Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
1998-08-06
2002-02-26
Davie, James W. (Department: 2881)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S070000
Reexamination Certificate
active
06351477
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optically pumped amplifier, especially a solid-state amplifier, with an amplifying medium and with an optical pumping array, by means of which the pumping radiation is coupled to the amplifying medium; whereby the pumping radiation is formed before the coupling; and whereby the volume of the amplification medium is only partially pumped.
Optically pumped amplifiers in the form of laser arrays have made their entry into almost all areas of technology. Current developments in the area of laser arrays are directed, among other things, toward increasing the output, improving beam quality, and forming and transforming the output radiation in a defined way.
One class of lasers which, in recent years, has found increased applications in materials processing and medicine is solid state lasers. They are distinguished in that with them, particularly in low power classes, high beam quality can be produced. Such solid state lasers are further distinguished by small attainable design sizes, typically with a length of about 8 cm and a diameter of 1 cm.
While solid state lasers have been pumped in the past using lamps, increasingly the solid state medium is pumped by means of diodes or diode fields. As opposed to lamp-pumped solid state lasers, diode-pumped solid state lasers are distinguished, among other things, by high efficiency, high beam quality, long service life and small dimensions. These can be attained especially with a diode pump array. Various types of laser systems can be implemented in connection with diode-pumped laser arrays. In solid state lasers, distinctions are principally made between axially and transversally pumped solid state lasers (for example, solid state lasers pumped using diodes). Generally the axial pumping array for lasers is used with an output up to several tens of watts, while the transverse pumping array is preferred for scaling the output up to several kilowatts.
The limiting factor for beam quality and output performance of optically pumped amplifiers, which also holds true for diode-pumped solid state lasers, is thermal interference. This is caused by unavoidable heat losses in the amplification medium and in the lasing medium. Additionally, the adjustment between the pumped volume and the mode volume of the resonator plays a decisive role in efficiency and beam quality. To comply with these requirements, the amplification medium—in solid state lasers, it is the solid state medium—is pumped via the end (“end-on”), making possible an optimal overlap of active volume and mode volume. If diode lasers or diode laser arrays or field arrays are used for such pumping, the radiation of diode lasers, being asymmetric by nature, is so formed that it can be focused on a circular spot. The homogenized radiation is then coupled through the end into the solid state medium, as is also depicted in
FIG. 19
from the drawings. If the resonator is designed so that the mode diameter roughly corresponds to the pumping spot diameter, then the laser can be operated efficiently with a high beam quality.
One problem that exists with end-on pumping is that relatively expensive beam formation is needed to focus the pump radiation, and that the limited pump volume limits the attainable laser performance.
To scale the laser output to higher performances, laterally and transversely pumped arrays are used. One such array is depicted in FIG.
20
. One such coupling of pump radiation is designated as closed coupling in the technical terminology. It is distinguished by its simple design. It is true that attainable laser performance per length, particularly for pulsed lasers, is limited, since only limited pumping performance can be made available with this array. For this array, high fabrication precision in relation to the relative position of diode laser billets to the rods to be pumped is required. Otherwise, a large part of the diode radiation cannot be coupled into the amplification medium owing to the large divergence angle.
Additional arrays for pumping of solid state bodies according to the state of the art are depicted in
FIGS. 20
to
22
. In accordance with these arrays, the highly divergent diode laser beams are coupled using cylindrical lenses or elliptical cylinder mirrors into the solid state medium. In these arrays, the gain and amplification distribution can be optimized, depending on the application, through varied focusing. However, focusing components are required, which considerably increase the fabrication costs of the arrays.
The previously mentioned pumping arrays are used for amplification media, i.e. as regards solid state lasers, the solid state media, in the form of rod geometries. It is true that similar pumping arrays can also be used for amplification media or solid state media with so-called slab geometries or plate geometries. Two examples of arrays which preferably can be used in connection with plate-shaped amplification media, are depicted schematically in FIGS.
23
and
24
of the drawings. In the pumping array depicted in
FIG. 23
, the radiation of the diode laser stack is coupled to the amplification medium by means of a so-called non-imaging concentrator. It is in fact difficult with such an arrangement to illuminate the amplification medium uniformly, i.e., homogeneously, from all sides. Optimization regarding this is attained with the array of
FIG. 24
, with the diode laser beam coupled through the two narrow sides into the plate-shaped amplification or solid-state medium. Here also it is in fact difficult to achieve a homogeneous optical stimulation or irradiation of the plate-shaped solid-state medium, and thus a homogeneous pumping distribution within the solid state medium.
One feature common to the previously described arrays is that the amplification medium (solid state medium) is pumped in full-volume fashion by means of the pump radiation (diode laser radiation). Owing to this, an amplification profile is produced that is clearly defined by the dimensioning of the amplification medium in all directions. Fundamentally, however, it is not possible that such a clearly delimited amplification profile is fully covered through the laser mode. This, however, is a prerequisite for efficient laser operation and high beam quality of effective radiation. Additionally, the measurements of a solid state medium that is pumped with diode laser radiation cannot be kept arbitrarily small. This is because of the particular absorption coefficient of diode laser radiation. To operate the laser with a high beam quality, therefore, the laser mode volume must be selected to be appropriately large. This, in turn, results in a resonator length which is technically difficult to master. Not lastly, the attainable output performance is limited by thermal disturbances, such as birefringence and thermal lenses.
SUMMARY OF THE INVENTION
Proceeding from the state of the art described above, and the problems connected therewith, the task of the present invention is to provide an optical amplifier in which it is possible to attain an optimal overlap of the pumped volume through the mode volume while simultaneously minimizing the thermal degradation, thermal aberration and depolarization loss.
In regard to optically pumped amplifiers, especially in regard to solid state amplifiers of the types previously described, this problem is solved by having the volume of the amplification medium only partially pumped. The pumped volume of the amplification medium in cross section exhibits an approximately rectangular cross section perpendicular to the optical axis. By means of these measures, through suitable coupling arrangements, efforts are made to have only defined partial volumes of the amplification medium (such as a solid state medium) by means of pumping radiation, preferably in connection with solid state amplifiers by means of diode laser beams, with an approximately rectangular cross section. A defined rectangular cross section of the amplification medium can be pumped, and in fact independently of it
Davie James W.
Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung
Inzirillo Gioacchino
Milde Hoffberg & Macklin, LLP
LandOfFree
Optically pumped intensifying agent, in particular a solid... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optically pumped intensifying agent, in particular a solid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optically pumped intensifying agent, in particular a solid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2969892