Coherent light generators – Particular active media – Gas
Patent
1995-03-08
1997-04-01
Scott, Jr., Leon
Coherent light generators
Particular active media
Gas
372 65, 372 34, H01S 303
Patent
active
056174403
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for holding a cylindrical laser tube in a stable radiation direction in the internal space of a metallic housing, the internal space having a larger diameter than the laser tube and O-rings for mounting the laser tube being fitted in the end regions of the internal space and the metallic housing being mounted on a baseplate.
Cylindrical laser tubes, especially for HeNe gas discharge lasers, are nowadays obtainable as operationally ready, sealed units with fused-on resonator mirrors. The currently emitted wavelength of the laser is also dependent on the spacing and the inclination of the mirrors with respect to one another. The spacing of the mirrors can be controlled by means of thermal expansion of the laser tube. The metallic housing serves as an oven for setting the temperature of the laser tube. The heating is intended to avoid stressing the laser tube, in order not to vary the inclination of the mirrors with respect to one another.
The direction of the laser beam depends on the mounting of the laser tube in the housing. For a low-stress mounting of the laser tube, springs or elastic O-rings are provided (DE 28 32 117 C2, SIEMENS Publication B6-P 8808 "Fur die HeNe-Lasertechnik: Rohre, Module, Stromversorgungen [Tubes, Modules, Power supplies], Issue 2, page 10"). Thermal gradients in the metallic housing can, however, lead to stresses which cannot be accommodated by the O-rings. In addition, because of external thermal radiation from the housing or cooling air streams, thermal gradients can be produced in the baseplate, which likewise influence the longitudinal directional stability of the housing and thus of the laser beam axis. Vibrations of the system can also lead to transverse displacements of the laser tube in the elastic O-rings.
Lasers of the abovementioned type are, for example, used in coordinate measuring technology. For precise length measurements, especially using interferometric methods and accuracies, a stabilization of the laser wavelength is a basic precondition. For angle measurements, especially polar angle measurements, the stability of the radiation direction is of the greatest importance.
SUMMARY OF THE INVENTION
The invention was therefore based on the object of equipping the known mounting with improved temperature control, and providing small temperature gradients and more stable longitudinal directional mounting of the laser tube.
This object is achieved in the case of a device of the type mentioned at the outset, according to the invention, by means of the characterizing features of claim 1. Advantageous refinements are yielded by the features of the dependent claims.
By means of filling a soft, thermally conducting compound into the interspace between the inner housing wall and the laser tube, a good temperature distribution is achieved by means of thermal conduction. The O-rings are simultaneously used as a holder for the laser tube and as a seal for the thermally conducting compound. The compound filled in additionally stabilizes the laser tube against transverse displacements and equalizes temperature gradients. The temperature control by means of thermal conduction also makes possible the removal of heat from the system by means of cooling elements fitted on the outer wall of the housing. By means of the cooling capability, a temperature control range is also available which lies below the ambient temperature, so that the working temperature of the housing, serving as an oven, can be set to the ambient temperature. The connection, in a fixed position on only one side, of the housing to the baseplate allows different thermal expansions between the two components, without these leading to a stressing of the longitudinal axis of the housing.
The use of Peltier elements, which can heat and cool, is of especial advantage. In the case of a symmetrical arrangement of a plurality of Peltier elements on the outer wall of the housing, the size of the individual elements can be kept relatively small. In the case of a predetermined housing lengt
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Jr. Leon Scott
Leica AG
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