Coherent light generators – Particular resonant cavity – Folded cavity
Patent
1989-08-21
1990-12-11
Epps, Georgia
Coherent light generators
Particular resonant cavity
Folded cavity
372 92, 372 94, 372102, 372106, 372107, 372108, A01S 3081
Patent
active
049775740
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-output power laser oscillator for use in a laser cutting machine for cutting metals or non-metals. More particularly, the invention relates to a laser oscillator which generates a circularly polarized laser beam.
2. Description of the Related Art
It is known in the art that, when cutting with a laser beam, a circularly polarized beam is preferable, and conventionally, to provide the circularly polarized beam, a linearly polarized beam generated directly from a laser oscillator is converted to a circularly polarized beam with the use of an external optical unit.
Such a conventional arrangement is shown in FIG. 9, in which only the optical unit is illustrated and conventionally known laser exciting components, such as a discharge tube, are omitted. The arrangement of FIG. 9 includes a rear mirror 1, folding mirrors 2 and 3, and an output-coupling mirror 4, all of which constitute a laser resonator. A laser beam 9 from the resonator exhibits a linear polarization having an electric vector direction orthogonal to a plane determined by three optical axes 7a, 7b and 7c. In FIG. 9, this plane is rotated by .pi./4 about the optical axis 7a. The beam 9 from the resonator has a linear polarization and a polarization direction thereof is inclined by .pi./4 with respect to a horizontal plane. This beam 9 is reflected by phase retarders 5 and 6, whereby the beam 9 is given a circular polarization.
The above-described conventional arrangement is disadvantageous in the following respects.
First, a large number of optical elements are required, which increases cost. Secondly, the system is large in size and is complicated. Finally the arrangement of the external optical system must be as precise as that of the laser resonator. In any other case, the directional stability of the laser beam will be lowered, and accordingly, the cutting characteristics degraded.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to eliminate the above disadvantages of the conventional laser oscillator.
In order to attain the above and other objects, there is provided a laser oscillator for oscillating a laser beam, the oscillator comprising an output coupling mirror, at least one folding mirror operating as a whole as a phase retarder imposing a .pi./2 phase delay with respect to parallel and perpendicular polarization components of the laser beam, and a rear mirror having a maximum reflectivity with respect to a linear polarization component of the laser beam, the linear polarization component having an E vector whose direction is rotated from an incident plane of the nearest one of the folding mirror by the .pi./4 phase.
The rear mirror ensures the maximum reflectivity of the above mentioned linear polarization component, so that the linear polarization is obtained in the optical path between the rear mirror and the nearest folding mirror. This folding mirror or mirrors serve as a phase retarder as a whole and imposes a phase delay of .pi./2 so that the resultant beam has a circular polarization.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing an arrangement of a laser oscillator according to a first embodiment of the present invention;
FIG. 2 is a schematic perspective view showing a rear mirror employed in the first embodiment;
FIG. 3 is a vertical cross-sectional view showing a rear mirror provided with an array of deep grooves;
FIG. 4 is a vertical cross-sectional view showing a rear mirror provided with an array of shallow grooves;
FIG. 5 is an enlarged perspective view showing a single crystal copper mirror cut by a diamond lathe;
FIG. 6 is an enlarged perspective view showing a polycrystal copper mirror cut by a diamond lathe;
FIG. 7 is a schematic diagram showing an arrangement of a laser oscillator according to a second embodiment of the present invention;
FIG. 8 is a schematic diagram showing an arrangement of a laser oscillator according to a third embodiment of the present inventi
REFERENCES:
patent: 3496483 (1970-02-01), Max et al.
patent: 4084883 (1978-04-01), Eastman et al.
patent: 4340969 (1982-07-01), Hamilton et al.
patent: 4757514 (1988-07-01), Hoag
Epps Georgia
Fanuc Ltd.
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