CN112799089A - Eye-safe laser range finder and method - Google Patents

Eye-safe laser range finder and method Download PDF

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CN112799089A
CN112799089A CN202110176246.4A CN202110176246A CN112799089A CN 112799089 A CN112799089 A CN 112799089A CN 202110176246 A CN202110176246 A CN 202110176246A CN 112799089 A CN112799089 A CN 112799089A
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reflector
light
laser
beam splitter
detector
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CN112799089B (en
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赵辉
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Suzhou Tongren Laser Technology Co ltd
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Suzhou Tongren Laser Technology Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/46—Indirect determination of position data
    • G01S17/48—Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

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Abstract

The invention provides a human eye safety laser range finder and a method, which have the advantages of simple operation, small volume and high test precision, and can output human eye safety waveband laser; the laser comprises a light source, erbium glass, a first reflector and a second reflector, wherein the first reflector and the second reflector are arranged at the light-emitting end of the erbium glass, an included angle between the normal line of the first reflector and the normal line of the light-emitting surface of the erbium glass is a Brewster angle, the first reflector and the second reflector form a V-shaped resonant cavity with the erbium glass, light emitted by the light source enters the erbium glass and then is emitted from the first reflector and the second reflector, and the light emitted from the first reflector sequentially passes through a first total reflector, an acousto-optic frequency shifter, a first beam splitter and a detector; the light emitted from the second reflector sequentially passes through the second total reflector, the Q-switched crystal, the Faraday optical rotation isolator, the second beam splitter, the third beam splitter and the telescopic system and is emitted to a target to be detected, and the light scattered or reflected by the target to be detected sequentially passes through the third beam splitter, the second beam splitter and the first beam splitter and then enters the detector.

Description

Eye-safe laser range finder and method
Technical Field
The invention relates to the technical field of laser equipment, in particular to a human eye safety laser range finder and a method.
Background
Laser ranging is the earliest application of laser in military affairs and is one of the most mature technologies, laser ranging is used for calculating the distance length by utilizing the transmission time of light between two objects, the laser ranging machine has good laser divergence, and a divergence angle is small, so that the target position can be measured accurately.
At present, the laser range finder has extensive application in military weapons, and the use of laser range finder has improved the probability that weapons such as tank, unmanned aerial vehicle and long-range gun hit the target to a great extent. The modern war is characterized by small scale and high speed, which requires the military weapon to be capable of accurate guidance, quick response and flexible maneuvering during operation, and the laser weapon shows great superiority. At present, the wavelengths used by laser in the aspect of distance measurement are 1.06 μm, 1.5 μm, 10.6 μm and the like, but the 1.06 μm and 10.6 μm wavelengths allow the exposure of human eyes to be smaller, so that the human eyes sensitive to light can be easily and extremely injured in the moment, and the danger of blindness is easily brought to personnel in battlefields and training; the existing eye-safe laser range finder also has the problems of complex operation, large volume, poor testing precision, low repetition frequency (within 20 Hz) and low output energy (micro-focus level), and the conventional photon pulse counting method is adopted, so that when the measuring distance is increased, the returned energy is sharply reduced, the pulse shape is difficult to distinguish, and further application of the laser range finder is limited.
Disclosure of Invention
Aiming at the problems, the invention provides the eye-safe laser range finder and the method, which have the advantages of simple operation, small volume and high test precision, can output the eye-safe waveband laser, and ensure the quality of light beams.
The technical scheme is as follows: the utility model provides an eye safety laser rangefinder, its includes laser instrument, detector, the laser instrument includes the light source, its characterized in that: the laser also comprises erbium glass, a first reflector and a second reflector which are arranged at the light-emitting end of the erbium glass, included angles between the normal lines of the first reflector and the second reflector and the normal line of the light-emitting surface of the erbium glass are Brewster angles, a resonant cavity formed by the first reflector, the second reflector and the erbium glass is V-shaped, light emitted by the light source enters the erbium glass and then is emitted from the first reflector and the second reflector respectively, and the light emitted from the first reflector sequentially passes through the first total reflector, the acousto-optic frequency shifter and the first beam splitter to reach the detector; the light emitted from the second reflector sequentially passes through a second total reflector, a Q-switching crystal, a Faraday optical rotation isolator, a second beam splitter, a third beam splitter and a telescopic system and is emitted to a target to be detected, and the light scattered or reflected by the target to be detected sequentially passes through the third beam splitter, the second beam splitter and the first beam splitter and then enters the detector.
The laser beam emitted by the indicating laser and the light emitted from the second reflector are coaxial, and the laser beam sequentially passes through the fourth beam splitter, the third beam splitter and the telescopic system in the direction of the laser beam emitted by the indicating laser and then is coaxially emitted to a target to be detected together with the light emitted from the second reflector; the fourth beam splitter transmits the transmitted light to the camera, so that the camera acquires an image of a target to be detected;
furthermore, the light source is a pumping light source, a resonant cavity formed by the first reflector, the second reflector and the erbium glass is in a V shape, and the pumping light emitted by the light source satisfies that the gain is larger than the consumption in the resonant cavity;
further, the wavelength of the pump light emitted by the light source is 940nm or 980 nm; the light source is emitted by a laser diode or a fiber laser;
furthermore, the Q-switched crystal adopts an active Q-switched crystal, and comprises an electrical crystal and an acousto-optic crystal; the width-thickness ratio of the erbium glass is more than 2;
furthermore, the first reflector and the second reflector are both plane reflectors or spherical reflectors; the mirror surfaces of the first reflector and the second reflector are plated with 940nm or 980nm anti-reflection films and 1535nm high-reflection films;
further, the frequency shift amount of the acousto-optic frequency shifter is 80 MHz; the camera adopts any one of a CCD camera, a CMOS camera, a thermal imager and an infrared camera; the telescope system adopts any one of Galileo telescope, Newton telescope, reflective telescope and foldback telescope; the wavelength of the indicating laser is 400 nm-2500 nm;
furthermore, the mirror surfaces of the first total reflector and the second total reflector are plated with 1.5um total reflection films; the mirror surfaces of the first beam splitter and the second beam splitter are respectively plated with a semi-transparent and semi-reflective film at the position of 1.5 um; the mirror surface of the third beam splitter is plated with a 1.5um full-transparent and indicating laser wave band full-reflecting film; the fourth beam splitter mirror surface is plated with the semi-transparent and semi-reflective film of the indication laser wave band;
further, the light source is arranged at one side end of the erbium glass, pump light emitted by the light source enters the erbium glass from the end face of the erbium glass, and the end face of the erbium glass is plated with a 940nm or 980nm high-transmittance film;
a human eye safety laser ranging method is characterized in that: which comprises the following steps:
s1, emitting continuous laser generated by the laser from a first reflecting mirror and a second reflecting mirror, wherein the light emitted from the first reflecting mirror is signal light, and reaches a detector after sequentially passing through a first total reflecting mirror, an acousto-optic frequency shifter and a first beam splitter; the light emitted from the second reflector is local oscillation light, and is transmitted to a target to be measured after passing through a Q-switching crystal, a Faraday optical rotation isolator, a second beam splitter, a third beam splitter and a telescopic system in sequence after passing through a second total reflector;
s2, collecting the light scattered or reflected by the target to be detected by the telescopic system, sequentially passing through the third beam splitter, the second beam splitter and the first beam splitter, and then entering the detector;
s3, mixing the arriving signal light and the local oscillator light on the photosensitive surface of the detector to obtain the round-trip flight time of the pulse, thereby obtaining the distance between the detector and the target to be measured.
Further, in step S3, the data processing after mixing includes the following steps:
s3.1, respectively representing the optical wave fields of the local oscillator light and the signal light as follows:
Figure BDA0002940787040000031
Figure BDA0002940787040000032
wherein ,
Figure BDA0002940787040000033
and
Figure BDA0002940787040000034
unit vectors in the polarization directions of the local oscillator light and the signal light are respectively;
A1(r) and As(r)、
Figure BDA0002940787040000035
And
Figure BDA0002940787040000036
the amplitude and the initial phase of the local oscillation light and the signal light respectively;
ω1 and ωsThe frequencies of the local oscillator light and the signal light are respectively;
Sr(t) is a time waveform function of the Q-switched laser pulse, expressed by a normalization function as:
r is a position vector; t is time;
Figure BDA0002940787040000037
pulse width PwAnd parameter taupThe relationship of (1) is: pw＝3.5τp， (4)
The output intermediate frequency signal of the detector is:
Figure BDA0002940787040000038
wherein e is a primary charge; h is the Planck constant; v is the frequency of the light wave; sigma is the photosensitive area of the detector; etaqQuantum efficiency; d2r represents the integration of the position vector;
time of flight of the pulse
Figure BDA0002940787040000039
wherein ,TsFor the detector from the door start time, τdThe pulse echo relative range gate start time;
s3.2, because the detector does not detect the distance from the door, the distance starting points are used as relative timing zero points, and therefore the rate function of the initial electron number generated on the detector is as follows:
Figure BDA00029407870400000310
wherein ,NLOIs the average of the number of local oscillator light initial electrons, NsFor averaging the initial number of electrons of the signal light, MeFor mixing efficiency, heterodyne beat frequency omega1F＝|ω1-ωsI, phase difference
Figure BDA00029407870400000311
S3.3, setting the initial electron number caused by background radiation noise and the detector dark counting noise as NPEAt a distance of T from the door widthGThe rate function of the initial number of electrons is:
Figure BDA0002940787040000041
then, during the detection time t, the average initial number of electrons detected by the detector is:
Figure BDA0002940787040000042
s3.4, setting the time interval t1，t2]The probability of detecting k initial electrons in-flight is:
Figure BDA0002940787040000043
time interval t1，t2]I.e. the time interval during which the pulses are counted twice within a certain time period from the gate, then at the time interval t1，t2]The probability of no initial electron generation is P (k ═ 0), and the probability of at least one initial electron generation is:
Figure BDA0002940787040000044
the probability of detecting a signal within the range gate is:
Figure BDA0002940787040000045
the obtained target detection probability is:
Figure BDA0002940787040000046
s3.5, according to probability theory, the probability density function of the target detected by the detector is as follows:
Figure BDA0002940787040000047
thus, the mean of the arrival times of the echo photons detected by the detector is:
Figure BDA0002940787040000051
thereby obtaining the round-trip flight time of the pulse, and then calculating the formula
Figure BDA0002940787040000052
And obtaining the distance L between the detector and the target to be measured, wherein c is the light speed.
The invention has the beneficial effects that the operation is simple, the laser output is double output, one path of laser is modulated into pulse laser to realize pulse distance measurement, the distance measurement precision is greatly improved, and because the included angles between the normals of the first reflector and the second reflector and the normal of the light-emitting surface of the erbium glass are Brewster angles, the laser can be transmitted in a zigzag light path in the erbium glass, at the moment, different parts of the light beam experience each area of temperature distribution in the same way in the thickness direction of the erbium glass, the heat effect caused in the thickness direction is eliminated, the quality of the generated light beam is close to a TEM00 film, and meanwhile, the temperature adaptability is stronger; and the resonant cavity formed by the first reflector, the second reflector and the erbium glass is V-shaped, so that the miniaturization of the laser can be kept while the cavity length is increased, the divergence angle of the light beam can be compressed when the cavity length is increased, the measuring distance can be greatly increased, and therefore, the laser can not only output the laser with the safe wave band to eyes, but also ensure the quality of the light beam, and has better economic use value.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a diagram illustrating an operation timing sequence according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly or indirectly secured to the other element. When an element is referred to as being "connected to" another element, it can be directly or indirectly connected to the other element. The terms "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positions based on the orientations or positions shown in the drawings, and are for convenience of description only and not to be construed as limiting the technical solution. The terms "first", "second" and "first" are used merely for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features. The meaning of "plurality" is two or more unless specifically limited otherwise.
In order to explain the technical solution of the present invention, the following detailed description is made with reference to the specific drawings and examples.
As shown in fig. 1, the laser range finder for human eye safety of the present invention comprises a laser and a detector 1, wherein the laser comprises a light source 2, erbium glass 3, and a first reflector 4 and a second reflector 5 which are arranged at a light-emitting end of the erbium glass 3, included angles θ between normals of the first reflector 4 and the second reflector 5 and a normal of a light-emitting surface of the erbium glass 3 are brewster angles, a resonant cavity formed by the first reflector 4, the second reflector 5 and the erbium glass 3 is V-shaped, light emitted from the light source 2 enters the erbium glass 3 and then is emitted from the first reflector 4 and the second reflector 5, and light emitted from the first reflector 4 sequentially passes through a first total reflector 6, an acousto-optic frequency shifter 7, a first beam splitter 8 and reaches the detector 1; the light emitted from the second reflecting mirror 5 passes through the second total reflecting mirror 9, the Q-switched crystal 10, the faraday rotation isolator 11, the second beam splitter 12, the third beam splitter 13 and the telescopic system 14 in sequence and is emitted to a target to be detected (not shown in the figure), and the light scattered or reflected by the target to be detected passes through the third beam splitter 13, the second beam splitter 12 and the first beam splitter 8 in sequence and then enters the detector 1.
The refractive index of the erbium glass 3 at a wavelength of 1.54um is 1.531; brewster angle 56.8 °; the reflection angles of the light entering the erbium glass 3 are all larger than the critical angle, and the reflection angle is 33.1 °.
The laser light emitted by the indicating laser 17 is coaxial with the light emitted from the second reflecting mirror 5, and after sequentially passing through the fourth beam splitter 16, the third beam splitter 13 and the telescopic system 14 in the direction of the laser beam emitted by the indicating laser 17, the laser light and the light emitted from the second reflecting mirror 5 are coaxially emitted to a target to be detected, so that the position of the laser light on the target to be detected can be known more clearly; the fourth beam splitter 16 transmits the light to the camera 15, so that the camera 15 collects an image of the target to be measured; through setting up camera 15, can survey the target that awaits measuring in real time when the range finding, convenient operation is when accomplishing the range finding, is favorable to carrying out further reading to target information.
The light source 2 is a pumping light source, a resonant cavity formed by the first reflector 4, the second reflector 5 and the erbium glass 3 is V-shaped, and the pumping light emitted by the light source 2 satisfies that the gain is larger than the consumption in the resonant cavity; the wavelength of the pump light emitted by the light source 2 is 940 nm; the light source 2 is emitted by a laser diode or a fiber laser.
The Q-switched crystal 10 adopts an active Q-switched crystal, including an electrical crystal and an acousto-optic crystal; the generated laser is pulse laser by adding a Q-switching crystal; the width to thickness ratio of the erbium glass 3 is greater than 2, the preferred size of the erbium glass 3 is 2mm by 1mm by 8 mm.
The first reflector 4 and the second reflector 5 are both plane reflectors or spherical reflectors; and the mirror surfaces of the first reflecting mirror 4 and the second reflecting mirror 5 are both plated with 940nm anti-reflection films and 1535nm high-reflection films.
The frequency shift amount of the acousto-optic frequency shifter 7 is 80 MHz; the camera 15 adopts any one of a CCD camera 15, a CMOS camera 15, a thermal imager and an infrared camera 15; the telescope system 14 is any one of a Galileo telescope, a Newton telescope, a reflective telescope and a return telescope; the wavelength range of the indicator laser 17 is visible light to near infrared, i.e. the wavelength is 1500 nm; the Faraday rotation isolator 11 is used for preventing echo signals from entering the laser so as to achieve the purpose of protecting the laser; the detector 1 adopts an indium gallium arsenic detector 1, an avalanche photodiode, a PMT and other photoelectric converters sensitive to a 1.5um wave band.
The mirror surfaces of the first total reflector 6 and the second total reflector 9 are plated with 1.5um total reflection films; the mirror surfaces of the first beam splitter 8 and the second beam splitter 12 are respectively plated with a semi-transparent and semi-reflective film at the position of 1.5 um; the mirror surface of the third beam splitter 13 is plated with a 1.5um full-transparent and indicating laser 17 wave band full-reflecting film; the mirror surface of the fourth beam splitter 16 is coated with a semi-transparent and semi-reflective film of the wave band of the indicating laser 17.
The light source 2 is arranged at one side end part of the erbium glass 3, pumping light emitted by the light source 2 enters the erbium glass 3 from the end face of the erbium glass 3, and a 940nm high-transmittance film is plated on the end face of the erbium glass 3; erbium glass 3 can be bonded to copper or copper substrate by gallium adhesive for heat conduction.
A human eye safety laser ranging method comprises the following steps:
s1, emitting continuous laser generated by a laser from a first reflector 4 and a second reflector 5, wherein the light emitted from the first reflector 4 is signal light, and reaches the detector 1 after sequentially passing through a first total reflector 6, an acousto-optic frequency shifter 7 and a first beam splitter 8; the light emitted from the second reflector 5 is local oscillation light, and after passing through the second total reflector 9, the local oscillation light is sequentially transmitted to a target to be measured after passing through a Q-switched crystal 10, a Faraday optical rotation isolator 11, a second beam splitter 12, a third beam splitter 13 and a telescopic system 14;
s2, collecting the light scattered or reflected by the target to be detected by the telescopic system 14, passing through the third beam splitter 13, the second beam splitter 12 and the first beam splitter 8 in sequence, and entering the detector 1;
s3, mixing the arriving signal light and the local oscillator light on the photosensitive surface of the detector to obtain the round-trip flight time of the pulse, thereby obtaining the distance between the detector and the target to be measured.
Further, in step S3, the data processing after mixing includes the following steps:
s3.1, respectively representing the optical wave fields of the local oscillator light and the signal light as follows:
Figure BDA0002940787040000071
Figure BDA0002940787040000072
wherein ,
Figure BDA0002940787040000073
and
Figure BDA0002940787040000074
unit vectors in the polarization directions of the local oscillator light and the signal light are respectively;
A1(r) and As(r)、
Figure BDA0002940787040000075
And
Figure BDA0002940787040000076
the amplitude and the initial phase of the local oscillation light and the signal light respectively;
ω1 and ωsThe frequencies of the local oscillator light and the signal light are respectively;
Sr(t) is a time waveform function of the Q-switched laser pulse, expressed by a normalization function as:
r is a position vector; t is time;
Figure BDA0002940787040000077
pulse width PwAnd parameter taupThe relationship of (1) is: pw＝3.5τp， (4)
The output intermediate frequency signal of the detector is:
Figure BDA0002940787040000081
wherein e is a primary charge; h is the Planck constant; v is the frequency of the light wave; sigma is the photosensitive area of the detector; etaqQuantum efficiency; d2r represents the integration of the position vector;
time of flight of the pulse
Figure BDA0002940787040000082
wherein ,TsFor the detector from the start time of the door, τdThe pulse echo relative range gate start time;
s3.2, because the detector is not detected outside the distance gate, the distance starting points are used as relative timing zero points, and the rate function of the initial electron number generated on the detector is as follows:
Figure BDA0002940787040000083
wherein ,NLOIs the average of the number of local oscillator light initial electrons, NsFor averaging the initial number of electrons of the signal light, MeFor mixing efficiency, heterodyne beat frequency omega1F＝|ω1-ωsI, phase difference
Figure BDA0002940787040000084
S3.3, setting the initial electron number caused by background radiation noise and detector dark counting noise as NPEAt a distance of T from the door widthGThe rate function of the initial number of electrons is:
Figure BDA0002940787040000085
then, during the detection time t, the average initial number of electrons detected by the detector is:
Figure BDA0002940787040000086
s3.4, setting the time interval t1，t2]The probability of detecting k initial electrons in-flight is:
Figure BDA0002940787040000087
time interval t1，t2]I.e. the time interval during which the pulses are counted twice within a certain time period from the gate, then at the time interval t1，t2]The probability of no initial electron generation is P (k ═ 0), and the probability of at least one initial electron generation is:
Figure BDA0002940787040000091
the probability of detecting a signal within the range gate is:
Figure BDA0002940787040000092
the obtained target detection probability is:
Figure BDA0002940787040000093
s3.5, according to the probability theory, the probability density function of the detector for detecting the target is as follows:
Figure BDA0002940787040000094
thus, the mean of the arrival times of the echo photons detected by the detector is:
Figure BDA0002940787040000095
thereby obtaining the round-trip flight time of the pulse, and then calculating the formula
Figure BDA0002940787040000096
And obtaining the distance L between the detector and the target to be measured, wherein c is the light speed and is a known quantity.
The range gate technology is widely used in a direct detection laser radar system, a detector does not work outside the range gate, the range gate is opened in the interested detection distance, thus the influence of background radiation and backscattering noise can be greatly reduced, the detection time sequence of the photon pulse heterodyne detection system adopting the range gate technology is shown in figure 2, and the starting time of the range gate is TsPulse echo with respect to the time of start of range gate of τdAnd the width of the distance door is TG。
The conventional photon pulse direct distance measurement method is that a laser is adopted to emit a series of photon pulses to a target to be measured, then a detector is used for sampling the emitted photon pulses, the time is counted from the triggering test of a measurement system, the photon pulses reach the target to be measured and then return to the detector through diffuse reflection to trigger the time counting to stop, and finally the target distance is calculated according to a formula L which is 0.5 x c x t.
In the invention, pumping light enters the erbium glass 3 from the end face of the erbium glass 3, the erbium glass 3 undergoes energy level transition, and laser can be generated in an optical resonant cavity formed by the first reflector 4, the second reflector 5 and the erbium glass 3 when the gain is larger than the loss.
In summary, compared with the prior art, because the included angles between the normals of the first reflecting mirror 4 and the second reflecting mirror 5 and the normal of the light-emitting surface of the erbium glass 3 are all Brewster angles, the laser can be transmitted in the erbium glass 3 through zigzag optical paths, at the moment, different parts of the light beam experience each region of temperature distribution in the same way in the thickness direction, and thus the heat effect caused in the thickness direction is eliminated, so that the light beam quality of the laser is close to that of a TEM00 film, and meanwhile, the temperature adaptability is stronger; because the structure eliminates the influence of thermal effect on the laser, the output power of the laser can reach mJ level, thus greatly improving the measuring distance;
the resonant cavity structure is V-shaped, the miniaturization of the laser can be kept while the cavity length is increased, and the divergence angle of the light beam can be compressed when the cavity length is increased; in the prior art, in order to compress the divergence angle of a light beam, the cavity length needs to be increased, however, the increase of the cavity length causes the heat effect of erbium glass to be more obvious, and the laser output quality is seriously influenced; compared with the prior art, the invention adopts a side pumping mode, greatly enhances the output power of the laser through a V-shaped cavity structure, can reach about 50mJ, and compresses the divergence angle of the laser.
The laser output is set to be double output, one path of light is set to be local oscillation light and frequency shift, the other path of light is set to be signal light and modulated to be pulse laser, and the distance measurement is carried out in a photonic pulse heterodyne mode, so that the distance measurement precision is greatly improved; and the integrated design of a laser and a heterodyne measurement light path is adopted; and the volume of laser ranging is compressed by adopting a coaxial mode of indicating laser, echo signals and signal light.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims (10)

1. The utility model provides an eye safety laser rangefinder, its includes laser instrument, detector, the laser instrument includes the light source, its characterized in that: the laser also comprises erbium glass, a first reflector and a second reflector which are arranged at the light-emitting end of the erbium glass, included angles between the normal lines of the first reflector and the second reflector and the normal line of the light-emitting surface of the erbium glass are Brewster angles, a resonant cavity formed by the first reflector, the second reflector and the erbium glass is V-shaped, light emitted by the light source enters the erbium glass and then is emitted from the first reflector and the second reflector respectively, and the light emitted from the first reflector sequentially passes through the first total reflector, the acousto-optic frequency shifter and the first beam splitter to reach the detector; the light emitted from the second reflector sequentially passes through a second total reflector, a Q-switching crystal, a Faraday optical rotation isolator, a second beam splitter, a third beam splitter and a telescopic system and is emitted to a target to be detected, and the light scattered or reflected by the target to be detected sequentially passes through the third beam splitter, the second beam splitter and the first beam splitter and then enters the detector.
2. The eye-safe laser rangefinder of claim 1, wherein: the laser beam emitted by the indicating laser and the light emitted from the second reflector are coaxial, and the laser beam sequentially passes through the fourth beam splitter, the third beam splitter and the telescopic system in the direction of the laser beam emitted by the indicating laser and then is coaxially emitted to a target to be detected together with the light emitted from the second reflector; and the fourth beam splitter transmits the transmitted light to the camera, so that the camera acquires an image of the target to be measured.
3. The eye-safe laser rangefinder of claim 1, wherein: the light source is a pumping light source, a resonant cavity formed by the first reflector, the second reflector and the erbium glass is V-shaped, and pumping light emitted by the light source meets the condition that gain is larger than consumption in the resonant cavity.
4. An eye-safe laser rangefinder according to claim 3, wherein: the wavelength of the pump light emitted by the light source is 940nm or 980 nm; the light source is emitted by a laser diode or a fiber laser; the light source is arranged at one side end part of the erbium glass, pump light emitted by the light source enters the erbium glass from the end face of the erbium glass, and the end face of the erbium glass is plated with a 940nm or 980nm high-transmittance film.
5. The eye-safe laser rangefinder of claim 1, wherein: the Q-switched crystal adopts an active Q-switched crystal and comprises an electrical crystal and an acousto-optic crystal; the width-thickness ratio of the erbium glass is more than 2.
6. The eye-safe laser rangefinder of claim 1, wherein: the first reflector and the second reflector are both plane reflectors or spherical reflectors; and the first reflector and the second reflector are plated with 940nm or 980nm anti-reflection films and 1535nm high-reflection films.
7. The eye-safe laser rangefinder of claim 2, wherein: the frequency shift amount of the acousto-optic frequency shifter is 80 MHz; the camera adopts any one of a CCD camera, a CMOS camera, a thermal imager and an infrared camera; the telescope system adopts any one of Galileo telescope, Newton telescope, reflective telescope and foldback telescope; the wavelength of the indicating laser is 400 nm-2500 nm.
8. The eye-safe laser rangefinder of claim 2, wherein: the mirror surfaces of the first total reflector and the second total reflector are plated with 1.5um total reflection films; the mirror surfaces of the first beam splitter and the second beam splitter are respectively plated with a semi-transparent and semi-reflective film at the position of 1.5 um; the mirror surface of the third beam splitter is plated with a 1.5um full-transparent and indicating laser wave band full-reflecting film; and the mirror surface of the fourth beam splitter is plated with the semi-transparent and semi-reflective film of the wave band of the indicating laser.
9. A human eye safety laser ranging method is characterized in that: the eye-safe laser range finder as claimed in any one of claims 1 to 9, the eye-safe laser range finding method comprising the steps of:
s1, emitting continuous laser generated by the laser from a first reflecting mirror and a second reflecting mirror, wherein the light emitted from the first reflecting mirror is signal light, and reaches a detector after sequentially passing through a first total reflecting mirror, an acousto-optic frequency shifter and a first beam splitter; the light emitted from the second reflector is local oscillation light, and is transmitted to a target to be measured after passing through a Q-switching crystal, a Faraday optical rotation isolator, a second beam splitter, a third beam splitter and a telescopic system in sequence after passing through a second total reflector;
s2, collecting the light scattered or reflected by the target to be detected by the telescopic system, sequentially passing through the third beam splitter, the second beam splitter and the first beam splitter, and then entering the detector;
s3, mixing the arriving signal light and the local oscillator light on the photosensitive surface of the detector to obtain the round-trip flight time of the pulse, thereby obtaining the distance between the detector and the target to be measured.
10. The eye-safe laser ranging method of claim 9, wherein: in step S3, the data processing after mixing includes the following steps:
s3.1, respectively representing the optical wave fields of the local oscillator light and the signal light as follows:
Figure FDA0002940787030000021
Figure FDA0002940787030000022
wherein ,
Figure FDA0002940787030000023
and
Figure FDA0002940787030000024
unit vectors in the polarization directions of the local oscillator light and the signal light are respectively;
A1(r) and As(r)、
Figure FDA0002940787030000025
And
Figure FDA0002940787030000026
the amplitude and the initial phase of the local oscillation light and the signal light respectively;
ω1 and ωsAre respectively the bookThe frequencies of the vibration light and the signal light;
Sr(t) is a time waveform function of the Q-switched laser pulse, expressed by a normalization function as:
r is a position vector; t is time;
Figure FDA0002940787030000027
pulse width PwAnd parameter taupThe relationship of (1) is: pw＝3.5τp，(4)
The output intermediate frequency signal of the detector is:
Figure FDA0002940787030000031
wherein e is a primary charge; h is the Planck constant; v is the frequency of the light wave; sigma is the photosensitive area of the detector; etaqQuantum efficiency; d2r represents the integration of the position vector;
time of flight of the pulse
Figure FDA0002940787030000032
wherein ,TsFor the detector from the door start time, τdThe pulse echo relative range gate start time;
s3.2, because the detector does not detect the distance from the door, the distance starting points are used as relative timing zero points, and therefore the rate function of the initial electron number generated on the detector is as follows:
Figure FDA0002940787030000033
wherein ,NLOIs the average of the number of local oscillator light initial electrons, NsFor averaging the initial number of electrons of the signal light, MeFor mixing efficiency, heterodyne beat frequency omega1F＝|ω1-ωsI, phase difference
Figure FDA0002940787030000034
S3.3, setting the initial electron number caused by background radiation noise and the detector dark counting noise as NPEAt a distance of T from the door widthGThe rate function of the initial number of electrons is:
Figure FDA0002940787030000035
then, during the detection time t, the average initial number of electrons detected by the detector is:
Figure FDA0002940787030000036
s3.4, setting the time interval t1，t2]The probability of detecting k initial electrons in-flight is:
Figure FDA0002940787030000037
time interval t1，t2]I.e. the time interval during which the pulses are counted twice within a certain time period from the gate, then at the time interval t1，t2]The probability of no initial electron generation is P (k ═ 0), and the probability of at least one initial electron generation is:
Figure FDA0002940787030000041
the probability of detecting a signal within the range gate is:
Figure FDA0002940787030000042
the obtained target detection probability is:
Figure FDA0002940787030000043
s3.5, according to probability theory, the probability density function of the target detected by the detector is as follows:
Figure FDA0002940787030000044
thus, the mean of the arrival times of the echo photons detected by the detector is:
Figure FDA0002940787030000045
thereby obtaining the round-trip flight time of the pulse, and then calculating the formula
Figure FDA0002940787030000046
And obtaining the distance L between the detector and the target to be measured, wherein c is the light speed.
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