Optical: systems and elements – Diffraction – From grating
Patent
1991-03-18
1993-04-13
Arnold, Bruce Y.
Optical: systems and elements
Diffraction
From grating
359572, G02B 2744
Patent
active
052027945
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an attenuator for a laser beam of a high-power laser comprising a diffraction element which in an attenuating position extends in an area oriented transversely to a beam direction of the laser beam and is irradiated by the laser beam.
It is known from U.S. Pat. No. 4,561,721 to attenuate a laser beam by introducing diffraction elements into the latter and aligning these such that the diffracted laser radiation propagating in the beam direction exhibits a considerably lower intensity than the original laser radiation in order to then determine this by a measuring technique.
Such an attenuator has the disadvantage that the laser beam of a high-power laser heats the diffraction element up so strongly that additional cooling measures, for example, in the form of air cooling, have to be taken, but, in many cases, these are insufficient to protect the diffraction element against thermal destruction owing to excessive heating-up by the laser beam.
The object underlying the invention is, therefore, to so improve an attenuator of the generic kind that it will also withstand the laser beams of high-power lasers.
This object is accomplished in accordance with the invention with an attenuator of the kind described at the beginning by the diffraction element extending beyond the laser beam in the direction transverse to the beam direction so only a partial region of the diffraction element is irradiated by the laser beam and by the diffraction element being continuously moveable in this direction by a drive such that the laser beam irradiates constantly changing partial regions of the diffraction element.
The advantage of the inventive solution lies in the fact that owing to the irradiated partial regions constantly changing, the partial regions which are not irradiated have an opportunity to cool down, thereby avoiding heating-up, and so one can work at the power customary for high-power lasers without additional cooling. It is, at any rate, ensured that with additional cooling, the diffraction element will also withstand the substantially higher power of future high-power lasers.
It is particularly advantageous within the scope of the present invention for the movement of the diffraction element to take place periodically so the individual partial regions that are irradiated change constantly with respect to time, which results in a uniform, mean thermal load on the partial regions.
In a particularly preferred embodiment of the inventive solution, provision is made for the diffraction element to be rotatable about an axis arranged beside the laser beam and to be made to rotate by the drive, and for the partial regions that are alternately irradiated by the laser beam to lie in a ring which is coaxial with the axis. This embodiment of the inventive solution is particularly advantageous because it is thus made possible in a very simple way for all of the partial regions to be irradiated on average with the same thermal power and, in addition, to have on average the same time for cooling down again.
An embodiment of the inventive solution has proven particularly advantageous wherein the diffraction element is moveable from an ineffective position into the attenuating position and so, in particular, where there are several diffraction elements, a different number of diffraction elements can be selectively moved into the laser beam. Structurally, the simplest way to implement this is for the diffraction element to be held on a pivot arm.
To simultaneously enable the diffraction element to be driven in a simple way, it is expedient for the drive to be held on the pivot arm so there is no need for a complicated transmission of the drive onto the diffraction element held on the pivot arm.
The simplest way to implement the drive for rotating the diffraction element is for the diffraction element to be seated on a motor shaft of a motor acting as drive.
The simplest possibility of designing the diffraction element is that of the diffraction element having the shape of a circular disc as, in this case,
REFERENCES:
patent: 4167666 (1979-09-01), Miller et al.
patent: 4560252 (1985-12-01), Mori
patent: 4561721 (1985-12-01), Keilmann et al.
Hall Thomas
Schnee Peter
Arnold Bruce Y.
Deutsche Forschungsanstalt fuer Luft - und Raumfahrt e.V.
Lipsitz Barry R.
Ryan J. P.
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