CN103197322A - 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 femtosecond laser frequency comb synthesis wave to interfere distance-finding method and range measurement system that is applicable to absolute distance measurement.

Background technology

The femtosecond laser frequency comb refers to the repetition frequency (f with femtosecond pulse laser _Rep, be called for short repetition) and phase deviation frequency (f _Ceo) with frequency reference source locking after device.The laser that the femtosecond laser frequency comb sends is made up of a series of equally spaced ultrashort laser pulses (pulsewidth is some femtoseconds) on time domain, (spectrum line looks like a comb to have a series of equally spaced discrete light spectral lines on the corresponding frequency domain, therefore be called frequency comb), the frequency interval of adjacent light spectral 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 the laser absolute distance measurement, and therefore over past ten years, the femtosecond laser frequency comb is widely used in the research of laser absolute distance measurement.

The most frequently used method is to utilize the equally spaced characteristic of femtosecond laser frequency comb pulse in the prior art, the light that when measuring the femtosecond laser frequency comb is sent is transmitted on the Michelson interferometer, and the pulse that reference arm and gage beam return closed light and surveys by photodetector.Relative position relation between reference arm pulse and the gage beam pulse is relevant with the brachium of reference arm and gage beam itself, when poor (being tested distance B) of gage beam and reference arm brachium equals adjacent pulse light path (D at interval _P-p=c/f _Rep, c is the light velocity in the vacuum) during half m (m is integer) times, the pulse of returning from gage beam and reference arm can superpose the corresponding peak signal of output on the photodetector.When measuring one section unknown distance, by the repetition of change femtosecond laser frequency comb, thereby change D _P-p, making the signal peak maximum (think this moment two pulses aims at) of the superimposed pulses that gage beam and reference arm are returned, tested distance can be expressed as D=mD at this moment _P-p/ (2n _g), n _gBe the aerial group index of pulse train, wherein D _P-pCan accurately measure f by frequency meter _RepAfter calculate, generally at rice magnitude, n _gCan calculate formula according to refractive index according to the atmospheric parameter of measuring obtains.Therefore as long as by behind the definite m of conventional means (as pulse laser laser welder) bigness scale distance, namely can obtain distance B.By above-mentioned analysis as can be known, the key factor that influences this method distance accuracy is exactly the alignment error of two pulses, and comparatively limited by judging method (the present invention is referred to as " looking for the extremum method ") precision that the signal peak maximum determines pulse and whether aim at, thereby influenced measuring accuracy.

Are laser heterodyne interferometries of single wavelength for the highest means of range measurement accuracy at present, but must solving, this method determines that interference fringe changes the problem of level time (being commonly called as " number greatly " of interferometric phase) when measuring absolute distance, and to determine this big number, the thick side precision that need adjust the distance is better than single wavelength of 1/4th, because the extremum method of looking in the range finding of above-mentioned femtosecond laser frequency comb can't realize being better than the precision of 1/4th single wavelength, therefore can't be directly improve the distance accuracy of looking for extremum method with the laser heterodyne interference of single wavelength.

Summary of the invention

At the problems referred to above, the purpose of this invention is to provide a kind of synthetic wavelength of dual wavelength formation that utilizes as bridge, difference interference phase place and " looking for extremum method " are connected to get up femtosecond laser frequency comb synthesis wave to interfere distance-finding method and the range measurement system of aiming at for pulse, can effectively 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 may further comprise the steps: 1) femtosecond laser frequency that includes femtosecond laser frequency comb and Michelson interference system is set combs the synthesis wave to interfere range measurement system, described Michelson interference system comprises first spectroscope, first catoptron, second spectroscope, first single wavelength produces and the shift frequency light path, second single wavelength produces and the shift frequency light path, second catoptron and the 3rd catoptron, getting back to described first spectroscopical pulse through described first mirror reflects is the gage beam pulse, is the reference arm pulse through described second spectroscope and the 3rd mirror reflects and through the synthetic light pulse of described second spectroscope; 2) described first catoptron is placed on the baseline position place, and finely tune the position of described first catoptron, make the intensity of reference arm pulse and gage beam light pulse difference interference signal reach maximum, suppose that i pulse of reference arm pulse this moment and j pulse generation of gage beam pulse superpose, the offset deviation between the two spike is δ _I, this moment, status indication was state I, the phase place of reference arm pulse and the corresponding difference interference signal of gage beam pulse is designated as respectively:

With Repetition is designated as

The adjacent pulse light path is spaced apart

Wherein c is the light velocity in the vacuum; 3) described first catoptron is placed on position to be measured, distance between this position and the baseline is designated as testing distance L, adopt " looking for extremum method " to carry out coarse adjustment, that is: change the repetition of described femtosecond laser frequency comb, make the intensity of reference arm pulse and gage beam pulse difference interference signal reach maximum, i pulse of hypothetical reference arm pulse and the j+k of gage beam pulse _rIndividual pulse generation stack, the offset deviation between the two spike is δ _II, status indication is state I I at this moment, the phase place of the difference interference signal of reference arm pulse and gage beam pulse correspondence is designated as respectively:

With

Repetition is designated as

The adjacent pulse light path is spaced apart

Wherein c is the light velocity in the vacuum; 4) calculate tested distance L:

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

When

This moment k _r=0, tested distance L equals the registration distance B, when namely changing to state I I from state I, all is i pulse of reference arm pulse and j pulse generation stack of gage beam pulse, and 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 the formula, λ _C1And λ _C2Be the centre wavelength of difference interference signal, n _P1And n _P2Be λ _C1And λ _C2Corresponding airborne phase refractive index, n _gBe the aerial group index of pulse train, the solution procedure of registration distance B is: 1. pass through the composite wave method to δ _II-δ _ICalculate, formula (2) and formula (3) put in order obtained 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 the formula, Δ φ _s=Δ φ ₂-Δ φ ₁Be 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. the δ that 1. described step is calculated _II-δ _ISubstitution formula (2) or formula (3) calculate k ₁Or k ₂, and to k ₁Or k ₂Carry out round; 3. the k after will rounding ₁Or k ₂Substitution formula (2) or formula (3) are according to Δ φ ₁Or Δ φ ₂Calculate the registration distance B; When

The time, this moment k _rBe positive integer, L determines k by the pulse laser laser welder bigness scale _rValue, and calculate the registration distance B by said method and can calculate tested distance L.

A kind of femtosecond laser frequency comb synthesis wave to interfere range measurement system that realizes described distance-finding method, it is characterized in that: it comprises femtosecond laser frequency comb, a Michelson interference system, a diffraction grating, two photodetectors and a computing machine, and described Michelson interference system comprises that first spectroscope, first catoptron, second spectroscope, first single wavelength generation and shift frequency light path, second single wavelength produce and shift frequency light path, second catoptron and the 3rd catoptron; Described second spectroscope is identical to the distance of described the 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, is transmitted into first catoptron through the light of the described first spectroscope transmission, and pulse turns back to described first spectroscope as gage beam through the light of described first mirror reflects; Light through described first spectroscope reflection is transmitted into described second spectroscope, produce and the shift frequency light path is transmitted into described second catoptron through described first single wavelength through the light of described second spectroscope reflection, produce and the shift frequency light path turns back to described second spectroscope through described first single wavelength again through the light of described second mirror reflects; Produce and the shift frequency light path is transmitted into described the 3rd catoptron through described second single wavelength through the light of the described second spectroscope transmission, produce and the shift frequency light path turns back to described second spectroscope through described second single wavelength again through the light of described the 3rd mirror reflects; Close light through the light of described second mirror reflects with through the light of described the 3rd mirror reflects at the described second spectroscope place; Describedly close the light light beam light pulse is transmitted into and is transmitted into described diffraction grating after light is closed in described first spectroscope and gage beam light pulse as the reference arm, described diffraction grating separates the difference interference signal of two wavelength, and survey reception by described first photodetector and second photodetector respectively, two photodetectors send to described computing machine with measured signal respectively and carry out computing, finish range observation.

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

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

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

Described second single wavelength produces and the 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 to the single wavelength light signal generating frequency displacement of described arrowband.

The present invention is owing to take above technical scheme, it has the following advantages: 1, the present invention includes the femtosecond laser frequency comb, the Michelson interference system, diffraction grating, two photodetectors and computing machine, the Michelson interference system comprises first spectroscope, first catoptron, second spectroscope, first single wavelength produces and the shift frequency light path, second single wavelength produces and the shift frequency light path, second catoptron and the 3rd catoptron, second spectroscope is identical with the distance of second spectroscope to the, three catoptrons to the distance of second catoptron, the present invention is owing to utilized the wide spectral characteristics of femtosecond laser frequency comb, producing two close long composite waves of wavelength composition wavelength by two single wavelength generations and shift frequency light path interferes, and utilize synthetic wavelength as bridge dexterously, difference interference phase place and " looking for extremum method " are connected to get up to aim at for pulse, therefore femto-second laser pulse can be aimed at and directly trace back to single wavelength difference interference phase place, realize superhigh precision pulse aligning, thereby realize the superhigh precision range finding.2, the present invention adopts the method that measuring accuracy is refined step by step, at first adopt " looking for extremum method " to carry out pulse aligning and range finding, realize micron-sized bigness scale precision, next adopts synthesis wave to interfere measuring accuracy to be brought up in single wavelength of 1/4th, finally further improve precision to nanometer scale with single wavelength difference interference, prove that by experiment the method that the present invention proposes can bring up to nanoscale from the micron order precision of looking for extremum method with the pulse alignment precision, thereby can improve distance accuracy greatly.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 the absolute distance measurement.

Description of drawings

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 synoptic diagram of the embodiment of the invention, and horizontal ordinate is wavelength, and ordinate is the normalization spectral intensity, and wherein (a) is femtosecond laser frequency comb spectral distribution, (b) centered by wavelength be λ _R1Narrow-band spectrum, (c) centered by wavelength be λ _R2Narrow-band spectrum, (d) centered by wavelength be λ _C1Difference interference signal spectrum, (e) centered by wavelength be λ _C2Difference interference signal spectrum;

Fig. 3 is the effect synoptic diagram under the state I situation of j pulse generation stack of i pulse of reference arm pulse of the embodiment of the invention and gage beam pulse;

Fig. 4 is the j+k of i pulse and the gage beam pulse of reference arm pulse of the present invention _rThe effect synoptic diagram under state I I situation of individual pulse generation stack.

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 of the present invention comb synthesis wave to interfere range measurement system comprises femtosecond laser frequency comb FLFC(adjustable repetitive frequency), a Michelson interference system, a diffraction grating G and two photoelectric detector PD ₁, PD ₂, wherein, the Michelson interference system comprises the first spectroscope BS ₁, first mirror M ₁, the second spectroscope BS ₂, the first single wavelength produces and the shift frequency light path, second single wavelength produces and shift frequency light path, second mirror M ₂With the 3rd mirror M ₃The light pulse sequence (spectral distribution is (a) as shown in Figure 2) 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 first mirror M ₁, through first mirror M ₁Pulse turns back to the first spectroscope BS to the light of reflection as gage beam 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 is transmitted into second mirror M through first single wavelength generation and shift frequency light path ₂, through second mirror M ₂The light of reflection turns back to the second spectroscope BS through first single wavelength generation and shift frequency light path again ₂Through the second spectroscope BS ₂The light of transmission is transmitted into the 3rd mirror M through second single wavelength generation and shift frequency light path ₃, through the 3rd mirror M ₃The light of reflection turns back to the second spectroscope BS through second single wavelength generation and shift frequency light path again ₂Through second mirror M ₂The reflection light and through the 3rd mirror M ₃The light of reflection is at the second spectroscope BS ₂Light is closed at the place, and this closes the light light beam, and light pulse is transmitted into the first spectroscope BS as the reference arm ₁Be transmitted into diffraction grating G after closing light with the gage beam light pulse, reference arm light pulse meeting this moment and gage beam light pulse generation difference interference, because the reference arm pulse comprises the light (spectral distribution (b) and (c) as shown in Figure 2) of two wavelength, so can produce the difference interference signal of two wavelength, the centre wavelength of two difference interference signals is designated as λ respectively _C1And λ _C2(spectral distribution (d) and (e) as shown in Figure 2)), diffraction grating G with the difference interference signal of these two wavelength separately, and respectively by first photoelectric detector PD ₁With second photoelectric detector PD ₂Survey and receive two photoelectric detector PD ₁, PD ₂Respectively measured signal is sent to a computing machine and carry out computing, finish accurate distance and measure.For the light pulse of two wavelength guaranteeing the reference arm pulse can be simultaneously and the gage beam pulse generation interfere, therefore need to guarantee the second spectroscope BS ₂To second mirror M ₂Distance and the second spectroscope BS ₂To the 3rd mirror M ₃Distance identical.

In above-described embodiment, first single wavelength produces and the shift frequency light path can comprise an acousto-optic modulator AOM ₁, because the light pulse that femtosecond laser frequency comb FLFC sends has wideer spectrum (tens nanometer, (a) as shown in Figure 2), it is through acousto-optic modulator AOM ₁Behind the diffraction, can differently owing to the angle of diffraction of each wavelength form a diffracted beam of dispersing, so by regulating second mirror M ₂Angle, can select centre wavelength is λ _R1The former road of narrow band light pulse train (spectral distribution is (b) as shown in Figure 2) return and by acousto-optic modulator AOM ₁Produce frequency displacement; First single wavelength produces and the shift frequency light path can also be to comprise an arrowband band pass filter F ₁With an acousto-optic modulator AOM ₁, by arrowband band pass filter F ₁Light signal is selected, and obtaining centre wavelength is λ _R1Narrow band light pulse train (spectral distribution is (b) as shown in Figure 2), acousto-optic modulator AOM ₁This narrow-band impulse sequence is carried out shift frequency.

In the various embodiments described above, second single wavelength produces and the 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 with centre wavelength _R2The former road of narrow band light pulse train (spectral distribution is (c) as shown in Figure 2) return and by acousto-optic modulator AOM ₂Produce frequency displacement; Second single wavelength produces and the shift frequency light path can also be to comprise an arrowband band pass filter F ₂With an acousto-optic modulator AOM ₂, by arrowband band pass filter F ₂Light signal is selected, and obtaining centre wavelength is λ _R2Light pulse sequence (spectral distribution is (c) as shown in Figure 2), acousto-optic modulator AOM ₂This pulse train is carried out shift frequency.

Adopt femtosecond laser frequency comb synthesis wave to interfere range measurement system of the present invention to the method that testing distance L accurately measures, may further comprise the steps:

1, with first mirror M ₁(measurement mirror) is placed on baseline position BL place (baseline refers to measure when gage beam length and reference arm are isometric the position at mirror place) (as shown in Figure 1), and the fine setting mirror M ₁The position, make that (the difference interference signal of two wavelength can be chosen one wantonly, and it is λ that the present invention selects centre wavelength for reference arm pulse and gage beam light pulse difference interference signal _C1Interference signal) intensity reach maximum, as shown in Figure 2, suppose that i pulse of reference arm pulse this moment and j pulse generation of gage beam pulse superpose, only depending on this moment judgement interference signal intensity maximum the spike of two pulses can't be transferred to fully aims at, generally have 1～2 micron deviation, suppose that the offset deviation between the two spike is δ _I, this moment, the state note was labeled as state I, and the phase place of reference arm pulse and the corresponding difference interference signal of gage beam pulse is designated as respectively: With

Repetition is designated as

The adjacent pulse light path is spaced apart

(c is the light velocity in the vacuum), this state is the system works original state, can be fixed up in case regulate just;

2, with first mirror M ₁Be placed on position to be measured, be testing distance L with the distance between this position and the baseline BL, adopt existing " looking for extremum method " to carry out coarse adjustment, that is: the repetition of change femtosecond laser frequency comb FLFC, make the intensity of reference arm pulse and gage beam pulse difference interference signal reach that maximum (select the interference signal identical with step 1 centre wavelength, it is λ that the present invention selects centre wavelength _C1Interference signal), suppose i pulse of reference arm this moment and the j+k of gage beam _rIndividual pulse generation stack, the deviation between the spike of the two is δ _II(1～2 micron), status indication is state I I at this moment, the phase place of the difference interference signal of reference arm pulse and gage beam pulse correspondence is designated as respectively: With

Repetition is designated as

The adjacent pulse light path is spaced apart

3, calculate tested distance L:

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

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

When

This moment k _r=0, tested distance L equals the registration distance B, and this moment is when changing to state I I from state I, all is that i pulse of reference arm pulse and j pulse generation of gage beam pulse superpose the deviation of two superimposed pulse spikes variation δ when changing to state I I from state I _II-δ _IThe relative shift that has reflected two pulses, this relative shift also can cause the variation of interference signal phase place, can represent 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 the formula, λ _C1And λ _C2Be the centre wavelength of difference interference signal, n _P1And n _P2Be λ _C1And λ _C2Corresponding airborne phase refractive index, n _gBe the aerial group index of pulse train, k ₁And k ₂Be integer undetermined, because Δ D _P-pCan calculate by the repetition of measuring under the two condition, phase refractive index and group index can calculate according to refractive index calculating formula by recording atmospheric parameter, therefore only need the k in definite formula ₁Or k ₂Can obtain registration distance B accurately.To determine k ₁Carry out finding the solution of registration distance B described for example, that is: at first bigness scale goes out δ _II-δ _IValue, substitution formula (2) is obtained k ₁, because the k that obtains ₁Integer not necessarily therefore need be to the k that obtains ₁Carry out round, in order to guarantee not produce round-off error, need satisfy δ _II-δ _IBigness scale ratio of precision λ _C1/ 2 high conditions, however such bigness scale precision only can't realize by " looking for extremum method " that the solution procedure of registration distance B is:

1) passes through the composite wave method to δ _II-δ _ICalculate, formula (2) and (3) put in order obtained 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 the formula, Δ φ _s=Δ φ ₂-Δ φ ₁Phase place for composite wave; λ _s=λ _Air1λ _Air2/ (λ _Air1-λ _Air2) be the wavelength of composite wave, wherein λ _Air1=λ _C1/ n _P1λ _Air2=λ _C2/ n _P2k _sBe integer undetermined, k _s=k ₂-k ₁

Because λ _C1And λ _C2Relatively near (differing tens nanometer), so λ _Air1And λ _Air2Also more approaching, the wavelength X of composite wave _sCan reach λ _Air1Tens times, about tens microns to hundred microns, by the extremum method of looking for of step 1 and step 2, can determine δ _IAnd δ _IIAll about 1～2 micron, so δ _II-δ _IAlso be one several microns a small amount of, can not cause the variation of composite wave phase place generation integer level, therefore can determine the k in the formula (7) _sBe 0, therefore according to Δ φ _sAnd λ _sCalculate δ _II-δ _I, be example with 0.5 ° of phase measurement accuracy, the δ that obtain this moment _II-δ _IPrecision is: λ _s/ (2 * 360/0.5) have been far superior to λ _C1/ 4 or λ _C2/ 4.

2) δ that step 1) is calculated _II-δ _ISubstitution formula (2) or formula (3) calculate k ₁Or k ₂, and to k ₁Or k ₂Carry out round, because δ _II-δ _IPrecision be higher than λ _C1/ 4 and λ _C2/ 4, thereby guaranteed k ₁Or k ₂Do not round and can produce deviation.

3) k after will rounding ₁Or k ₂Substitution formula (2) or formula (3) are according to Δ φ ₁Or Δ φ ₂Calculating the registration distance B, is example with phase measurement accuracy 0.5 still, and the precision that realize this moment is: λ _C1/ (2 * 360/0.5) or λ _C2/ (2 * 360/0.5) are about about 1nm.

When

The time, this moment k _rBe positive integer, k _rThe sequence number that has reflected overlapping pulses when changing to state I I from state I changes number, also reflected simultaneously tested distance approximately be the recurrent interval half

What doubly because the recurrent interval generally all is a meter magnitude, therefore can namely can determine k by existing normal pulsed laser range finder bigness scale distance _rValue, and calculate the registration distance B by said method and can calculate tested distance L.

In order more clearly to illustrate the principle of femtosecond laser frequency comb synthesis wave to interfere distance-finding method of the present invention, be elaborated below by specific embodiment and in vacuum environment, realize the process that pulse aligning and distance measuring precision are refined step by step by the composite wave transition:

Suppose λ _C1=1570nm, λ _C2=1550nm, then composite wave λ _s=121.675 μ m, repetition f _Rep=50MHz(D _P-p=6m), tested is 300m, then k apart from actual value _r=100, phase measurement accuracy 0.5 degree, " looking for extremum method " alignment precision 2 μ m.According to femtosecond laser frequency comb synthesis wave to interfere distance-finding method of the present invention, carry out pulse by " looking for extremum method " earlier and aim at, obtain δ _II-δ _ILess than 4 μ m, therefore can determine k _s=0, therefore can obtain δ according to the composite wave phase calculation _II-δ _I, its error is λ _s/ (2 * 360/0.5)=0.084 μ m is because this precision is better than λ _C1/ 4, therefore can be further and single wavelength X _C1Interferometric phase be connected, being connected the back alignment error is λ _C1/ (2 * 360/0.5)=1.1nm can bring up to nanoscale from the micron order precision of looking for extremum method with the pulse alignment precision by the method that the present invention proposes as can be seen by embodiments of the invention, thereby can improve distance accuracy greatly.

The various embodiments described above only are used for explanation the present invention; wherein step of the structure of each parts, connected mode and implementation method etc. all can change to some extent; each optical element can adopt support commonly used to carry out support fixation in addition; and the position of optical element etc. all can change to some extent; as long as satisfy light path propagation conditions of the present invention; every equivalents and improvement of carrying out on the basis of technical solution of the present invention all should do not got rid of outside protection scope of the present invention.

Claims (6)

1. a femtosecond laser frequency is combed the synthesis wave to interfere distance-finding method, and it may further comprise the steps:

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

2) described first catoptron is placed on the baseline position place, and finely tune the position of described first catoptron, make the intensity of reference arm pulse and gage beam light pulse difference interference signal reach maximum, suppose that i pulse of reference arm pulse this moment and j pulse generation of gage beam pulse superpose, the offset deviation between the two spike is δ _I, this moment, status indication was state I, the phase place of reference arm pulse and the corresponding difference interference signal of gage beam pulse is designated as respectively:

With Repetition is designated as

The adjacent pulse light path is spaced apart

Wherein c is the light velocity in the vacuum;

3) described first catoptron is placed on position to be measured, distance between this position and the baseline is designated as testing distance L, adopt " looking for extremum method " to carry out coarse adjustment, that is: change the repetition of described femtosecond laser frequency comb, make the intensity of reference arm pulse and gage beam pulse difference interference signal reach maximum, i pulse of hypothetical reference arm pulse and the j+k of gage beam pulse _rIndividual pulse generation stack, the offset deviation between the two spike is δ _II, status indication is state I I at this moment, the phase place of the difference interference signal of reference arm pulse and gage beam pulse correspondence is designated as respectively:

With

Repetition is designated as The adjacent pulse light path is spaced apart Wherein c is the light velocity in the vacuum;

4) calculate tested distance L:

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

When

This moment k _r=0, tested distance L equals the registration distance B, when namely changing to state I I from state I, all is i pulse of reference arm pulse and j pulse generation stack of gage beam pulse, and 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 the formula, λ _C1And λ _C2Be the centre wavelength of difference interference signal, n _P1And n _P2Be λ _C1And λ _C2Corresponding airborne phase refractive index, n _gBe the aerial group index of pulse train, the solution procedure of registration distance B is:

1. pass through the composite wave method to δ _II-δ _ICalculate, formula (2) and formula (3) put in order obtained 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 the formula, Δ φ _s=Δ φ ₂-Δ φ ₁Be 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. the δ that 1. described step is calculated _II-δ _ISubstitution formula (2) or formula (3) calculate k ₁Or k ₂, and to k ₁Or k ₂Carry out round;

3. the k after will rounding ₁Or k ₂Substitution formula (2) or formula (3) are according to Δ φ ₁Or Δ φ ₂Calculate the registration distance B;

When

The time, this moment k _rBe positive integer, L determines k by the pulse laser laser welder bigness scale _rValue, and calculate the registration distance B by said method and can calculate tested distance L.

2. realize the femtosecond laser frequency comb synthesis wave to interfere range measurement system of distance-finding method according to claim 1 for one kind, it is characterized in that: it comprises femtosecond laser frequency comb, a Michelson interference system, a diffraction grating, two photodetectors and a computing machine, and described Michelson interference system comprises that first spectroscope, first catoptron, second spectroscope, first single wavelength generation and shift frequency light path, second single wavelength produce and shift frequency light path, second catoptron and the 3rd catoptron; Described second spectroscope is identical to the distance of described the 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, is transmitted into first catoptron through the light of the described first spectroscope transmission, and pulse turns back to described first spectroscope as gage beam through the light of described first mirror reflects;

Light through described first spectroscope reflection is transmitted into described second spectroscope, produce and the shift frequency light path is transmitted into described second catoptron through described first single wavelength through the light of described second spectroscope reflection, produce and the shift frequency light path turns back to described second spectroscope through described first single wavelength again through the light of described second mirror reflects; Produce and the shift frequency light path is transmitted into described the 3rd catoptron through described second single wavelength through the light of the described second spectroscope transmission, produce and the shift frequency light path turns back to described second spectroscope through described second single wavelength again through the light of described the 3rd mirror reflects; Close light through the light of described second mirror reflects with through the light of described the 3rd mirror reflects at the described second spectroscope place;

Describedly close the light light beam light pulse is transmitted into and is transmitted into described diffraction grating after light is closed in described first spectroscope and gage beam light pulse as the reference arm, described diffraction grating separates the difference interference signal of two wavelength, and survey reception by described first photodetector and second photodetector respectively, two photodetectors send to described computing machine with measured signal respectively and carry out computing, finish range observation.

3. a kind of femtosecond laser frequency as claimed in claim 2 is combed the synthesis wave to interfere range measurement system, it is characterized in that: described first single wavelength produces and the 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 to the single wavelength light signal generating frequency displacement of described arrowband.

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

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

6. as claim 2 or 3 or 4 described a kind of femtosecond laser frequency comb synthesis wave to interfere range measurement systems, it is characterized in that: described second single wavelength produces and the 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 to the single wavelength light signal generating frequency displacement of described arrowband.

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