CA2288305A1 - Device for recognizing and locating laser radiation sources - Google Patents
Device for recognizing and locating laser radiation sources Download PDFInfo
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- CA2288305A1 CA2288305A1 CA 2288305 CA2288305A CA2288305A1 CA 2288305 A1 CA2288305 A1 CA 2288305A1 CA 2288305 CA2288305 CA 2288305 CA 2288305 A CA2288305 A CA 2288305A CA 2288305 A1 CA2288305 A1 CA 2288305A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/095—Monitoring or automatic control of welding parameters
- B23K9/0953—Monitoring or automatic control of welding parameters using computing means
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Abstract
The present invention leverages a co-located communication component to provide remote management of a portable construction device. This provides a means to monitor and/or control the portable construction device from a central management site.
The communication component allows the central site, or another communication component, to interact with the portable construction device to retrieve information such as, for example, usage information and/or status information. The communication component also allows remote control of the devices such as, for example, remote power control and/or control of auxiliary devices that facilitate the functionality of the portable construction devices. The present invention can also incorporate global positioning systems and/or location indicating systems to facilitate in determining where the portable construction devices are located and/or when the devices are properly positioned. The systems themselves can be distributed to form a communication network with bi-directional communication capabilities.
The communication component allows the central site, or another communication component, to interact with the portable construction device to retrieve information such as, for example, usage information and/or status information. The communication component also allows remote control of the devices such as, for example, remote power control and/or control of auxiliary devices that facilitate the functionality of the portable construction devices. The present invention can also incorporate global positioning systems and/or location indicating systems to facilitate in determining where the portable construction devices are located and/or when the devices are properly positioned. The systems themselves can be distributed to form a communication network with bi-directional communication capabilities.
Description
Docket # P607939CA
DEVICE FOR RECOGNIZING AND LOCATING LASER
RADLA.TION SOURCES
FIELD OF THE INVENTION
The present invention pertains to a device for recognizing and locating laser radiation sources with a radiation-sensitive detector arranged in the image field of an imaging optical system and with an electronic signal evaluation unit connected to the S detector as well as to a process for recognizing and locating laser radiation sources with such a device. .
BACKGROUND OF THE INVENTION
Since laser devices are used for a great variety of purposes in military applications, sensors that can detect such laser sources are necessary for protection and to initiate countermeasures against threats. Such devices have been known from, e.g., DE-33 23 828 C2 or DE 35 25 518 C2. These devices are used to deteat aad-locate pulsed laser sources as they are used, e.g., for target illuminators or range finders. The laser radiation used for this purpose is usually in the near infrared range and thus it is invisible to the human eye. The prior-art, so-called laser warners require that the extremely short laser pulses fall on the detector, so that its sensitivity is sufficient at an aperture of only a few mm.
Weapons, such as grenades and missiles, are guided in a number of other applications by means of a laser beam that is initially directed first to the grenades or the missile, in which a laser sensor is located, rather than directly to the target. The flight along the axis of the beam is then guided by means of this sensor, and the human operator guides the grenades or the missile toward the target on a flight path desired by him by specifically guiding the beam. This type of guidance is called beam rider.
Since the laser beam is directed directly toward the target only during the final phase in this type of application, the laser radiation can be detected, when viewed from the target, only indirectly as scattered radiation or as reflected radiation during the phase of approach of the particular projectile. However, these indirect radiation components are considerably weaker than the radiation falling in directly. Since, furthermore, low-power continuous-wave laser and pulsed laser with high pulse repetition frequency and low pulse peak power are used, the sensitivity of the prior-art laser warner sensors is usually insufficient to recognize this threat. The situation is further aggravated by the fact that the weak laser radiation must be detected in the atmosphere against the strong radiation background of daylight and against the lighting caused by-bright, artificial light sources.
SUMMARY AND OBJECTS OF THE INVENTION
The priunary object of the present invention is therefore to provide a device and a process for recognizing and locating laser radiation sources that reliably detects not only the light falling in directly from a pulsed laser or a continuous-wave laser, but also the indirect, diffracted, reflected or scattered light from the exit aperture of the laser or from objects that are illuminated by the laser, distinguishes it as laser light from daylight or other radiation sources and possibly indicates the direction of the laser source at a high accuracy.
According to the invention, a device is provided for recognizing and locating laser radiation sources with a radiation-sensitive detector arranged in the image field of an imaging optical system and with an electronic signal evaluation unit connected to the detector. A cross grating is arranged between the laser radiation source and the said optical system such that the diffraction orders of the cross grating are imaged on the detector.
According to another aspect of the invention, a process is provided for recognizing and locating laser radiation sources with a device as discussed above. The image generated on the detector is searched by the signal evaluation unit for punctiform light spots, their position within the- image field is registered, and that the location of an image spot representing the 0th order of the imaged light spot.pattern is determined. As an alternative, the image generated on the detector is searched by the signal evaluation unit for at least one punctiform light spot that determines the 0th order of an imaged light spot pattem and its position within the image field is registered.
The present invention is based on the use of a cross grating, with which coherent and incoherent radiation are imaged differently on a radiation-sensitive detector. Point light sources with a broad spectral band, i.e., point light sources that are incoherent in time, e.g., lamps or reflectors, are no longer imaged by this measure as points in the focal plane of the detector, e.g., a CCD camera, but as line images of their spectrum. Lasers as sources with a narrow spectral band, i.e., coherent sources, are, in contrast, imaged by the cross grating as point patterns and they can thus be distinguished from the incoherent radiation sources.
To locate a light source recognized as a laser, the location of the 0th order of the diffraction pattern is to be determined on the detector. Depending on the cross grating used, this may be done in various ways. In the simplest case, the punctiform light spot with the highest intensity is the 0th order of the diffraction pattern and thus it is identical to the position of the laser light source in the image field.
In the knowledge of the instantaneous alignment of the optical axis and of the focal distance of the optical system, the direction of the radiation source in the space being observed is thus known as wll.
Higher reliability is achieved in the determination of the position :af a laser source by determining the center of symmetry of the particular light spot pattern. This can in turn be done in a simple manner by consecutively blanking out the individual light spots by means of an adjustable threshold value, e.g., by a gray scale arranged in front or by reducing the sensitivity of the detector. Since the image spots of equal order also have equal intensity in a cross grating and they are arranged symmetrically around the 0th order, the image spots of equal order disappear simultaneously with increasing threshold value, so that the center of symmetry and consequently the position of the 0th order can be unambiguously determined from the locations of the particular image spots that have disappeared.
Another possibility of determining the position of the 0th order is to rotate the cross grating around the optical axis. All image spots of higher order rotate in this case around the image spot of 0th order, which remains steady in the image in the given position and thus it can be easily recognized.
Furthermore, the wavelength of the laser can be easily determined from the distance of the individual light spots of a symmetrical pattern, which makes possible an additional characterization of the particular type of threat.
The present invention will be described in greater detail below on the basis of the exemplary embodiment schematically shown in the figures.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For lp, objects a belter understanding of the invention, its operating advantages and specif attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodimentsof the invention arelustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figure 1 is a schematic diagram showing the general design of a laser warner receiver with a cross grating arranged in front of it;
Figure 2 is a schematic diagram showing the general design of a laser warner receiver with integrated low-light amplifier;
Figure 3 is a schematic diagram showing the general design- of a laser warner receiver with a deflecting optical system arranged in front of it for panoramic detection; and Figure 4a is a view showing the diffraction patterns of an incoherent radiation source, which pattern was generated with a cross grating; and Figure 4b is a view showing the diffraction pattern of a coherent punctiform radiation source, which pattern was generated with a cross grating.
DEVICE FOR RECOGNIZING AND LOCATING LASER
RADLA.TION SOURCES
FIELD OF THE INVENTION
The present invention pertains to a device for recognizing and locating laser radiation sources with a radiation-sensitive detector arranged in the image field of an imaging optical system and with an electronic signal evaluation unit connected to the S detector as well as to a process for recognizing and locating laser radiation sources with such a device. .
BACKGROUND OF THE INVENTION
Since laser devices are used for a great variety of purposes in military applications, sensors that can detect such laser sources are necessary for protection and to initiate countermeasures against threats. Such devices have been known from, e.g., DE-33 23 828 C2 or DE 35 25 518 C2. These devices are used to deteat aad-locate pulsed laser sources as they are used, e.g., for target illuminators or range finders. The laser radiation used for this purpose is usually in the near infrared range and thus it is invisible to the human eye. The prior-art, so-called laser warners require that the extremely short laser pulses fall on the detector, so that its sensitivity is sufficient at an aperture of only a few mm.
Weapons, such as grenades and missiles, are guided in a number of other applications by means of a laser beam that is initially directed first to the grenades or the missile, in which a laser sensor is located, rather than directly to the target. The flight along the axis of the beam is then guided by means of this sensor, and the human operator guides the grenades or the missile toward the target on a flight path desired by him by specifically guiding the beam. This type of guidance is called beam rider.
Since the laser beam is directed directly toward the target only during the final phase in this type of application, the laser radiation can be detected, when viewed from the target, only indirectly as scattered radiation or as reflected radiation during the phase of approach of the particular projectile. However, these indirect radiation components are considerably weaker than the radiation falling in directly. Since, furthermore, low-power continuous-wave laser and pulsed laser with high pulse repetition frequency and low pulse peak power are used, the sensitivity of the prior-art laser warner sensors is usually insufficient to recognize this threat. The situation is further aggravated by the fact that the weak laser radiation must be detected in the atmosphere against the strong radiation background of daylight and against the lighting caused by-bright, artificial light sources.
SUMMARY AND OBJECTS OF THE INVENTION
The priunary object of the present invention is therefore to provide a device and a process for recognizing and locating laser radiation sources that reliably detects not only the light falling in directly from a pulsed laser or a continuous-wave laser, but also the indirect, diffracted, reflected or scattered light from the exit aperture of the laser or from objects that are illuminated by the laser, distinguishes it as laser light from daylight or other radiation sources and possibly indicates the direction of the laser source at a high accuracy.
According to the invention, a device is provided for recognizing and locating laser radiation sources with a radiation-sensitive detector arranged in the image field of an imaging optical system and with an electronic signal evaluation unit connected to the detector. A cross grating is arranged between the laser radiation source and the said optical system such that the diffraction orders of the cross grating are imaged on the detector.
According to another aspect of the invention, a process is provided for recognizing and locating laser radiation sources with a device as discussed above. The image generated on the detector is searched by the signal evaluation unit for punctiform light spots, their position within the- image field is registered, and that the location of an image spot representing the 0th order of the imaged light spot.pattern is determined. As an alternative, the image generated on the detector is searched by the signal evaluation unit for at least one punctiform light spot that determines the 0th order of an imaged light spot pattem and its position within the image field is registered.
The present invention is based on the use of a cross grating, with which coherent and incoherent radiation are imaged differently on a radiation-sensitive detector. Point light sources with a broad spectral band, i.e., point light sources that are incoherent in time, e.g., lamps or reflectors, are no longer imaged by this measure as points in the focal plane of the detector, e.g., a CCD camera, but as line images of their spectrum. Lasers as sources with a narrow spectral band, i.e., coherent sources, are, in contrast, imaged by the cross grating as point patterns and they can thus be distinguished from the incoherent radiation sources.
To locate a light source recognized as a laser, the location of the 0th order of the diffraction pattern is to be determined on the detector. Depending on the cross grating used, this may be done in various ways. In the simplest case, the punctiform light spot with the highest intensity is the 0th order of the diffraction pattern and thus it is identical to the position of the laser light source in the image field.
In the knowledge of the instantaneous alignment of the optical axis and of the focal distance of the optical system, the direction of the radiation source in the space being observed is thus known as wll.
Higher reliability is achieved in the determination of the position :af a laser source by determining the center of symmetry of the particular light spot pattern. This can in turn be done in a simple manner by consecutively blanking out the individual light spots by means of an adjustable threshold value, e.g., by a gray scale arranged in front or by reducing the sensitivity of the detector. Since the image spots of equal order also have equal intensity in a cross grating and they are arranged symmetrically around the 0th order, the image spots of equal order disappear simultaneously with increasing threshold value, so that the center of symmetry and consequently the position of the 0th order can be unambiguously determined from the locations of the particular image spots that have disappeared.
Another possibility of determining the position of the 0th order is to rotate the cross grating around the optical axis. All image spots of higher order rotate in this case around the image spot of 0th order, which remains steady in the image in the given position and thus it can be easily recognized.
Furthermore, the wavelength of the laser can be easily determined from the distance of the individual light spots of a symmetrical pattern, which makes possible an additional characterization of the particular type of threat.
The present invention will be described in greater detail below on the basis of the exemplary embodiment schematically shown in the figures.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For lp, objects a belter understanding of the invention, its operating advantages and specif attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodimentsof the invention arelustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figure 1 is a schematic diagram showing the general design of a laser warner receiver with a cross grating arranged in front of it;
Figure 2 is a schematic diagram showing the general design of a laser warner receiver with integrated low-light amplifier;
Figure 3 is a schematic diagram showing the general design- of a laser warner receiver with a deflecting optical system arranged in front of it for panoramic detection; and Figure 4a is a view showing the diffraction patterns of an incoherent radiation source, which pattern was generated with a cross grating; and Figure 4b is a view showing the diffraction pattern of a coherent punctiform radiation source, which pattern was generated with a cross grating.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings in particular, the exemplary embodiment of a laser warner receiver for the near and middle infrared range, which is shown in Figure 1, provides a camera with a so-called "focal plan array (FPA)," i.e., a two 'dimensional matrix detector 1, which is arranged in the focal plane of an imaging optical system 2.
Such a detector array typically comprises 256 x 256 individual detectors and is provided with an integrated electronic evaluation unit 5. The individual detectors of the FPA
integrate the incident radiation over a fixed or variable integration time of, e.g., 16 msec in parallel. As a result, these detectors differ from the individual detectors of the usual laser warner sensors, which, having a short time constant in the nanosec range, are adapted exclusively for the detection of pulsed radiation sources of the same pulse time. Two different types of matrix detectors with different selection and transmission methods for the further signal processing are known as "Charge-Coupled Devices (CCD)" and as "Complementary Metal Oxide Semiconductor (CMS)," both of which may be used here.
Commercially available cameras with silicon detectors, which are used to record images in the visible range (optionally with a low-light amplifier arranged in front), may be used in the near infrared range of 0.75-1.1 m. Infrared cameras with platinum silicide (Pt:Si) or indium antimonide (In:Sb) detectors are available for the wavelength range between 1 and 5 m, and mercury-cadmium telluride detectors are available in the wavelength range between 9 and 12 m. Some of these detectors require additional cooling.
A cross grating 3 and optionally a spectral filter 4 are arranged according to the present invention in front of such a camera. The optical bandwidth of the system is narrowed with the spectral filter to the spectral range in which laser--soarces are assumed to occur. This in turn reduces the effect of the background radiation.
Depending on the type of the signal evaluation, the cross grating 3 may be rotated by means of a drive 6 around the optical axis of the camera.
Tfie significance of the cross grating will be explained in greater detail below on the basis of Figures 4a and b:
If two identical, usual ruled gratings are placed one on top of another, a two-dimensional cross grating is obtained. If a light point is projected through such a grating onto a screen or onto the focal plane of a camera, the diffraction pattern shown in Figure 4a is formed in the case of a broad-band light; a large number of colored diffraction spectra are grouped in a regular arrangement around a round spot in this diffraction pattern such that their longitudinal direction points toward the central spot, and the shorter-wave component of the spectrum is located inside and the longer-wave component outside. In the case of monochromatic light, the phenomenon passes over into Figure 4b. in which punctiform light spots are formed, which are located in the intersections of a nearly straight quadratic network. The position of the image spots and their intensity distribution in a cross grating is obtained by means of the Fraunhofer grating calculation. The intersections of two sets of hyperbolas form the locations of the interference maximum during diffraction on a flat point grating. If the grating constant is designated by d and the incidence angle in the plane parallel to one of the gratings by ao and the incidence angle in the plane parallel to the other grating by fi~, the following equation is obtained for the angles a and ig of tha diffraction patterns in these two mutually parallel planes:
sin a - sin ao = n - X/d (n = 0, +/-1, +/-2, .....) sin /3 - sin /30 = m .X/d (m = 0, +/-1, +/-2, ....) The following properties are of significance for the use of a cross grating according to the present invention in a laser warner sensor:
= Monochromatic point sources are imaged as point gratings with sharp intensity ma3rima in the image plane of the camera and broad-band point sources are imaged as extended lines and thus they can be distinguished from one another.
= Two-dimensional broad-band light sources generate a blurred mosaic over the entire image surface; the background radiation is homogenized as a result over the entire image surface, which facilitates the recognition of punctiform images of laser sources.
Referring to the drawings in particular, the exemplary embodiment of a laser warner receiver for the near and middle infrared range, which is shown in Figure 1, provides a camera with a so-called "focal plan array (FPA)," i.e., a two 'dimensional matrix detector 1, which is arranged in the focal plane of an imaging optical system 2.
Such a detector array typically comprises 256 x 256 individual detectors and is provided with an integrated electronic evaluation unit 5. The individual detectors of the FPA
integrate the incident radiation over a fixed or variable integration time of, e.g., 16 msec in parallel. As a result, these detectors differ from the individual detectors of the usual laser warner sensors, which, having a short time constant in the nanosec range, are adapted exclusively for the detection of pulsed radiation sources of the same pulse time. Two different types of matrix detectors with different selection and transmission methods for the further signal processing are known as "Charge-Coupled Devices (CCD)" and as "Complementary Metal Oxide Semiconductor (CMS)," both of which may be used here.
Commercially available cameras with silicon detectors, which are used to record images in the visible range (optionally with a low-light amplifier arranged in front), may be used in the near infrared range of 0.75-1.1 m. Infrared cameras with platinum silicide (Pt:Si) or indium antimonide (In:Sb) detectors are available for the wavelength range between 1 and 5 m, and mercury-cadmium telluride detectors are available in the wavelength range between 9 and 12 m. Some of these detectors require additional cooling.
A cross grating 3 and optionally a spectral filter 4 are arranged according to the present invention in front of such a camera. The optical bandwidth of the system is narrowed with the spectral filter to the spectral range in which laser--soarces are assumed to occur. This in turn reduces the effect of the background radiation.
Depending on the type of the signal evaluation, the cross grating 3 may be rotated by means of a drive 6 around the optical axis of the camera.
Tfie significance of the cross grating will be explained in greater detail below on the basis of Figures 4a and b:
If two identical, usual ruled gratings are placed one on top of another, a two-dimensional cross grating is obtained. If a light point is projected through such a grating onto a screen or onto the focal plane of a camera, the diffraction pattern shown in Figure 4a is formed in the case of a broad-band light; a large number of colored diffraction spectra are grouped in a regular arrangement around a round spot in this diffraction pattern such that their longitudinal direction points toward the central spot, and the shorter-wave component of the spectrum is located inside and the longer-wave component outside. In the case of monochromatic light, the phenomenon passes over into Figure 4b. in which punctiform light spots are formed, which are located in the intersections of a nearly straight quadratic network. The position of the image spots and their intensity distribution in a cross grating is obtained by means of the Fraunhofer grating calculation. The intersections of two sets of hyperbolas form the locations of the interference maximum during diffraction on a flat point grating. If the grating constant is designated by d and the incidence angle in the plane parallel to one of the gratings by ao and the incidence angle in the plane parallel to the other grating by fi~, the following equation is obtained for the angles a and ig of tha diffraction patterns in these two mutually parallel planes:
sin a - sin ao = n - X/d (n = 0, +/-1, +/-2, .....) sin /3 - sin /30 = m .X/d (m = 0, +/-1, +/-2, ....) The following properties are of significance for the use of a cross grating according to the present invention in a laser warner sensor:
= Monochromatic point sources are imaged as point gratings with sharp intensity ma3rima in the image plane of the camera and broad-band point sources are imaged as extended lines and thus they can be distinguished from one another.
= Two-dimensional broad-band light sources generate a blurred mosaic over the entire image surface; the background radiation is homogenized as a result over the entire image surface, which facilitates the recognition of punctiform images of laser sources.
= The 0th order of the diffraction pattern is located on the main beam, i.e., it passes through the grating without diffraction. This direction is also the - direction of symmetry of the diffraction pattern of higher orders. 'Ffie-cfirection toward the radiation source can thus be unambiguously determined from the diffraction pattern.
= The diffraction angle is shifted with the wavelength 0l according to the formula Da = n/d = 0I (this is also true of the angle 0), i.e., the wavelength of the light source can be determined from the angular position of the diffraction maxima.
= The light spot pattern also rotates around the symmetry axis during the rotation of the cross grating. The direction of the light source in relation to the optical axis of the camera can thus be determined unambiguously.
A numerical example shall be presented to illustrate the conditions during the recognition of two laser sources of different wavelengths:
At the assumed wavelengths of X1 = 1.064 m (e.g., Nd:YAG laser) and X2 =
0.904 m (e.g., GaAs laser diode), a grating constant of d = 10 m and incidence angles of ao =/3o = 0, the diffraction angles are a=/3 = 6.1 for the longer wavelength and 5.4 for the shorter wavelength. The diffraction angle is multiplied at higher orders. The wavelength resolution increases at shorter grating distances, and so does the diffraction angle at the same time. With about 600 lines and rows of a detector array and an angle of first indication of the camera of 90 , the angle resolution of one pixel is 0.15 .
At a grating constant of 2 m, the spectral resolution of one pixel in the first diffraction order is about 5 nm. For comparison, the spectral bandwidth of a laser diode for a beam rider weapon is about 3 nm.
If a plurality of isolated light spots are registered by the detector array, it can be inferred from their location distribution in the image whether the higher orders of a coherent laser source are involved. This can be determined from the symmetry of the light spot pattern and the identical brightness of all light spots belonging to a certain order. The problem can be solved electronically, i.e., by comparing the signals of every individual pixel in the focal plane concerning its intensity with the signals of the respective adjacent pixels. If it is found that the intensity of a pixel is markedly higher than that of the adjacent pixels, their coordinates and signal values are noted.
The entire image can thus be reduced to a point pattern of individual pixels of higher intensity. Signal disturbances can be eliminated now by considering only pixels that form concentric squares. If an irregular point pattern is now left, the presence of a laser source is very likely.
The wavelength of the laser source can also be calculated from the diameter of the squares and it can be compared, e.g., with values of a threat library in order to find an additional confirmation for the threat. If the point patterns of an image series of a camera are now compared with one another, movements of the laser source in relation to the target can be calculated and followed. A plurality of laser sources can also be distinguished, classified and examined separately according to this simple_.instruction.
A person skilled in the art of electronic signal processing can solve this problem with a simple microprocessor without needing a special image processing in a computer.
Cross gratings can be manufactured either as transmission gratings or as reflection gratings. These may be designed either as amplitude gratings or as phase gratings. The advantage of the phase gratings is their substantially higher transmission, because the radiation is lost on the part of the grating that happens to cause blocking in amplitude gratings.
A special case of gratings is the so-called sine grating with a local cos2 curve of the amplitude transmission in the case of the use of an amplitude grating or of the refractive indices in the case of a phase grating. Only the 0th order and the +/-lth order are generated in the diffraction spectrum in this type of grating. In addition, these gratings are particularly suitable for the detection of weak laser sources because of their high efficiency in light transmission in the first order.
The holographic manufacture of gratings has become increasingly widespread in the manufacture of gratings. Two waves generated by laser beam splitting fall here with a slight direction difference on a photosensitive resist layer and generate an interference fringe pattern there, which can be converted into grating structures. Cross gratings can thus be manufactured by the two-time exposure of such interference fringe patterns located at right angles to one another. Both amplitude and phase gratings can be manufactured according to this technique for the transmission operation;
phase gratings are formed by the known bleaching out of the amplitude structttre.
The different exposure of the layer in the bright and dark fringes can also be converted into a change in layer thickness (furrow profile) and be used as a phase grating in transmission. The vapor deposition of aluminum analogously yields a reflection grating.
The transmission sine phase gratings are particularly well suited for use in a laser warner for the visible and near infrared range of 0.35 to 2.5 m. These may be applied, e.g., to quartz glass and be used as a transmission attachment in front of a camera. Either amplitude transmission holograms for the transmission operation or reflection gratings for the reflection operation may be used in front of a camera in the infrared range above 2 m. Mainly reflection gratings are used in the infrared range at 10 m (CO2 laser). So-called echelette gratings, which have a sawtooth-like furrow profile, are particularly favorable for a laser warner. The slope of the furrows is selected to be such that the reflection and diffraction directions are identical for a desired "blaze" wavelength (blaze = maximum, intensity). The corresponding order n will also be preferred in this case.
Another possibility of optimizing cross gratings is to appropriately design the depth of modulation and the grating constants or the spatial frequency of the grating.
Gratings with low spatial frequency are known to have many diffraction orders, whose intensities change according to the second powers of the Bessel functions. The intensity consequently increases in the higher orders due to a strong modulation. If the modulation is decreased, the intensity will decrease in the higher orders in favor of the lower orders. The optimization problem for laser warners now is to maximize the intensity in the first orders. This maidmum is theoretically at 33% for a linear grating. It follows from this for a cross grating that 10% each will remain for the four interesting orders. The remaining 60% of the incident light are distributed among the other orders.
The diffraction efficiency can be considerably increased in cross gratings by increasing the spatial frequency. For spatial frequencies of about 400-500 line pairs per mm in holographic transmission phase gratings, we are in the transition range between thin and thick holograms. Substantially higher orders will already occur here.
If even higher spatial frequencies are used, e.g., 700 line pairs per mm, the higher orders can be suppressed almost completely. The percentage of.light of the 0th order can be kept below 20%, so that each of the four diffraction patterns of the first order contains about 20% of the light.
The lasers used for military and safety engineering applications are limited to a few, relatively narrow wavelength ranges between 800 and 850 nm, between 1,050 and 1,070 nm, between 1,450 and 1,650 nm, and between 9.5 and 11.5 Fcm. To correspondingly attenuate the interfering background radiation, it is advantageous to arrange a spectral filter in front of the imaging lens of the camera in addition to the cross grating being used. The background can be reduced by a factor of 10 to 20 with a filter width of, e.g., 10-20 nm in the rear infrared range.
The absolute sensitivity of commercially available CCD cameras for detecting a continuous-wave laser source at an integration time of 20 msec through the cross grating is about 6 pW. The signals caused by the scattered radiation of a beam rider from a distance of 10-1 km are, for comparison, in the range of 1 pW to 1 nW, i.e., in the detection range of a laser warner according to the present invention. The sensitivity can be further increased in the case of CCD cameras by prolonging the integration time, cooling the detector and by arranging an electron multiplier stage (e.g., a microchannel plate with 10,000-fold amplification) before the detector array.
The latter possibility is shown in the exemplary embodiment according to Figure 2.
A luminescent screen 26, an electron multiplier 27, a photocathode 28, another lens 22.2, a cross grating 23, and a spectral filter 24 are arranged here in front of a first lens 22.1, in the focal plane of which a detector array 21 connected to a microprocessor 25 is located. The elements 26, 27 and 28 form a so-called low-light amplifier here, whose image is then imaged on the detector array 21.
The necessary angle resolution range of a laser warner will differ depending on the applica.tion. Normal lenses with a field angle of 40 -55 will be sufficient for many applications. Four such laser warners are installed in different areas of the outer skin for panoramic acquisition, e.g., for a helicopter, with each laser warner covering an angle of 90 .
Another possibility for the panoramic acquisition of laser threats is shown in Figure 3. A convex mirror 34, which detects the light from a horizontally directed plane I at a horizontal image angle of 90 (e.g., 60 above the plane I and 3A. - below the plane I) and images the range thus detected in an annular surface II on the detector 31, is arranged here in front of a laser warner according to Figure 1 or 2 with a detector array 31, an imaging optical system 32 and a cross grating 33.
The process being described here for detecting laser sources can be embodied and combined with a great variety of cameras. In particular, specifically designed individual detectors with optical scanning means (scanner) arranged in front of them may also be used instead of detector arrays.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
= The diffraction angle is shifted with the wavelength 0l according to the formula Da = n/d = 0I (this is also true of the angle 0), i.e., the wavelength of the light source can be determined from the angular position of the diffraction maxima.
= The light spot pattern also rotates around the symmetry axis during the rotation of the cross grating. The direction of the light source in relation to the optical axis of the camera can thus be determined unambiguously.
A numerical example shall be presented to illustrate the conditions during the recognition of two laser sources of different wavelengths:
At the assumed wavelengths of X1 = 1.064 m (e.g., Nd:YAG laser) and X2 =
0.904 m (e.g., GaAs laser diode), a grating constant of d = 10 m and incidence angles of ao =/3o = 0, the diffraction angles are a=/3 = 6.1 for the longer wavelength and 5.4 for the shorter wavelength. The diffraction angle is multiplied at higher orders. The wavelength resolution increases at shorter grating distances, and so does the diffraction angle at the same time. With about 600 lines and rows of a detector array and an angle of first indication of the camera of 90 , the angle resolution of one pixel is 0.15 .
At a grating constant of 2 m, the spectral resolution of one pixel in the first diffraction order is about 5 nm. For comparison, the spectral bandwidth of a laser diode for a beam rider weapon is about 3 nm.
If a plurality of isolated light spots are registered by the detector array, it can be inferred from their location distribution in the image whether the higher orders of a coherent laser source are involved. This can be determined from the symmetry of the light spot pattern and the identical brightness of all light spots belonging to a certain order. The problem can be solved electronically, i.e., by comparing the signals of every individual pixel in the focal plane concerning its intensity with the signals of the respective adjacent pixels. If it is found that the intensity of a pixel is markedly higher than that of the adjacent pixels, their coordinates and signal values are noted.
The entire image can thus be reduced to a point pattern of individual pixels of higher intensity. Signal disturbances can be eliminated now by considering only pixels that form concentric squares. If an irregular point pattern is now left, the presence of a laser source is very likely.
The wavelength of the laser source can also be calculated from the diameter of the squares and it can be compared, e.g., with values of a threat library in order to find an additional confirmation for the threat. If the point patterns of an image series of a camera are now compared with one another, movements of the laser source in relation to the target can be calculated and followed. A plurality of laser sources can also be distinguished, classified and examined separately according to this simple_.instruction.
A person skilled in the art of electronic signal processing can solve this problem with a simple microprocessor without needing a special image processing in a computer.
Cross gratings can be manufactured either as transmission gratings or as reflection gratings. These may be designed either as amplitude gratings or as phase gratings. The advantage of the phase gratings is their substantially higher transmission, because the radiation is lost on the part of the grating that happens to cause blocking in amplitude gratings.
A special case of gratings is the so-called sine grating with a local cos2 curve of the amplitude transmission in the case of the use of an amplitude grating or of the refractive indices in the case of a phase grating. Only the 0th order and the +/-lth order are generated in the diffraction spectrum in this type of grating. In addition, these gratings are particularly suitable for the detection of weak laser sources because of their high efficiency in light transmission in the first order.
The holographic manufacture of gratings has become increasingly widespread in the manufacture of gratings. Two waves generated by laser beam splitting fall here with a slight direction difference on a photosensitive resist layer and generate an interference fringe pattern there, which can be converted into grating structures. Cross gratings can thus be manufactured by the two-time exposure of such interference fringe patterns located at right angles to one another. Both amplitude and phase gratings can be manufactured according to this technique for the transmission operation;
phase gratings are formed by the known bleaching out of the amplitude structttre.
The different exposure of the layer in the bright and dark fringes can also be converted into a change in layer thickness (furrow profile) and be used as a phase grating in transmission. The vapor deposition of aluminum analogously yields a reflection grating.
The transmission sine phase gratings are particularly well suited for use in a laser warner for the visible and near infrared range of 0.35 to 2.5 m. These may be applied, e.g., to quartz glass and be used as a transmission attachment in front of a camera. Either amplitude transmission holograms for the transmission operation or reflection gratings for the reflection operation may be used in front of a camera in the infrared range above 2 m. Mainly reflection gratings are used in the infrared range at 10 m (CO2 laser). So-called echelette gratings, which have a sawtooth-like furrow profile, are particularly favorable for a laser warner. The slope of the furrows is selected to be such that the reflection and diffraction directions are identical for a desired "blaze" wavelength (blaze = maximum, intensity). The corresponding order n will also be preferred in this case.
Another possibility of optimizing cross gratings is to appropriately design the depth of modulation and the grating constants or the spatial frequency of the grating.
Gratings with low spatial frequency are known to have many diffraction orders, whose intensities change according to the second powers of the Bessel functions. The intensity consequently increases in the higher orders due to a strong modulation. If the modulation is decreased, the intensity will decrease in the higher orders in favor of the lower orders. The optimization problem for laser warners now is to maximize the intensity in the first orders. This maidmum is theoretically at 33% for a linear grating. It follows from this for a cross grating that 10% each will remain for the four interesting orders. The remaining 60% of the incident light are distributed among the other orders.
The diffraction efficiency can be considerably increased in cross gratings by increasing the spatial frequency. For spatial frequencies of about 400-500 line pairs per mm in holographic transmission phase gratings, we are in the transition range between thin and thick holograms. Substantially higher orders will already occur here.
If even higher spatial frequencies are used, e.g., 700 line pairs per mm, the higher orders can be suppressed almost completely. The percentage of.light of the 0th order can be kept below 20%, so that each of the four diffraction patterns of the first order contains about 20% of the light.
The lasers used for military and safety engineering applications are limited to a few, relatively narrow wavelength ranges between 800 and 850 nm, between 1,050 and 1,070 nm, between 1,450 and 1,650 nm, and between 9.5 and 11.5 Fcm. To correspondingly attenuate the interfering background radiation, it is advantageous to arrange a spectral filter in front of the imaging lens of the camera in addition to the cross grating being used. The background can be reduced by a factor of 10 to 20 with a filter width of, e.g., 10-20 nm in the rear infrared range.
The absolute sensitivity of commercially available CCD cameras for detecting a continuous-wave laser source at an integration time of 20 msec through the cross grating is about 6 pW. The signals caused by the scattered radiation of a beam rider from a distance of 10-1 km are, for comparison, in the range of 1 pW to 1 nW, i.e., in the detection range of a laser warner according to the present invention. The sensitivity can be further increased in the case of CCD cameras by prolonging the integration time, cooling the detector and by arranging an electron multiplier stage (e.g., a microchannel plate with 10,000-fold amplification) before the detector array.
The latter possibility is shown in the exemplary embodiment according to Figure 2.
A luminescent screen 26, an electron multiplier 27, a photocathode 28, another lens 22.2, a cross grating 23, and a spectral filter 24 are arranged here in front of a first lens 22.1, in the focal plane of which a detector array 21 connected to a microprocessor 25 is located. The elements 26, 27 and 28 form a so-called low-light amplifier here, whose image is then imaged on the detector array 21.
The necessary angle resolution range of a laser warner will differ depending on the applica.tion. Normal lenses with a field angle of 40 -55 will be sufficient for many applications. Four such laser warners are installed in different areas of the outer skin for panoramic acquisition, e.g., for a helicopter, with each laser warner covering an angle of 90 .
Another possibility for the panoramic acquisition of laser threats is shown in Figure 3. A convex mirror 34, which detects the light from a horizontally directed plane I at a horizontal image angle of 90 (e.g., 60 above the plane I and 3A. - below the plane I) and images the range thus detected in an annular surface II on the detector 31, is arranged here in front of a laser warner according to Figure 1 or 2 with a detector array 31, an imaging optical system 32 and a cross grating 33.
The process being described here for detecting laser sources can be embodied and combined with a great variety of cameras. In particular, specifically designed individual detectors with optical scanning means (scanner) arranged in front of them may also be used instead of detector arrays.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
Claims (43)
1. A system that facilitates management of portable construction devices, comprising:
at least one portable construction device utilized to facilitate construction activities; and a communication component that interacts with at least one other communication device to monitor and/or control the portable construction device.
at least one portable construction device utilized to facilitate construction activities; and a communication component that interacts with at least one other communication device to monitor and/or control the portable construction device.
2. The system of claim 1, the communication component is integral to the portable construction device.
3. The system of claim 1, the communication component employs an analog and/or digital interface to monitor and/or control the portable construction device.
4. The system of claim 1, the communication component utilizes Ethernet to communicate with the portable construction device and/or the other communication device.
5. The system of claim 1, the portable construction device comprising a welding device.
6. The system of claim 5, the welding device comprising a plurality of welding units.
7. The system of claim 6, the welding device comprising a rack system that contains the plurality of welding units.
8. The system of claim 1, the portable construction device comprising an auxiliary welding device.
9. The system of claim 1, the communication component is co-located with the portable construction device.
10. The system of claim 1, the communication component utilizes audio and/or video communications to interact with the other communication device.
11. The system of claim 1, the communication component utilizes wireless communications, wired communications, optical communications, and/or satellite communications to interact with the other communication device.
12. The system of claim 1 further comprising:
a power component that supplies power to the portable construction device and/or the communication component.
a power component that supplies power to the portable construction device and/or the communication component.
13. The system of claim 1 further comprising:
a global positioning system (GPS) component that provides positioning information of the portable construction device.
a global positioning system (GPS) component that provides positioning information of the portable construction device.
14. The system of claim 13, the communication component interacts with the global positioning system to relay position data to another communication device and/or to direct the global positioning system to a different location.
15. The system of claim 14 further comprising:
a location indicator component that interacts with the communication component and/or the GPS component to indicate correct positioning of the portable construction device.
a location indicator component that interacts with the communication component and/or the GPS component to indicate correct positioning of the portable construction device.
16. The system of claim 1, the communication component provides usage information of the portable construction device to the other communication device.
17. The system of claim 1, the communication component controls usage of the portable construction device based on its interactions with the other communication device.
18. The system of claim 17, the communication component controls usage of the portable construction device based on a monetary value determined by operating costs and/or expendable material usage related to the portable construction device.
19. The system of claim 1, the communication component controls power levels and/or amounts to the portable construction device based on its interactions with the other communication device.
20. The system of claim 1, the communication component provides information related to expendable items related to facilitate operation of the portable construction device.
21. The system of claim 1, the communication component provides one-way communications and/or two-way communications to the other communication device.
22. The system of claim 21, the two-way communications comprising voice and/or video communications.
23. The system of claim 21, the two-way communications comprising an Internet link.
24. A method of facilitating management of portable construction devices, comprising:
providing at least one portable construction device that is utilized to facilitate construction activities; and remotely communicating with the portable construction device via a communication component that interacts with the portable construction device.
providing at least one portable construction device that is utilized to facilitate construction activities; and remotely communicating with the portable construction device via a communication component that interacts with the portable construction device.
25. The method of claim 24, the communication component is integral to the portable construction device.
26. The method of claim 24 further comprising:
monitoring the portable construction device via interactions with the communication component.
monitoring the portable construction device via interactions with the communication component.
27. The method of claim 24 further comprising:
controlling the portable construction device via interactions with the communication component.
controlling the portable construction device via interactions with the communication component.
28. The method of claim 24, the portable construction device comprising a welding device.
29. The method of claim 28, the welding device comprising a plurality of welding units.
30. The method of claim 29, the welding device comprising a rack system that contains the plurality of welding units.
31. The method of claim 24, the portable construction device comprising an auxiliary welding device.
32. The method of claim 24 further comprising:
employing wireless communications, wired communications, optical communications, and/or satellite communications to interact with the communication component.
employing wireless communications, wired communications, optical communications, and/or satellite communications to interact with the communication component.
33. The method of claim 24 further comprising:
utilizing a global positioning system (GPS) that is co-located with the portable construction device to provide positioning information relating to the portable construction device via the communication component.
utilizing a global positioning system (GPS) that is co-located with the portable construction device to provide positioning information relating to the portable construction device via the communication component.
34. The method of claim 33 further comprising:
employing the positioning information to facilitate in positioning the portable construction device to a different location.
employing the positioning information to facilitate in positioning the portable construction device to a different location.
35. The method of claim 24 further comprising:
obtaining usage information relating to the portable construction device via the communication component.
obtaining usage information relating to the portable construction device via the communication component.
36. The method of claim 24 further comprising:
controlling usage of the portable construction device via the communication component.
controlling usage of the portable construction device via the communication component.
37. The method of claim 36 further comprising:
controlling usage of the portable construction device based on a monetary value determined by operating costs and/or expendable material usage related to the portable construction device.
controlling usage of the portable construction device based on a monetary value determined by operating costs and/or expendable material usage related to the portable construction device.
38. The method of claim 24 further comprising:
controlling power levels and/or amounts to the portable construction device via the communication component.
controlling power levels and/or amounts to the portable construction device via the communication component.
39. The method of claim 24 further comprising:
obtaining information related to expendable items related to facilitating operation of the portable construction device via the communication component.
obtaining information related to expendable items related to facilitating operation of the portable construction device via the communication component.
40. The method of claim 24 further comprising:
providing one-way communications and/or two-way communications via the communication component.
providing one-way communications and/or two-way communications via the communication component.
41. The method of claim 40, the two-way communications comprising voice and/or video communications.
42. The method of claim 40, the two-way communications comprising an Internet link.
43. A system that facilitates management of portable construction devices, comprising:
means to interact with at least one portable construction device utilized to facilitate construction activities; and means to interact with the portable construction device and communicate with a remote location to facilitate monitoring and/or controlling of the portable construction device.
means to interact with at least one portable construction device utilized to facilitate construction activities; and means to interact with the portable construction device and communicate with a remote location to facilitate monitoring and/or controlling of the portable construction device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2288305 CA2288305A1 (en) | 1999-11-08 | 1999-11-08 | Device for recognizing and locating laser radiation sources |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2288305 CA2288305A1 (en) | 1999-11-08 | 1999-11-08 | Device for recognizing and locating laser radiation sources |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2288305A1 true CA2288305A1 (en) | 2006-04-13 |
Family
ID=36177373
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2288305 Abandoned CA2288305A1 (en) | 1999-11-08 | 1999-11-08 | Device for recognizing and locating laser radiation sources |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2288305A1 (en) |
-
1999
- 1999-11-08 CA CA 2288305 patent/CA2288305A1/en not_active Abandoned
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