GB2320316A

GB2320316A - Laser countermeasure

Info

Publication number: GB2320316A
Application number: GB9626117A
Authority: GB
Inventors: Richard C N Woolnough; Michael Pywell
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1996-12-16
Filing date: 1996-12-16
Publication date: 1998-06-17
Also published as: GB9626117D0; JPH10307195A; EP0849612A2; EP0849612A3

Abstract

Apparatus for disrupting a beam of electromagnetic radiation, e.g. a laser beam incident upon a target, comprises a plurality of elements each having a partially reflective coating, the elements being adapted in use to be ejected into the path of the electromagnetic energy. The elements may be in the form of a flat surface (figure 1), a metallised lens (figure 2) or a sphere 16 having a hemispherical metal coating 20.

Description

2320316 ELECTROMAGNETIC RADIATION- DISRUPTION ELEMENTS

This invention relates to the field of disruption of electromagnetic energy incident upon an object and more particularly, but not exclusively to decoys used to protect aircraft, ships and land vehicles against the potential threat posed by weapons and weapon systems.

Many modem weapon systems utilise the abilities of seeking apparatus to identify, follow and ultimately detonate in the vicinity of a target. Such weapons systems utilise a range of methods by which targets may be identified, including both the thermal signature of the vehicle and/or the use of radar to locate and track the target. More recently weapon systems have begun to incorporate the use of electromagnetic energy systems, usually in the form of lasers, which enable such systems to provide high quality targeting information to give highly accurate missile and/or gun fire in ground to air, air-to-air and air-to-ground scenarios. Additionally some weapon systems utilise lasers as a target proximity detonation system for determining the detonation time and/or distance of the weapon from the target.

A more recent addition to the field of military weapon systems has been that of the new classes of high powered lasers (Laser Directed Energy Weapons) These can be used to dazzle and/or damage crew and/or electrooptic sensors on board both military and civilian vehicles. The use of such high powered lasers poses a threat ftom both hostile military forces and that of terrorists whereby such weapon system could easily be utilised to threaten the safety of civilian aircraft. The invention has particular advantages in the field of decoys used for vehicle protection against weapon systems which additionally utilise lasers to enable high quality targeting information.

The proliferation of these threats has resulted in the development of a relatively small number of laser warning systems now fitted to United States aircraft, helicopters and tanks, but as yet no in service UK aircraft has been fitted with such a laser warning system. It would be anticipated that most future vehicles designed for use in military conditions will require a laser warning system as standard.

Research into the field of laser warning systems indicates that although audio and/or visual warnings can be flagged to the crew of a vehicle to which they are fitted, there are currently no countermeasures which can be deployed when the vehicle is illuminated by laser energy or targeted by a laser/radar tracking system.

The invention provides apparatus and a method to provide a passive countermeasure to laser threats, including such threats from both directed energy laser weapons and lower power targeting/ proximity detonation lasers.

Accordingly there is provided apparatus for the disruption of electromagnetic energy, comprising a plurality of element means, each said element means having at least part of one surface adapted to reflect incident electromagnetic energy.

Furthermore there is also provided method of disrupting electromagnetic energy incident upon an object, comprising means for ejecting a plurality of elements into the path of said electromagnetic energy, each element having at least part of one surface adapted to reflect said incident electromagnetic energy.

The invention will now be described by way of example only with reference to the following drawings.

Figure 1 shows a diagram of a "flat type" laser countermeasure element; Figure 2 shows a diagram of a 9ens type" countermeasure element; Figure 3 shows a diagram of a "spherical type" laser countermeasure element; In figure 1, a substantially flat type countermeasure element 2 is shown, comprising a plastic portion 4 and a metalised coating 6, forming an extruded 'V' shape. The metalised coating 6 could be applied via a spluttering process or as metal foil suitably glued to the plastic, giving the flat type element 2 a dual reflective surface on one face. The lip 5 assists in the separation of the flat elements once ejected into the air stream. The element has a thin film, anti-static, non-stick outer coating to both faces to ensure that the individual elements do not stick to each other when jettisoned from the aircraft.

Figure 2 shows a circular lens type element 8 having a plastic face 10, the reverse face 12 having both a similar metalised coating 14 and thin fihn coating to that of the flat type element 2.

In figure 3 a spherical countermeasure element 16 is shown, being comprised of a plastic material 18 comprising a hemispherical metalised coating 20, the materials therefore being identical to those described in the metalised coatings of the flat type countermeasure 2 and the flat lens type countermeasure 8. The spherical element may be solid or, for lower mass (which is important for aircraft applications), can be hollow. Hollow elements have the added advantage of increased countermeasure effectiveness time, due to the lower altitude loss rate when compared with the solid spherical elements.

In use, the method by which the three types of countermeasure elements, namely flat 2, substantially flat lens 8 and spherical 16 achieve their purpose as laser countermeasures, lies in their potential to reflect incident laser beam energy due to the nature of the mirror finished metalised coatings 6, 14, 20 and in some cases additionally act on the incident energy so as to modify its power and/or direction. The flat type elements 2 are utilised for their ability to reflect incident laser beam energy, whereas botle lens type 8 and the spherical elements 16 utilise the optical functions of their shape to both reflect and/or disperse laser energy.

The lens type elements 8 act as an effective counterTneasure to laser energy by reducing the power density of an incident laser beam, the lens being optically divergent thereby reducing the power level of any laser beam which passes through it and is still incident on the vehicle which is being targeted or tracked. This reduction in power density weakens the ability of any laser targeting or ranging equipment to assess the true distance of the vehicle from the laser seeking head thereby acting as an effective laser countermeasure.

The spherical countermeasure elements 16 are coated with a hemispherical metalised coating 20 which gives the said elements the ability to totally internally reflect any incident laser energy.

A plurality of similar types of countermeasure elements, namely 2, 8, 16 would be housed in a suitable container attached to or positioned in proximity to the vehicle which is to be protected from laser directed energy andlor targeting systems utilising these reflective type countermeasure elements. When a suitable laser warning system identifies that the vehicle is being illuminated and/or targeted by incident laser energy, the countermeasure element container would be so designed to eject the contained plurality of countermeasure elements thereby causing the vehicle.

To be most effective as a countermeasure element, a maximum potential reflective area of the countermeasure elements in the incident laser beam is required. This is achieved the required interruption and/or dispersion of the laser beam thus protecting by maximising both the number and area of the individual countermeasure elements in the containers. Each element will be dispersed so as to utilise the maximum area available within the cross section of the container in which it is fitted. In the case of the flat type element 2 the number per container is limited only by the container volume. For the lens type countermeasure element 8, a trade off between lens thickness and number per container volume has to be made. This is threat scenario dependent because the level of internal reflection which can be achieved within the flat type lens 8 is dependent on the wavelength(s) of the incident laser(s), the dielectric constant of the plastic and the lens thickness. In the extreme, the container volume could be filled with spheres, which could be much smaller than the diameter of cross-section of the container, and thus each of which would provide a total internal reflection of laser energy at a given wavelength.

When ejected at appropriate angles from the host vehicle the very low mass countermeasure elements form a floating mirror to reflectand/or divert the laser energy from the vehicle being protected. This effect is sustained for an appropriate time until the elements float down to earth. The invention also offers the opportunity to enable premature detonation of weapons which utilise laser proximity fuses, the possibility of break lock of laser targeting and ranging systems along with offering some measure of protection to the vehicle crew and electro-optic sensors from laser directed energy weapon threats.

Claims

Claims

Apparatus for the disruption of electromagnetic energy, comprising a plurality of element means, each said element means having at least part of one surface adapted to reflect incident electromagnetic energy.

Apparatus in accordance with claim 1, wherein said element means comprises an optically divergent lens means.

Apparatus in accordance with claim 1 wherein said element means are substantially spherical.

4. Apparatus in accordance with claim 3, wherein said element means are designed to substantially totally internally reflect said incident electromagnetic energy.

A method of disrupting electromagnetic energy incident upon an object, comprising means for ejecting a plurality of elements into the path of said electromagnetic energy, each element having at least part of one surface adapted to reflect said incident electromagnetic energy.

A method in accordance with claim 5 wherein said element means comprises an optically divergent lens means.

7. A method as in accordance with claim 5, wherein said element means are substantially spherical.

8. A method in accordance with claim 7, wherein said element means is designed to substantially totally internally reflect said incident electromagnetic energy.

9. An apparatus or method in accordance with any preceding claim, wherein said electromagnetic energy is produced by a laser.

jo. Apparatus substantially as herein before described with reference to the accompanying drawings.

11. A method of disrupting electromagnetic energy as herein before described with reference to the accompanying drawings.