CN1332518C - Laser receiving and echo apparatus with Bragg acousto-optic modulator - Google Patents

Abstract

The present invention relates to a laser receiving and echo device with a Bragg acoustic-optic modulator, which is composed of three convex lenses which are placed in parallel, a light splitting plate, a plane reflection mirror and a Bragg acoustic-optic modulator, wherein centerlines of the convex lenses are coincident. After being received by the lens 1, inquiry light is converted into a narrow light beam through the lens 2. Then, through the light splitting plate, the narrow light beam is divided into transmitted light and reflected light, wherein the transmitted light is a received signal. After being reflected by the plane reflection mirror, the reflected light forms an echo wave light beam and returns in parallel along the direction of the inquiry light after passing through the Bragg acoustic-optic modulator. A light diaphragm and a light filter can also be added in the laser receiving and echo device so as to carry out the filtering of space and frequency on the inquiry light beam and reduce noise generated by stray light and background radiation, and thus, the detection signal-to-noise ratio of a responder is enhanced. The present invention has the characteristics of little light energy loss, simple structure, small volume, etc., and at the same time, the laser receiving and echo device can enhance the signal-to-noise ratios and increase communication and identification distances. In addition, due to the adoption of the Bragg acoustic-optic modulator, the laser receiving and echo device has better modulation effects.

Description

A kind of laser pick-off and echo apparatus with Bragg acousto-optic modulator

Technical field

The invention belongs to the Application Optics technical field, it is particularly related to laser pick-off and echo apparatus in a kind of laser communication or the target identification.

Background technology

Laser communication is a kind of communication mode that utilizes laser beam to communicate as carrier.Basic laser communication system is made up of transmitter (inquiry side), receiver (answer party) and space atmospheric channel.Laser eyepiece identification comes down to a kind of laser communication under given conditions, and basic laser target recognition system also is made up of transmitter (inquiry side), receiver (answer party) and space atmospheric channel.In laser communication or the laser eyepiece identification, the inquiry light beam that inquiry side sends is after answer party reception antenna (being generally the receiving system that optical lens is formed) receives, need the inquiry light beam is divided into two, a part is changed by the photosignal of answer party and the detector of information processing part receives, and changes and the signal amplification of information processing part and the information that treatment circuit demodulates inquiry side through the answer party photosignal; Another part will be returned as echo beam along former road by the echo apparatus of answer party, after echo beam is modulated, " carry " information of answer party, the receiver lens of directive inquiry side, behind the detector and signal processing circuit of the side of inquiry, demodulate the information of answer party, thereby finish laser communication and laser eyepiece identification mission.

Laser communication system or laser target recognition system are divided into active response system and passive answering system dual mode according to the difference of its response mode.Active response is meant that answer party has the LASER Light Source of oneself, utilize light that oneself LASER Light Source sends as echo beam, echo beam is after modulators modulate, and the information of " carrying " answer party is returned the receiving system of inquiry side, thereby finishes laser communication and laser eyepiece identification mission.Because active response need be known the position of inquiry side, just must carry out target following and aiming, and the tracking of target and point technique difficulty are big to the side of inquiry, implement difficulty, so the active response technical difficulty is big, complex structure, the stability of a system is poor, is used less usually.Passive replying is meant that answer party does not have the LASER Light Source of oneself, it is not to rely on laser to make light source to inquiry side's emission echo beam, but use will the side of inquiry based on the echo apparatus of optical means light beam return along former road, and on the echo beam that Yuan Lu returns, load answer party information, thereby finish laser communication and laser eyepiece identification mission.Passive replying do not need the side of inquiry is carried out target following and aiming, but directly utilizes the echo beam of returning along former road just can determine the position of the side of inquiry, and former inquiry light beam just can obtain the echo beam that Yan Yuanlu returns through echo apparatus; Passive replying do not need to make light source with laser simultaneously, makes the simple in structure of receiver, and volume is little, and cost is low, the reliability height.In laser communication and laser eyepiece identification, the answering machine that all needs function admirable, and passive response receiver has bigger advantage than active response receiver under certain conditions, so passive response receiver will be widely used in laser communication and the laser eyepiece recognition technology.And laser pick-off and echo apparatus are one of piths of passive response receiver, so the design of laser pick-off and echo apparatus is significant.

Two power that major issue is echo direction and echo beam of laser pick-off and echo apparatus.In laser communication and laser eyepiece recognition technology, finish communication or target identification task, the echo beam that answer party (by the side of inquiry) returns must be received by the optical receiving system of inquiry side when arriving inquiry side, otherwise, can not finish communication or target identification task.This just requires the echo apparatus of answer party will inquire when light beam returns, must can not depart from along former inquiry light direction, to guarantee simultaneously the center of echo beam and inquiry light beam in the heart distance equal the diversing lens center of the side of inquiry and the distance between the receiver lens center.Another major issue is the power problem of echo beam.Even echo beam can be received by the receiver lens of inquiry side, if but the power of echo beam is too low, add the atmospheric loss of long Distance Transmission and the influence of background emission, the signal to noise ratio that echo-signal arrives on inquiry side's detector will be very little, inquiry side can't finish the detection of echo-signal like this, also just can't finish the identification of laser communication or laser eyepiece.Therefore, except requiring the high-power inquiry light beam of the side of inquiry emission, also require each part of system all as much as possible to reduce the loss of light energy.

Usually people will obtain the parallel echo beam of returning with former direction, will expect using right-angle prism, can obtain strict parallel echo beam with the right angle corner angle really, but it have certain limitation in some practical problem.

In recent years, many people are carrying out useful exploration aspect laser communication and the laser eyepiece identification.Yin Fuchang as Changchun University of Science and Technology teaches a kind of laser pick-off and the echo apparatus of being developed, as shown in Figure 1, it is by 5 lens, 1 right-angle prism and optical modulator are formed, wherein, part inquiry light is through lens 1, lens 2, the photosignal conversion and the information processing part of input receiver behind the receiving unit of the whole device that lens 3 are formed, another part inquiry light is through lens 4, form echo beam behind the echo apparatus that lens 5 and right-angle prism are formed and after light modulator modulates, return and (see that document Yin Fu is prosperous along former road, Zhang Jin's wind, " laser enemy and we identification " photon journal, 1995.Vol.24, No.3.).

This laser pick-off and echo apparatus the place ahead need to receive inquiry side's emitted light beams with two lens as reception antenna, the photodetector of final directive answer party photosignal conversion of a part and processing section, another part is received after right-angle prism produces echo beam.The weak point of this scheme is that the light energy loss is bigger, and system configuration is complicated.Because in this system, need 5 convex lens and a right-angle prism altogether, angle from energy loss, because the inquiry light beam of emission is an entire light, thus in the slit of two receiver lenss inevitable some light can not be received less than and lose; While 5 lens and right-angle prism are also lossy to light energy.Because the power of the inquiry light beam that inquiry side sent itself is just not really high, make echo beam that sufficiently high power be arranged and can be received by the detector of inquiry side, and higher signal to noise ratio is arranged, just must the laser pick-off and the echo apparatus of answering machine be redesigned and improve.

The application number of application in University of Electronic Science and Technology on May 23rd, 2005 is that the level crossing with orthogonal beam-splitter and high reflectance obtains echo beam as echo apparatus in 200510020924.9 the patent application, echo beam and former inquiry parallel beam, how this acousto-optic medical treatment device is modulated echo beam with Raman.This scheme has reduced the loss of light energy, has simplified system configuration.But this scheme can not be used for Prague acoustooptic modulation because in this scheme if echo beam is modulated with Bragg acousto-optic modulator, then not parallel from the echo-signal light beam and the former inquiry light beam of modulator outgoing.And Bragg acousto-optic modulator has many advantages, as Prague acoustooptic modulation diffraction lights at different levels are interfered mutually, each senior diffraction light is cancelled out each other, 0 grade and+1 grade of (or-1 grade) (deciding on the incident direction of light) diffraction light only appear, can make the incident light energy almost all transfer to+1 grade of (or-1 grade) diffraction extreme value on, with Bragg acousto-optic modulator echo beam is modulated and to make full use of beam energy, obtain higher diffraction efficiency, thereby make the detector of inquiry side obtain higher signal to noise ratio.And Raman how the level of this diffraction is time many, beam energy disperses, diffraction efficiency is low.Therefore, want in laser communication and laser eyepiece identification, to obtain high modulation efficiency, just must use Bragg acousto-optic modulator, and want just must partly redesign and improve echo apparatus with Bragg acousto-optic modulator.

Summary of the invention

The purpose of this invention is to provide a kind of laser pick-off and echo apparatus that is applicable to Prague acoustooptic modulation, it has characteristics such as the echo-signal of making light beam returns along former road, light energy losses is little, simple in structure.

A kind of laser pick-off and echo apparatus with Bragg acousto-optic modulator that the present invention states is made up of 3 convex lens, a beam-splitter, a plane mirror and a Bragg acousto-optic modulator.The placement that is parallel to each other of three convex lens, its center line coincides together, and lens 2 are between lens 1 and lens 3; Beam-splitter is between lens 2 and lens 3, and its plane, place and central line of lens angle are any acute angle; Plane mirror places the beam-splitter next door, angle between its plane, place and the plane, beam-splitter place is the complementary angle of Bragg acousto-optic modulator Bragg angle, Bragg acousto-optic modulator also is the complementary angle of Bragg angle with the angle of inquiry beam direction, makes echo beam can return abreast along the direction of inquiry light beam after the Bragg acousto-optic modulator modulation like this.

The present invention is a kind of return laser beam device that is applicable to Prague acoustooptic modulation, its essence is that the application number in application in University of Electronic Science and Technology on May 23rd, 2005 is described in 200510020924.9 the patent application on the technical scheme basis, making the beam-splitter and the angle of inquiry beam direction is any acute angle, angle between beam-splitter and high reflectance level crossing is designed to the complementary angle of Bragg angle, makes the Bragg acousto-optic modulator and the angle of inquiry beam direction also be the complementary angle of Bragg angle.So just can guarantee echo beam with Bragg angle incident Bragg acousto-optic modulator, can also guarantee simultaneously the echo-signal light beam of answer party information along returning inquiry side's receiving system with the direction of former inquiry parallel beam from Bragg acousto-optic modulator outgoing " carrying ".The structure of this scheme and operation principle are as shown in Figure 4.

Operation principle of the present invention is: make reception antenna with the bigger convex lens 1 of relative aperture, lens 1 and lens 2 are formed telescopic system, angle pencil of ray is become narrow beam of light, this narrow beam of light is divided into transmitted light and reverberation through beam-splitter, the photodetector of transmitted light directive receiver photosignal conversion and information processing part wherein, reverberation through plane mirror reflect to form echo beam and through Bragg acousto-optic modulator modulation back along inquiring that light direction returns abreast.

Between lens 3 and detector, can add diaphragm and filter and carry out filtering on space and the frequency, reducing the noise that stray light and background emission produce, thereby improve the detection signal to noise ratio of answer party.

The power of the inquiry light beam that the reflectivity of beam-splitter and transmissivity can be sent according to the distance and the inquiry side of practical communication or identification is decided.The transmitance of beam-splitter and reflectivity can be realized by plating multilayer highly reflecting films on glass substrate.

Angle between plane mirror and the beam-splitter is the Bragg angle of Bragg acousto-optic modulator, and purpose is in order to guarantee that echo beam and former inquiry parallel beam return inquiry side.

As shown in Figure 3, the line of band arrow is represented beam direction, and solid line is represented each parts such as beam-splitter, the level crossing of high reflectance and the direction of Bragg acousto-optic modulator, and dotted line is represented the normal direction of each parts direction.Inquiry light beam along continuous straight runs, the direct projection that lets droop after making the inquiry light beam by the beam-splitter reflection is gone, and then requires beam-splitter and inquires that the angle between light beam is any acute angle.Each angle as shown in FIG..

Get by the geometrical relationship among the figure:

θ＝π-2α-β (1)

In triangle BCD

$\frac{\mathrm{\π}}{2}-{\mathrm{\θ}}_B+\mathrm{\θ}+\mathrm{\γ}=\mathrm{\π}---\left(2\right)$

Get by (1) formula and (2) formula:

$\mathrm{\γ}-\mathrm{\β}=2\mathrm{\α}+{\mathrm{\θ}}_B-\frac{\mathrm{\π}}{2}---\left(3\right)$

Again because

$\mathrm{\γ}+\mathrm{\β}=\frac{\mathrm{\π}}{2}-{\mathrm{\θ}}_B---\left(4\right)$

Get by (3) formula and (4) formula:

γ＝α， $\mathrm{\β}=\frac{\mathrm{\π}}{2}-\mathrm{\α}-{\mathrm{\θ}}_B---\left(5\right)$

So have

$\mathrm{\α}+\mathrm{\β}=\frac{\mathrm{\π}}{2}-{\mathrm{\θ}}_B---\left(6\right)$

The angle that is beam-splitter and high reflectance level crossing direction is

The angle of acousto-optic modulator and horizontal direction also is θ wherein _BBragg angle for acousto-optic modulator.So just can guarantee that the echo-signal light beam returns along former horizontal direction.

The reflectivity of level crossing is high more good more, it is desirable to preferably can reach 100%.So plane mirror preferably adopts the plane mirror of high reflectance, the high reflectance of the plane mirror of high reflectance also can be realized by plating multilayer highly reflecting films on glass substrate.

Luminous power and the echo beam power that receives on the detector to the technical scheme that adopts right-angle prism in the technical background and technical scheme of the present invention compares below.

1) technical scheme described in the technical background (adopting the scheme of right-angle prism)

If the inquiry light beam power of incident is P ₀, two lens slits are S to the proportion of goods damageds of inquiring light, the transmitance of lens is η ₁, the transmitance of right-angle prism is η ₂, the luminous power ratio of two lens receptions is

Then the luminous power that receives on answer party (by the side of the inquiry) detector is:

$P_1=(1-S)P_0\frac{m}{m+n}{\mathrm{\η}}_1^3---\left(1\right)$

The echo beam power that arrives on the answer party modulator is:

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">P</figure-callout>}}_2=(1-S)P_0\frac{n}{m+n}{\mathrm{\&eta;}}_1^2{\mathrm{\&eta;}}_2---\left(2\right)$

2) technical scheme of the present invention

The inquiry light beam power of establishing incident equally is P ₀, the transmitance of lens is η ₁, the reflectivity of high plane of reflection mirror is 100%, beam-splitter to the ratio of optical transmission rate and reflectivity is

Then the luminous power that receives on answer party (by the side of the inquiry) detector is:

$P_1^{\&prime;}=P_0{\mathrm{\&eta;}}_1^3\frac{m}{m+n}---\left(3\right)$

The echo beam power that arrives on the answer party modulator is:

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">P</figure-callout>}}_2^{\&prime;}=P_0{\mathrm{\&eta;}}_1^2\frac{n}{m+n}---\left(4\right)$

More than the luminous power ratio of two kinds of schemes on the answer party detector be:

$\frac{P_1^{\&prime;}}{P_1}=\frac{P_0{\mathrm{\&eta;}}_1^3\frac{m}{m+n}}{(1-S)P_0\frac{m}{m+n}{\mathrm{\&eta;}}_1^3}=\frac{1}{1-S}---\left(5\right)$

The transmitance of lens generally can reach more than 99%, two lens of preceding a kind of scheme can between the proportion of goods damageds estimate to reach 10%, so the luminous power ratio of two kinds of schemes on the answer party detector is:

$\frac{P_1^{\&prime;}}{P_1}=\frac{1}{(1-S)}=\frac{1}{1-0.1}=1.1>1---\left(6\right)$

Equally, the power ratio on the echo beam of the two kinds of schemes arrival answer party modulator is:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">P</figure-callout>}}_2^{\&prime;}}{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">P</figure-callout>}}_2}=\frac{P_0{\mathrm{\&eta;}}_1^2\frac{n}{m+n}}{(1-S)P_0\frac{n}{m+n}{\mathrm{\&eta;}}_1^2{\mathrm{\&eta;}}_2}=\frac{1}{(1-S){\mathrm{\&eta;}}_2}---\left(7\right)$

Right-angle prism is 95% to the transmitance of light, and the proportion of goods damageds between two lens of preceding a kind of scheme are estimated to reach 10%, and then the power ratio on the echo beam of the two kinds of schemes arrival answer party modulator is:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">P</figure-callout>}}_2^{\&prime;}}{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">P</figure-callout>}}_2}=\frac{1}{(1-S){\mathrm{\&eta;}}_2}=\frac{1}{(1-0.1)\&times;0.95}=1.13>1---\left(8\right)$

From the comparison of above two kinds of schemes as seen: no matter technical scheme of the present invention still can obtain than the high luminous power of technical scheme that adopts right-angle prism on the modulator at answer party at the detector of answer party, therefore the design of this programme can improve the detection signal to noise ratio of inquiry side and answer party, under sufficiently high signal to noise ratio condition, it can also increase the distance of laser communication and laser eyepiece identification simultaneously.

In addition, compare with the prior art that adopts right-angle prism, technical scheme of the present invention has reduced lens numbers and has simplified light path, makes its structure simpler, and whole device volume can be littler.

The patent " a kind of laser pick-off and echo apparatus " of technical scheme of the present invention and University of Electronic Science and Technology's application, (application number: 200510020924.9 dates of application: 2005.5.23, be called for short last application) compare, technical scheme of the present invention is except that having last application all technical characterictic and beneficial effect, also has the technical characterictic that utilizes Bragg acousto-optic modulator to modulate to echo beam, thereby have better modulation effect, can finish the task of laser communication and laser eyepiece identification more with flying colors.

Description of drawings

Fig. 1 is existing laser pick-off and the echo apparatus structure principle chart that is used for laser communication or laser eyepiece identification, and wherein, 1,2,3,4,5 are convex lens, and 1 and 4 bore is bigger, and 2,3,5 bore is less, and 6 is right-angle prism, and 7 is acousto-optic modulator.

The application number that Fig. 2 applies for for University of Electronic Science and Technology is 200510020924.9 laser pick-off that patent application proposed and echo apparatus, wherein, 1,2,3 is convex lens, 1 bore is bigger, and 2,3 bore is less, and 8 is beam-splitter, 10 is diaphragm, 11 is filter, and 9 is plane mirror, and 7 is modulator.

Fig. 3 is for being used to ask the auxiliary schematic diagram of angle between angle between beam-splitter and plane mirror and Bragg acousto-optic modulator and inquiry light beam among the present invention.

Fig. 4 laser pick-off of the present invention and echo apparatus structure principle chart, wherein, 1,2,3 are convex lens, and 1 bore is bigger, 2,3 bore is less, and 8 is beam-splitter, and 10 is diaphragm, and 11 is filter, 12 is photodetector, and 9 is plane mirror, and 7 is Bragg acousto-optic modulator.

Embodiment

Whole laser pick-off and echo apparatus as shown in Figure 4, its composition and position relation is identical with summary of the invention technical scheme part, is not described in detail in this.

The transmitance of 3 convex lens is all got more than 99%, and the bore of lens 2 and lens 3 is got 1cm, and the reflectivity of beam-splitter gets 95%, and transmissivity gets 5%.The bore of lens 1 can be decided according to the peak power of the inquiry light of inquiry side emission and the distance of identification, the peak power P=15W of the inquiry light that sends when inquiry side, and the visibility of atmosphere is 15Km, loss factor is α=0.2, the optical transmittance τ of emission system _t=0.95, the optical transmittance of receiving system is τ _r=0.98, when communication and decipherment distance Z=500m～1000m, the desirable d=6cm of the bore of lens 1, i.e. lens area A _s=(3 * 10 ^-2) ²π, at this moment, when z=1000m, the luminous power that arrives on the beam-splitter is:

$P_r=\frac{4P_r{\mathrm{\&tau;}}_t{A}_s{\mathrm{\&eta;}}_r\cos \mathrm{\&theta;}}{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">Z</figure-callout>}}^2{\mathrm{\&theta;}}_t^2}{e}^{-\mathrm{\&alpha;z}}$

$=\frac{4\&times;15\&times;0.95\&times;(3\&times;{10}^{-2})\mathrm{\&pi;}\&times;0.98\&times;e^{-0.2}}{\mathrm{\&pi;}\&times;{1000}^2\&times;(1.5\&times;{10}^{-3})}$

$=18.3\mathrm{mW}$

The luminous power that then arrives the answer party detector is:

P _r1＝0.05×0.99P _r

＝0.91mW

The luminous power that arrives on the answer party modulator is:

P _R2＝0.95×P _r

＝17.4mW

When communication and decipherment distance Z=500m, the luminous power that arrives on the answer party beam-splitter is:

$P_r^{\&prime;}=\frac{4P_t{\mathrm{\&tau;}}_t{A}_s{\mathrm{\&eta;}}_r\cos \mathrm{\&theta;}}{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20051002103100111.png"\; state="\{\{state\}\}">Z</figure-callout>}}^2{\mathrm{\&theta;}}_t^2}{c}^{-\mathrm{\&alpha;z}}$

$=\frac{4\&times;15\&times;0.95\&times;(3\&times;{10}^{-2})\mathrm{\&pi;}\&times;0.98\&times;e^{-0.2}}{\mathrm{\&pi;}\&times;{500}^2\&times;(1.5\&times;{10}^{-3})}$

$=73.2\mathrm{mW}$

The luminous power that then arrives on the answer party detector is:

P _r1’＝0.05×0.99×P _r’

＝3.6mW

The luminous power that arrives on the answer party modulator is:

P _r2’＝0.95×P _r2

＝69.5mW

Can find out from top calculating, under the condition that provides in the above, when communication and decipherment distance between 500m～1000m the time, if the bore of lens 1 is 6cm, then the luminous power on echo luminous power and the answer party detector is all enough high, can finish laser communication and laser eyepiece identification mission.

In the design of native system, make the carrier of information with the light of wavelength X=0.9 μ m, modulator Bragg acousto-optic modulator, water are done the acousto-optic medium, and the refractive index of water is n=1.33, ultrasonic frequency f _s=500MHz, the ultrasonic wave speed υ in water _s=1.5 * 10 ³M/s, then Bragg angle θ _B=6.5 °, inquiry light beam along continuous straight runs, angle between beam-splitter and inquiry light beam is 45 °, therefore the level crossing of high reflectance and the angle of beam-splitter are 83.5 °, the angle of acousto-optic modulator and horizontal direction also is 83.5 °, in design, make simultaneously distance between inquiry light beam and the echo-signal light beam equal distance between diversing lens center, the side of inquiry and the receiver lens center, the echo-signal light beam can be mapped on the receiving system of inquiry side.

Claims (7)

1, a kind of laser pick-off and echo apparatus with Bragg acousto-optic modulator, form by 3 convex lens, a beam-splitter (8), a plane mirror (9) and a Bragg acousto-optic modulator (7), it is characterized in that, the placement that is parallel to each other of three convex lens, its center line coincides together, and second convex lens (2) are positioned between first convex lens (1) and the 3rd convex lens (3); Beam-splitter (8) is positioned between second convex lens (2) and the 3rd convex lens (3), and its plane, place and central line of lens are any acute angle; Plane mirror (9) places beam-splitter (8) next door, and the angle between its plane, place and the plane, beam-splitter place is the complementary angle of Bragg acousto-optic modulator Bragg angle, makes echo beam to return abreast along the direction of inquiry light beam.

2, a kind of laser pick-off according to claim 1 and echo apparatus is characterized in that, in described 3 convex lens, the bore of first convex lens (1) is greater than the bore of second convex lens (2) and the 3rd convex lens (3).

3, a kind of laser pick-off according to claim 1 and 2 and echo apparatus is characterized in that, the reflectivity of described beam-splitter (8) is 95%, and transmissivity is 5%.

4, a kind of laser pick-off according to claim 1 and 2 and echo apparatus is characterized in that, described plane mirror is the high reflectance plane mirror.

5, a kind of laser pick-off according to claim 1 and echo apparatus, it is characterized in that, back at described the 3rd convex lens (3) adds diaphragm (10) and filter (11), to inquiring that light beam carries out the filtering on space and the frequency, reducing the noise that stray light and background emission produce, thereby improve the detection signal to noise ratio of answer party.

6, a kind of laser pick-off according to claim 1 and echo apparatus is characterized in that, in the described Bragg acousto-optic modulator (7), water is cooked the acousto-optic medium, and its Bragg angle is 6.5 degree.

7, according to each described a kind of laser pick-off and echo apparatus in the claim 1 to 6, it is characterized in that the bore of described first convex lens (1) is 6 centimetres; The bore of described second convex lens (2) and the 3rd convex lens (3) is 1 centimetre.

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