Coherent light generators – Particular resonant cavity – Specified cavity component
Patent
1990-07-19
1992-03-17
Davie, James W.
Coherent light generators
Particular resonant cavity
Specified cavity component
372 99, 372105, H01S 308, H01S 310
Patent
active
050974815
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is directed to a gas laser comprising an optical resonator formed of two integrated mirrors, more than one longitudinal mode of the laser oscillation being excited therein during operation. Such gas lasers are described, for example, in Klaus Tradowsky "Laser", Vogel-Buchverlag Wuerzburg, 4th Edition, pages 44-45; 50. A laser resonator having more than one longitudinal mode is described on page 44, 45; and a laser having integrated mirrors is described on page 50. The "inner modulation" is described on pages 95-96 and a structure is shown wherein an electro-optical (birefringent) crystal, the modulator, and an analyzer are arranged in the beam path between the resonator mirrors. This, however, proceeds on the basis of a linearly polarized laser beam and the energy thereof is controlled with a phase rotation in the modulator.
When two longitudinal modes oscillating in polarized fashion are excited in the laser, their planes of oscillation being orthogonal to one another, then these laser oscillations tend to vary the angular position of the polarization planes of the longitudinal modes in what are frequently spontaneously occurring rotations around the axis of the laser beam. These rotations are undesired since--for example, for the purpose of a spatial separation of the two modes and for the formation of two coherent laser beams--the polarization planes should retain their angular position relative to a reference plane of the laser housing.
SUMMARY OF THE INVENTION
An object on which the present invention is based is comprised of stabilizing the angular position of the polarization planes of lasers without allowing linear polarization, i.e. without one of the two modes oscillating in directions perpendicular to one another being disturbingly attenuated. This object is achieved by providing a gas laser where spacing of the two mirrors is selected such that two longitudinal modes are excited whose oscillatory planes are perpendicular to one another. A birefringent element is provided for laser emission and which is arranged in a beam path of the optical resonator. The optically birefringent element has two preferred oscillatory planes for linearly polarized light which are perpendicular relative to one another. An anisotropy of the birefringement element is such that a difference between refractive indices of the two preferred oscillatory planes of the birefringement element is no more than 0.3%.
The birefringent element is advantageously a birefringent layer, whereby the layer is arranged on a resonator mirror. It preferably has an optical density of m.lambda./4. The m is thereby a whole number and is advantageously to be set equal to 1. In this structure, the birefringent layer is very advantageously the uppermost layer of an interference mirror whose layers have two different refractive indices and the birefringent layer has the lower of the two refractive indices. No additional outlay for material and no increased absorption of laser light in the resonator thus occur, linear polarization is avoided, and both modes oscillate with approximately the same strength.
In an advantageous development of the invention, the birefringent layer is a layer vapor-deposited onto the mirror, whereby the deposition direction is inclined by about 50.degree. through 70.degree. relative to the normal onto the mirror surface. It has been shown that column-shaped layer parts are formed on the mirror surface in this structuring, whereby the alignment of the column-shaped layer parts corresponds to the deposition direction. Birefringency is achieved with the layer produced in this way. The recited angular range is thereby critical. For example, given an angle of 80.degree. or more, a polarizing layer that is not birefringent arises.
A helium-neon laser wherein the obliquely vapor-deposited layer is composed of one of the substances SiO.sub.2, TiO.sub.2, or Ta.sub.2 O.sub.3, Al.sub.2 O.sub.3 is thereby preferably suitable for the gas laser. Of these, SiO.sub.2 and Al.sub.2 O.s
REFERENCES:
patent: 3549236 (1970-12-01), Mink
patent: 3609585 (1971-09-01), Hufnagel
patent: 4800568 (1989-01-01), Krueger et al.
Kamprath-Reihe Technik im Vogel-Buchverl. Wurzburg: Prof. Dr.-Ing. Klaus Tradowsky: "Laser", vol. 4, pp. 44, 45, 50, 95 and 96.
No. 58-53875(A) "Semi-Transparent Mirror for Laser and Preparation Thereof", by Michihiko Tominaga, vol. 7, No. 140 (E-182) [1285], Jun. 18, 1983.
2319 Optics Communications, vol. 46 (1983) Jul., No. 3/4, Amsterdam, Netherlands, E. W. Weber et al., "Multi-Mode CW Dye Laser", pp. 231-236.
Journal of the Optical Society of America, vol. 1, No. 3, Jun. 1984, pp. 438 and 439, "Stable Two-Mode Operation of a Continuous-Wave Dye Laser Using a Michelson Mode Selector".
Fritzsche Helmut
Krueger Hans
Davie James W.
Siemens Aktiengesellschaft
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