GB2226132A

GB2226132A - Apparatus for detecting the position of a laser beam

Info

Publication number: GB2226132A
Application number: GB8925114A
Authority: GB
Inventors: Horst-Ulf Schottelius; Rolf Mosandl
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1988-11-30
Filing date: 1989-11-07
Publication date: 1990-06-20
Anticipated expiration: 2009-11-07
Also published as: FR2640775B1; FR2640775A1; GB2226132B; GB8925114D0; DE3840278C2; DE3840278A1

Description

1 APPARATUS FOR DETECTING THE POSITION OF A LASER BEAM The invention

relates to an apparatus f or detecting the displacement of a high-energy laser beam from a desired beam direction.

An arrangement for adjusting a laser beam at a target is described in DEOS 34 22 232. This works with a 2-axis tilting mirror. Provided in the beam path in front of this is a compensation mirror which compensates for distortions which the departing beam experiences an the way to the target as a result of atmospherically occasioned disturbances.

An object of the invention is to propose apparatus, of the type mentioned at the beginning hereof, with which the displacement or drift of a laser beam relative to a desired beam direction is evaluable.

In accordance with the invention there is provided apparatus for detecting the displacement of a laser beam from a desired beam direction characterised in that:- (a) an array of several thermoelements is provided 25 around the desired position of the laser beam, (b) the cross-sectional profile of the array corresponds to the cross-sectional profile of the laser beam, and 2 (c) the thermoelements are connected to a control circuit, which evaluates the different electrical states, e. g. voltages, of the thermoelements which arise upon displacement of the laser beam, passing through the array, from the desired beam position.

If the actual beam position (or axis) of the laser beam coincides with the desired beam direction, then all of the thermoelements are struck or affected equally little or are not struck or affected by the laser beam so that the electrical states of the thermoelements are the same. For example, where the thermoelements are thermocouples, the initial voltages, standing at the control circuit, from the thermoelements are identical. The control circuit indicates that the laser beam has not drifted away from or relative to the desired beam direction.

If the laser beam deviates from the desired beam direction, then at least one thermoelement is acted upon more strongly by the radiation energy of the laser beam than at least one of the others. This asymmetry of the radiation impingement results in correspondingly different electrical states, e.g. thermoelectric voltages. The control circuit evaluates this.

The -thermoelements preferably extend towards the centre of the desired beam position, and are preferably 0 k 3 1 equally distributed in said array.

Also time-dependent deformation of the crosssectional profile e.g. in shape or size, of the laser beam can be detected with the described arrangement, and a beam profile correction device may be provided, in the beam path and may be controlled by the apparatus.

For the adjustment of the direction of the laser beam to the desired beam direction, a 2-axis tilting mirror is preferably provided in the beam path in front of the array, and the control circuit preferably controls the 2-axis tilting mirror until the position of the laser beam relative to the array again coincides with the desired beam direction. In this way an automatic stabilisation of the laser beam to the desired bee=. direction is achieved.

Further advantageous developments of the invention, will become apparent from the following description of an. exemplified embodiment shown in the diacrammatic drawina in accompanying which the single FIGURE shows apparatus for adjusting a laser beam to a desire-cl direction represented by a beam arrow A.

A laser-beam source 1 is directed at a 2-axis tilting mú=or 2. in the beam path of the laser beam 3, connected subsequently to the tilting mirror 2 is a ring- 4 shaped array 4. This is so fastened that its centre Z is intersected by the desired beam axis A of the laser beam 3. The cross-sectional profile, perpendicular to the desired beam axis A, of the array 4 in the exemplified instance is, like the cross-sectional profile of the laser beam 3, circular.

The ring-shaped array 4 has several, for example eight, equidistantly spaced thermoelements 5, which are of plate-shaped form and stand radially to the array 4. The thermoelements 5 are thermocouple devices which generate electrical voltages which are dependent upon their temperatures.

The thermoelements 5 are connected to a converter such as an analogue to digital converter 6, which is connected to a control circuit 7, for example a microcomputer. The control circuit 7 controls an adjusting unit 8, which is connected to the tilting mirror 2. Moreover, a recording instrument 9, for example a plotter, can be connected to the control circuit 7.

The mode of operation of the described apparatus is generally as follows:

So long as the axis of the laser beam 3 coincides with the desired beam axis A, the thermoelements 5 are 4 scarcely, but at least uniformly, heated by the laser beam 3. Accordingly from all the thermoelements 5 the same voltages occur at the control circuit 7. The adjusting member 8 and thus the tilting mirror 2 are not 5 adjusted.

If the laser beam 3 deviates, for example in the xdirection, from the desired beam axis A, then it heats the right-hand thermoelements 5 more than the left-hand, upper and lower thermoelements 5. Accordingly different voltages occur at the control circuit 7 from the thermoelements 5. The control circuit 7 now controls the adjusting member 8 in such a way that the tilting mirror is adjusted until the axis of the laser beam 3 again coincides with the desired beam axis A.

The same applies to displacements of the laser beam in the other directions.

0 6 I_

Claims

Apparatus f or detecting the displacement of a laser beam from a desired beam direction characterised in 5 that: - (a) an array of several thermoelements is provided around the desired position of the laser beam, (b) the cross-sectional profile of the array corresponds to the crosssectional prof ile of the laser beam, and the thermoelements are connected to a control circuit, which evaluates the different electrical states, e. g. voltages, of the thermoelements which arise upon displacement of the laser beam, passing through the array, from the desired beam position.

(c)
2. Apparatus according to claim 1, characterised in that for the adjustment of the laser beam to the desired beam direction a 2-axis tilting mirror is provided in the beam path in front of the array, and in that the control circuit controls the 2-axis tilting mirror until the position of the laser beam again coincides with the desired beam direction.

2ES
3. Apparatus according to claim 1 or 2, characterised in that the thermoelements are fastened in the array to extend perpendicular to the cross-section of the array.

( a- 7
4. Apparatus according to claim 1,2 or 3, characterised in that the thermoelements are f astened in the array to extend towards the centre of said desired beam position.
5. Apparatus according to any one of the preceding claims, characterised in that eight or more thermoelements are provided in the array.
6. Apparatus according to any one of the preceding claims, characterised in that the thermoelements are equally or equidistantly distributed in the array.
7. Apparatus according to any preceding claim wherein said array is of circular ring form; wherein said laser beam is circular in cross-section, and wherein the thermoelements extend radially towards a desired beam axis A.
8. Apparatus for detecting the displacement of a high- energy-rich laser beam from a desired beam axis, characterised in that a ring-shaped arrangement of several thermoelements is provided concentrically to the desired beam axis (A), in that the cross-sectional profile of the ring-shaped arrangement corresponds to the cross-sectional profile of the laser beam and in that the thermoelements are connected to a control circuit, which evaluates the different voltages of the thermoelements which arise upon displacement of the laser beam, 8 kI conducted through the ring-shaped arrangement, from the desired beam axis (A).
9. Apparatus according to Claim 8, characterised in that for the adjustment of the laser beam to the desired beam axis (A) a 2-axis tilting mirror is provided in the beam path in front of the ring-shaped that the control circuit controls mirror until the axis of the laser
10 with the desired beam axis (A).

arrangement and in the 2-axis tilting beam acain coincides 10. Apparatus according to Claim 8 or 9, characterised in that the thermoelements are fastened to the ringshaped arrangement radially to the cross-section of the 15 arrangement.
11. Apparatus according to Claims 8,9 or 10, characterised in that eight or more thermoelements are provided on the ring-shaped arrangement.
12. Apparatus according to one of the preceding claims, characterised in that the thermoelements are e qually distributed on the ring-shaped arrangement.
13. Apparatus for detecting the displacement of a laser beam substantially as hereinbefore described with i-eference to the accompanying drawing.

PublistedI990atThe Patent Office, State House, 66171 High Holborn. LondonWClR4TP. Further copies maybe obtainedfroin The Patent Office. Sales Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex tecbxAques ltd. St Mary Cray, Kent. Con V87 14