Coherent light generators – Particular beam control device
Reexamination Certificate
1999-02-16
2001-11-27
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Particular beam control device
C372S008000
Reexamination Certificate
active
06324190
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention has to do with an arrangement for geometric reshaping of a radiation field, especially a radiation field of a diode laser array. This field propagates in a z-direction. It has a radiation cross section, which in one direction defined as the x-direction, runs perpendicular to the z-direction, a direction which is perpendicular to it, defined as the y-direction, exhibiting a greater propagation with lower beam quality. In this case, x, y and z form a rectangular (Cartesian) coordinate system, whereby the radiation is or will be grouped into radiation components in the x-direction. The radiation components, in relation to their beam cross sections, are reoriented. This arrangement includes at least two reflectors.
Such an arrangement is generally known.
There are several areas in such arrangements as are presented above are applied. Among other things, they include geometric reshaping of diode laser outputs, in order to build up defined radiation fields. Additionally, the applications include reshaping of a rectangular radiation field of a laser with an amplification medium having such shapes as slabs or rods. This is done in order to homogenize the beam quality over the cross section of the beam, and to adapt it to specific applications.
High-performance diode laser arrays or field arrangements typically have active media with a cross section of 1 &mgr;m×10 mm. Because of this, the diode laser radiation is characterized, among other things, by a typically elliptical beam cross section and a large divergence angle in the fast relatively small divergence in the slow direction (parallel to the PN transition).
Such a diode laser array with a beam cross section of 1 &mgr;m ×10 mm possesses extremely varied beam qualities in the two directions parallel and perpendicular to the PN transition. The beam quality in the fast direction is diffraction limited, an ca. 1000 to 2000 times as diffraction limited in the slow direction. For this reason, radiation emitted from a diode laser array cannot be focused by cylindrical and spherical lenses onto a small and circular spot. For this reason, applications of high-performance diode lasers to individual areas are limited, where only small intensities per surface unit are necessary. Expansion of applications to areas such as medical technology and materials processing, fiber coupling and end-on pumping of solid state lasers and fiber lasers, require that the beam quality be homogenized in both directions.
SUMMARY OF THE INVENTION
Proceeding from the previously indicated state of the art and the problem described above that is posed when using diode laser radiation, the objective of the present invention is to configure an arrangement of the type described above so that the beam quality perpendicular to the propagation direction is homogeneous.
The objective is achieved by an arrangement with the features indicated at the outset. Each reflector exhibits a pair of reflection surfaces, which are approximately 90° or exactly 90° to each other. This opening angle is directed against the propagation direction. Its line of intersection is oriented approximately at 45° to the x-direction.
With such an arrangement, the radiation field of diode laser arrays can be grouped by projecting individual emitter groups. The radiation field is directed at the arrangement with at least two reflectors. Each of the individual reflection surfaces is oriented in paired fashion at 90° to the other, and the radiation is guided at 45° onto the mirror surfaces. Therefore, each part of the radiation is double-reflected in each instance on the reflection surfaces assigned in pairs, and is rotated by a defined angle, preferably 90°. By this means, the beam components or groups are oriented in a direction perpendicular to the original grouping. In other words, the groups which initially were grouped in the X-direction, now stand above the other as individual sections in the y-direction after the double refection at the pair of reflection surface of the reflectors. Thus, the individual radiation components are geometrically reshaped and reoriented. This permits the beam quality to be homogenized over the cross section. The line of intersection of the two reflection surfaces, forming a pair, of each reflector, can be oriented at an angle not equal to 90° to the z-direction, so that no polarization beam splitter is needed.
In another preferred embodiment of the arrangement, the intersection line of a pair of reflection surfaces assigned to each other of a reflector is oriented at a 90° angle to the z-direction. Seen in the beam propagation direction, the radiation first impinges on a polarization splitter. After retroflection by the pair of reflection surfaces, it is brought back with a rotated polarization direction to the polarization splitter and is there decoupled.
Several reflectors can be fitted to each other for reshaping the radiation of a radiation field. A continuing w-shaped arrangement of reflection surfaces is thus produced. The reflection surfaces are oriented to each other alternately at an angle of 90° . The radiation components of the radiation field which inking on such an arrangement are grouped via the intersection lines of the immediately adjacent reflection surfaces of each two adjacent pairs of reflection surfaces.
It is obvious that the radiation field which is reoriented by the invention-specific arrangement can be composed from the radiation components of several radiation sources. The individual radiation sources or radiation components are then projected onto each pair of surfaces for grouping by means of a projection lens. This is done in such a way that then a pair of reflection surfaces is assigned to each radiation component. At the mirror surfaces of a pair of reflection surfaces, the radiation is subjected to double reflection. Each radiation component is rotated, in order of turn this radiation component in its position in relation to a plane of observation on the starting side of the second reflection surface, i.e., after the second reflection.
With the preferred embodiments, the individual radiation and beam components have large divergence angles. This is advantageous, for a lens is assigned to each of the radiation components reflected by a pair of reflection surfaces. This lens enlarges the dimension of the beam cross section in the y-direction or the direction of higher beam quality, and reduces the divergence angle in this direction.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
REFERENCES:
patent: 5592333 (1997-01-01), Lewis
Du Keming
Loosen Peter
Fraunhofer-Gesellschaft zur Foerderung der Angewandten Forschung
Jr. Leon Scott
Milde Hoffberg & Macklin, LLP
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