Coherent light generators – Particular active media – Gas
Reexamination Certificate
1998-02-24
2001-04-10
Font, Frank G. (Department: 2875)
Coherent light generators
Particular active media
Gas
C372S023000, C372S055000, C372S057000, C372S087000, C372S095000
Reexamination Certificate
active
06215807
ABSTRACT:
FIELD OF INVENTION
This invention relates to a multiple beam laser system which is made coherent by combining and optically phase-locking multiple individual lasing medium outputs into a single coherent laser beam.
BACKGROUND OF INVENTION
Today's industrial manufacturing lines are far more complex and automated than they were only a few years ago. Quite often, hi-tech manufacturing techniques have replaced the more traditional methods previously used. An example of this is the growing use of lasers during component prototyping and high volume manufacturing. Components that were traditionally cut with dies or flame cutters are often made with production lasers.
When these production lasers are used to cut materials of considerable strength or thickness, such as plate steel, the energy level of the laser must be raised to provide the required cutting strength. Unfortunately, as the power level of these lasers increases, so does their size and their cooling requirements. High average power continuous wave (CW) or pulsed gas lasers (such as CO
2
) of the type used on product production or processing lines have traditionally been cooled by large forced convection cooling systems. As a result, these laser systems are very large in design and incorporate complex gas-transportation and heat-exchanging systems. In addition to being exceptionally large, these laser systems are very complex in design and incorporate many moving parts, which make these systems very costly to design and install. Besides the one-time cost associated with purchasing and installing these laser systems, they often require constant supervision and a high level of maintenance to keep them operating at peak efficiency. Because of these factors, high power continuous wave or pulsed gas lasers are often unsuitable for a number of applications where mobility, size, weight or freedom from frequent service and maintenance are prime considerations.
In response to this need for lightweight, high powered laser systems, slab laser systems were developed. Slab lasers generally incorporate two or more laser slabs (or plates) which are stacked on top of and spaced apart from each other to form gaps between the slabs. These gaps are filled with a lasing medium, forming a laser cavity, which is excited by applying energy to adjacent slabs to produce a laser beam. There are numerous benefits associated with slab lasers when compared to their pulsed or CW laser forced gas counterparts. Slab lasers are very simple in design, have no moving parts, require little maintenance, and are inexpensive to manufacture.
Concerning slab laser systems, it is well known that by decreasing the size of the gap between the individual slabs, the power output of the individual laser beam being generated between each slab increases. However, there are physical limitations as to how narrow this gap can be made. When the gap becomes too small, the laser beam interacts more intensely with the slabs, which results in the slabs becoming excessively hot. This heating of the slabs substantially reduces the output of the individual laser beams causing a substantial reduction in operating efficiency.
In order to increase the power output of a slab laser system, additional slabs can be stacked upon each other to form additional gaps and produce additional laser beams. These additional laser beams, through the use of mirrors or other reflective devices, can then be combined into a single beam.
However, there are problems associated with these multiple beam slab laser systems. While the numerous laser beams generated between the individual slabs of the slab laser system can be combined into a single output beam, the phase of each of the individual laser beams is not synchronized and, therefore, the single output beam will not be coherent. This can result in the individual laser beams destructively interfering with each other, substantially reducing the focussing ability and uniformity of the single output beam.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an improved coherent multiple beam laser system.
It is a further object of this invention to provide such a laser system which synchronizes the phase of the individual laser beam outputs, allowing these individual laser beams to be combined into a single coherent output beam.
It is a further object of this invention to provide such a laser system which incorporates no moving parts and greatly reduces the need for supervision and maintenance.
It is a further object of this invention to provide such a laser system which has reduced thermal control requirements, is compact in design and may be coupled into a high power fiber optic beam delivery system.
It is a further object of this invention to provide such a laser system which can operate as both a continuous power laser system and a pulsed laser system.
It is a further object of this invention to provide such a laser system which is modular in design so that the power output of the laser system can be custom tailored to meet the needs of the user.
This invention results from the realization that the phase of the individual laser beams of a multiple beam slab laser system can be synchronized by feeding back a portion of one or more of the individual laser beams to the remaining laser beams and combining them to form a single coherent output beam.
This invention features a coherent multiple beam laser system including a plurality of slab lasers and a feedback device responsive to an output of at least one slab laser for feeding back a portion of the slab laser output to the remaining slab lasers for synchronizing the output phase of all the slab lasers.
In a preferred embodiment, the plurality of slab lasers may include a plurality of slabs essentially parallel to and spaced from each other for forming gaps therebetween in which each gap is filled with a lasing medium. There may be means for exciting the plurality of slab lasers for generating the slab laser outputs. The means for exciting may include at least one RF generator connected between alternating slabs in the plurality of slabs. The means for exciting may include a waveguide in each gap and at least one microwave source coupled with the plurality of waveguides. The means for exciting may include at least one AC generator connected between alternating slabs in the plurality of slabs. The means for exciting may include at least one DC generator connected between alternating slabs in the plurality of slabs. The plurality of slabs may be stacked to form a slab laser module. There may be a resonant cavity surrounding at least one of the slab laser modules and responsive to the plurality of slab laser outputs for producing a plurality of laser beams. The resonant cavity may be an unstable resonator including a primary reflective device positioned at a first end of the unstable resonator and a secondary reflective device positioned at a second end of said unstable resonator. The primary reflective device may be convex shaped and the secondary reflective device may be concave shaped. The secondary reflective device may include a raised center section. The secondary reflective device may further include a retroreflector. The reflective devices may be mirrors. The plurality of laser beams may be repeatedly reflected between the primary reflective device and the secondary reflective device. The curvature of the primary reflective device may be different from the curvature of the secondary reflective device for directing the plurality of laser beams toward at least one exit aperture in the unstable resonator. There may be a beam compacting device responsive to the plurality of laser beams passing through at least one exit aperture for combining the plurality of laser beams into a composite output beam. The beam compacting device may include at least one output collecting mirror. The at least one exit aperture may include a first and a second exit aperture. The at least one output collecting mirror may include a first outer collecting mirror, a second outer collecting mirror and
Font Frank G.
Iandiorio & Teska
Northeast Science & Technology
Rodriguez Armando
LandOfFree
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