GB2284681A - Optical apparatus for stabilising a laser beam - Google Patents

Abstract

Apparatus for stabilising a laser beam comprises a first lens 2 for focusing a laser beam onto optical means 4 which may be in the form of a block of glass or a prism. The block of glass or prism may be gimbal mounted and is stationary throughout the frequencies of interest in a frame of reference, in relation to which the apparatus is moving. The beam that is outputted from the optical means 4 is passed to a further lens 6 which performs the dual function of magnifying the displacement caused by any movement of the optical means 4 and also provides a reversal of the displacement, such that the output of the beam will be displaced by the correct angle in the correct direction. Then a further lens 8 focuses the beam onto a target. As an alternative to the optical means being gimbal mounted, a disk of glass may be used which is spun at high speed. In an alternative embodiment as applied to optical rotating joints, the optical means 4 may be mounted on a rotor, and the lenses 2, 4 and 8 may be mounted on a stator 12, or vice versa. <IMAGE>

Description

APPARATUS FOR STABILISING A LASER BEAM The present invention relates to apparatus for stabilising a laser beam.

The invention relates to a problem encountered when using a laser beam as a projector screen pointer. When the laser is hand-held, its beam tends to wander uncontrollably, due to handshake, which can be very annoying to those who are watching the presentation.

The aim of the invention is to provide apparatus which significantly reduces hand-shake and in some circumstances eliminates it.

The invention can also be applied to the stabilisation of images as, for example, in the shaking of an optical system as attached to a moving platform.

According to the present invention there is provided apparatus for stabilising a laser beam comprising a first lens for receiving and focusing a laser beam, means mounted in such manner that said means remains stationary for vibration frequencies of interest in a frame of reference, in relation to which the apparatus is moving, a second lens for magnifying and reversing any displacement of the beam received from the prism, and a third lens for projecting the beam to a target.

According to an aspect of the present invention, said means is in the form of a block of glass or a prism which is gimbal mounted.

According to a further aspect of the present invention, said means may form a disk of glass arranged to be spun at high speed.

According to still a further aspect of the present invention, a balancing chromatic abberation system may be included in the lens system.

According to yet another aspect of the present invention, said means may be mounted on a rotor and said first, second and third lens may be mounted on a stator or vice versa.

Various embodiments of the present invention will now be described with reference to the accompanying drawings, wherein, FIGURE 1 shows a block diagram of apparatus for stabilising a laser beam, and, FIGURE 2 shows a diagram relating to an alternative embodiment of the invention for stabilising an optical path through a rotating boundary.

Referring to Figure 1, the apparatus uses a visible semiconductor laser, with a collimated beam, which is focused by a singlet lens 2. This focused beam passes through a block of glass or prism 4 that is arranged in a gimbal or other mount, such that for vibration frequencies of interest the block remains stationary in the frame of reference in relation to which the optics is moving.

The effect of this block of glass is to displace the beam by an amount determined (amongst others) by the tilt of the glass block.

The focused beam is relayed to another image point by the relay lens 6 which in this case is a Steinheil Triplet. This lens performs the dual function of magnifying the displacement caused by the movement of the glass block and providing a reversal of the displacement, such that the output beam will be displaced by the correct angle and in the correct direction so that the beam remains fixed on the target under movement of the laser source and associated optics. The final image is projected to the target by a third lens 8, which may be a singlet lens. The powers of the lens and the thickness of the glass block are such that any vibration in the holding unit will be nulled by the optics such that the laser beam will remain on target for variations of positions, due to hand-shake.

As an alternative to the gimbal mounted block of glass, a disk of glass could be used that is spun at high speed so that the optical path 'sees' a plain parallel block of glass. This spinning has the effect of turning the glass disk into a gyroscope and thus the glass disk will remain steady under any movement. Therefore, any vibration of the optical system, e.g. hand-shake, will be removed.

This apparatus could also be used for image stabilisation, e.g.

binoculars, and other systems using an optical system being used on a moving platform. In this case it will be necessary to compensate for the chromatic dispersion that will be introduced by the prism. This can be accomplished by introducing balancing chromatic aberration into the lens system.

Referring to Figure 2, a variant of the invention is shown that can be used to stabilise the optical path through a rotating boundary. The components operate in the same way as before, and bear the same reference numeral to Figure 1, except that the prism is attached to the stator 12, or rotor 10, and the rest of the optics are attached to the rotor 10, or stator 12. This is of use for example for the optical rotating joint (ORJ) as described in copending patent application numbers GB 2250652A and GB 2271034A, where the use of very high precision bearings for the mechanical rotary joint are required. As can be seen from the ORJ patent, it is important for the angular deviation between the two planes, upon which the two halves of the optics are mounted, is very small. This is required to ensure the accurate mapping of the source onto the corresponding receiver optics. One way to accomplish this is to use highly accurate bearings, which are very expensive and will wear with use. These limitations can be overcome by using the techniques of this patent application for the compensation of the angular deviation between the two planes. This allows the use of cheaper bearings and can compensate for bearing wear.

Claims (7)

1. Apparatus for stabilising a laser beam comprises a first lens for receiving and focusing a laser beam, means mounted in such manner that said means remains stationary for vibration frequencies of interest in a frame of reference, in relation to which the apparatus is moving, a second lens for magnifying and reversing any displacement of the beam received from the prism, and a third lens for projecting the beam to a target.

2. Apparatus as claimed in Claim 1, wherein said means is a block or glass or prism and is gimbal mounted.

3. Apparatus as claimed in Claim 1, wherein said means is a disk of glass arranged to be spun at high speed.

4. Apparatus as claimed in any preceding claim including a balancing chromatic abberation system in the lens system.

5. Apparatus as claimed in any preceding claim, wherein said means is mounted on a rotor, and said first, second and third lenses are mounted on a stator or vice versa.

6. Apparatus as claimed in Claim 5, wherein said apparatus forms part of an optical rotating joint.

7. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.