CN101261322A - Double frequency He-Ne laser optical feedback distance measuring apparatus - Google Patents

Double frequency He-Ne laser optical feedback distance measuring apparatus Download PDF

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CN101261322A
CN101261322A CNA2008101042608A CN200810104260A CN101261322A CN 101261322 A CN101261322 A CN 101261322A CN A2008101042608 A CNA2008101042608 A CN A2008101042608A CN 200810104260 A CN200810104260 A CN 200810104260A CN 101261322 A CN101261322 A CN 101261322A
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laser
feedback
inner chamber
piezoelectric ceramics
catoptron
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CN101261322B (en
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张书练
谈宜东
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Tsinghua University
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Abstract

The invention relates to a light feedback telemeter for a double frequency He-Ne laser, belonging to the technical field of laser measurement. The telemeter comprises the double frequency He-Ne laser, an external cavity of laser feedback, a measurement circuit and a data processing system, wherein, the He-Ne laser comprises a gain tube, an antireflective window plate fixed on one end of the gain tube and a resonator; the resonator comprises a reflecting mirror of a first internal cavity fixed on the other end of the gain tube, a reflecting mirror of a second internal cavity fixed on the other end of the antireflective window plate, quartz crystal and a first piezoceramics. In the course of measuring, a second piezoceramics pushes the reflecting mirror of the external cavity of laser feedback to move from left to right along the laser axes so as to produce two lines of cross-polarized laser feedback signals and a phase difference exists between the two lines of cross-polarized laser feedback signals in direct proportion to the length of feedback external cavity. The telemeter is characterized by simple and compact structure as well as high performance.

Description

Double frequency He-Ne laser optical feedback distance measuring apparatus
Technical field
The present invention relates to a kind of double frequency He-Ne laser optical feedback distance measuring apparatus, belong to the laser measuring technique field.
Background technology
Self-mixed interference or light feedback are meant in the laser application system, laser instrument output light reflected by exterior object or scattering after, part light feeds back in the laser instrument and the phenomenon that causes the output power variation of laser instrument after light in the chamber mixes, and its output signal and traditional two-beam interference class signal are seemingly.
Because self-mixed interference has had a strong impact on the performance of laser instrument, therefore, the influence of light feedback to laser system eliminated or avoided to researchist's initial interest how.1963, the King reported first self-mixed interference phenomenon, when one movably external mirror laser instrument is exported light reflected back laser resonant cavity, laser power fluctuates, and external mirror whenever moves the displacement of half optical wavelength, laser power changes a striped, and the fluctuation degree of depth of striped and traditional double beam interference system can compare.This research has fundamentally changed the idea of people to the light feedback, and from passive elimination, to initiatively utilizing, feedback has launched a large amount of research to light, has obtained a series of achievement.At present, laser self-mixing interference has been widely used in measurement, speed and the vibration survey etc. of topography measurement, displacement and distance now.
Ranging technology based on laser feedback is simple and compact for structure because of having, and light path system has only a sublaser and an external reflection thing, and advantages such as sensitivity height were risen since the eighties in last century, and main research concentrates on the feedback of semiconductor laser light.1986, G.Beheim etc. reported light feedback mode jump telemetry.In light feedback LD, modulate the injection current of LD continuously, laser output power is because mode jump produces fluctuation, and the mode jump number of times is proportional to external cavity length, realized measurement to the feedback external cavity length according to this principle.But the measuring accuracy of this method is subject to the modulating frequency of injection current and the temperature drift effect of LD, and measuring speed also is subject to the modulating frequency of injection current simultaneously.F.Gouaux rebuilds the LD injection current by considering thermal effect compensation, has greatly improved the resolution of mode jump range finding.2002, Ho Khai Weng studied the mode jump ranging scheme among the VCSEL, has realized measurement range 0.2-0.6 rice, and maximum relative error is less than 6%.Because the semiconductor laser beam angle of divergence is big, in the feedback optical system, the collimation focusing system is essential, has limited its range of application.And the temperature drift of semiconductor laser is bigger, has had a strong impact on the precision of laser ranging.
Summary of the invention
The object of the invention is to propose a kind of simple and compact for structure, and exocoel need not to collimate concentrating element, and signal Processing is simple, the optical feedback distance measuring apparatus that cost performance is high.
To achieve these goals, the present invention has taked following technical scheme.It contains: double frequency He-Ne laser, laser feedback exocoel, metering circuit and four parts of data handling system, wherein:
A: double frequency He-Ne laser, described double frequency He-Ne laser contains:
Gain tube 2, inside are filled with He, Ne mixed gas;
Anti-reflection window 3; Described anti-reflection window 3 is fixed on an end of described gain tube 2;
Resonator cavity, described resonator cavity comprises:
The first inner chamber catoptron 1, the described first inner chamber catoptron 1 is fixed on the other end of described gain tube 2;
The second inner chamber catoptron 4 is positioned at the other end of above-mentioned anti-reflection window 3;
Quartz crystal 14, between above-mentioned second inner chamber catoptron 4 and anti-reflection window 3, these quartz crystal 14 two sides all are coated with anti-reflection film;
First piezoelectric ceramics 5 is fixed on the above-mentioned first inner chamber catoptron 1, and under the input voltage effect, above-mentioned piezoelectric ceramics 5 promotes the above-mentioned first inner chamber catoptron 1 along laser axis direction move left and right, changes laser frequency;
B: the laser feedback exocoel, described laser feedback exocoel contains:
Second piezoelectric ceramics 7 is fixed on the object under test;
Laser feedback exocoel catoptron 6, be fixed on above-mentioned second piezoelectric ceramics 7, described laser feedback exocoel catoptron 6 is driven by second piezoelectric ceramics 7 and moves along the laser axis direction, making the pairwise orthogonal polarized light that incides on the object under test be reflected back toward laser resonant cavity mixes with pairwise orthogonal polarized light in the chamber respectively, cause the light-intensity variation separately of pairwise orthogonal polarized light, produce the laser feedback signal;
C: metering circuit, contain:
Polarization splitting prism 8 is positioned at a side of the above-mentioned first inner chamber catoptron 1, is used for the laser of pairwise orthogonal polarization separately;
First photodetector 9, second photodetector 10 are surveyed the feedback signal of the pairwise orthogonal polarized light that described polarization splitting prism 8 separated respectively;
D: data handling system, described data handling system comprises:
A/D converter 11, input signal are respectively the laser feedback signal of first photodetector 9 and 10 outputs of second photodetector;
D/A 12, the output of this D/A links to each other with the input end of described first piezoelectric ceramics 5, second piezoelectric ceramics 7;
Computing machine 13, link to each other with the output terminal of described A/D converter 11, read the laser feedback signal, and deal with data, calculate the distance of object under test, simultaneously apart from light source, link to each other with the input end of described D/A 12, the output terminal of D/A 12 links to each other with second piezoelectric ceramics 7 with first piezoelectric ceramics 5, controls first piezoelectric ceramics 5 and second piezoelectric ceramics 7, is respectively applied for to realize the control laser frequency and produce the laser feedback signal.
Described quartz crystal 14 and anti-reflection window 3 all are coated with the anti-reflection window 3 of anti-reflection film and replace with a stress bringing device 15 that is clipped on this window by a two sides, this is anti-reflection, and window 3 is fixed on the end of above-mentioned gain tube 2 near the second inner chamber catoptrons 4;
Described quartz crystal 14 and anti-reflection window 3 are replaced by the quartz crystal wedge 16 that a two sides all is coated with anti-reflection film, and this quartz crystal wedge 16 is fixed in the end of above-mentioned gain tube near the second inner chamber catoptron 4.
Double frequency He-Ne laser optical feedback distance measuring apparatus provided by the invention need not to collimate focusing system in the feedback exocoel, simple and compact for structure, it is simple to have signal Processing, the characteristics that cost performance is high.
Description of drawings
Fig. 1: one of double-refraction external cavity displacement measuring system embodiment of the present invention
Fig. 2: two of double-refraction external cavity displacement measuring system embodiment of the present invention
Fig. 3: three of double-refraction external cavity displacement measuring system embodiment of the present invention
Fig. 4: during the long l=67.5mm of exocoel, the feedback curve of pairwise orthogonal polarized light
Fig. 5: during the long l=135mm of exocoel, the feedback curve of pairwise orthogonal polarized light
Fig. 6: during the long l=202.5mm of exocoel, the feedback curve of pairwise orthogonal polarized light
Fig. 7: during the long l=270mm of exocoel, the feedback curve of pairwise orthogonal polarized light
Among the figure: 1, the first inner chamber catoptron, 2, gain tube, 3, anti-reflection window, 4, the second inner chamber catoptron, 5, first piezoelectric ceramics, 6, laser feedback exocoel catoptron, 7, second piezoelectric ceramics, 8, polarization splitting prism, 9, first photodetector, 10, second photodetector, 11, A/D converter, 12, D/A, 13, computing machine, 14, quartz crystal, 15, the stress bringing device, 16, the quartz crystal wedge.
Embodiment
The invention will be further described below in conjunction with accompanying drawing:
Embodiment one:
The experimental provision of present embodiment includes the first inner chamber catoptron 1, the second inner chamber catoptron 4, gain tube 2, anti-reflection window 3, first piezoelectric ceramics 5, quartz crystal 14, second piezoelectric ceramics 7, laser feedback exocoel catoptron 6, polarization splitting prism 8, first photodetector 9, second photodetector 10 and computing machine 13 as shown in Figure 1.Among Fig. 1, the reflectivity of the first inner chamber catoptron 1 and the second inner chamber catoptron 4 is respectively 99.9% and 99.4%, the distance between them, and promptly the long L of laserresonator is 135mm.He, Ne mixed gas are arranged in the gain tube 2, and the air pressure ratio of He, Ne gas is 7: 1.Anti-reflection window 3 is fixed on an end of above-mentioned gain tube 2.The first inner chamber catoptron 1, gain tube 2, anti-reflection window 3, the second inner chamber catoptron 4 have constituted the He-Ne laser instrument of half exocoel 632.8nm jointly.The light source that present embodiment uses is two-frequency laser, produces birefringence effect by place a quartz crystal 14 in the chamber, and half common exocoel He-Ne laser instrument has been made the double frequency He-Ne laser of cross polarization.First piezoelectric ceramics 5 is fixed on the above-mentioned first inner chamber catoptron, and under the effect of input voltage, it promotes the above-mentioned first inner chamber catoptron and moves along the laser axis direction is left and right, makes that pairwise orthogonal polarized light light intensity equates when unglazed feedback.The reflectivity of laser feedback exocoel catoptron 6 is 30%, and the distance between the laser feedback exocoel catoptron 6 and the second inner chamber catoptron 4 is long for the feedback exocoel, and note is made l.Second piezoelectric ceramics 7 is fixed on the above-mentioned laser feedback exocoel catoptron 6, and under the effect of input voltage, it promotes above-mentioned laser feedback exocoel catoptron 6 and moves along the laser axis direction is left and right, produces the light feedback signal.Polarization splitting prism 8 separates the pairwise orthogonal polarization laser from the space, first photodetector 9 and second photodetector 10 are two photodetectors; A/D converter 11 is converted to digital quantity to the light feedback signal that above-mentioned photodetector receives; The output signal of D/A 12 is respectively applied for control first piezoelectric ceramics 5 and second piezoelectric ceramics 7.Computing machine 13 is realized the control of first piezoelectric ceramics 5 and second piezoelectric ceramics 7 is produced suitable light feedback signal by D/A 12, realize the collection of light feedback signal by A/D converter 11, obtain the laser feedback external cavity length by data analysis at last, i.e. testing distance l.
Principle of the present invention is as follows:
Single mode He-Ne laser instrument is under light feedback situation, and the change in gain amount Δ g in the unit length is:
Δg＝g-g 0＝-ξcos(4πνl/c)， (1)
In the formula, g is the interior linear gain of unit length when the light feedback is arranged, g 0Linear gain in the unit length during for unglazed feedback, ξ is the laser feedback factor, and ν is a laser frequency, and c is the light velocity in the vacuum, and l is the long variation of laser feedback exocoel.
Because the variation of laser intensity is proportional to the variation of linear gain during feedback, promptly
I＝I 0-kΔg， (2)
In the formula, I 0Initial light intensity when not having feedback, k is a constant.
Then exist under the condition of light feedback, the light intensity of the pairwise orthogonal polarized light of laser instrument (being o light, e light) is:
I o = I o 0 + ζ o cos ( 4 π c v o l )
(3)
I e = I e 0 + ζ e cos ( 4 π c v e l )
In the formula, ν oAnd ν eBe o light and e light frequency, I O0The initial light intensity of o light when not having feedback, I E0The initial light intensity of e light when not having feedback, ξ oBe the o light feedback factor, ξ eBe the e light feedback factor.(3) formula shows when the long l of feedback exocoel changes λ/2, the pairwise orthogonal polarization light intensity one-period that all fluctuates, but have a phasic difference δ between them:
I o = I o 0 + ζ o cos ( 4 π c v o l )
I e = I e 0 + ζ e cos ( 4 π c v o l + δ )
δ = 4 πΔvl / c = 2 π l L Δv Λ - - - ( 4 )
In the formula: Δ ν=ν o-ν eBe the frequency difference of two crossed polarized lights, Λ is the laser longitudinal module interval.Know that by (4) formula after laser instrument was chosen, δ will be by long l of laser feedback exocoel (being testing distance) and frequency difference Δ ν decision.If Δ ν is less than HOMOGENEOUS BROADENING gain trace live width (approximately 200MHz), the hole burning of two orthogonal polarization modes will be overlapping, therefore must consider the influence of mode competition, at this moment I oAnd I ePhase relation will not merely depend on (4) formula, and the phenomenon that an intensity of polarization light increase causes another intensity of polarization light to reduce can appear.If Δ ν is greater than HOMOGENEOUS BROADENING gain trace live width, the influence of mode competition can be left in the basket, then I oAnd I eBetween phase relation δ determine unique decision by (4) formula.
Because the used double frequency He-Ne laser of system, its frequency difference is about 550MHz, is far longer than the HOMOGENEOUS BROADENING (about 200MHz) of laser medium spectrum, so phase differential δ and mode competition between the pairwise orthogonal polarized light o light, e light have nothing to do.At this moment, phase differential δ between the two is proportional to the long l of feedback exocoel, and the long L of laserresonator, the frequency difference Δ ν of pairwise orthogonal polarized light and laser longitudinal module these parameters of Λ are at interval all determined, therefore, only the o light of pairwise orthogonal polarization and the phase differential δ between the e light be need measure, just can the long l of laser feedback exocoel, i.e. testing distance be calculated according to (4) formula very easily.Theoretical foundation of the present invention that Here it is.
It is down long that Fig. 4～Fig. 7 is respectively different exocoels, the experimental result of pairwise orthogonal polarized light feedback signal.Find that along with feedback exocoel length is changed to 270mm from 67.5mm, the phase differential between the pairwise orthogonal polarized light feedback signal also correspondingly is changed to 2 π from about 0.5 π, and is linear between the two.According to (4) formula, when feedback exocoel length is respectively: l=67.5mm; L=135mm; L=202.5mm; During l=270mm, the phase differential that Theoretical Calculation obtains between the pairwise orthogonal polarized light feedback signal is respectively: δ=0.5 π, δ=π, δ=1.5 π, δ=2 π.Theoretical Calculation result and experimental result are consistent.Therefore, the phase differential δ between the pairwise orthogonal polarized light feedback signal is proportional to this phenomenon of feedback external cavity length l, can be used for range observation.According to (4) formula, for specific parameter Δ ν and Λ, the cycle of phase differential δ is
Figure A20081010426000101
Be the every variation of the long l of feedback exocoel 2L, phase differential changes 2 π.And the phase differential δ scope between the feedback signal of the pairwise orthogonal polarized light that experiment obtains is 0～2 π, and therefore, the range observation scope of native system is that 2 times laserresonator is long, i.e. 2L.Certainly, by adjusting laser parameter Δ ν and Λ, its measurement range can also enlarge.When knowing that at first object under test is beyond several resonator cavitys of laser instrument are long,, calculate according to (4) formula again and obtain the feedback external cavity length, thereby determine the position of object under test by measuring the phase differential δ between the pairwise orthogonal polarized light feedback signal.
Embodiment two:
As shown in Figure 2, the structure of present embodiment and embodiment one is basic identical, and difference only is anti-reflection window 3 and quartz crystal 14.Present embodiment all is coated with the anti-reflection window 3 of anti-reflection film by a two sides and is clipped in quartz crystal 14 and anti-reflection window 3 in a stress bringing device 15 alternative embodiments one on this window.Anti-reflection window 3 is a window, and the two sides all is coated with anti-reflection film, is fixed on an end of gain tube 2.Stress bringing device 15 among Fig. 2 is reinforcing rings that stud with screw, and it applies a stress along the axis direction of vertical laser to anti-reflection window 3, because the stress-birefringence effect of anti-reflection window 3, a frequency is split into two frequencies.The first inner chamber catoptron 1, gain tube 2, anti-reflection window 3, the second inner chamber catoptron 4 and stress bringing device 15 common formation double frequency He-Ne lasers.
Embodiment three:
As shown in Figure 3, the structure of present embodiment and embodiment one is basic identical, and difference only is anti-reflection window 3 and quartz crystal 14.Present embodiment all is coated with quartz crystal 14 and the anti-reflection window 3 in quartz crystal wedge 16 alternative embodiments one of anti-reflection film by a two sides, this quartz crystal wedge 16 is fixed in the end of above-mentioned gain tube near the second inner chamber catoptron 4.Quartz crystal wedge 16 two sides all are coated with anti-reflection film, are fixed on an end of gain tube 2, are used to produce frequency splitting.The first inner chamber catoptron 1, gain tube 2, quartz crystal wedge 16 and the second inner chamber catoptron, 4 common formation double frequency He-Ne lasers.
The designed double frequency He-Ne laser optical feedback distance measuring apparatus of the present invention is by double frequency He-Ne laser, The laser feedback exocoel, four parts of measuring circuit and data handling system form. In the measuring process, feedback Mirror produces the laser feedback signal along laser axis move left and right. Between the feedback signal of pairwise orthogonal polarised light Have a phase difference, it is long that this phase difference is proportional to the feedback exocoel. The present invention utilizes outside this characteristic determines Thereby range measurement is realized in the position of cavity reflection mirror. The optical feedback distance measuring apparatus of the present invention's design has the structure letter Single compactness, signal are processed the characteristics simple, that cost performance is high.

Claims (3)

1. double frequency He-Ne laser optical feedback distance measuring apparatus is characterized in that: contain double frequency He-Ne laser, laser feedback exocoel, metering circuit and four parts of data handling system, wherein:
A: double frequency He-Ne laser, described double frequency He-Ne laser contains:
Gain tube (2), inside are filled with He, Ne mixed gas;
Anti-reflection window (3); Described anti-reflection window (3) is fixed on an end of described gain tube (2);
Resonator cavity, described resonator cavity comprises:
The first inner chamber catoptron (1), the described first inner chamber catoptron (1) is fixed on the other end of described gain tube (2);
The second inner chamber catoptron (4) is positioned at the other end of above-mentioned anti-reflection window (3);
Quartz crystal (14) is positioned between above-mentioned second inner chamber catoptron (4) and the anti-reflection window (3), and this quartz crystal (14) two sides all is coated with anti-reflection film;
First piezoelectric ceramics (5) is fixed on the above-mentioned first inner chamber catoptron (1), and under the input voltage effect, above-mentioned piezoelectric ceramics (5) promotes the above-mentioned first inner chamber catoptron (1) along laser axis direction move left and right, changes laser frequency;
B: the laser feedback exocoel, described laser feedback exocoel contains:
Second piezoelectric ceramics (7) is fixed on the object under test;
Laser feedback exocoel catoptron (6), be fixed on above-mentioned second piezoelectric ceramics (7), described laser feedback exocoel catoptron (6) is driven by second piezoelectric ceramics (7) and moves along the laser axis direction, making the pairwise orthogonal polarized light that incides on the object under test be reflected back toward laser resonant cavity mixes with pairwise orthogonal polarized light in the chamber respectively, cause the light-intensity variation separately of pairwise orthogonal polarized light, produce the laser feedback signal;
C: metering circuit, contain:
Polarization splitting prism (8) is positioned at a side of the above-mentioned first inner chamber catoptron (1), is used for the laser of pairwise orthogonal polarization separately;
First photodetector (9), second photodetector (10) are surveyed the feedback signal of the pairwise orthogonal polarized light that described polarization splitting prism (8) separated respectively;
D: data handling system, described data handling system comprises:
A/D converter (11), input signal are respectively the laser feedback signal of first photodetector (9) and second photodetector (10) output;
D/A (12), the output of this D/A links to each other with the input end of described first piezoelectric ceramics (5), second piezoelectric ceramics (7);
Computing machine (13), link to each other with the output terminal of described A/D converter (11), read the laser feedback signal, and deal with data, calculate the distance of object under test apart from light source, simultaneously, link to each other with the input end of described D/A (12), the output terminal of D/A (12) links to each other with second piezoelectric ceramics (7) with first piezoelectric ceramics (5).
2. double frequency He-Ne laser optical feedback distance measuring apparatus according to claim 1, it is characterized in that: described quartz crystal (14) and anti-reflection window (3) all are coated with the anti-reflection window (3) of anti-reflection film by a two sides and the stress bringing device (15) that is clipped on this window is replaced, and this anti-reflection window (3) is fixed on the end of above-mentioned gain tube (2) near the second inner chamber catoptron (4).
3. double frequency He-Ne laser optical feedback distance measuring apparatus according to claim 1, it is characterized in that: described quartz crystal (14) and anti-reflection window (3) are replaced by the quartz crystal wedge (16) that a two sides all is coated with anti-reflection film, and this quartz crystal wedge (16) is fixed in the end of above-mentioned gain tube near the second inner chamber catoptron (4).
CN2008101042608A 2008-04-18 2008-04-18 Double frequency He-Ne laser optical feedback distance measuring apparatus Expired - Fee Related CN101261322B (en)

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