Coherent light generators – Particular pumping means – Electrical
Reexamination Certificate
2000-12-07
2003-03-25
Leung, Quyen (Department: 2828)
Coherent light generators
Particular pumping means
Electrical
C372S087000, C372S055000, C372S031000
Reexamination Certificate
active
06539045
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a laser with a housing such as at least one laser tube for a laser gas or a mixture of laser gases, with an electrode arrangement that comprises at least two electrodes, with a voltage supply unit by means of which a voltage can be fed to electrodes of the electrode arrangement in such a way that a discharge area forms in the laser gas or laser gas mixture, in which the laser gas or laser gas mixture is excited, and with a system for modifying the distribution of the intensity of the laser light over the laser beam cross-section (mode).
Lasers with a housing, an electrode arrangement and a voltage supply unit of the type described above are described in U.S. Pat. No. 4,757,511, for example. From this publication—which is moreover expressly referred to for explaining all details not described more thoroughly here—lasers are known in which the laser gas is a mixture of a laser-active gases—particularly CO or CO
2
—and a few other components, e.g. N
2
and helium. Such lasers are used, among other things, for the processing—i.e., cutting or welding—of workpieces. In this connection, the voltage fed to the electrodes of the electrode arrangement can be a direct or alternating voltage. A high-frequency alternating voltage (HF voltage) is preferred. In the process, the electrodes of the electrode arrangement can be arranged on or in the housing.
In the case of the types of lasers described in U.S. Pat. No. 4,757,511, individual electrode pairs are twisted against each other in order to obtain—“integrated” over the length of the laser—as uniform a discharge as possible.
When processing workpieces, factors that play a role are, principally the output of the laser and the beam diameter, which depend on the geometry of the laser tube and the electrode arrangement and on the respective output, and the distribution of the intensity of the laser light over the cross-section of the unfocussed laser beam (also referred to as “mode”). The width of a cutting clearance, or kerf or of a welding seam, is determined by the beam diameter and the aforementioned intensity distribution. The thickness of material able to be cut as well as the attainable cutting speed are likewise dependent upon the two aforementioned parameters. Furthermore, beam diameter and mode are decisive for the thermal load of the optic elements used for beam shaping and beam guidance.
A laser beam with a high intensity maximum in the middle, from which the intensity decreases all around (also referred to as “Gauss mode”), can very well be focused on a small spot, thus resulting in a very high energy density. High cutting speeds can thereby be achieved. In addition, very narrow cutting clearances are obtained, which is desirable when cutting thin metal sheets. On the other hand, however, with the Gaussian mode the optic elements used for beam formation and beam guidance are under considerable thermal load precisely at high outputs due to the intensity maximum.
When cutting thick metal sheets, more than a high laser output is necessary. In addition, a certain minimum width of the cutting gap or kerf is desirable for blowing out the slag. These requirements can be best fulfilled by a laser beam in which the intensity maximum of the unfocused beam is situated not in the middle but rather at the periphery (so-called “ring mode”). In the case of the ring mode, even at high laser outputs, the optic elements of the concerned laser are less burdened than with the Gaussian mode because the energy density is lower.
In welding, the required laser output is likewise quite high, while the demands on the laser beam's ability to focus are comparably slight because no cutting clearance needs to be produced. In welding, the work is also typically done with a laser beam that has no pronounced intensity maximum in the middle. On the other hand, with other processing a nearly rectangular intensity distribution (so-called “flat top mode”) can be useful.
Under the circumstances described in the preceding discussion, it is particularly advantageous if the distribution of the intensity of the laser light over the cross-section of the unfocused laser beam, i.e. the mode, can be adapted to the processing method carried out in each case.
With most currently known lasers, the mode is determined by the unalterable geometry of the laser tube, the arrangement of the electrodes and the mirrors, by the feed of energy and the properties of the lasing gas. Practically speaking, this predetermined mode cannot be influenced by the laser user. Setting the distribution of the intensity of the laser light over the cross-section of the laser beam to adapt to the respective case of application is not easily possible.
For this reason, it was attempted in the past to achieve an adaptation of the laser mode to the respective processing case by replacing essential components or entire laser systems or machines (cutting lasers—welding lasers). This method of procedure requires not only high investment costs but also makes a quick retooling for different processing methods impossible.
A laser of the kind indicated hereinbefore, i.e. a laser with a system for modifying the distribution of the intensity of the laser light over the laser beam cross-section, is known from German Patent No. 44 01 597. However, this publication leaves unresolved the question of what technical measures are used to bring about the modification of the mode.
It is an object of the present invention is to provide a novel laser of the kind hereinbefore described which permits facile modification of the distribution of the intensity of the laser light over the laser beam cross-section, i.e., a modification of the mode, to adapt the intensity distribution or mode to the desired application with low structural/equipment expenditure.
Another object is to provide such an adjustable laser with relatively low additional cost and relatively little additional components.
SUMMARY OF THE INVENTION
It has now been found that this technical problem may be solved according to the present invention by incorporating in a gas laser a system for modifying the mode which comprises means for adjusting the amplification profile of the laser over the excitation cross-section of the housing for the laser gas or the laser gas mixture. The excitation cross-section in the aforementioned sense refers to a cross-section perpendicular to the laser beam propagation direction, in which the excitation of the laser gas or laser gas mixture takes place. There is a different amplification in each point of an excitation cross-section. The spatial distribution of these amplification points is referred to as the amplification profile which is in turn decisive for the mode being set. In that the present invention applies to mode modification on the amplification profile of a laser, it differs from “mode diaphragms” of the known kind, for example. Such mode diaphragms are aperture diaphragms used to bring about a damping of modes that were first set. As will be described in detail below, the mode can be set according to the invention by means of systems that are present on lasers anyway or that can be provided in such lasers without great expense.
In one embodiment the amplification profile of the laser may be adjusted over the excitation cross-section of the housing for the laser gas or the laser gas mixture by including a device by means of which the excitation potential fed by the electrodes into the laser gas or the laser gas mixture is able to be modified. By setting the supplied excitation potential at relatively high values, the light amplification in the area of the beam axis can be minimized. The result is then a ring mode. This is conveniently effected by varying the amplitude of the HF voltage fed to the electrodes or by modifying the keying into of the pulsing excitation.
Generally, the excitation potential fed into the laser gas is variable from
0
to KW and ever higher. In one embodiment, several predetermined or fixed values or ranges for the excitation potential can be
Ackermann Frank
Borstel Michael Von
Geschwandner Mark
Leung Quyen
Pepe & Hazard LLP
Trumpf Lasertechnik GmbH
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