GB2275543A

GB2275543A - Laser beam alignment device

Info

Publication number: GB2275543A
Application number: GB9221818A
Authority: GB
Inventors: Timothy Hamish Holloway; Trevor William Spencer
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1992-10-16
Filing date: 1992-10-16
Publication date: 1994-08-31
Also published as: GB9221818D0

Abstract

A laser beam alignment device 10 incorporates a laser 12, a sighting tube 16 and adjustable mirrors 24, 26 for directing a laser beam 22 through the sighting tube 16. The sighting tube 16 is axially aligned with a remote target (not shown). The path of the laser beam is then adjusted so that it is aligned with the sighting tube, and hence the laser beam is aligned with the target. Telescopic sight 28 is attached to the tube 16 but replaced by mirror 26 after alignment with the target. <IMAGE>

Description

LASER BEAM ALIGNMENT DEVICE This invention relates to a laser beam alignment device, and in particular to a device for aligning a laser beam with a distant target.

The alignment of laser beams over distances greater than 20 metres can often be difficult and time consuming. When a laser beam is to be aligned over distances greater than 1000 metres, it can take of the order of half a day to accomplish.

Laser beam alignment devices are known in the prior art. One known technique involves pointing the laser beam in the general direction of a target, observing where the beam strikes the target area, and then adjusting the axis of the beam to centre it at a desired target position.

However, this technique has several disadvantages. If the beam is being aligned over a large distance, the initial alignment error can be considerable. The beam may miss the target completely and be difficult to locate in the target area. It is potentially hazardous to unprotected personnel to have high power laser beams pointing in unknown directions.

Furthermore, the alignment procedure is time consuming.

It is an object of this invention to provide an alternative form of laser beam alignment device.

The present invention provides a laser beam alignment device including sighting means arranged to be alignable with a target and a laser light source having in operation a laser beam arranged to be alignable with the sighting means.

The invention provides the advantage that it is a means for aligning a laser beam making possible laser beam alignment in successive stages, each of which can be performed to a high degree of precision.

In one preferred embodiment, the sighting means is a sighting tube having two ends, a narrow aperture being located at one end and a reticle at the other. The sighting tube may then be used both for sighting a target and aligning the laser beam. Alternatively, a telescopic sight may be incorporated into the sighting means for alignment with distant targets.

Conveniently, the invention may include reflecting means to deflect the laser beam through the sighting means. This has the advantage that the laser beam alignment device may be made compact.

According to the present invention there is provided a method of aligning a laser beam on to a target comprising the steps of: (1) aligning sighting means with a target, and (2) aligning the laser beam with the sighting means.

The method of the invention provides the advantage that alignment of a laser beam is carried out in simple steps. allowing rapid and accurate alignment of the beam on to a target. Furthermore, the method of the invention reduces the risk of stray laser beams causing injury or damage.

Conveniently the method may be adapted for alignment with distant targets by the use of a telescopic sight. The method may also be adapted to use lasers producing light in the visible spectrum and lasers producing light in the non-visible spectrum by the use of a video camera for monitoring the laser beam.

In order that the invention might be more fully understood, examples thereof will now be described, by way of example only, with reference to the accompanying drawings. in which: Figure 1 is a schematic plan view of a laser beam alignment device of the invention; and Figure 2 is a schematic plan view of a telescopic sight mounted on the device of Figure 1.

Referring to the drawing, there is shown a schematic plan view of a laser beam alignment device of the invention indicated generally by 10. It comprises an argon ion laser light source 12 mounted on a rigid plate 14.

The plate 14 incorporates a hole 15 for mounting the device 10 on a commercially available tripod (not shown). Also mounted on the plate 14 is a sighting tube 16, which has a median axis 17. A first end 16A of the tube 16 has a removable reticle 18 connected to it. The reticle 18 incorporates cross-wires 19. A second tube end 16B has an end piece 20 with a narrow aperture 21 connected to it. The aperture has a diameter of 3 mm which corresponds to the diameter of the human eye pupil.

The laser light source 12 emits a beam of light 22. Two adjustable mirrors 24, 26 are mounted on the plate 14 so that the beam of light 22 emanating from the laser 12 is reflected from the mirror 24 to the mirror 26 and thence towards the sighting tube 16 through the aperture 21. The mirror 24 is permanently mounted on to the plate 14 and the mirror 26 is removable. The beam 22 is reflected through two successive angles of approximately 90" at the mirrors 24 and 26, which consequently define a doubly folded light path. This doubly folded light path has the advantage that it allows the use of mirrors with only one degree of freedom of rotation. One of the mirrors 24 and 26 is adjustable about a vertical axis of rotation and the second mirror is adjustable about a horizontal axis of rotation.

In Figure 2, there is shown a telescopic sight 28 attached to the sighting tube 16. The sight 28 has an optical axis 30, which is coaxial with the median axis 17 of the sighting tube 16.

The laser beam alignment device is operated as follows. The mirror 26 is removed from the plate 14. The sighting tube 16 is then aligned with a target (not shown) by eye; an operator looks through the aperture 21, and adjusts the axis 17 of the sighting tube 16 until the cross-wires 19 are centred on the target. This adjustment is achieved by manipulating the orientation of the plate 14 by means of controls on the tripod.

Once the sighting tube 16 has been aligned with the target, mirror 26 is replaced. Mirrors 24 and 26 are then adjusted so that the light beam 22 from the laser 12 passes through the aperture 21 on to the centre of the cross-wires 19, thus aligning the beam 22 with the axis 17. This is indicated by the formation of a shadow image of the cross on a card (not shown) held up in front of the reticle 18 by the operator. Once the laser beam 22 is aligned with the cross-wires, the reticle 18 is removed.

This leaves the laser beam 22 approximately lined up with the target.

Subsequent fine adjustment of the beam 22 can be made by observing where it strikes the target.

Using an aperture diameter of 3 mm and a sighting tube length of 1 m with cross-wires of diameter 0.5 mm, the maximum angle of error in aligning the sighting tube is 3.5 mrad, and in practice a better accuracy than this may be obtained.

For situations where it is not convenient to mount the plate 14 on an attitude controllable tripod, the sighting tube 16 is mounted on adjustable supports (not shown) which allow movement of the tube axis 17 in angle of elevation and azimuth.

For the alignment of the laser beam with distant targets where the above procedure does not give sufficient accuracy, due to inaccuracy in the initial alignment of the sighting tube, a telescopic sight is used. The end piece 20 is removed from the tube 16 and replaced by a telescopic sight 28. The tube 16 is threaded for attachment of the telescopic sight 28 so that the optical axis 30 and the tube axis 17 are coaxial. The sighting tube alignment process is performed as before except that the target is sighted through the telescopic sight 28 and a virtual image of the target is aligned with reference markings in the sight. The telescopic sight is subsequently removed and the end piece 20 replaced prior to aligning the laser beam 22 with the tube 16.

It is possible to attach the telescopic sight 28 on to the side of the sighting tube 16 so that the optical axis 30 is simply parallel with the axis 17. Optimally the means of attachment includes a means of adjustment allowing the optical axis 30 to be zeroed to the axis 17.

This zeroing is achieved by aligning the laser beam with a target as before without the telescopic sight, then adjusting the telescopic sight axis until the target is sighted. If the sight is fitted in this manner, its removal to align the laser beam with the sighting tube is unnecessary.

The procedure described above is applicable to other types of laser producing radiation in the visible part of the spectrum, for example a helium neon laser. For lasers producing non-visible radiation, the alignment procedure of the laser beam 22 on to the cross-wires of reticle 18 is modified. For example, a video camera (not shown), which operates in the requisite wavelength band, may be placed in front of the reticle 18 and used to observe when the laser beam is aligned with the centre of the cross-wires 19.

If a tripod is used to adjust the orientation of the sighting tube with respect to the target, the laser beam may be aligned with the sighting tube in a controlled area, prior to the use of the device in the field.

This reduces the danger of causing injury to unprotected personnel by stray laser beams.

Claims

1. A laser beam alignment device including sighting means arranged to be alignable with a target and a laser light source having in operation a laser beam arranged to be alignable with the sighting means.

2. A laser beam alignment device according to Claim 1 including reflecting means arranged for alignment of the laser beam with the sighting means.

3. A laser beam alignment device according to Claim 2 wherein the reflecting means comprises two mirrors defining a doubly folded light path, at least one of the mirrors being movable relative to the laser beam.

4. A laser beam alignment device according to any preceding claim wherein the sighting means comprises a sighting tube having an aperture at a first end and a removable reticle with reference markings at a second end.

5. A laser beam alignment device according to Claim 1, 2 or 3 wherein the sighting means includes a telescopic sight attached to a sighting tube.

6. A laser beam alignment device according to Claim 5 wherein the telescopic sight is attached to one end of the sighting tube.

7. A laser beam alignment device according to Claim 5 wherein the telescopic sight is attached to one side of the sighting tube.

8. A method of aligning a laser beam with a target comprising the steps of: (1) aligning sighting means with a target, and (2) aligning the laser beam with the sighting means.

9. A method of aligning a laser beam according to Claim 8 wherein step (1) is achieved by an operator looking through an aperture and aligning markings of a reticle with a target.

10. A method of aligning a laser beam according to Claim 8 wherein step (1) is achieved by an operator aligning a virtual image of a target in a telescopic sight with reference markings in the sight.

11. A method of aligning a laser beam according to Claim 8 wherein step (2) is achieved by an operator adjusting a series of mirrors.

12. A method of aligning a laser beam according to Claim 8 wherein step (2) is achieved by an operator using an imaging means to monitor the position of the laser beam relative to the sighting means.

13. A laser beam alignment device as substantially as herein described with reference to, and illustrated in, the accompanying drawings.

14. A method of aligning a laser beam as substantially as herein described with reference to the accompanying drawings.