Coherent light generators – Particular active media – Active media with particular shape
Reexamination Certificate
2001-01-03
2003-08-26
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Active media with particular shape
C372S033000, C372S036000, C372S106000, C331S094100, C334S029000, C359S333000, C606S013000
Reexamination Certificate
active
06611545
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active element for a laser source, and to a laser source comprising such an active element.
DESCRIPTION OF THE PRIOR ART
In a known manner, such a laser source generally comprises:
an active element comprising an elongate rod, generally, but not exclusively, of circular cross section, including a doped matrix capable of absorbing a pump beam in order to amplify laser radiation propagating longitudinally with or without reflection; and
at least one pump source, for example a laser diode, capable of emitting a pump beam into said rod.
In a known manner, said pump beam may be emitted:
either longitudinally with respect to the axis of said elongate rod. In this case, the cylindrically shaped rod is used directly as a lightguide, either by generating a total reflection on the walls of the cylinder, or by arranging a reflector outside the walls in order to limit the amplification of the spontaneous emission;
or transversely to the axis of said rod, as described for example in documents EP-0 377 207 and U.S. Pat. No. 4,756,002.
It is known that one of the main restrictions, with regard to pumping an amplifying medium (rod) with a pump source, is connected with the amplitude of the wavelength drift, which has to be accepted, while keeping parameters constant over the emitted laser beam. This restriction means that it is necessary, whatever the temperature, to maintain:
a maximum absorption rate (and/or to increase the distance of the active medium though which the pump beam passes); and
a transverse homogeneity of the optimum pumping.
In order to satisfy these restrictions, it is known that a rod of rectangular cross section is generally more suitable than a rod of circular cross section, in particular since it allows thermo-optical distortions to be offset. Furthermore, the pumping distance may be increased by placing a reflector on the face opposite the input face of the pump beam.
However, even in this case, with a double pass of the pump beam, the distance of the amplifying medium through which the pump beam passes is generally still much too short to accept drifts in wavelength from the pump source, when it is not temperature regulated.
SUMMARY OF THE INVENTION
The object of the present invention is to remedy these drawbacks. The invention relates to an active element for a laser source, enabling a pump beam to pass homogeneously through the amplifying medium, over an increasing and controllable distance.
For this purpose, according to the invention, said active element for a laser source comprises an optical block which includes:
an elongate rod, which comprises a doped matrix capable of absorbing a pump beam in order to amplify laser radiation propagating longitudinally, and which is incorporated into said optical block;
at least one input face for the pump beam;
a first reflection face for the pump beam which is inclined with respect to the longitudinal axis of said rod; and
at least one second reflection face which interacts with said first reflection face,
is remarkable in that said input face is inclined with respect to the longitudinal axis of said rod.
Thus, by virtue of the multiple reflections capable of being made on said interacting reflection faces and by the oblique transmission of the pump beam, obtained by the inclination of said inclined faces, said pump beam can pass through the amplifying medium (i.e. said rod) over an increased distance, which enables the aforementioned drawbacks to be remedied. This distance may be controlled, especially by choosing suitable inclination angles, with respect to the longitudinal axis of the rod.
Furthermore, by a suitable choice of said inclination angles, the transverse pumping can also be made homogeneous.
Note that the prior documents EP-0 404 635 and U.S. Pat. No. 5,048,026 describe active elements for a laser source having a structure close to that of the active element in accordance with the present invention. However, these known active elements do not have an input face which is inclined with respect to the longitudinal axis of the rod, such that the distance traveled through the amplifying medium passes cannot be controlled, the pumping cannot be transversely homogenized and the return of the pump beam cannot be accurately adjusted.
In one preferred embodiment of the active element in accordance with the present invention, said rod has a rectangular, for example square, cross section, and said optical block comprises at least one first optical element which is made from a material having substantially the same optical index as the matrix of said rod, which is fixed to a first face of said rod and which has at least one face inclined with respect to the longitudinal axis of said rod, and said first inclined reflection face is formed on said inclined face of said first optical element.
In this case, in a first variant, said optical block further comprises a second optical element which is made from a material having substantially the same optical index as the matrix of said rod, which is fixed to a second face of said rod and which has at least one face inclined with respect to the longitudinal axis of said rod, and the second reflection face is formed on said inclined face of said second optical element.
In this case, preferably, said first and second optical elements are identical and are symmetrically fixed to said rod, which especially enables the homogenization of the pumping to be made easier.
Moreover, in a second variant, said second reflection face is directly formed on one face of said rod.
In addition, according to the invention, said reflection faces are:
either flat;
or rounded.
In the latter case, preferably, each of said reflection faces forms a part of a conical surface of a first conical section of an optical element.
Moreover, advantageously, said optical element comprises a second conical section, said first and second conical sections coaxially surround said rod and are made from a material having substantially the same optical index as the matrix of said rod, and the conical surface of said second conical section comprises said input face of said optical block.
In addition, advantageously, said input face is provided with an antireflection coating.
Moreover, advantageously, at least one of said optical elements:
is doped, preferably differently to the rod, in particular in order to control any undesirable phenomena; and/or
is made from at least one of the following materials: yttrium aluminum garnet, vanadate, glass or sapphire; and/or
is fixed by diffusion bonding to said rod. The separate production of the rod and of the optical elements means they can be machined in a simple manner, thus facilitating the production of said active element for a laser source.
In addition, each of said optical elements can be fixed to one rod face, preferably in the aforementioned manner:
either directly;
or indirectly, for example in a particular embodiment where the active element includes a flow of coolant between one face of the rod and the opposite face of an optical element.
The present invention also relates to a laser source of the type comprising:
an active element for a laser source; and
at least one pump source capable of emitting a pump beam into said active element.
According to the invention, said laser source is noteworthy in that said active element is such as that mentioned above.
In addition, advantageously, the pump source has an emission surface for the pump beam, the width of which is smaller, by a predefined margin, than the width of said input face of the active element.
REFERENCES:
patent: 3660779 (1972-05-01), Cuff et al.
patent: 4088964 (1978-05-01), Clow
patent: 4756002 (1988-07-01), Ruggigre et al.
patent: 4935932 (1990-06-01), Johnson et al.
patent: 5001718 (1991-03-01), Burrows et al.
patent: 5048026 (1991-09-01), Shaw et al.
patent: 5868731 (1999-02-01), Budnik et al.
patent: 5872804 (1999-02-01), Kan et al.
patent: 5974061 (1999-10-01), Byren et al.
patent: 6061377 (2000-05-01), Brassart et al.
patent: 6144484 (2000-11-
Cabaret Louis
Montagne Jean-Eucher
Compagnie Industrielle des Lasers Cilas
Ip Paul
Nguyen Tuan M
Stevens Davis Miller & Mosher LLP
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