Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-12-06
1995-08-08
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
2502062, 3561412, G01S 3782
Patent
active
054401160
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a laser warning device. In a military connection, such devices have the task to register laser radiation from e.g. laser rangefinders or laser designators and by a warning signal make clear to the illuminated person that laser illumination has occurred or continues. The laser warning device can be located on or in close vicinity of military objects that are especially exposed to systems using a laser for target acquisition and the like, for instance tanks, ships and permanent installations, such as airfields etc. Laser beams for the mentioned reasons have very little divergence. Typically the cross-section of the main beam is 1 m after 1 km. It could therefore be necessary to place several laser warning devices in different places around an object in order to get a reasonable security of detection, if the object is large. Due to the atmospheric conditions there is also a weeker more or less scattered radiation of considerably greater cross-section.
The laser warning device shall indicate that laser illumination has occurred and it is also desirable that it is able to establish the direction (bearing and elevation) and the type of laser (laser wavelength, pulse length and pulse repetition frequency).
There are several previous types of laser warning devices. Most of them require a great number of light collection elements or detectors in order to determine the direction to the light source with high resolution. That what is shown in the German Offenlegungsschrift 3 300 849, U.S. Pat. No. 4,868,378 and the Swedish Patent 459 529 can be mentioned as examples. They all have different drawbacks.
SUMMARY OF THE INVENTION
The present invention, and however, solves the raised problem to determine the direction to a laser radiation source, without having the drawbacks of the previous laser warning devices, by being designed in the way that is evident from the following independent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in more detail in relation to the accompanying drawings where,
FIG. 1 shows a principal sketch of a laser warning device according to the invention,
FIG. 2 shows a cross-section of said laser warning device when the laser radiation source is located above the plane of the detector surface and
FIG. 3 shows the same cross-section when the laser radiation source is located below said plane.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS
The laser warning device comprises a position sensitive photodetector or a position sensitive photodetector arrangement. Position sensitive detectors are previously known and in the Swedish published patent application 368 741 such a detector is described and direction is also given about basic knowledge about them. Instead of one such detector, a detector arrangement, a detector array or the like, which gives a signal that depends on the position of the illuminated spot, can be used. Therefore, when in the following a position sensitive detector is mentioned, both a single one and a position sensitive detector arrangement is referred to.
Basis for the invention is that the laser warning device is provided with a reflector, which focus the incoming laser radiation towards the photodetector, and that the detector surface must be protected against directly incoming radiation. The focusing results in a larger signal from the detector than would otherwise have been the case. In FIG. 1 it is shown how the protection against directly incoming radiation can take the form of a roof 3 above the laser warning device. In the figure it is further shown how it is possible to implement the invention by locating the detector 1, in this case an annular position sensitive photodetector, in the focus of a surrounding reflector 2, in this case located on the inner surface of a spherical segment. The radiation that falls on the detector 2 and that is more or less parallel to the plane of the detector surface is thereby focused towards the detector as seen both in a pla
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patent: 4467194 (1984-08-01), Foreman
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patent: 4868378 (1989-09-01), Biverot
patent: 5103088 (1992-04-01), Halldorsson et al.
patent: 5258609 (1993-11-01), Holmes
Patent Abstracts of Japan, vol. 10, No. 64, P436, abstract of JP 60-205381, Oct. 16, 1985.
Bolander Goran
Nissborg Kurt
Forsvarets Forskningsanstalt
Lee John R.
Nelms David C.
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