Coherent light generators – Particular resonant cavity
Reexamination Certificate
1999-08-11
2001-08-28
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular resonant cavity
C372S098000, C372S099000
Reexamination Certificate
active
06282223
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to solid-state lasers for medical applications. The invention relates in particular to a multimode, solid-state laser having a gain-medium rod located in a stable resonator formed between a concave high-reflection mirror and a plane output-coupling mirror.
DISCUSSION OF BACKGROUND ART
For many medical applications, such as dermatological applications, a laser is not required to have the highest possible beam quality and accordingly is not required to operate in a single fundamental mode. For these applications, efficiency, stability and compactness are important characteristics of a laser. Multimode operation of a laser typically provides higher efficiency than single-mode operation.
One laser preferred for dermatological applications is a flashlamp-pumped solid-state laser having a resonator including an Er:YAG gain medium. Such a laser is typically arranged to provide laser-radiation having a wavelength of 2.94 micrometers (&mgr;m). A preferred design of such a laser includes a symmetrical resonator formed between two plane (flat) mirrors. This can be defined as a flat-flat resonator. One of the mirrors is a maximally-reflecting mirror. The other mirror is a partially-transmitting mirror serving as an output-coupling mirror.
The gain medium is in the form of a rod of circular cross-section and is symmetrically disposed between the mirrors. The ends of the rod have a concave radius of curvature. The radius of curvature is the same at both ends of the rod. The concave radius of the rod ends serves to partially offset a positive thermal-lensing effect in the rod, the thermal-lensing effect resulting from absorption of pump-light. This resonator arrangement produces a multimode laser-beam having the same width on each end of the resonator mirrors. That portion of thermal-lensing which is not offset by the concave ends of the rod provides that the resonator operates as a stable resonator. An advantage of this type of resonator is that the laser beam optimally “fills” the gain-medium rod permitting optimum extraction of energy from the rod.
Medical lasers are usually operated over a wide range of power levels. Consequently, the thermally-induced positive dioptric power of the gain-medium varies. An advantage of the flat-flat resonator is that the resonator remains in a stable regime for a wide range of thermally-induced dioptric powers.
A characteristic of this type of resonator, however, is that as the thermally-induced dioptric-power increases, the width at the resonator mirrors of a laser-beam circulating in the resonator decreases. This increases the possibility of laser-damage to the resonator mirrors. In particular, it has been observed that the maximally-reflecting mirror is more susceptible to laser-damage than the output-coupling mirror. Accordingly, there is a need for a laser-resonator design which has the multimode operating characteristics and gain-medium energy extracting characteristics of the symmetrical flat-flat resonator but which is not limited in output-power by the laser-damage resistance characteristics of the maximally reflecting mirror.
SUMMARY OF THE INVENTION
In one aspect of the present invention, the above-discussed shortcomings of the prior-art flat-flat resonator are overcome in a laser comprising a laser-resonator formed between a concave, maximally-reflecting mirror and a plane output-coupling mirror. A rod of a solid-state gain-medium is located in the laser-resonator on a longitudinal axis thereof. The gain-medium rod is closer to the output-coupling mirror than to the maximally-reflecting mirror. A source of pump-light is provided for delivering pump-light to the rod for energizing the gain-medium. Components of the laser-resonator are configured, dependent upon a thermal-lensing coefficient of the gain-medium and the power of the pump-light delivered to the rod, such that the laser-resonator operates as a stable resonator, generating a multimode laser-beam circulating therein. Components of the resonator are also configured such that the circulating laser-beam has a width at the maximally-reflecting mirror greater than its width at the output-coupling mirror thereby reducing the possibility of laser-damage to the maximally-reflecting mirror. The resonator components are further configured such that even though the resonator is asymmetrical and the rod is asymmetrically located therein, the circulating laser-beam symmetrically fills the gain-medium rod, thereby optimizing laser-energy extraction therefrom.
The gain-medium rod has first and second ends, the first end being closest the maximally reflecting mirror. Preferably the first and second ends have respectively first and second negative radii of curvature, the first radius of curvature being less than or equal to the second radius of curvature.
In one preferred embodiment, the inventive laser includes a lens having negative dioptric-power. The lens is located in the laser-resonator proximate the first end of the rod between the first end of the rod and the maximally-reflecting mirror. The first and second radii of curvature the ends of the rod are equal.
In another preferred embodiment of the inventive laser, above-discussed beam-parameters at the mirrors and in the rod are achieved without a negative lens by incorporating an equivalent negative dioptric-power in the first end of the rod. Accordingly, in this embodiment of the inventive laser, the first radius of curvature is less than the second radius of curvature.
A laser in accordance with the present invention is particularly suited for use when single-mode operation can be sacrificed in favor of increased efficiency, and when it is desired to couple about 10% or more of circulating laser-energy out of a laser resonator. For coupling 10% or more of circulating laser-energy out of a laser resonator, the output-coupling mirror has a reflectivity of about 90% or less. The inventive laser is also particularly suited for use with a gain-medium having a strong thermal-lensing coefficient, such as Er:YAG.
REFERENCES:
patent: 3680000 (1972-07-01), Chesler et al.
patent: 4554666 (1985-11-01), Altman
patent: 4803694 (1989-02-01), Lee et al.
patent: 5097471 (1992-03-01), Negus et al.
patent: 5249190 (1993-09-01), Kortz et al.
patent: 5289479 (1994-02-01), Oka et al.
patent: 5786929 (1998-07-01), Nabors
patent: 5907574 (1999-05-01), Karni
Arroyo Teresa M.
Eitan Pearl Latzer & Cohen-Zedek
Lumenis Inc.
Monbleau Davienne
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