CN212586558U - Micro-pulse polarization aerosol laser radar - Google Patents
Micro-pulse polarization aerosol laser radar Download PDFInfo
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- CN212586558U CN212586558U CN202020927200.2U CN202020927200U CN212586558U CN 212586558 U CN212586558 U CN 212586558U CN 202020927200 U CN202020927200 U CN 202020927200U CN 212586558 U CN212586558 U CN 212586558U
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- 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
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- Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation
Abstract
The utility model provides a micropulse polarization aerosol laser radar, including telescope (13), telescope (13) adopt cassegrain formula telescope, and this telescope (13) include primary mirror (18) and secondary mirror (17), its characterized in that focal plane (19) and the field stop setting of telescope (13) are on primary mirror (18) summit or between secondary mirror (17) and primary mirror (18).
Description
Technical Field
The utility model relates to a micropulse polarization aerosol laser radar using a small-volume optical antenna.
Background
At present, astronomical telescopes are generally adopted as telescopes used by aerosol laser radars. On the one hand, the focal plane of the astronomical telescope is designed outside the telescope, i.e. at a distance below the primary mirror, due to the need for mounting an image detector. The focal plane is far away from the secondary telescope mirror, so that the secondary telescope mirror is large in size, the shielding of the detection light is large, and particularly the detection blind area of the laser radar is large. On the other hand, the F number (focal length/caliber) of the telescope in the prior art is generally more than 8, so that the telescope is large in size and inconvenient to transport and carry, and the height of the lowest complete overlapping area of the laser radar is large.
SUMMERY OF THE UTILITY MODEL
In order to solve the problem, the utility model provides a micropulse polarization aerosol laser radar which comprises a telescope (13), the telescope (13) adopts Cassegrain telescope, and this telescope (13) includes primary mirror (18) and secondary mirror (17), focal plane (19) and the field diaphragm setting of telescope (13) are at primary mirror (18) summit or between secondary mirror (17) and primary mirror (18).
Preferably, the focal plane (19) of the telescope (13) and the field stop are arranged at the vertex of the primary mirror (18).
Preferably, the lidar further comprises a first light detector (15) and a second light detector (16) arranged downstream of the return optical path primary mirror (18) for receiving the first light signal and the second light signal, respectively, split by the polarization beam splitter (14).
Preferably, the F-number of the telescope (13) is less than 3.
Preferably, the aperture of the telescope (13) is 200mm, and the distance from the primary mirror to the secondary mirror is 120 mm. Preferably, the radar has a housing with a laser emitting and receiving window in the top, the window being circular and provided with an optical glass seal.
Preferably, the radar further comprises a wiper for the transmitting window, provided on an edge of the transmitting window.
Preferably, 4 feet are arranged at the lower part of the laser radar shell, and at least 3 feet are independently adjustable in height and used for adjusting levelness.
Preferably, the laser wavelength is about 532nm, the pulse width is less than 20ns, the pulse energy is less than or equal to 300 muJ, and the repetition frequency is 1-10 kHz.
Preferably, the photodetector is a photomultiplier tube or an avalanche photodiode.
Because the focal plane (19) and the field diaphragm are arranged at the position near the vertex of the primary mirror (18) or between the secondary mirror (17) and the primary mirror (18), the diameter of the secondary mirror is reduced, thereby reducing the shielding of light rays, and particularly greatly reducing the detection blind area; because a telescope with small F number is adopted, the portability is greatly increased, and the height of the lowest complete overlapping area of the laser radar is reduced.
Drawings
Fig. 1 is an embodiment of the novel lidar.
Fig. 2a,2b and 2c show a comparative example of the telescope structure of the present invention with the prior art. Wherein fig. 2a represents the prior art and fig. 2b represents an embodiment of the present invention wherein the focal plane is disposed at the location of the vertex of the primary mirror; fig. 2c shows another embodiment of the present invention, which further employs a design with a small F-number, based on the structure of fig. 2 b.
Fig. 3 is an outline view of an embodiment of the micro-pulse polarized aerosol lidar with a small-volume optical antenna.
Reference numerals: 1-an optical portion; 2-electrical part. 3-a power supply part; 11-a laser; 12-a mirror; 13-Cassegrain telescope; 14-a light splitting sheet; 15-a first light detector; 16-a second optical detector, 17-a secondary mirror, 18-a main mirror, 19-a focal plane, 21-a signal acquisition card, 22-a computer, 31-a laser divergence angle delta, 32-a telescope field angle FOV, 33-a distance from the secondary mirror to the main mirror, 41-an emission window, 42-a wiper and 43-a ground foot.
Detailed Description
Fig. 1 is a schematic structural diagram of an embodiment of the novel aerosol detection lidar, wherein reference numeral 1 represents an optical part, 2 represents an electrical part, and 3 represents a power supply part.
Laser pulse of laser instrument transmission among this radar system expands the back through the beam expanding lens, (the beam expanding lens uses three-dimensional adjustable device and is connected with the laser instrument to ensure that laser gets into the beam expanding lens and all perpendicular with the lens through the angle of beam expanding lens, and guarantee that the position of laser incidence point and exit point all is at the centre of a circle position of beam expanding lens), the divergence angle of transmission laser obtains the compression, is less than 0.5mrad generally, then launches to the atmosphere.
The laser collides with atmospheric molecules, aerosol and the like in the atmosphere, a backscattering signal is received by a telescope 13 of the radar, the field angle of the whole receiving system is generally 2 times or more of the divergence angle of the transmitted laser, and the telescope 13 and the main body frame are fixed and cannot be adjusted. After the echo signal passes through the telescope, the converged light is shaped into parallel light by a convex lens at the exit of the telescope, and the upper and lower positions of the convex lens can be adjusted.
Parallel light is divided into 532nm vertical polarized light and 532nm horizontal polarized light after passing through the polarization beam splitter 14, two beams of polarized light are converged through the convex lens and then irradiate on photosensitive surfaces of the light detectors 15 and 16, the two converging lenses are fixed through the adjustable device, and the position between the two converging lenses and the light detectors is adjustable. The position of the light detector is not adjustable.
Here, the embodiment of the photodetector may include, for example, a photomultiplier tube (PMT), an Avalanche Photodiode (APD), or the like.
The optical detectors, such as the photomultiplier tubes 15, 16, are connected with the signal acquisition card, the connecting wire adopts a high-frequency coaxial cable with good shielding property, and the length is as short as possible, so as to ensure that weak electrical signals are not interfered by external electromagnetic noise, the power supply of the optical detectors requires small ripple waves, and the noise introduced by the power supply is reduced. The fixed position of the acquisition card requires good ventilation and heat dissipation conditions and is far away from electric interference sources such as a laser and a switching power supply.
The signal acquisition card 21 converts the laser atmospheric echo analog electric signal into a digital signal, accumulates a plurality of laser pulse echo signals, and transmits the signal to the computer 22, the computer 22 stores the transmitted signal, which is the original data, then the original data is subjected to quality control and product processing, the product is displayed and stored on a radar end software interface, which is the processed product data, and under the condition of demand, the original signal and the product data can be transmitted to a server of a user at other places through a network or a satellite and displayed in client software.
The optical part 1 comprises a compact diode-pumped solid-state laser 11 as a laser light source, the laser wavelength being 532nm, the pulse width being less than 20ns, preferably 5 ns; the pulse energy is less than or equal to 300 muJ, preferably the pulse energy is 200 muJ; repetition frequency 1-10kHz, preferably, pulse frequency: 1kHz, and an average power of 200 mW. After the laser light wave output by the collimating beam expander (not shown) is expanded, the laser light wave is emitted through the reflector 12 and emitted into the atmosphere. After the laser light waves interact with atmospheric molecules and aerosol, echo signals generated by scattering action are received by the Cassegrain telescope 13. The telescope 13 includes a primary mirror 18 and a secondary mirror 17. In this embodiment, the aperture of the primary mirror of the telescope 13 is 200 mm.
In the telescope system of the laser radar in the prior art, the focal plane 19 and the field stop (field stop is arranged on the focal plane) of the system are usually arranged at the downstream of the telescope, i.e. at the side of the primary mirror 18 facing away from the secondary mirror 17, the focal plane 19 and the field stop having a larger distance from the primary mirror 18
Because the focal plane position of telescope need install the field of view diaphragm among the laser radar, rather than image detector, consequently, different with prior art, this is novel to the focal plane 19 of telescope and the position of field of view diaphragm (not shown) so set up for focal plane 19 is as little as possible with secondary mirror 17's distance, in order to realize this neotype purpose.
In one embodiment, the focal plane 19 and the field stop are arranged between the primary mirror 18 and the secondary mirror 17, i.e. inside the telescope 13.
In another embodiment, the focal plane 19 and the field stop are positioned on the optical axis downstream of the primary mirror 18, but as close as possible to the vertex of the primary mirror 18.
Preferably, the focal plane 19 and the field stop are disposed at positions on the optical axis near the vertex of the primary mirror 18.
More preferably, the focal plane 19 and the field stop are disposed at the position of the vertex of the main mirror 18.
The signal received by the telescope 13 is split into two parts by a polarising beam splitter 14, the first part being received by a first light detector 15 and the second part being received by a second light detector 16. The 532nm receiving channel corresponding to the first optical detector 15 is a polarization parallel (P) channel, and the 532nm receiving channel corresponding to the second optical detector 16 is a polarization perpendicular (S) channel. The photodetectors 15 and 16 convert the optical signals into analog electrical signals. The analog signal enters an electric signal collector or a photon counting card, is converted into a digital signal by the analog signal, enters a computer for quality control and product processing, and is finally stored in a hard disk.
Fig. 2a,2b, 2c provide three comparative examples.
Fig. 2a is a prior art telescope configuration. The parameter F # -10, the focal length F-2000 mm, the diameter of the primary mirror 200mm, the diameter of the secondary mirror 80mm, and the distance between the primary mirror 18 and the secondary mirror 17 is 500 mm. The focal plane 19 and the field stop are arranged 288mm below the primary mirror on the optical axis.
Fig. 2b shows a telescope configuration used in an embodiment of the present invention, in which the focal plane 19 and the field stop are arranged at the vertex of the primary mirror, with the following parameters: f # -10, focal length F-2000 mm, primary mirror diameter 200mm, secondary mirror diameter 50mm, and primary mirror 18 and secondary mirror 17 are 500mm apart. Fig. 2b differs from fig. 2a in that the focal plane of fig. 2b is moved upward and is disposed at a position opposite to the vertex of the main mirror 18. The F-number and the focal length F of the telescope of this example remain unchanged, i.e. the exit aperture angle of the telescope is unchanged. After the focal plane of the telescope moves up to the vertex position of the primary mirror from the lower part of the primary mirror, the distance between the focal plane and the secondary mirror is reduced, and the diameter of the secondary mirror can be reduced under the condition that the exit aperture angle is not changed. The diameter of the secondary mirror in this example is reduced from 80mm to 50 mm.
Optical detection of lidarThe efficiency can be expressed in terms of the overlap factor η of the laser emission beam with the optical axis of the telescope. The overlap factor η can be divided into three regions as shown: detection blind area (0)<d<dlη ═ 0); incomplete overlap region (d)l<d<df，0<η); complete overlap region (d)f<d<Infinity, η ═ 1). Obtaining the blind zone distance d of the overlapping factor from the geometric relation in the graphlComprises the following steps:
in the formula, phi is the diameter of the secondary telescope, delta is the divergence angle of the laser beam, and FOV is the angle of field of the telescope, wherein a is the diameter of a field diaphragm, and f is the focal length of the telescope. The distance d of the laser radar detection blind area is known from the formula under the condition that the laser divergence angle and the telescope field angle are constantlProportional to the diameter phi of the telescope secondary mirror. The smaller the secondary mirror, the smaller the detection blind area. The focal plane 19 of the astronomical telescope is arranged below the primary mirror (fig. 2a) and the image detector is arranged at the position of the focal plane. The novel laser radar telescope is provided with only a field stop at the focal plane, and therefore is capable of moving the focal plane 19 up to near the vertex of the primary mirror 18, preferably at the vertex. Since the distance of the focal plane from the secondary mirror is reduced, the size of the secondary mirror is reduced for the same exit aperture angle of the telescope (fig. 2 b). The reduction in the diameter of the secondary mirror 17 not only reduces the detection dead zone but also greatly reduces the light-shielding area of the secondary mirror (proportional to the square of the diameter of the secondary mirror), thereby increasing the detection efficiency of the entire detection region.
For comparison, the diameter of the primary mirror is 200mm, the telescope focal length F is 2000mm, the F number is 10, the distance between the primary mirror and the secondary mirror is 500mm, the telescope field angle FOV is 1mrad, and the laser divergence angle δ is 0.5 mrad. When the secondary mirror is moved up 288mm from below the telescope to the primary mirror vertex position of the telescope, the diameter of the secondary mirror 17 is reduced from 80mm (FIG. 2a) to 50mm (FIG. 2 b). The light-shielding area is reduced by 2.56 times. Detecting blind zone from dlDecrease to d when 53ml＝33m。
Fig. 2c is a telescope configuration of one embodiment of the present invention employing a small F-number, wherein the focal plane is at a location disposed at the vertex of the primary mirror 18. The parameter is F # -2.5, the focal length F is 500mm, the diameter of the primary mirror is 200mm, the diameter of the secondary mirror is 50mm, and the distance between the primary mirror 18 and the secondary mirror 17 is 120 mm.
As previously mentioned, the lowest full overlap distance dfWith respect to the telescope focal length, i.e. with respect to the telescope F-number. From the lens equation 1/f-1/u +1/p, the following equation can be obtained: ,
in the formula, f is the focal length of the telescope, u is the object distance, and v is the image distance. The field diaphragm of the telescope is placed at the focal plane of the telescope, and when the object distance is infinity, u is infinity, and the image distance v is f. Coefficient of performance
Representing the relative deviation of the image distance v of the laser spot with respect to the field stop when the object distance u is elsewhere. When this deviation is small, i.e. when the laser spot is imaged at the field stop position, the lidar system can receive the full scattered energy, i.e. the full overlap region of the lidar, since the laser divergence angle is smaller than the field of view of the telescope. When u is a finite distance, the laser spot is imaged below the field stop, and when the v distance f is larger,
the deviation ratio is large, and the receiving system can only receive a part of laser scattering energy, and the area is an incomplete overlapping area of the laser radar. The lowest complete overlap distance d can be obtained from the above formulafProportional to the focal length f of the telescope. Because the field angle of the telescope is larger than the divergence angle of the laser, namely the field stop is larger than the size of the laser spot imaged on the focal plane, the field stop is generally equal to the field stop
In the process, scattered light can enter the field diaphragm completely without being shielded, namely the lowest complete overlapping distance d of the laser radarf201 f. Therefore, the reduction of the F number of the telescope not only can reduce the geometric length of the telescope, but also can greatly reduce the height of the lowest complete overlapping area of the laser radar because the focal length F of the telescope is reduced.
In one embodiment, a telescope with an F-number of 2.5 is used, the telescope focal length F is 500mm, and the primary and secondary mirror distances are 120mm (FIG. 2 c). From the formula dfIt is known that the lowest total overlap of the lidar is reduced to around 100m (400 m for telescopes with F number equal to 10 in fig. 2a, b). The detection blind area of the laser radar of this example is 33m, and the perfect coincidence distance is 100 m. These parameters are much better than the detectable regions of the same-caliber lidar on the market today.
Fig. 3 is an external view of the small radar according to an embodiment of the present invention. Wherein, in operation, the radar is positioned as shown. The top of the machine is provided with a transmission and reception window 41, which in this embodiment is circular. The size of the telescope is adapted to the caliber of the telescope. The window uses optical glass as a transparent seal and is provided with a wiper 42. The lower part of the laser radar shell is provided with 4 feet 43, wherein at least 3 heights can be independently adjusted for adjusting the level.
The utility model provides a micropulse polarization aerosol laser radar has carried out the detailed introduction above, and it is right to have used specific individual example in this paper the utility model discloses a principle and implementation mode have explained, and the description of above embodiment is only used for helping understanding the utility model discloses a method and core thought thereof, and the description content should not be understood as right the utility model discloses a restriction. For example, when the focal plane and the field stop are described as being disposed at the vertex of the primary mirror, they are also disposed near the vertex. Meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and applications, and the protection scope of the present invention should also be covered.
Claims (10)
1. A micropulse polarized aerosol laser radar comprises a telescope (13), wherein the telescope (13) adopts a Cassegrain telescope, and the telescope (13) comprises a primary mirror (18) and a secondary mirror (17), and is characterized in that a focal plane (19) and a field diaphragm of the telescope (13) are arranged on the vertex of the primary mirror (18) or between the secondary mirror (17) and the primary mirror (18).
2. Micropulsed polarized aerosol lidar according to claim 1, characterized in that the focal plane (19) and the field stop of the telescope (13) are arranged at the vertex of the primary mirror (18).
3. Micro-pulse polarized aerosol lidar according to claim 1 or 2, characterized by comprising a first light detector (15) and a second light detector (16) arranged downstream of the return optical path primary mirror (18) for receiving the first light signal and the second light signal, respectively, split by the polarization beam splitter (14).
4. Micropulsed polarized aerosol lidar according to claim 1, characterized in that the F-number of the telescope (13) is less than 3.
5. Micropulsed polarized aerosol lidar according to claim 4, characterized in that the aperture of the telescope (13) is 200mm and the primary mirror to secondary mirror distance is 120 mm.
6. A micropulsed polarized aerosol lidar as claimed in claim 1 wherein the lidar has a housing with a laser transmitting and receiving window at the top, the window being circular and provided with an optical glass seal.
7. The micropulsed polarized aerosol lidar of claim 6, further comprising a wiper for the transmission window disposed on the transmission window.
8. The micropulsed polarized aerosol lidar of claim 7, wherein 4 feet are provided at a lower portion of the lidar housing, at least 3 of which are independently adjustable in height for levelness adjustment.
9. The micropulsed polarized aerosol lidar of claim 1, wherein the laser wavelength is about 532nm, the pulse width is less than 20ns, the pulse energy is no greater than 300 μ J, and the repetition rate is 1-10 kHz.
10. The micropulsed polarized aerosol lidar of claim 3, wherein said photodetector comprises a photomultiplier tube (PMT) or an Avalanche Photodiode (APD).
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115079135A (en) * | 2022-06-18 | 2022-09-20 | 桂林理工大学 | Stray light suppression device of unmanned shipborne water depth detection laser radar |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115079135A (en) * | 2022-06-18 | 2022-09-20 | 桂林理工大学 | Stray light suppression device of unmanned shipborne water depth detection laser radar |
| CN115079135B (en) * | 2022-06-18 | 2023-11-07 | 桂林理工大学 | Stray light suppression device for unmanned ship-borne water depth detection laser radar |
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