Coherent light generators – Particular pumping means – Pumping with optical or radiant energy
Patent
1996-12-18
1998-11-17
Bovernick, Rodney B.
Coherent light generators
Particular pumping means
Pumping with optical or radiant energy
H01S 309, H01S 3091
Patent
active
058387129
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a diode-pumped high performance solid state laser. An arrangement of this kind is known in a very broad sense from U.S. Pat. No. 4,945,544.
b) Description of the Related Art
In general, solid state lasers are excited to laser activity by supplying optical energy ("optical pumping"). The sources of this energy are conventional krypton lamps or xenon lamps and, recently, semiconductor diodes emitting in the near infrared range.
Semiconductor lasers are virtually ideal light sources for the optical excitation of solid state lasers. In comparison with conventional lamps, they are characterized especially by a good spectral adaptation of the pumping radiation to the absorption bands of the laser-active crystal and by a long lifetime and they enable the development of compact, efficient laser systems which are constructed only from solid state materials and which are distinguished by small dimensions and high efficiency. At present, the so-called longitudinal and transverse pumps of generally cylindrical media represent the state of the art. The most efficient laser systems can be realized with longitudinal pump geometry. Thus, along with favorable tuning of the laser diode radiation to an absorption band of the solid state laser material, systems can be developed in which the ratio between optical pump output and optical output power is greater than 50%. The output power of these systems is limited on the one hand by the lack of an available semiconductor laser which has a sufficiently high output power and a small emitting aperture at the same time and on the other hand by the limited ability of the laser diode crystals to withstand thermal loading. Higher output powers can be realized only with transverse pump geometry which makes it possible for light from a plurality of laser diodes or laser diode arrays to be coupled into the laser medium.
Arrangements conceived in this way may basically be divided into direct transverse arrangements and indirect transverse arrangements. Due to the direct irradiation of the laser medium, direct transverse arrangements have the advantage of a highly efficient, low-loss pumped light transmission into the laser medium with a comparatively minor expenditure on adjustment. Strict limits are imposed on the quantity of laser diode arrays that can be arranged around the laser medium and with respect to minimizing the cross section of the laser medium, since the diodes must be arranged as near as possible in front of the laser medium because of their high divergence.
In the case of indirect transverse arrangements, the sharply divergent beam bundles of the emission radiation are shaped into parallel or convergent beam bundles via coupling optical elements. Accordingly, a greater distance from the laser medium can be selected. As a result of the saved space, a much larger quantity of diode arrays can be arranged around the laser medium. In addition to the high expenditure on adjustment and the resulting stability problems, the compactness of such arrangements is also reduced.
A number of requirements must be met in order to achieve a high performance laser with high efficiency and favorable beam product. These requirements are met in different ways and to varying degrees by the solutions known from the prior art. Ultimately, every solution represents a compromise since, on the one hand, the requirements are contradictory in part and, on the other hand, there is naturally a permanent requirement for maintenance-free systems with long-term stability at minimum effort in terms of design and cost.
A chief requirement stems from the temperature dependency (approximately 0.25 nm/.degree.C.) of the laser diodes, on which basis the emission wavelength can be precisely tuned to an absorption band of the solid state laser material. The extremely narrow half-width of the excitation band which is generally less than 1 nm leads to the compulsory requirement for a necessary temperature stabilization. If the pump a
REFERENCES:
patent: 4969155 (1990-11-01), Kanan
Applied Optics, 20 Sep. 1994, vol. 33 No. 27 "23-W Average Power at 0.537 .mu.m from an Externally Frequency-Doubles Q-Switched Diode-Pumped Nd:YOS Laser Oscillator" Comaskey, et al.
IEEE Journal of Quantum Electronics, 28 Apr. 1992, No. 4 "High Average Power Diode Pumped Slab Laser" Comaskey, et al.
Kraenert Juergen
Kuehn Holger
Kufert Siegfried
Mueller Holger
Bovernick Rodney B.
Jenoptik Aktiengesellschaft
Wise Robert E.
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