Coherent light generators – Particular resonant cavity – Unstable resonator
Patent
1992-06-01
1994-07-05
Scott, Jr., Leon
Coherent light generators
Particular resonant cavity
Unstable resonator
372 97, 372 99, 372108, H01S 308
Patent
active
053274490
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The invention relates to a laser resonator, particularly for carbon dioxide lasers, with two cavity resonator end mirrors, which have active material between two fully reflecting end mirror faces, which form an unstable resonator cavity and with at least one third, completely reflecting mirror face with which the laser radiation is reflected prior to its coupling out brought about by a coupling-out opening of the resonator.
The coupling out of laser radiation or illumination and therefore laser power from the optical resonator of the laser is normally brought about in that a resonator mirror is either constructed in partly transmitting manner, or by it radiating out from the resonator area laser radiation. Resonators with partly transmitting mirrors are preferably stable resonators, in which the laser beam as a result of the focussing action of one or both mirrors remains localized around the resonator axis in the area defined by the mirrors. Such a construction of stable resonators with rotational symmetry about the resonator axis has the advantage that the coupled out laser radiation has a high beam quality. This is e.g. determined by the distance over which the laser beam propagates in an approximately parallel manner or is a measure for how small the focal spot can be on which the laser beam can be focussed or how large is the maximum achievable intensity. The theoretically highest quality for the beam distribution is obtained according to the Gaussian predominant mode TEM 00. Other beam distributions, e.g. TEM 01 have decreasing beam quality with increasing beam diameter. However, a large beam diameter is necessary to achieve high output power levels, if it is assumed that the latter require large active material volumes and the resonator length is limited for obvious reasons. Thus, in principle, an increase in the output power by increasing the beam diameter is linked with a deterioration of the beam quality. In addition, the transmitting mirrors cannot be loaded to a random high level, i.e. must not be excessively heated by the laser radiation passing through them, so that their optical effect is not impaired and their material is not destroyed.
2. Prior Art
It is generally known to equip optical resonators with fully reflecting mirrors, which are constructed and arranged in such a way that a certain proportion of the laser radiation leaves the resonator area following several revolutions. Coupling out conventionally takes place with a pinhole or so-called scraper mirror, which produces the hollow beam characteristic of unstable resonators. Such unstable resonators normally have a high degree of coupling out and consequently presuppose active material with a correspondingly high amplification or gain. The beam quality is generally lower by a factor of 3 to 4. It is particularly low if the degree of coupling out is kept low, e.g. by a corresponding dimensioning of the reflecting faces bringing about coupling out. An additional fundamental disadvantage of the unstable resonator construction is the comparatively high adjustment sensitivity of its mirrors and its sensitivity to optical reactions, i.e. with respect to light reflection from the processing point into the resonator.
Apart from the generally known unstable resonator, U.S. Pat. No. 3,681,709 discloses a laser resonator, particularly for carbon dioxide lasers, with two resonator end mirrors, which have active material between two fully reflecting end mirror faces, which form a resonator cavity, and with at least one third completely reflecting mirror face with which the laser radiation or illumination is coupled out of the resonator. The third mirror face used for coupling the laser radiation from the resonator is constructed as the end mirror face of one of the two end mirrors. The resonator chamber between the two end mirror faces is stable and the third mirror face of one mirror is used exclusively for coupling out from the stable resonator laser light oscillating in the predominant mode. An unstable resonato
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Du Keming
Loosen Peter
Fraunhoefer-Gesellschaft zur Foerderung der Angewandten Forschun
Jr. Leon Scott
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