CN103197322B - Ranging method and ranging system of femtosecond laser frequency comb synthesis wave interference - Google Patents

Abstract

The invention relates to a ranging method and a ranging system of femtosecond laser frequency comb synthesis wave interference. The ranging method and the ranging system of the femtosecond laser frequency comb synthesis wave interference comprises a femtosecond laser frequency comb, a Michelson interference system and the like. The light emitted by the femtosecond laser frequency comb enters a first spectroscope, transmission light through the first spectroscope is emitted to a first reflecting mirror, and reflected light returns to the first spectroscope through the first reflecting mirror. The emitted light is emitted to a second spectroscope through the first spectroscope, reflected light through the second spectroscope is emitted to a second reflecting mirror through a first single wavelength generating and frequency shifting light path, and the reflected light through the second reflecting mirror and the first single wavelength generating and frequency shifting light path returns to the second spectroscope. The emitted light through the second reflecting mirror is emitted to a third reflecting mirror through a second single wavelength generating and frequency shifting light path, and reflected light through the third reflecting mirror returns to the second spectroscope through the second single wavelength generating and frequency shifting light path. The reflected light through the second reflecting mirror and the reflected light through the third reflecting mirror are combined on the position of the second spectroscope, and are combined with light pulses of a gage beam, the interference signals of two wavelengths are divided through a diffraction grating and are respectively detected and received by two photoelectric detectors, and range measurement is completed.

Description

A kind of femtosecond laser frequency comb synthesis wave to interfere distance-finding method and range measurement system

Technical field

The present invention relates to a kind of distance measurement method and range measurement system, particularly about a kind of the femtosecond laser frequency comb synthesis wave to interfere distance-finding method and the range measurement system that are applicable to absolute distance measurement.

Background technology

Femtosecond laser frequency comb refers to the repetition frequency (f of femtosecond pulse laser _rep, be called for short repetition) and phase offset frequency (f _ceo) with frequency reference source lock after device.The laser that femtosecond laser frequency comb sends is made up of a series of equally spaced ultrashort laser pulse (pulsewidth is some femtoseconds) in time domain, corresponding frequency domain exists a series of equally spaced discrete light spectral line, and (spectrum line looks like a comb, therefore frequency comb is called), the frequency interval of adjacent spectrum line equals the repetition of femto-second laser, and the spectral range that these spectrum lines cover is tens nanometer.The characteristic of this time domain and frequency domain is highly beneficial to laser absolute distance measurement, and therefore nearly ten years, femtosecond laser frequency comb is widely used in the research of laser absolute distance measurement.

Method the most frequently used in prior art utilizes the equally spaced characteristic of femtosecond laser frequency comb pulse, light femtosecond laser frequency comb sent when measuring is transmitted on a Michelson interferometer, and closes light with reference to the pulse that arm and gage beam return and detected by photodetector.Relative position relation between reference arm pulse and gage beam pulse is relevant with the brachium of reference arm and gage beam itself, when the difference (i.e. tested distance D) of gage beam and reference arm brachium equals adjacent pulse light path interval (D _p-p=c/f _rep, c is the light velocity in vacuum) m (m is integer) times of half time, the pulse of returning from gage beam and reference arm can superpose, and photodetector exports corresponding peak signal.When measuring one section of unknown distance, by changing the repetition of femtosecond laser frequency comb, thus change D _p-p, the signal peak of the superimposed pulses that gage beam and reference arm are returned is maximum (thinking that now two pulses are aimed at), and now tested distance can be expressed as D=mD _p-p/ (2n _g), n _gfor the aerial group index of pulse train, wherein D _p-paccurately f can be measured by frequency meter _repafter calculate, generally in rice magnitude, n _gcan obtain according to refractive index computing formula according to the atmospheric parameter measured.As long as after therefore determining m by conventional means (as pulse laser laser welder) bigness scale distance, namely can distance D be obtained.Known by above-mentioned analysis, the key factor affecting the method distance accuracy is exactly the alignment error of two pulses, and comparatively limited by judging maximum method (the present invention is referred to as " looking for the extremum method ") precision determining whether pulse aims at of signal peak, thus have impact on measuring accuracy.

Laser heterodyne interferometries of Single wavelength at present for the means that range measurement accuracy is the highest, but this method must solve the problem determining interference fringe change level time (being commonly called as " several greatly " of interferometric phase) when measuring absolute distance, and this large number will be determined, the thick side precision of adjusting the distance is needed to be better than the Single wavelength of 1/4th, because the extremum method of looking in above-mentioned femtosecond laser frequency comb range finding cannot realize being better than the precision of 1/4th Single wavelength, therefore directly the distance accuracy of looking for extremum method cannot be improved with the laser heterodyne interference of Single wavelength.

Summary of the invention

For the problems referred to above, the object of this invention is to provide a kind of synthetic wavelength utilizing dual wavelength to be formed as bridge, difference interference phase place and " looking for extremum method " are linked up the femtosecond laser frequency comb synthesis wave to interfere distance-finding method and range measurement system aimed at for pulse, effectively can improve the precision of measurement.

For achieving the above object, the present invention takes following technical scheme: a kind of femtosecond laser frequency comb synthesis wave to interfere distance-finding method, it comprises the following steps: 1) arrange the femtosecond laser frequency comb synthesis wave to interfere range measurement system that includes femtosecond laser frequency comb and Michelson interference system, described Michelson interference system comprises the first spectroscope, first catoptron, second spectroscope, first Single wavelength produces and shift frequency light path, second Single wavelength produces and shift frequency light path, second catoptron and the 3rd catoptron, reflecting back into described first spectroscopical pulse through described first catoptron is gage beam pulse, light pulse through described second spectroscope and the reflection of the 3rd catoptron and through described second spectroscope synthesis is reference arm pulse, 2) described first catoptron is placed on baseline position place, and finely tune the position of described first catoptron, the intensity of reference arm pulse and gage beam light pulse heterodyne interference signal is made to reach maximum, suppose i-th pulse of now reference arm pulse and a jth pulse generation superposition of gage beam pulse, the two sharp peak-to-peak offset deviation is δ _i, now status indication is state I, and the phase place of reference arm pulse and the heterodyne interference signal corresponding to gage beam pulse is designated as respectively: with repetition is designated as adjacent pulse light path is spaced apart wherein c is the light velocity in vacuum, 3) described first catoptron is placed on position to be measured, distance between this position and baseline is designated as testing distance L, " looking for extremum method " is adopted to carry out coarse adjustment, that is: the repetition of described femtosecond laser frequency comb is changed, the intensity of reference arm pulse and gage beam pulsed laser heterodyne interference signal is made to reach maximum, i-th pulse of hypothetical reference arm pulse and the jth+k of gage beam pulse _rindividual pulse generation superposition, the two sharp peak-to-peak offset deviation is δ _iI, will status indication be now state I I, the phase place of reference arm pulse and heterodyne interference signal corresponding to gage beam pulse be designated as respectively: with repetition is designated as adjacent pulse light path is spaced apart wherein c is the light velocity in vacuum, 4) tested distance L is calculated:

$L=k_r\frac{D_{p-p}^{\mathrm{II}}}{{2n}_g}+D---\left(1\right)$

When now k _r=0, tested distance L equals registration distance D, and when namely changing to state I I from state I, be all i-th pulse of reference arm pulse and a jth pulse generation superposition of gage beam pulse, the relative shift of two pulses is δ _iI-δ _i:

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{\mathrm{\Δ}{D}_{p-p}}{n_g}-2D=(k_1+\frac{{\mathrm{\Δ\φ}}_1}{2\mathrm{\π}})\·\frac{{\mathrm{\λ}}_{c1}}{n_{p1}}---\left(2\right)$

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{{\mathrm{\ΔD}}_{p-p}}{n_g}-2D=(k_2+\frac{{\mathrm{\Δ\φ}}_2}{2\mathrm{\π}})\·\frac{{\mathrm{\λ}}_{c2}}{n_{p2}}---\left(3\right)$

Wherein:

${\mathrm{\Δ\φ}}_1={\mathrm{\φ}}_1^{\mathrm{II}}-{\mathrm{\φ}}_1^I---\left(4\right)$

$\mathrm{\Δ}{\mathrm{\φ}}_2={\mathrm{\φ}}_2^{\mathrm{II}}-{\mathrm{\φ}}_2^I---\left(5\right)$

${\mathrm{\ΔD}}_{p-p}=D_{p-p}^{\mathrm{II}}-D_{p-p}^I---\left(6\right)$

In formula, λ _c1and λ _c2for the centre wavelength of heterodyne interference signal, n _p1and n _p2for λ _c1and λ _c2phase refractive index in corresponding air, n _gfor the aerial group index of pulse train, the solution procedure of registration distance D is: 1. pass through composite wave method to δ _iI-δ _icalculate, formula (2) and formula (3) carried out arrangement and obtains following formula:

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=(k_s+\frac{{\mathrm{\Δ\φ}}_s}{2\mathrm{\π}})\·{\mathrm{\λ}}_s---\left(7\right)$

In formula, Δ φ _s=Δ φ ₂-Δ φ ₁for the phase place of composite wave, λ _s=λ _air1λ _air2/ (λ _air1-λ _air2) be the wavelength of composite wave, wherein λ _air1=λ _c1/ n _p1, λ _air2=λ _c2/ n _p2, k _sbe 0; 2. by δ that 1. described step calculates _iI-δ _isubstitute into formula (2) or formula (3) calculating k ₁or k ₂, and to k ₁or k ₂carry out round; 3. by the k after rounding ₁or k ₂substitute into formula (2) or formula (3), according to Δ φ ₁or Δ φ ₂calculate registration distance D; When time, now k _rfor positive integer, determine k by pulse laser laser welder bigness scale L _rvalue, and calculate registration distance D by said method and can calculate tested distance L.

A kind of femtosecond laser frequency comb synthesis wave to interfere range measurement system realizing described distance-finding method, it is characterized in that: it comprises a femtosecond laser frequency comb, a Michelson interference system, a diffraction grating, two photodetectors and a computing machine, described Michelson interference system comprises the first spectroscope, the first catoptron, the second spectroscope, the first Single wavelength produces and shift frequency light path, the second Single wavelength generation and shift frequency light path, the second catoptron and the 3rd catoptron; Described second spectroscope is identical to the distance of described 3rd catoptron with described second spectroscope to the distance of described second catoptron; The light pulse sequence that described femtosecond laser frequency comb sends incides described first spectroscope, and the light through described first spectroscope transmission is transmitted into the first catoptron, and the light through described first catoptron reflection turns back to described first spectroscope as gage beam pulse; Light through described first dichroic mirror is transmitted into described second spectroscope, light through described second dichroic mirror is transmitted into described second catoptron through described first Single wavelength generation and shift frequency light path, and the light through described second catoptron reflection produces through described first Single wavelength again and shift frequency light path turns back to described second spectroscope; Light through described second spectroscope transmission is transmitted into described 3rd catoptron through described second Single wavelength generation and shift frequency light path, and the light through described 3rd catoptron reflection produces through described second Single wavelength again and shift frequency light path turns back to described second spectroscope; Light through described second catoptron reflection and the light through described 3rd catoptron reflection are at described second spectroscope place conjunction light; Described conjunction light light beam is transmitted into described diffraction grating as with reference to arm light pulse emission after described first spectroscope and gage beam light pulse close light, described diffraction grating by the heterodyne interference signal of two wavelength separately, and detect reception by described first photodetector and the second photodetector respectively, measured signal is sent to described computing machine and carries out computing by two photodetectors respectively, completes range observation.

Described first Single wavelength produces and shift frequency light path comprises an acousto-optic modulator, by regulating the angle of described second catoptron, obtains arrowband single wavelength light signal, and produces frequency displacement by described acousto-optic modulator to described arrowband single wavelength light signal.

Described first Single wavelength produces and shift frequency light path comprises an arrowband band pass filter and an acousto-optic modulator, by arrowband band pass filter, light signal is selected, obtain arrowband single wavelength light signal, and by described acousto-optic modulator, frequency displacement is produced to described arrowband single wavelength light signal.

Described second Single wavelength produces and shift frequency light path comprises an acousto-optic modulator, by regulating the angle of described 3rd catoptron, obtains arrowband single wavelength light signal, and produces frequency displacement by described acousto-optic modulator to described arrowband single wavelength light signal.

Described second Single wavelength produces and shift frequency light path comprises an arrowband band pass filter and an acousto-optic modulator, by described arrowband band pass filter, light signal is selected, obtain arrowband single wavelength light signal, and by described acousto-optic modulator, frequency displacement is produced to described arrowband single wavelength light signal.

The present invention is owing to taking above technical scheme, it has the following advantages: 1, the present invention includes femtosecond laser frequency comb, Michelson interference system, diffraction grating, two photodetectors and computing machine, Michelson interference system comprises the first spectroscope, first catoptron, second spectroscope, first Single wavelength produces and shift frequency light path, second Single wavelength produces and shift frequency light path, second catoptron and the 3rd catoptron, second spectroscope is identical to the distance of the 3rd catoptron with the second spectroscope to the distance of the second catoptron, the present invention is owing to make use of the wide spectral characteristics of femtosecond laser frequency comb, to be produced by two Single wavelength and composite wave that shift frequency light path produces two close wavelength composition wavelength longer is interfered, and utilize synthetic wavelength as bridge dexterously, difference interference phase place and " looking for extremum method " are linked up and aims at for pulse, Single wavelength difference interference phase place is directly traced back to therefore, it is possible to aimed at by femto-second laser pulse, realize superhigh precision pulse to aim at, thus realize superhigh precision range finding.2, the present invention adopts the method for measuring accuracy refining accuracy, first " looking for extremum method " is adopted to carry out pulse aligning and range finding, realize micron-sized bigness scale precision, secondly within adopting synthesis wave to interfere measuring accuracy to be brought up to the Single wavelength of 1/4th, final Single wavelength difference interference improves precision further to nanometer scale, prove that pulse alignment precision can be brought up to nanoscale from looking for the micron accuracies of extremum method by the method that the present invention proposes by experiment, thus greatly can improve distance accuracy.Distance-finding method of the present invention is simple and reliable, has had both wide range and high-precision advantage, can be widely used in absolute distance measurement.

Accompanying drawing explanation

Fig. 1 is the structural representation of femtosecond laser frequency comb synthesis wave to interfere range measurement system of the present invention;

Fig. 2 is the spectral distribution schematic diagram of the embodiment of the present invention, and horizontal ordinate is wavelength, and ordinate is normalization spectral intensity, and wherein (a) is femtosecond laser frequency comb spectral distribution, and centered by (b), wavelength is λ _r1narrow-band spectrum, centered by (c), wavelength is λ _r2narrow-band spectrum, centered by (d), wavelength is λ _c1heterodyne interference signal spectrum, centered by (e), wavelength is λ _c2heterodyne interference signal spectrum;

Fig. 3 is the effect schematic diagram in state I situation of i-th pulse of the reference arm pulse of the embodiment of the present invention and a jth pulse generation superposition of gage beam pulse;

Fig. 4 is i-th pulse of reference arm pulse of the present invention and the jth+k of gage beam pulse _rthe effect schematic diagram in state I I situation of individual pulse generation superposition.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in detail.

As shown in Figure 1 and Figure 2, femtosecond laser frequency comb synthesis wave to interfere range measurement system of the present invention to comprise a femtosecond laser frequency comb FLFC(repetition frequency adjustable), a Michelson interference system, a diffraction grating G and two photoelectric detector PD ₁, PD ₂, wherein, Michelson interference system comprises the first spectroscope BS ₁, the first mirror M ₁, the second spectroscope BS ₂, first Single wavelength produce and shift frequency light path, second Single wavelength produce and shift frequency light path, the second mirror M ₂with the 3rd mirror M ₃; The light pulse sequence (spectral distribution as shown in Figure 2 (a)) that femtosecond laser frequency comb FLFC sends incides the first spectroscope BS of Michelson interference system ₁;

Through the first spectroscope BS ₁the light of transmission is transmitted into the first mirror M ₁, through the first mirror M ₁the light of reflection turns back to the first spectroscope BS as gage beam pulse ₁;

Through the first spectroscope BS ₁the light of reflection is transmitted into the second spectroscope BS ₂, through the second spectroscope BS ₂the light of reflection produces through the first Single wavelength and shift frequency light path is transmitted into the second mirror M ₂, through the second mirror M ₂the light of reflection produces through the first Single wavelength again and shift frequency light path turns back to the second spectroscope BS ₂; Through the second spectroscope BS ₂the light of transmission produces through the second Single wavelength and shift frequency light path is transmitted into the 3rd mirror M ₃, through the 3rd mirror M ₃the light of reflection produces through the second Single wavelength again and shift frequency light path turns back to the second spectroscope BS ₂; Through the second mirror M ₂reflection light and through the 3rd mirror M ₃the light of reflection is at the second spectroscope BS ₂light is closed at place, this conjunction light light beam as with reference to arm light pulse emission to the first spectroscope BS ₁diffraction grating G is transmitted into after closing light with gage beam light pulse, now reference arm light pulse meeting and gage beam light pulse generation difference interference, because reference arm pulse comprises the light (spectral distribution (b) and (c) as shown in Figure 2) of two wavelength, so the heterodyne interference signal of two wavelength can be produced, the centre wavelength of two heterodyne interference signal is designated as λ respectively _c1and λ _c2(spectral distribution (d) and (e) as shown in Figure 2)), the heterodyne interference signal of these two wavelength separates by diffraction grating G, and respectively by the first photoelectric detector PD ₁with the second photoelectric detector PD ₂detection receives, two photoelectric detector PD ₁, PD ₂respectively measured signal is sent to a computing machine and carries out computing, complete accurate distance and measure.In order to ensure that the light pulse of two wavelength of reference arm pulse can be interfered with gage beam pulse generation simultaneously, therefore need guarantee second spectroscope BS ₂to the second mirror M ₂distance and the second spectroscope BS ₂to the 3rd mirror M ₃distance identical.

In above-described embodiment, the first Single wavelength produces and shift frequency light path can comprise an acousto-optic modulator AOM ₁, the light pulse sent due to femtosecond laser frequency comb FLFC has wider spectrum (tens nanometer, as shown in Figure 2 (a)), and it is through acousto-optic modulator AOM ₁after diffraction, a diffracted beam dispersed can be formed because the angle of diffraction of each wavelength is different, therefore by adjustment second mirror M ₂angle, can select centre wavelength is λ _r1narrow band light pulse train (spectral distribution as shown in Figure 2 (b)) former road to return and by acousto-optic modulator AOM ₁produce frequency displacement; First Single wavelength produces and shift frequency light path can also be comprise an arrowband band pass filter F ₁with an acousto-optic modulator AOM ₁, by arrowband band pass filter F ₁select light signal, obtaining centre wavelength is λ _r1narrow band light pulse train (spectral distribution as shown in Figure 2 (b)), acousto-optic modulator AOM ₁shift frequency is carried out to this narrow-band impulse sequence.

In the various embodiments described above, the second Single wavelength produces and shift frequency light path can comprise an acousto-optic modulator AOM ₂, principle is the same, by regulating the 3rd mirror M ₃angle, can be λ by centre wavelength _r2narrow band light pulse train (spectral distribution as shown in Figure 2 (c)) former road to return and by acousto-optic modulator AOM ₂produce frequency displacement; Second Single wavelength produces and shift frequency light path can also be comprise an arrowband band pass filter F ₂with an acousto-optic modulator AOM ₂, by arrowband band pass filter F ₂select light signal, obtaining centre wavelength is λ _r2light pulse sequence (spectral distribution as shown in Figure 2 (c)), acousto-optic modulator AOM ₂shift frequency is carried out to this pulse train.

Adopt femtosecond laser frequency comb synthesis wave to interfere range measurement system of the present invention testing distance L to be carried out to the method accurately measured, comprise the following steps:

1, by the first mirror M ₁(measurement mirror) be placed on baseline position BL place (baseline refer to gage beam length and reference arm isometric time measure the position at mirror place) (as shown in Figure 1), and finely tune mirror M ₁position, (heterodyne interference signal of two wavelength can optional one, and the present invention selects centre wavelength to be λ to make reference arm pulse and gage beam light pulse heterodyne interference signal _c1interference signal) intensity reach maximum, as shown in Figure 2, suppose i-th pulse of now reference arm pulse and a jth pulse generation superposition of gage beam pulse, now only by judging that the maximum spike of two pulses cannot being transferred to of interference signal intensity is aimed at completely, generally have the deviation of 1 ~ 2 micron, both supposing, sharp peak-to-peak offset deviation is δ _i, now state note is labeled as state I, and the phase place of reference arm pulse and the heterodyne interference signal corresponding to gage beam pulse is designated as respectively: with repetition is designated as adjacent pulse light path is spaced apart (c is the light velocity in vacuum), this state is system works original state, just can be fixed up once regulate;

2, by the first mirror M ₁be placed on position to be measured, be testing distance L by the distance between this position and baseline BL, existing " looking for extremum method " is adopted to carry out coarse adjustment, that is: the repetition of femtosecond laser frequency comb FLFC is changed, reference arm pulse and the intensity of gage beam pulsed laser heterodyne interference signal are reached, and maximum (select the interference signal identical with step 1 centre wavelength, the present invention selects centre wavelength to be λ _c1interference signal), suppose i-th pulse of now reference arm and the jth+k of gage beam _rindividual pulse generation superposition, the peak-to-peak deviation of point of the two is δ _iI(1 ~ 2 micron), will status indication be now state I I, the phase place of reference arm pulse and heterodyne interference signal corresponding to gage beam pulse be designated as respectively: with repetition is designated as adjacent pulse light path is spaced apart

3, tested distance L is calculated:

$L=k_r\frac{D_{p-p}^{\mathrm{II}}}{{2n}_g}+D---\left(1\right)$

According to length and the relation in recurrent interval of the tested distance L of reality, the calculating of tested distance L is divided into two kinds of situations:

When now k _r=0, tested distance L equals registration distance D, when now changing to state I I from state I, is all i-th pulse of reference arm pulse and a jth pulse generation superposition of gage beam pulse, the change of error δ of two superimposed pulse spikes when changing to state I I from state I _iI-δ _ireflect the relative shift of two pulses, this relative shift also can cause the change of interference signal phase place, can be represented by following formula:

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{{\mathrm{\ΔD}}_{p-p}}{n_g}-2D=(k_1+\frac{{\mathrm{\Δ\φ}}_1}{2\mathrm{\π}})\·\frac{{\mathrm{\λ}}_{c1}}{n_{p1}}---\left(2\right)$

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{{\mathrm{\ΔD}}_{p-p}}{n_g}-2D=(k_2+\frac{{\mathrm{\Δ\φ}}_2}{2\mathrm{\π}})\·\frac{{\mathrm{\λ}}_{c2}}{n_{p2}}---\left(3\right)$

Wherein:

${\mathrm{\Δ\φ}}_1={\mathrm{\φ}}_1^{\mathrm{II}}-{\mathrm{\φ}}_1^I---\left(4\right)$

$\mathrm{\Δ}{\mathrm{\φ}}_2={\mathrm{\φ}}_2^{\mathrm{II}}-{\mathrm{\φ}}_2^I---\left(5\right)$

${\mathrm{\ΔD}}_{p-p}=D_{p-p}^{\mathrm{II}}-D_{p-p}^I---\left(6\right)$

In formula, λ _c1and λ _c2for the centre wavelength of heterodyne interference signal, n _p1and n _p2for λ _c1and λ _c2phase refractive index in corresponding air, n _gfor the aerial group index of pulse train, k ₁and k ₂for integer undetermined, due to Δ D _p-pcan be calculated by the repetition under measurement two state, phase refractive index and group index can calculate formulae discovery by record atmospheric parameter according to refractive index and obtain, and therefore only need determine the k in formula ₁or k ₂registration distance D accurately can be obtained.To determine k ₁for example carries out being described solving of registration distance D, that is: first bigness scale goes out δ _iI-δ _ivalue, substitute into formula (2) obtain k ₁, due to the k obtained ₁not necessarily integer, therefore needs the k to obtaining ₁carry out round, in order to ensure not produce round-off error, demand fulfillment δ _iI-δ _ibigness scale ratio of precision λ _c1/ 2 high conditions, but such bigness scale precision cannot realize only by " looking for extremum method ", the solution procedure of registration distance D is:

1) by composite wave method to δ _iI-δ _icalculate, formula (2) and (3) carried out arrangement and obtains following formula:

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{{\mathrm{\ΔD}}_{p-p}}{n_g}-2D=(k_s+\frac{{\mathrm{\Δ\φ}}_s}{2\mathrm{\π}})\·{\mathrm{\λ}}_s---\left(7\right)$

In formula, Δ φ _s=Δ φ ₂-Δ φ ₁for the phase place of composite wave; λ _s=λ _air1λ _air2/ (λ _air1-λ _air2) be the wavelength of composite wave, wherein λ _air1=λ _c1/ n _p1; λ _air2=λ _c2/ n _p2; k _sfor integer undetermined, k _s=k ₂-k ₁.

Due to λ _c1and λ _c2relatively (difference tens nanometer), therefore λ _air1and λ _air2also relatively, the wavelength X of composite wave _sλ can be reached _air1tens times, at tens microns to hundred microns, look for extremum method by step 1 and step 2, can δ be determined _iand δ _iIall at 1 ~ 2 microns, therefore δ _iI-δ _ialso be a small amount of of several microns, the change of composite wave phase place generation integer level can not be caused, therefore can determine the k in formula (7) _sbe 0, therefore according to Δ φ _sand λ _scalculate δ _iI-δ _i, for phase measurement accuracy 0.5 °, the δ now obtained _iI-δ _iprecision is: λ _s/ (2 × 360/0.5), are far superior to λ _c1/ 4 or λ _c2/ 4.

2) δ step 1) calculated _iI-δ _isubstitute into formula (2) or formula (3) calculating k ₁or k ₂, and to k ₁or k ₂carry out round, due to δ _iI-δ _iprecision higher than λ _c1/ 4 and λ _c2/ 4, thus ensure that k ₁or k ₂round and can not produce deviation.

3) by the k after rounding ₁or k ₂substitute into formula (2) or formula (3), according to Δ φ ₁or Δ φ ₂calculate registration distance D, still for phase measurement accuracy 0.5, the precision now realized is: λ _c1/ (2 × 360/0.5) or λ _c2/ (2 × 360/0.5) are about about 1nm.

When time, now k _rfor positive integer, k _rreflect the sequence number change number of overlapping pulses when changing to state I I from state I, also reflects tested distance is approximately recurrent interval half simultaneously how many times, because the recurrent interval is all generally a meter magnitude, therefore namely can determine k by existing normal pulsed laser range finder bigness scale distance _rvalue, and calculate registration distance D by said method and can calculate tested distance L.

In order to more clearly illustrate the principle of femtosecond laser frequency comb synthesis wave to interfere distance-finding method of the present invention, the process of the precision refining accuracy being realized pulse aligning and range finding in vacuum environment by composite wave transition that is described in detail below by specific embodiment:

Suppose λ _c1=1570nm, λ _c2=1550nm, then composite wave λ _s=121.675 μm, repetition f _rep=50MHz(D _p-p=6m), tested distance actual value is 300m, then k _r=100, phase measurement accuracy 0.5 degree, " looking for extremum method " alignment precision 2 μm.According to femtosecond laser frequency comb synthesis wave to interfere distance-finding method of the present invention, first carry out pulse aligning by " looking for extremum method ", obtain δ _iI-δ _ibe less than 4 μm, therefore can determine k _s=0, therefore can obtain δ according to composite wave phase calculation _iI-δ _i, its error is λ _s/ (2 × 360/0.5)=0.084 μm, because this precision is better than λ _c1/ 4, therefore can further with Single wavelength λ _c1interferometric phase be connected, be connected after alignment error be λ _c1by embodiments of the invention ,/(2 × 360/0.5)=1.1nm, can find out that pulse alignment precision can be brought up to nanoscale from looking for the micron accuracies of extremum method by the method proposed by the present invention, thus greatly can improve distance accuracy.

The various embodiments described above are only for illustration of the present invention; wherein the step etc. of the structure of each parts, connected mode and implementation method all can change to some extent; in addition each optical element can adopt conventional support carry out support fix; and the position etc. of optical element all can change to some extent; as long as meet paths condition of the present invention; every equivalents of carrying out on the basis of technical solution of the present invention and improvement, all should not get rid of outside protection scope of the present invention.

Claims (6)

1. a femtosecond laser frequency comb synthesis wave to interfere distance-finding method, it comprises the following steps:

1) the femtosecond laser frequency comb synthesis wave to interfere range measurement system that includes femtosecond laser frequency comb and Michelson interference system is set, described Michelson interference system comprises the first spectroscope, first catoptron, second spectroscope, first Single wavelength produces and shift frequency light path, second Single wavelength produces and shift frequency light path, second catoptron and the 3rd catoptron, reflecting back into described first spectroscopical pulse through described first catoptron is gage beam pulse, light pulse through described second spectroscope and the reflection of the 3rd catoptron and through described second spectroscope synthesis is reference arm pulse,

2) described first catoptron is placed on baseline position place, and finely tune the position of described first catoptron, the intensity of reference arm pulse and gage beam light pulse heterodyne interference signal is made to reach maximum, suppose i-th pulse of now reference arm pulse and a jth pulse generation superposition of gage beam pulse, the two sharp peak-to-peak offset deviation is δ _i, now status indication is state I, and the phase place of reference arm pulse and the heterodyne interference signal corresponding to gage beam pulse is designated as respectively: with repetition is designated as adjacent pulse light path is spaced apart wherein c is the light velocity in vacuum; Baseline refer to gage beam length and reference arm isometric time measure the position at mirror place;

3) described first catoptron is placed on position to be measured, distance between this position and baseline is designated as testing distance L, " looking for extremum method " is adopted to carry out coarse adjustment, that is: the repetition of described femtosecond laser frequency comb is changed, the intensity of reference arm pulse and gage beam pulsed laser heterodyne interference signal is made to reach maximum, i-th pulse of hypothetical reference arm pulse and the jth+k of gage beam pulse _rindividual pulse generation superposition, the two sharp peak-to-peak offset deviation is δ _iI, will status indication be now state I I, the phase place of reference arm pulse and heterodyne interference signal corresponding to gage beam pulse be designated as respectively: with repetition is designated as adjacent pulse light path is spaced apart wherein c is the light velocity in vacuum;

4) testing distance L is calculated:

$L=k_r\frac{D_{p-p}^{\mathrm{II}}}{{2n}_g}+D---\left(1\right)$

K _rfor integer undetermined; When now k _r=0, testing distance L equals registration distance D, and when namely changing to state I I from state I, be all i-th pulse of reference arm pulse and a jth pulse generation superposition of gage beam pulse, the relative shift of two pulses is δ _iI-δ _i:

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{{\mathrm{\ΔD}}_{p-p}}{n_g}-2D=(k_1+\frac{\mathrm{\Δ}{\mathrm{\φ}}_1}{2\mathrm{\π}})\·\frac{{\mathrm{\λ}}_{c1}}{n_{p1}}---\left(2\right)$

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=\frac{{\mathrm{\ΔD}}_{p-p}}{n_g}-2D=(k_2+\frac{\mathrm{\Δ}{\mathrm{\φ}}_2}{2\mathrm{\π}})\·\frac{{\mathrm{\λ}}_{c2}}{n_{p2}}---\left(3\right)$

Wherein:

$\mathrm{\Δ}{\mathrm{\φ}}_1={\mathrm{\φ}}_1^{\mathrm{II}}-{\mathrm{\φ}}_1^I---\left(4\right)$

$\mathrm{\Δ}{\mathrm{\φ}}_2={\mathrm{\φ}}_2^{\mathrm{II}}-{\mathrm{\φ}}_2^I---\left(5\right)$

$\mathrm{\Δ}{D}_{p-p}=D_{p-p}^{\mathrm{II}}-D_{p-p}^I---\left(6\right)$

In formula, λ _c1and λ _c2for the centre wavelength of heterodyne interference signal, k ₁and k ₂for integer undetermined; k _sfor integer undetermined, k _s=k ₂-k ₁; n _p1and n _p2for λ _c1and λ _c2phase refractive index in corresponding air, n _gfor the aerial group index of pulse train, the solution procedure of registration distance D is:

1. composite wave method is passed through to δ _iI-δ _icalculate, formula (2) and formula (3) carried out arrangement and obtains following formula:

${\mathrm{\δ}}_{\mathrm{II}}-{\mathrm{\δ}}_I=(k_s+\frac{\mathrm{\Δ}{\mathrm{\φ}}_s}{2\mathrm{\π}})\·{\mathrm{\λ}}_s---\left(7\right)$

In formula, Δ φ _s=Δ φ ₂-Δ φ ₁for the phase place of composite wave, λ _s=λ _air1λ _air2/ (λ _air1-λ _air2) be the wavelength of composite wave, wherein λ _air1=λ _c1/ n _p1, λ _air2=λ _c2/ n _p2, k _sbe 0;

2. by δ that 1. described step calculates _iI-δ _isubstitute into formula (2) or formula (3) calculating k ₁or k ₂, and to k ₁or k ₂carry out round;

3. by the k after rounding ₁or k ₂substitute into formula (2) or formula (3), according to Δ φ ₁or Δ φ ₂calculate registration distance D;

When time, now k _rfor positive integer, determine k by pulse laser laser welder bigness scale L _rvalue, and calculate registration distance D by said method and can calculate testing distance L.

2. one kind realizes the femtosecond laser frequency comb synthesis wave to interfere range measurement system of distance-finding method as claimed in claim 1, it is characterized in that: it comprises a femtosecond laser frequency comb, a Michelson interference system, a diffraction grating, two photodetectors and a computing machine, described Michelson interference system comprises the first spectroscope, the first catoptron, the second spectroscope, the first Single wavelength produces and shift frequency light path, the second Single wavelength generation and shift frequency light path, the second catoptron and the 3rd catoptron; Described second spectroscope is identical to the distance of described 3rd catoptron with described second spectroscope to the distance of described second catoptron;

The light pulse sequence that described femtosecond laser frequency comb sends incides described first spectroscope, and the light through described first spectroscope transmission is transmitted into the first catoptron, and the light through described first catoptron reflection turns back to described first spectroscope as gage beam pulse;

Light through described first dichroic mirror is transmitted into described second spectroscope, light through described second dichroic mirror is transmitted into described second catoptron through described first Single wavelength generation and shift frequency light path, and the light through described second catoptron reflection produces through described first Single wavelength again and shift frequency light path turns back to described second spectroscope; Light through described second spectroscope transmission is transmitted into described 3rd catoptron through described second Single wavelength generation and shift frequency light path, and the light through described 3rd catoptron reflection produces through described second Single wavelength again and shift frequency light path turns back to described second spectroscope; Light through described second catoptron reflection and the light through described 3rd catoptron reflection are at described second spectroscope place conjunction light;

Described conjunction light light beam is transmitted into described diffraction grating as with reference to arm light pulse emission after described first spectroscope and gage beam light pulse close light, described diffraction grating by the heterodyne interference signal of two wavelength separately, and detect reception by photodetector described in photodetector described in first and second respectively, measured signal is sent to described computing machine and carries out computing by two photodetectors respectively, completes range observation.

3. a kind of femtosecond laser frequency comb synthesis wave to interfere range measurement system as claimed in claim 2, it is characterized in that: described first Single wavelength produces and shift frequency light path comprises an acousto-optic modulator, by regulating the angle of described second catoptron, obtain arrowband single wavelength light signal, and by described acousto-optic modulator, frequency displacement is produced to described arrowband single wavelength light signal.

4. a kind of femtosecond laser frequency comb synthesis wave to interfere range measurement system as claimed in claim 2, it is characterized in that: described first Single wavelength produces and shift frequency light path comprises an arrowband band pass filter and an acousto-optic modulator, by arrowband band pass filter, light signal is selected, obtain arrowband single wavelength light signal, and by described acousto-optic modulator, frequency displacement is produced to described arrowband single wavelength light signal.

5. a kind of femtosecond laser frequency comb synthesis wave to interfere range measurement system as described in Claims 2 or 3 or 4, it is characterized in that: described second Single wavelength produces and shift frequency light path comprises an acousto-optic modulator, by regulating the angle of described 3rd catoptron, obtain arrowband single wavelength light signal, and by described acousto-optic modulator, frequency displacement is produced to described arrowband single wavelength light signal.

6. a kind of femtosecond laser frequency comb synthesis wave to interfere range measurement system as described in Claims 2 or 3 or 4, it is characterized in that: described second Single wavelength produces and shift frequency light path comprises an arrowband band pass filter and an acousto-optic modulator, by described arrowband band pass filter, light signal is selected, obtain arrowband single wavelength light signal, and by described acousto-optic modulator, frequency displacement is produced to described arrowband single wavelength light signal.