency interferometry, can reduce the low frequency noise of photodetector, 1/ Δ f noise of especially severe when reducing homodyne frequency (being the phase shifts signal when Δ f goes to zero) especially significantly, improve the antijamming capability of interferometer, make interferometer to temperature, humidity, the direct current zero point drift of the optical path difference that the variation of environmental factors such as air cleanliness causes is insensitive, also continuous working for a long time under the no constant temperature condition.So common mode inhibition of the present invention is floated the repertoire that disturbs the heterodyne frequency-shifting-type twin laser interferometer can substitute double frequency Frequency Stabilized Lasers interferometer frequently.
Twin laser interferometer of the present invention, the back and forth movement of its shared reflecting surface [4] can be realized by electricity (or magnetic) is caused the triangle wave voltage (or electric current) that telescopic element applies the appropriate amplitude of certain frequency, also can realize with other oscillator (preferably linear oscillator such as linear motor).
Twin laser interferometer of the present invention is eliminated fully for the measuring error that the laser frequency drift is caused, the light path of stellar interferometer should equal the light path of reference interferometer.That is to say, when being all the unequal arm interferometer, arrive the equivalent optical path of the two-way light of two photodetectors through shared reflecting surface [4] reflection, and also equate from the light path that laser instrument arrives the two-way light in addition of two photodetectors from laser instrument.When being all the equiarm interferometer, then the light path from above-mentioned four road light of laser instrument equates entirely.Actual interferometer always allows certain measuring errors, and equating of above-mentioned light path is also absolute equal with regard to not needing, but it is just passable to be adjusted to certain equal extent.For example: when twin laser interferometer measuring error Δ f/f requires to be not more than 1 * 10 -18, the service condition of design is to be placed on the vibrationless pedestal, and variation of ambient temperature was no more than 1 ℃ in per five minutes, and what select for use when laser instrument is the simple glass chamber He-Ne laser instrument of single-frequency single mode, and the linear expansion coefficient in laser instrument glass chamber is not more than 1 * 10 -5/ ℃, then equal should being accurate to of above-mentioned light path do not differ 1 centimetre.The mistiming of propagating in the path corresponding to light because of 1 centimetre optical path difference Δ 1 is Δ t=Δ 1/C=3 * 10 -11Second.The only emission successively in the time that differs Δ t that two photodetectors receive.Because the Laser emission frequency is drifted about in time, the frequency of light wave that synchronization two photodetectors receive just has minute differences, and this incomplete common mode variations causes error not offset fully, and causes remainder error.The laser frequency drift speed depends primarily on the rate of change of the long L of laser cavity, and long variation the in chamber mainly caused by the temperature T variation, that is:
Δf/f≈ΔL/L
Δ L/L=(dL/Ldt) Δ t ≈ (dL/LdT) (dT/dt) measuring error of failing to offset that causes of Δ t thereby laser frequency drift is:
Δf/f≈(dL/LdT)(dT/dt)Δt
≤ 1 * 10 -5/ ℃ * (1 ℃/300 seconds) * 3 * 10 -11Second=1 * 10 -18If require measuring error to be not more than 1 * 10 -19, then equivalent optical path should be accurate to and not differ 1 millimeter, if require measuring error to be not more than 1 * 10 -17Then equivalent optical path gets final product to not differing from 10 centimetres, or the like.When twin laser interferometer of the present invention when measuring length, because of the set positions of reference reflecting surface [8] well after, in measuring process, generally no longer change, the permissible error scope of above-mentioned equivalent optical path is the range of horizontal metroscope just in time just.The heal range of little horizontal metroscope of the measuring error that requires is just little.With the above-mentioned twin interferometer that makes with the simple glass cavity laser is example, when it is placed on the vibrationless pedestal, the speed of variation of ambient temperature is not more than 1 ℃/300 seconds, the measuring accuracy of twin interferometer with see the following form (when selecting quartzy cavity laser for use as the range of horizontal metroscope and the permissible error of equivalent optical path, under same accuracy requirement and service condition, the permissible error of equivalent optical path and as order of magnitude of numerical value increase in the range ratio table of horizontal metroscope):
The measuring accuracy of interferometer Range as horizontal metroscope The permissible error of equivalent optical path
1×10 -19 1 millimeter 1 millimeter
1×10 -18 1 centimetre 1 centimetre
1×10 -17 10 centimetres 10 centimetres
1×10 -16 1 meter 1 meter
1×10 -15 10 meters 10 meters
1×10 -14 100 meters 100 meters
Twin laser interferometer of the present invention is with the method for the method instead of lasers frequency stabilization of common mode inhibition laser frequency drift interference from function, substitutes double-frequency laser single-frequency laser is carried out the heterodyne shift frequency.It is simpler compared with the two-frequency laser interferometer structure with Zeeman effect frequency stabilitzation, and cost is cheaper, and its biggest advantage is that the measuring error that the laser frequency drift causes can be reduced to zero in principle.In fact also can be reduced to Δ f/f less than 1 * 10 -18, and Frequency Stabilization Technique now can only make the laser frequency drift error be reduced to Δ f/f=1 * 10 -14
Brief Description Of Drawings:
Fig. 1 is the synoptic diagram of twin laser interferometer of the present invention.
Fig. 2 is the structural representation of one of embodiment of the invention (equiarm interferometer).
Fig. 3 is the structural representation of two (unequal arm interferometers) of the embodiment of the invention.
Fig. 4 is the synoptic diagram of prior art.
Wherein: [1] laser instrument [2] part reflecting face [3] is measured the shared reflecting surface of reflecting surface [4] [5] photodetector [6] photoelectricity probe [7] part reflecting face [8] with reference to reflecting surface [9] triangular wave driving power [10] reflecting surface [11] reflecting surface [12] piezoelectric ceramics [13] reflecting surface [14] reflecting surface repeatedly
One of embodiment that twin laser interferometer of the present invention is specifically finished as shown in Figure 2.This is the twin laser interferometer of an equiarm.It is by laser instrument [1], reflecting surface [3,4,8,10,11], and part reflecting face [2,7], photodetector [5,6], piezoelectric ceramics [12], triangular wave driving power [9] are formed.Laser instrument [1] can be selected single-frequency single mode He-Ne laser instrument for use.Shared reflecting surface [4] joins together with piezoelectric ceramics [12].Triangular wave driving power [9] applies the audio frequency triangle wave voltage of certain amplitude on piezoelectric ceramics [12], makes shared reflecting surface [4] become heterodyne shift frequency reflecting surface.The light path of twin laser interferometer can be regulated according to following method.At first, will be adjusted to about equally (by the requirement of last table) through the light path that different reflectings surface reflex to four road light of two photoelectricity probes from laser instrument according to the measuring accuracy of interferometer target.Regulate the position of photodetector [5] and [6] again, make them receive the light beam that reflection comes from shared reflecting surface [4] respectively simultaneously.The position of accommodation reflex face [3,8] is also just in time dropped in the photodetection [5,6] light through they reflections respectively then.Regulate light path and it should be noted reflecting surface [3,8,4] be not adjusted to definitely vertically, and perpendicularity deviation about 1 ° will be arranged, make that dropping on hot spot on the part reflecting face through the incident beam of their reflections and folded light beam does not coincide and leave a little distance with incident light.Avoid their the direct return laser light pipe of reflected light simultaneously.The reflecting surface of the light path of turning back [10,11] is not that twin interferometer institute is requisite, only is in order to make the interferometer compactness, to dwindle the volume of instrument and arrange.
Twin interferometer of the present invention specifically finish embodiment two as shown in Figure 3.This is the twin laser interferometer of a unequal arm, is suitable for the motion of testee is at a distance measured.It and last routine difference are: the light path that reflexes to two photodetectors [5,6] through shared reflecting surface [4] is much smaller than the light path that reflexes to photodetector [5] through measurement reflecting surface [3].Reflecting surface [14] and repeatedly the arrangement of reflecting surface [13] be make reference path through repeatedly the reflection after, the light path that arrives photodetection [6] from laser instrument increases, thereby can be approximately equal to from laser instrument through measuring the light path that catoptron [3] arrives photodetector [5].The control method of light path is identical with embodiment 1 with requirement.

Claims (3)

1. a common mode inhibition is floated frequently and is disturbed the heterodyne frequency-shifting-type twin laser interferometer, it comprises by laser instrument [1], part reflecting face [2], the stellar interferometer that reflecting surface [3] and [4] and photodetector [5] are formed, also comprise by part reflecting face [7], the reference path that reflecting surface [8] and photodetector [6] are formed, the laser instrument of the shared aforementioned stellar interferometer of this reference path [1) and reference interferometer of reflecting surface [4] recomposition, it is characterized in that: said shared reflecting surface [4] is combined into the twin laser interferometer that common mode inhibition is floated interference frequently with said stellar interferometer and reference interferometer, and said shared reflecting surface [4] becomes heterodyne shift frequency reflecting surface with certain speed back and forth movement again simultaneously.
2. common mode inhibition according to claim 1 is floated frequently and disturbed the heterodyne frequency-shifting-type twin laser interferometer, it is characterized in that: the back and forth movement of shared reflecting surface [4] is to be applied on the electromagnetism telescopic element with the certain frequency and the appropriate triangular wave driving power of amplitude to realize.
3. common mode inhibition according to claim 1 is floated frequently and is disturbed the heterodyne frequency-shifting-type twin laser interferometer, it is characterized in that: the light path of stellar interferometer equals the light path of reference interferometer, that is to say, when being all the unequal arm interferometer, [arrive the equivalent optical path of the two-way light of two photodetectors through shared reflecting surface [4] reflection 1], and also equate from the light path that laser instrument arrives the two-way light in addition of two photodetectors from laser instrument; When being all the equiarm interferometer, equate entirely from the light path of the four road above-mentioned light of laser instrument.
CN93109465A 1993-07-29 1993-07-29 Heterodyne frequency-shifting-type twin laser interferometer with common-mode suppressed frequency shift interference Expired - Fee Related CN1034763C (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100350278C (en) * 2005-11-15 2007-11-21 郑睿敏 Apparatus for controlling thickness of digital optical film

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101404509B (en) * 2008-11-11 2012-08-29 桂林航天光比特科技股份公司 Signal interference canceller and signal interference canceling method
CN110017793B (en) * 2019-04-10 2020-09-18 南京理工大学 Double-channel anti-vibration interference measurement device and method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4886363A (en) * 1988-09-06 1989-12-12 Eastman Kodak Company Quadratic frequency modulated absolute distance measuring interferometry
US4995726A (en) * 1988-09-26 1991-02-26 Brother Kogyo Kabushiki Kaisha Surface profile measuring device utilizing optical heterodyne interference
US5061071A (en) * 1988-12-26 1991-10-29 Brother Kogyo Kabushiki Kaisha Method and apparatus for detecting surface condition by utilizing optical heterodyne interference

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4886363A (en) * 1988-09-06 1989-12-12 Eastman Kodak Company Quadratic frequency modulated absolute distance measuring interferometry
US4995726A (en) * 1988-09-26 1991-02-26 Brother Kogyo Kabushiki Kaisha Surface profile measuring device utilizing optical heterodyne interference
US5061071A (en) * 1988-12-26 1991-10-29 Brother Kogyo Kabushiki Kaisha Method and apparatus for detecting surface condition by utilizing optical heterodyne interference

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100350278C (en) * 2005-11-15 2007-11-21 郑睿敏 Apparatus for controlling thickness of digital optical film

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