Coherent light generators – Particular resonant cavity – Plural cavities
Patent
1997-09-30
2000-04-25
Lee, John D.
Coherent light generators
Particular resonant cavity
Plural cavities
372 68, H01S 307, H01S 316
Patent
active
060552638
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a solid-state laser oscillating device to be equipped and used in a laser machining apparatus or the like.
BACKGROUND ART
Solid-state laser oscillating devices such as YAG (yttrium-aluminum-garnet) lasers are capable of providing a high-power and stable laser beam, and thus are widely used in laser machining apparatuses for carrying out cutting, welding, etc. of metallic or nonmetallic materials. FIG. 4 is a schematic diagram illustrating a structure of a slab-type YAG laser oscillating device as an example of a conventional solid-state laser oscillating device.
In FIG. 4, a laser crystal (YAG laser crystal) 1 is disposed in a reflector 30 together with excitation lamps L1 and L2 each comprising a xenon lamp, for example. A total reflection mirror M1 and a partial reflection mirror M2 are arranged at opposite ends of the laser crystal 1, respectively, thereby constituting a Fabry-Perot type optical resonator. Inner walls 31 of the reflector 30 have surfaces of high light reflectivity.
Cooling water (pure water) is circulated through an interior of the reflector 30 to prevent overheating of individual parts of the device, including the laser crystal, the excitation lamps, the reflector, etc., thereby preventing the quality of a laser beam from being lowered due to the rise of temperature. Arrows C1 and C2 indicate an inlet and an outlet, respectively, of the circulating cooling water. The excitation lamps L1 and L2 are energized by an excitation power supply 40 and radiate excitation light 50.
The excitation light 50 radiated from the excitation lamps L1 and L2 falls upon the laser crystal 1 directly or indirectly after being reflected by the high-reflectivity inner walls 31 of the reflector 30, whereupon the laser crystal 1 is subjected to pumping to generate a laser beam S. The laser beam is amplified while traveling in the space of the optical resonator back and forth between the total reflection mirror M1 and the partial reflection mirror M2, and a part S' thereof is let out and used for the purpose of laser beam machining or the like.
A surface of the laser crystal 1 is in direct contact with the air or the cooling water (pure water). Accordingly, incoming and outgoing of light to and from the laser crystal 1 take place through an interface between the laser crystal 1 and the air or the cooling water (pure water). Naturally, there is a considerably large difference in refractive index between the laser crystal 1 and the air or the cooling water (pure water). Thus, in order to keep an efficiency of the optical resonator high, the laser crystal 1 has its opposite end faces 2 and 3 obliquely cut at an angle substantially satisfying the Brewster's condition. In the case of the YAG laser crystal, the Brewster's angle is ranging approximately from 60 to 62 degrees, and therefore the opposite end faces 2 and 3 of the laser crystal 1 are individually inclined at an angle .theta. of approximately 28 to 30 degrees in the illustrated example where the total reflection mirror M1, the laser crystal 1 and the partial reflection mirror M2 are arranged in a straight line.
Using a slab-type laser crystal, an optical path can be formed in zigzag within the laser crystal 1, as indicated by the broken line in the figure. A zigzag optical path in the laser crystal 1 is advantageous in preventing the quality of the laser beam from being lowered due to a refractive index gradient caused in the laser crystal 1. Specifically, in the laser crystal, a temperature distribution is liable to be present such that the temperature is lowered with distance from a central axis of the crystal toward the periphery, to cause a corresponding concentric profile of refractive index inside the laser crystal. Accordingly, if the optical path in the laser crystal 1 is made straight, a difference in optical-path length is caused depending on radial locations in the laser crystal where the laser beam passes back and forth, to adversely affect the optical resonation. Contrary, with the zigzag opt
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Iehisa Nobuaki
Karube Norio
Mitsui Kenji
Fanuc Ltd.
Lee John D.
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