Diode-pumped double frequency solid-state laser

Details Diode-pumped double frequency solid-state laser Diode-pumped double frequency solid-state laser

1999-09-21

2001-08-28

Arroyo, Teresa M. (Department: 2881)

Coherent light generators

Particular resonant cavity

Mirror support or alignment structure

C372S069000

Reexamination Certificate

active

06282227

ABSTRACT:

The invention relates to a diode-pumped, frequency-doubled solid-state laser according to the preamble of Claim
1
.
Solid-state lasers, usually built using rare-earth-doped crystals or glasses, for example Nd:YAG, Nd:YVO
4
, Nd:YAlO, ND:YLF, Nd:glass or other similar solid materials and equipped with resonator-internal frequency doubling, have been known for a long time and are used in many applications in laser technology. Generation of second or higher harmonic oscillations is used in materials, primarily crystals, which have no inversion centers—for example KTP, LBO, BBO, KNbO
3
, LiNbO
3
or others—with a high nonlinear coefficient, which generates light at twice or four times the frequency of the radiant energy received, by inharmonic oscillations of the lattice atoms, excited by an incident light wave. The process of generating higher harmonics is highly dependent upon the power density (see for example Köchner, Solid-State Laser Engineering) so that to produce frequency-doubled laser radiation with higher efficiency, the non-linear crystal is usually, at least in continuously operating (cw) lasers, accommodated in the resonator of the laser itself (see above or also for example Yariv, Quantum Electronics, third edition, Page 402). The resonator mirrors are usually chosen to be highly reflecting for the laser wavelength in order to achieve a maximum magnification in the resonator and hence a doubling efficiency that is as high as possible. The decoupling mirror is simultaneously highly transmitting for the frequency-doubled radiation in order to be able to decouple the latter readily from the resonator.
Usually such lasers are built on optical benches, in other words the elements for holding the laser crystal, frequency doubler, and decoupling mirror are usually screwed tight on the underside to a plate or lined up along a rail by means of displaceable structures. This design however, in cases of resonator-internal frequency doubling in which an especially slight adjustment tolerance is necessary because of the power-density-dependent conversion efficiency, is not sufficiently stable in the long term when exposed to changing environmental conditions or over a long operating life. In particular, bending of the optical bench or rail as well as tilting of the retaining elements that are fastened on only one side are responsible for this.
One known alternative design provides for mounting the retaining elements on three or for steel rods which are typically inserted through matching openings in the corners of the (usually rectangular) retaining elements, with the retaining and adjusting elements being secured by clamps to the rods. Although no significant tilting of the retaining elements with respect to one another can occur, practice shows that when the retaining elements are clamped to the rods, stresses are exerted on the rods which likewise lead to the elements going out of adjustment in the long term. In addition, good heat transfer from the holders is not possible, with the holders being subjected to heat for example from the laser crystal or the frequency doubler, since the rods have a small cross section and therefore a poor conductivity, as well as no possible contact with a larger thermal mass serving as the cooling body.
Yet another solution according to the prior art is provided by mounting the resonator elements either in threaded sleeves, with no independent retaining structure being formed and with the stability of an element depending on the stability of the mounting elements, or in tubes, which allows the resonator to be manufactured only in a certain sequence and not permitting subsequent removal of a central resonator element.
Finally, retaining and adjusting elements can be clamped displaceably on a (thicker) tube instead of a plate, which has the same disadvantages as the optical bench as far as tilting and heat removal are concerned.
Therefore the goal of the invention is to provide a resonator structure which is free of stress, has no internal twisting or tensioning by the retaining or adjusting elements, exhibits good heat transfer and the properties of a cooling body, as well as a large contact surface to receive retaining elements subject to thermal stress.
This is achieved by the features listed in the characterizing clause of Claim
1
. Details of the invention will be found in the subclaims and the specification, in which several embodiments are explained with reference to the drawing.


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