WO1986006844A1

WO1986006844A1 - Integration receiving device for laser radiation

Info

Publication number: WO1986006844A1
Application number: PCT/EP1986/000288
Authority: WO
Inventors: Kurt Eichweber
Original assignee: Precitronic Gesellschaft Für Feinmechanik Und Elec
Priority date: 1985-05-15
Filing date: 1986-05-15
Publication date: 1986-11-20
Also published as: DE3517650A1; EP0225895A1

Abstract

The receiving device (1) for laser radiation provided with a detector (6) is characterized by a structure (2, 4) similar to a light guide and arranged before the detector (6). The light guide may be flexible so that it is possible to determine the incidence direction of the laser beam (3) from differential transit times of signals to arrive to both extremities of the light guide (2, 4). The latter may be provided inside or at the surface of diffusion centers.

Description

Integrating receiving device for laser radiation

The invention relates to an integrating receiving device for laser radiation with a detector.

Laser radiation is usually sharply focused so that the atmospheric deflection of the light beam due to turbulence and different densities is noticeable due to temperature differences. Because of these disturbances in the air through which the laser beam passes, the laser beam does not always reach the same point and thus does not always fall on the detector, at least temporarily. This creates various disadvantages.

This means that a target marked with a detector can no longer be reliably hit by the laser radiation, which is noticeable, for example, when shooting is simulated. If information is transmitted with modulated laser radiation, some of the information can be lost if the laser beam temporarily does not hit the detector. Another disadvantage of the very limited size of known detectors is that the detector absorbs very little energy from the club-shaped laser beam.

The object of the invention is to provide a receiving device of the type mentioned, which is simple in construction and has a larger receiving area for the laser radiation.

The solution according to the invention is that the receiving device is an elongated, rod-shaped first element made of a first material and a surrounding tubular second element made of a second material, that the first and the second material is transparent to the laser radiation to be received, that the first material has a larger refractive index than the second, and that on an end face of the rod-shaped first element, a detector for the laser radiation is attached.

The receiving device thus has an elongated light guide which is connected to the detector. All of the laser radiation that strikes the relatively large light guide is then directed to the detector. A sufficient length of the cylindrical elements is of course essential for a sufficient size of the sensitive receiving surface.

Even in the event of fluctuations in the location where the laser radiation strikes as a result of air turbulence, laser radiation always falls into the receiving device and reaches the detector, so that the above-mentioned disadvantages cannot occur.

As already mentioned, the receiving device is constructed in such a way that it forms a light guide. The term "light guide" does not mean, however, that the invention is limited to rod-shaped elements in which the light is transmitted by multiple total reflection. Rather, it is the case that the laser radiation is also, possibly even predominantly, passed on to the detector by normal reflection. This is particularly the case with light guides, the length of which is relatively small. The particularly high efficiency observed here may be related to the fact that only relatively few normal reflections take place on the walls until the laser light reaches the detector. The light guide need not only be made up of two elements, that is to say an inner and an outer element. In many cases it is rather advantageous to provide a further element between the first and second elements which is also transparent to the laser radiation but has a refractive index whose value lies between that of the first and second materials. Several such other elements can also be provided.

Of course, the captured laser radiation does not only emerge at an end face of the rod-shaped first element, but also at the second. The sensitivity of the receiving device can be increased if a mirror is attached to the other end face of the rod-shaped first element, through which the laser radiation arriving at this end is reflected by the first rod-shaped element onto the detector.

But it can also be provided that a detector for the laser radiation is also attached to the other end face of the rod-shaped element; in this case the radiation components emerging at the two ends of the receiving device are detected separately.

For example, the receiving device could be rigid. However, there is a particular advantage if the elements are flexible or if the first element is liquid and the second element is flexible and tubular. In this case, the receiving device can be placed around bridges of ships, turrets of tanks during shooting simulation exercises and the like, so that laser radiation incident from different directions can also be detected. So far, there have always been several for this purpose and for another purpose, which will be described below Complicated receiving devices constructed detectors (DE-OSen 28 30 308, 33 00 849, 33 23 828; DE-PS 34 00 837) required. If additional elements are provided, they must also be flexible for this purpose.

If the receiving device is curved (the situation is particularly simple in the case of a receiving device curved in a circular shape), a modulated laser radiation, in particular pulsed laser radiation, will first reach the receiving device at various points, depending on the direction from which the laser radiation is coming. This results in time differences with which the laser radiation reaches the two end faces of the rod-shaped first element, depending on the direction of incidence. If a detector is provided on both end faces, then the incident direction of the laser radiation can be determined from these transit time differences. Of course, this is also possible if a mirror is attached to one of the end faces; in this case, the detector detects two pulses or a broadened pulse when a laser radiation pulse hits the detector.

It is thus possible to use the receiving device to determine the direction of incidence of laser radiation, which, as previously said, was only possible by means of very complex arrangements of many sensors.

If you provide several units made up of first, second and possibly further elements and detectors / mirrors, not only the sensitivity is increased. By simultaneously measuring the incoming pulses at the various units, additional information about the direction of the incident laser radiation can be obtained. So with a single horizontally arranged annular receiving device only the angle in the Horizontal from which the laser radiation comes. However, if two or more such circular or other curved elements are provided one above the other, the azimuth angle of the incident radiation can also be measured.

As mentioned at the beginning, a great deal of laser radiation is captured by the receiving device according to the invention. If, for example, the beam lobe of the laser radiation has a diameter of 2 m at the receiving location, and if the receiving device has a diameter of 3 cm for a given length, the effective receiving area is 600 cm ² . Even if it is assumed that the losses of the arrangement are not insignificant, the gain for the sensitivity on a small effective detector area is nevertheless great.

The first rod-shaped element and the further elements can have different cross-sectional shapes. For example, the first element could have an elliptical cross-section, a triangular cross-section, a rectangular cross-section, a square cross-section or other cross-sectional shapes. However, it is particularly advantageous if the first element is cylindrical and the further elements arranged around it have an annular cross section.

The sensitivity can be increased even further if the surface is roughened, so that the incident laser radiation is scattered more effectively into the interior of the receiving device. However, the surface can also be profiled in order to direct the incident laser radiation into the interior of the receiving device more effectively. For this purpose, a prism-like, groove-like or ring-like profile or a profile in the manner of a trapezoidal thread can be provided. The corresponding profiling can only be done on one Side of the receiving device or circumferentially provided, it can be applied for example in the case of a thermoplastic material of the outer tubular second element by deformation. Due to the roughened surface or profiled surface, the laser radiation is guided more effectively into the light guide, but there may be the disadvantage that the roughening or profiling deteriorates the light guide properties. Depending on the material and type of surface treatment, it will therefore be provided that the roughening or profiling is provided on the inner or outer surface of the second element or further element, wherein the other surface can also be roughened, profiled or smooth. This is particularly useful. But it is also conceivable that the surface of the first element is also profiled or roughened, at least in places.

It is particularly expedient if the surface of the first element is partially profiled or roughened, smooth surface parts then extending between these profiled or roughened surfaces. On the one hand, this causes a particularly large amount of radiation to be directed into the light guide at the profiled or roughened points, which radiation is then guided on the smooth surfaces in the direction of the longitudinal extension of the light guide to the detector or mirror on the end faces.

Another effective way of guiding the laser radiation into the light guide is to provide scattering centers in at least one of the elements, by means of which the laser radiation is extended into the light guide. Such scattering centers can in particular be dyes as are used for dye lasers. There are other possible scattering centers that are particularly suitable, for example from microspheres made of glass, diamond powder, corundum powder, rutile powder and similar materials. Diamond powder in particular has the advantage of scattering a lot of light into the light guide because of its particularly high refractive index. Depending on the design concept, the choice will be made in such a way that optimal amounts of the laser radiation are converted into the total reflection by scattering.

If the first material of the first element is liquid, then an oil-like or gel-like chemical substance without OH bands, in particular hexachloro-1,3-butadiene, is expediently used, namely materials which have a refractive index of more than n = 1.5. In this case the refractive index of the second material should be smaller, for example n = 1.35. If a transparent gel is used as the first material, the scattering centers can easily be introduced into it.

It has proven particularly expedient if the scattering centers are arranged on the surface or in the vicinity of the surface of the inner or outer wall of the first element. For this purpose, it is advisable to embed the scattering centers in a suitable lacquer or gel. In this way, the light is scattered particularly effectively into the light guide and thus converted into total reflection in larger quantities.

In a further advantageous embodiment it is provided that a material with a refractive index is provided between the first element and an outer, further element surrounding the first element at the points at which this element has smooth surface areas between scattering centers or rough surface areas on its surface that is smaller than that of the elements. This gives the advantage that the probability that the light scattered in the scattering areas is transmitted with total reflection is particularly large, or that the reflected light is reflected at an angle that is close to that of the total reflection, so that the reflection losses are low .

In this case, it is most expedient if the material with a lower refractive index is a gas. One could, for example, provide that rings with scattering centers are placed on the first rod-shaped element at intervals. These rings are then enclosed by a second element in such a way that spaces containing gas, for example air, remain between the rings.

If you provide the scattering centers in the first material, you should not use too many scattering centers, otherwise the light guide function will be impaired.

Since certain losses in the receiving device cannot be avoided, the diameter of the first element guiding the radiation should not be too small. This diameter can be a few mm, but also a few cm. The length of the receiving device will be adapted to the application; for example, it will correspond in whole or in part to the length of a ship if, for example, the receiving device is to be attached to the outside of the railing of a ship. However, the receiving device can also be pulled around a command bridge, for example; in this case their length is of course shorter.

The invention is described below using advantageous embodiments with reference to the accompanying drawings, for example. Show it:

1 shows a partial view of a receiving device according to the invention;

2 shows a view of another receiving device according to the invention;

3 shows a view of a circularly arranged receiving device;

4 shows in section the view of two receiving devices arranged one above the other;

5 shows a sectional view of another embodiment of a receiving device; 6 shows a sectional view of a further embodiment of a receiving device; and

7 is a sectional view of yet another embodiment of the receiving device,

The receiving device 1 of FIG. 1 consists of an inner first rod-shaped element 2 made of a material which is transparent to the laser radiation 3 and of a tubular element 4 surrounding the first rod-shaped element 2 made of a second material which is also transparent to the laser radiation 3, but has a smaller refractive index than the material of the first inner element 2. A detector element 6 is attached to an end face 5 of the first element 2 and is connected to lines 7 with a corresponding amplifier or detection circuit. At the front end, a casing 8 is also provided, which here encloses the tubular second element 4 and the detector 6.

The mode of action is as follows. The incident laser radiation 3 is scattered inside the receiving device 1. As shown by thinly drawn light rays, most of the radiation scattered to the right in FIG. 1 is directed to the detector 6, due to the fact that the receiving device acts in the manner of a light guide. Another part is scattered to the left, where it could also be picked up by a detector 6 or can be reflected by a mirror 9 to the detector 6, as shown in FIG. 2. Only a relatively small part of the radiation is lost.

The effectiveness of the light conduction to the detector is greater, the flatter the reflected light strikes the wall. The effectiveness is particularly great in the case of total reflection. However, it is not necessary that total reflection actually occur. Normal reflection will therefore take place with obliquely incident laser beams even without special scatter centers. The thick-drawn light beam 3 would also be partially reflected, but this is not shown in the figure, since otherwise the representation of the figure would be very confusing due to the large number of (normal) reflections.

Instead of the mirror 9 of FIG. 2, a second detector can also be provided on the second end face 10 of the first element 2. In this case, the location or the distance x from the first detector 6 at which the laser radiation occurs can be measured on the basis of the transit time differences. If L is the total length of the receiving device, the light running to the right must travel a distance x to the right detector, and a distance L - x to the left to the corresponding detector. In the case shown in FIG. 2 with a mirror, the part 3a of the laser radiation running to the right will have to cover a distance x, while the part 3b of the laser radiation running to the left and reflected must cover a distance of 2L-x. Because of these different distances, when the laser radiation is pulsed, two pulses or a broadened pulse occur at the detector 6, so that the location of the impact can be determined

In Fig. 3, a cylinder 11 is shown in a horizontal section as an element around which a detector 1 is placed in a circle. If the wavefront 12 of a laser radiation hits the receiving device 1 first at 13, then radiation components go from here clockwise and counterclockwise to the two detectors 6. The angles Φ ₁ and Φ ₂ and thus the horizontal component of the angle can be determined from the transit time difference , under which the laser radiation 3 is incident. If, as is shown in a horizontal section in FIG. 4, two receiving devices 1 are arranged one above the other, depending on the azimuth angle θ, there will be a travel distance difference 14 and thus a travel time difference with which the laser pulses arrive. The azimuth angle θ can be determined from the corresponding time difference.

As indicated schematically in FIG. 5, the second element 4 can be profiled on at least one side, for example with a trapezoidal profile 15.

This deflects the laser beam sideways, which increases the yield and thus the sensitivity.

Instead of the one-sided trapezoidal profile 15, a circumferential profile can also be provided, which can also have a different shape. It can also be provided that the outer tubular element 4 is roughened on its surface in order to increase the scatter of the laser radiation.

FIG. 6 shows a further embodiment of the invention, in which a further tubular or tubular element 16 is provided between the first cylindrical element 2 and the second tubular or tubular element 4, the refractive index of which has a value which is between that of the elements 2 and 4 lies. Scattering centers 17 are arranged in the material of the first element 2 and are formed, for example, by dyes, crystal or glass particles. The material of the element 2, if it is liquid, can be, for example, a transparent oil or gel, for example hexachloro-1,3-butadiene, into which the scattering centers 17 are then introduced. The scattering centers / bodies 17 can, however, also be provided in the material of the second element 4 or of the further element or elements 16. It has proven particularly expedient if the scattering centers are arranged on the surface of the first element or the second element (at 17 '). In the embodiment of FIG. 7, further elements 16 are also provided between the first element 2 and the second element 4, but here they have the shape of rings 16 that contain scattering centers 17. Between these rings, spaces 18 are formed in which a gas, in particular air, can be located. The light scattered into the first element 2 by the scattering centers 17 is particularly effectively reflected on the wall in the region of these gas spaces 18.

Claims

Integrating receiving device for laser radiation

1. Integrating receiving device for laser radiation with a detector, characterized in that it has an elongated rod-shaped first element made of a first material and a surrounding tubular second element made of a second material that the first and the second material for the laser radiation to be received transmissive is that the first material has a larger refractive index than the second, and that a detector for the laser radiation is attached to an end face of the rod-shaped first element.

2. Receiving device according to claim 1, characterized in that it has at least one further tubular element (16), which is arranged between the first (2) and second (4) element, made of a further material which is transparent to the laser radiation to be received and whose refractive index is greater than that of the first and less than that of the second material.

3. Receiving device according to claim 1 or 2, characterized in that a mirror is attached to the other end face of the rod-shaped first element.

4. Receiving device according to one of claims 1 to 3, characterized in that a further detector for the laser radiation is attached to the other end face of the rod-shaped first element.

5. Receiving device according to one of claims 1 to 4, characterized in that the elements (2, 4, 15) are flexible.

6. Receiving device according to one of claims 1 to 4, characterized in that the first element (2) is liquid and the second element (4) is flexible and tubular.

7. Receiving device according to claim 2 or 6, characterized in that the further element (15) or the further elements is or are flexible and tubular.

8. Receiving device according to one of claims 1 to 7, characterized in that the elements (2, 4, 15) are curved.

9. Receiving device according to one of claims 1 to 8, characterized in that the elements (2, 4, 15) are arranged or formed in a circular shape.

10. Receiving device according to one of claims 1 to 9, characterized in that the elements (2, 4, 15) have a circular or annular cross section.

11. Receiving device according to one of claims 1 to 10, characterized in that the surface of the first element (2) has roughened areas which alternate with smooth surface areas.

12. Receiving device according to one of claims 1 to 11, characterized in that the surface of the first element (2) is profiled.

13. Receiving device according to one of claims 1 to 12, characterized in that a surface of the second element (4) is roughened.

14. Receiving device according to one of claims 1 to 13, characterized in that a surface of the second element (4) is profiled.

15. Receiving device according to one of claims 1 to 14, characterized in that a surface of a further element (15) is roughened.

16. Receiving device according to one of claims 1 to 15, characterized in that a surface of a further element (15) is profiled.

17. Receiving device according to one of claims 1 to 16, characterized in that the material has at least one of the elements (2, 4, 15) scattering centers (17, 17 ') for the laser radiation.

18. Receiving device according to claim 17, characterized in that the centers (17, 17 ') are formed by dyes, in particular dyes for dye lasers, or by fluorinating, luminescent or phosphorescent centers.

19. Receiving device according to claim 17, characterized in that the scattering centers (17, 17 ') are formed by glass powder beads, in particular microspheres.

20. Receiving device according to claim 17, characterized in that the scattering centers (17, 17 ') are formed by diamond powder.

21. Receiving device according to claim 6, characterized in that the liquid material of the first element (2) is a transparent chemical substance of oily or gel-like consistency without OH bands, in particular hexachloro-1,3-butadiene.

22. Receiving device according to claim 6 or 21, characterized in that scattering centers (17, 17 ') are arranged in the liquid material of the first element (2).

23. Receiving device according to one of claims 17 to 19 or 22, characterized in that the scattering centers (17 ') are arranged on the surface or in the vicinity of the surface of the first element (2), e.g. are embedded with a low refractive index adhesive.

24. Receiving device according to one of claims 1 to 23, characterized in that between the first element (2) and an outer, the first element (2) surrounding further element (4, 15) at the points at which this element between scattering centers or rough surface areas on its surface has smooth surface areas, a material with a refractive index is provided which is smaller than that of the elements (2, 4, 15).

25. Receiving device according to claim 24, characterized in that the material with a smaller refractive index is a gas.

26. Receiving device according to one of claims 1 to 25, characterized in that the further elements (4, 15) consist of a transparent plastic, whose refractive index n is less than 1.45.

27. Receiving device according to one of claims 1 to 26, characterized in that it comprises several units constructed from elements (2, 4, 15) and detectors / mirrors (6, 9).