• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:

    公开号:NL1013383A
    申请号:NL1013383
    申请日:1999-10-25
    公开日:2015-03-12
    发明作者:Thorsteinn Halldorsson；Kurt-Volker Hechtenberg；Dietmar Krieger
    申请人:Daimler Chrysler Ag；
    IPC主号:
    专利说明:

    Title: Device for recognizing and locating sources of laser radiation.
    The invention relates to a device for recognizing and locating sources of laser radiation with a radiation-sensitive detector arranged in the image field of an imaging optic and an electronic signal utilizing device connected to the detector, and to a method for recognizing and locating sources of laser radiation with the aid of such a device.
    Since laser devices are used for military purposes for the most diverse purposes, for protection and to initiate countermeasures against threats, sensors are required that can detect such laser sources. Such devices are known, for example, from DE 33 23 828 C2 or DE 35 25 518 C2. These devices serve for detection and location of pulse laser sources, such as, for example, in use for target illuminators or distance meters. The laser radiation used for this is usually in the near infrared and therefore cannot be observed by the human eye. The known so-called laser warners assume that the extremely short laser pulses fall directly on the detector, so that their sensitivity with a recording aperture of only a few millimeters is sufficient.
    In a series of other applications, weapons, such as grenades and flying bodies, are steered by means of a laser beam, which is initially directed not directly at the target, but first at the grenade or flying body in which a laser sensor is located. With the aid of this sensor, the flight is then steered along the axis of the jet, whereby the shooter directs the grenade or flying body along a flight path desired by him by purposefully controlling the jet. This nature of control is referred to as beam rider control (beam rider). Since in this manner of application the laser beam is first directed directly at the target in the final phase, the laser radiation from the target viewed during the approach phase of the projectile can only be detected indirectly as scattered radiation or as reflected radiation. These indirect radiation parts, however, are considerably weaker than the direct incident radiation. Furthermore, since usually continuous lasers with a weak power or pulsed lasers with a large pulse repetition frequency and a low pulse stop power are used, the sensitivity of the previously known laser beam warning sensors is often not sufficient to recognize this threat. An additional disadvantage is that the weak laser radiation in the free space must be detected against the strong background radiation of the daylight or against the exposure by bright artificial light sources.
    The object of the invention is therefore to provide an apparatus and method for recognizing and locating sources of laser radiation, wherein not only the direct incident light from a pulsed laser or from a continuous laser, but also the indirect, diffracted, reflected or scattered light from the exit aperture of the laser or from objects that are exposed by the laser, is detected with certainty, as laser light is distinguished from daylight or from other radiation sources and possibly the direction of the laser source is indicated with great accuracy. This object is achieved with a device according to claim 1 or by a method according to claim 10 or 12, respectively.
    The invention is based on the use of a cross lattice, with which coherent and incoherent radiation is imaged in different ways on a radiation-sensitive detector. With this measure, spectrally broadband, that is, temporarily incoherent point light sources, such as for example lamps or spotlights, are no longer displayed as points in the focal plane of the detector, for example a CCD camera, but as stripe images of their spectrum. Lasers, on the other hand, are depicted as point samples through the cross lattice as spectral narrowband, i.e., coherent sources, and can therefore be distinguished from the incoherent radiation sources.
    The location of the zero order of the diffraction image on the detector can serve to gauge a light source recognized as a laser. This can be done in various ways depending on the nature of the cross grating used. In the simplest case, the point-shaped light spot with the greatest intensity is the zero order of the diffraction image and therefore identical to the location of the laser light source on the image field. If the instantaneous direction of the optical axis and the focal length of the optic are known, then also the direction of the radiation source in the observed space is known.
    Greater accuracy in the location of a laser source is achieved in that the center of symmetry of the light spot in question is determined. This can again be done in a simple manner in that the individual light spots are successively shielded by means of an adjustable threshold value, for example by a gray-gray wedge or by lowering the detector sensitivity. Since in a cross-grating the pixels of the same order also have the same intensity and are arranged symmetrically around the zero order, the pixels of the same order disappear with increasing threshold value at the same time, so that the symmetry center disappears from the locations of the pixels disappeared at a given moment and therefore the place of the zero order can be determined unambiguously.
    Another possibility for determining the location of the zero order consists in that the cross-grating is rotated about the optical axis. In that case, all higher-order pixels rotate around the zero-order pixel, which remains quietly in the image in the relevant location and therefore can be easily recognized.
    Furthermore, the wavelength of the laser can easily be determined from the distance of the individual light spots of a symmetrical sample, which makes an additional characterization of the relevant threat possible.
    The invention is elucidated on the basis of an exemplary embodiment schematically shown in the figures.
    In the drawing, Fig. 1 shows the basic structure of a laser-warning receiving device with pre-connected cross-screen grille, Fig. 2 shows the basic structure of a laser-warning device with integrated residual light amplifier, Fig. 3 shows the basic structure of a receiving device for laser warning laser warning with pre-connected reversing optics for all-round observation, and Figures 4a and 4b show the diffraction images of an a) incoherent and b) coherent point-shaped radiation source generated with a cross-grating.
    The exemplary embodiment of a laser warning receiving device for the near and middle infrared region shown in Fig. 1 is provided with a camera with a so-called "focal plan array (FPA)", i.e. a planar matrix detector 1 arranged in the focal plane of an imaging optic 2. Such a detector system consists of, for example, 256 x 256 individual detectors and is provided with an integrated readout electronics 5. The individual detectors of the FPA integrate the incident radiation over a fixed or variable integration time of, for example, 16 ms in parallel. This distinguishes these detectors from the individual detectors of the conventional laser warning sensors, which with a short time constant in the nanosecond range are only adapted for detection of pulsed radiation sources with the same pulse duration. Two different types of matrix detectors with different readout and transfer modes for further signal processing are known as charge coupled devices (CCD) and as complementary metal oxide semiconductor (CMS) and both can be used here.
    In the near infrared range of 0.75 - 1.1 µm, commercially available cameras with silicon detectors can be used, such as those used for recording images in the visible area (optionally with pre-connected residual light amplifier). Infrared cameras with platinum silicide (Pt: Si) or indium antimonide (In: Sb) detectors and in the wavelength range between 9 and 12μπ-mercury-cadmium telluride detectors are available for the wavelength range between 1 and 5μτη. Some of these detectors require additional cooling.
    For such a camera, according to the invention, a cross grating 3 and possibly a spectral filter 4 are connected. The latter limits the optical bandwidth of the system to the spectral region in which laser sources are suspected. This again reduces the influence of background radiation. Depending on the manner in which the signals are used, the cross grating 3 can be rotated about the optical axis of the camera by means of a drive 6.
    The meaning of the cross lattice is explained below with reference to Figures 4a and 4b.
    If two superimposed regular line gratings are superimposed, a two-dimensional cross grid is obtained. When a light point is projected through such a grid onto a screen or the focal plane of a camera, the diffraction image shown in Fig. 4a is produced in broadband light, wherein a large number of colored diffraction spectra are grouped in a regular arrangement around a circular spot such that their longitudinal direction points to the central spot, with the short-wave part of the spectrum on the inside and the long-wave part on the outside. With mono-chromatic light, the image merges with the image shown in Fig. 4b, and spot-shaped spots of light arise, which lie at the intersections of an almost linear quadratic net. The location of the pixels and their intensity distribution in a cross-lattice are obtained with the help of Fraunhofer roster calculations. The intersections of two hyperbola bundles represent the location of the interference maxima when bent on a flat point grid. If the grid constant is denoted by d, the angle of incidence in the plane parallel to the one grid with a0 and the angle of incidence in the plane parallel to the other grid with β0, then the angles α resp. β of the diffraction images in these two planes perpendicular to each other, the following relation:
    ........) ........)
    For the use according to the invention of a cross grating in a laser warning sensor, the following properties are of importance: distinguish. • Flat-shaped broadband light sources create a mottled mosaic over the entire image surface; the background radiation is thereby homogenized over the entire image surface, which facilitates the recognition of point-shaped images of laser sources • The zero order of the diffraction sample lies on the main beam and therefore passes through the grid without bending. This direction is also the direction of symmetry of higher order diffraction samples. The direction to the radiation source can therefore be unambiguously determined from the diffraction sample. • The diffraction angle shifts with the wavelength Δλ according to the formula Δα = .n / d. Δλ (the corresponding applies to the angle β), which means that the wavelength of the light source can be determined from the angular position of the diffraction maximum. • When the cross grille rotates, the light spot sample also rotates around the axis of symmetry. The direction of the light source with respect to the optical axis of the camera can therefore be determined unambiguously.
    To clarify the conditions for recognizing two laser sources with different wavelengths, a numerical example is given.
    At assumed wavelengths of λχ = 1.064 μιτι (for example Nd: YAG laser) and λ2 = 0.904 μτη (for example GaAs laser diode), a lattice constant d = 10 μιτι and incidence angles α0 = β0 = 0, the diffraction angles are α = β = 6, 1 ° for the longer wavelength and 5.4 ° for the shorter wavelength. At higher orders, the bending angle is a multiple. With shorter lattice distances, the wavelength solution and at the same time the diffraction angle is greater. With approximately 600 lines and lines of a detector system and a camera angle of 90 °, the corner solution of a pixel is 0.15 °. With a lattice constant of 2 μιτι, the spectral solution of a pixel in the first diffraction order is approximately 5 nm. For comparison, the spectral bandwidth of a laser diode for a jet rider weapon is approximately 3 nm.
    If several isolated light spots are now registered by a detector system, it can be determined from the position distribution thereof in the image whether it concerns the higher orders of a coherent laser source.
    This can be determined from the symmetry of the light spot sample and the identical brightness of all light spots associated with a certain order. This can be solved electronically, for example, by comparing the signals of each individual pixel in the focal plane in terms of intensity with the signals of each neighboring pixel. If it appears that the intensity of a pixel is clearly greater than that of the neighbors, then the coordinates and the signal value are noted. The entire image can be reduced in this way to a point sample of individual pixels with greater intensity. Signal disturbances can then be eliminated by considering only those pixels that form concentric squares. If a regular point sample then remains, the presence of a laser source is very likely.
    From the diameter of the squares, the wavelength of the laser source can now also be calculated and, for example, compared with the values of a threat catalog, in order to find further confirmation of the threat. Now, when the thus obtained point samples of an image series of a camera are compared with each other, movements of the laser source relative to the target can be calculated and monitored. Multiple laser sources can also be quickly distinguished from each other according to this simple instruction, classified and observed separately. For a person skilled in the art with electronic signal processing, this problem can be solved with a simple microprocessor without the need for special image processing in a computer.
    Cross grids can be made either as transmission grids or as a reflection grille. They can be formed as an amplitude as well as a phase grid. The advantage of a phase grid is the substantially larger transmission, since in the case of an amplitude grid radiation is lost to the relevant shadow-forming part of the grid.
    A special case of lattice is the so-called sine lattice with a local cos2 variation of the amplitude transmission when using an amplitude lattice or of the refractive indices at a phase lattice. With this lattice type, only the zero and the +/- 1st order occur in the diffraction spectrum. In addition, these gratings are particularly suitable for detecting weak laser sources because of their high efficiency in light transfer in the first order.
    With the production of grating, the holographic production of grating is becoming increasingly popular. Two waves with small directional differences resulting from laser beam fall onto a photoresist layer and there produce an interference line sample which can be converted into lattice structures. Thus, cross grids can be produced by double exposure of such perpendicular line samples. With this technique, both amplitude and phase grids can be produced for transmission operation, the latter being caused by the known bleaching of the amplitude structure. The different exposure of the layer in the clear and in the dark lines can also be converted into a change in layer thickness. (groove profile) and are used as a phase grid in transmission. Analogous to that, vapor deposition of aluminum provides a reflection grid.
    The transmission sine wave grids are particularly suitable for use in a laser warning device for the visible and near infrared range of 0.3 to 2.5 μιτι. Such gratings can, for example, be applied to quartz glass and used as a transmission cover for a camera. In the infrared region above 2 μπι either amplitude transmission holograms for transmission operation or reflection grids for reflection operation can be provided for a camera.
    In the infrared region at 10 μιτι (CO 2 laser), mainly reflection gratings are used. Particularly advantageous for a laser warning device are the so-called Echelette gratings, which have a saw-tooth-shaped groove profile. The groove slope is chosen such that for a desired "Blaze" wavelength (Blaze = maximum intensity) the reflection and diffraction direction correspond. Then the corresponding order n is also favored.
    A further possibility for optimizing cross grids consists in correctly selecting the modulation depth and the grid constants, or the location frequency of the grid. Grids with a low location frequency have, as is known, many bending orders, the intensities of which relate to the squares of the Besselfunctions. Due to strong modulation, the intensity in the higher orders increases as a result. If the modulation is reduced, the intensity in the higher orders decreases in favor of the lower orders. The optimization for warning devices for lasers now takes place by maximizing the intensity in the first orders. The maximum is theoretically 33% for a linear grid. For a cross roster it follows that 10% remains for the interesting four orders. The remaining 60% of the incident light is distributed over the other orders.
    The bending efficiency can be considerably increased in cross grids by increasing the location frequency. For site frequencies of about 400-500 line pairs / mm in holographic transmission phase grids, one is in the transition region between thin and thick holograms. Significantly fewer higher orders already occur here. In case even larger location frequencies are used, for example 700 line pairs / mm, the higher orders can be suppressed almost completely. The light contribution of the zero order can be kept below 20%, so that each of the four diffraction images of the first order receives about 20% of the light.
    The lasers used for military and security applications are limited to a few relatively narrow wavelength ranges between 800 - 850 nm, 1050 - 1070 nm, 1450 - 1650 nm and 9.5 - 11.5 μιη. In order to damp the disturbing background radiation accordingly, it is advantageous to connect a spectral filter to the imaging lens of the camera in addition to the cross-grating used. With a filter width of, for example, 10-20 nm in the near infrared region, the background can be reduced by a factor of 10 to 20.
    The edge sensitivity of commercially available CCD cameras for detecting a continuous line laser source at an integration time of 20 ms through the cross grating is about 6 pW. The scattered radiation signals from a beam rider at a distance of 10 - 1 Km are comparatively in the range of lpW - InW, that is to say, in the operating range of a laser warning device according to the invention. A further increase in the sensitivity of CCD cameras is possible by extending the integration time, cooling the detector and by switching an electron-amplification stage (for example, a micro-channel plate with 10,000-fold amplification) for the detector system. This last possibility is shown in the exemplary embodiment according to Fig. 2. Herein for a first lens 22.1, in the focal plane of which lies a detector system 21 connected to a microprocessor 25, a light screen 26, an electron multiplier 27, a photocathode 28, a further lens 22.2, a cross lattice 23 and a spectral filter 24. The elements 26, 27 and 28 form a so-called residual light amplifier, the image of which is then extracted on the detector system 21.
    The required angle range of a warning device for lasers will be different depending on the application. For many applications, normal lenses with a field angle of 40 ° - 55 ° will suffice. For an all-round observation, for example for a helicopter, four such warning devices for lasers will, as usual, be mounted on the outside in different places, each warning device for lasers covering an angle of 90 °.
    Another possibility for detecting laser threats all around is shown in FIG. Here, for a laser warning device according to Figs. 1 or 2, with a detector system 31, an imaging optic 32 and a cross grating 33, a convex mirror 34 is arranged which receives the light from a horizontally oriented plane I at a horizontal angle of view of 90 ° (e.g. 60 ° captures above the plane I and 30 ° below the plane I) and displays the region thus contained in a ring plane II on the detector 31.
    Each direction from the area thus covered corresponds to a pixel on the ring surface II.
    The method described above for detecting laser sources can be effected or combined with a wide variety of image-recording devices. In particular, instead of detector systems, it is also possible to use specifically formed single detectors with pre-positioned optical scanning devices (scanners).
    权利要求:
    Claims (11)
    [1]
    Page number 13 Conclusions
    What is claimed is: 1. An apparatus for recognizing and locating sources of laser radiation with a radiation-sensitive detector arranged in the image field of an imaging optic and an apparatus for utilizing electronic signals connected to the detector, characterized in that between the source of laser radiation and the imaging optics (2; 22.1), a cross grating (3; 23) and a residual light amplifier (26,27,28) are arranged in such a way that the diffraction orders of the cross grating (3) are imaged on the detector (1).
    [2]
    Device according to claim 1, characterized in that the cross grating (3) is designed as a transmission grating or as a reflection grating.
    [3]
    Device as claimed in claims 1-2, characterized in that the cross grating (3) is designed as an amplitude or phase grating.
    [4]
    Device according to claims 1-3, characterized in that the cross grating (3) is rotatable about the optical axis of the imaging optic.
    [5]
    Device according to claim 4, characterized in that the rotation of the cross grille (3) takes place continuously at predetermined speed.
    [6]
    Device as claimed in claims 1-5, characterized in that a cross lattice is used that only generates the zero and the first order, for example a sine lattice.
    [7]
    Device according to claims 1-6, characterized in that a spectral filter (4.24) is arranged in front of the cross lattice (3.23).
    [8]
    Device according to claims 1-7, characterized in that a reversing optic (34), in particular a convex mirror, is arranged in front of the cross grille (33).
    [9]
    A method for recognizing and locating sources of laser radiation with an apparatus according to claim 1, characterized in that the image generated on the detector is examined by signal processing for point light spots, that its position is recorded within the image field and that the location of the pixel representing the zero order of the displayed light spot sample is determined by successively extinguishing, by means of a variable threshold value, the images of the light spots with the lowest intensity each time, and from the location of the extinguished light spots the symmetry center of the light spot sample is determined.
    [10]
    A method for recognizing and locating sources of laser radiation with a device according to claim 4, characterized in that the image formed on the detector is examined by signal processing for at least one point-shaped light spot that determines the zero order of a displayed light spot sample or at the center of symmetry of the light spot sample relative to the image center and that its position within the image field is recorded to determine the angular position of the source of laser radiation with respect to the optical axis of the imaging optic.
    [11]
    A method according to claim 9 or 10, characterized in that when the cross lattice is resting, the image on the detector is examined for quadraticly arranged point-shaped light spots, the mutual distance of which is always adjacent to the nearest neighbor, and is compared with a predetermined certain area value.
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    同族专利:
    公开号 | 公开日
    DE19851010A1|2007-06-14|
    ITRM990683A1|2001-05-04|
    SE9903966L|2006-05-09|
    FR2888333A1|2007-01-12|
    DE19851010B4|2010-10-07|
    TR199902712A1|2007-10-22|
    NL1013383C2|2015-03-18|
    FR2888333B1|2008-06-27|
    SE529775C2|2007-11-20|
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    AU2012373183A1|2012-03-16|2014-10-16|Her Majesty The Queen In Right Of Canada As Represented By The Minister Of National Defence|Portable device for analysing a plurality of widely spaced laser beams|
    DE102012022258B4|2012-11-14|2017-03-16|Airbus Ds Electronics And Border Security Gmbh|Sensor for detection and localization of laser radiation sources|
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    法律状态:
    2018-06-06| MM| Lapsed because of non-payment of the annual fee|Effective date: 20171101 |
    优先权:
    申请号 | 申请日 | 专利标题
    DE19851010A|DE19851010B4|1998-11-05|1998-11-05|Device for the detection and localization of laser radiation sources|
    DE19851010|1998-11-05|
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