Coherent light generators – Particular active media
Reexamination Certificate
2001-11-13
2003-06-24
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
C372S098000
Reexamination Certificate
active
06584129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a solid laser. This invention particularly relates to a solid laser, wherein an etalon is located in a resonator in order to bring an oscillation mode to a single longitudinal mode.
2. Description of the Related Art
Various solid lasers, which utilize a solid laser medium doped with neodymium (Nd) and produce a laser beam having a wavelength of a 1 &mgr;m band (ranging from approximately 1.0 &mgr;m to 1.1 &mgr;m), have heretofore been proposed. Examples of the solid laser media doped with neodymium (Nd) include Nd:YVO
4
, Nd:YAG (Y
3
Al
5
O
12
), Nd:YLF (YLiF
4
), Nd:GdVO
4
, Nd:YAlO (YAlO
3
), and Nd:glass. In the solid lasers of such types, a technique is utilized broadly, wherein a Fabry-Pérot type of etalon is located within a resonator in order to bring an oscillation mode to a single longitudinal mode. The solid lasers utilizing the technique described above are described in, for example, Japanese Unexamined Patent Publication Nos. 5(1993)-218556 and 6(1994)-130328, and 7(1995)-263785. (In this specification, the term “etalon” means the Fabry-Pérot type of etalon.)
However, in the conventional single-longitudinal-mode solid lasers, wherein the oscillation mode is brought to the single longitudinal mode by the utilization of the etalon, conditions of the etalon (i.e., the thickness of the etalon, the reflectivity of the etalon, and the inclination of the etalon) and conditions of the resonator (i.e., resonator longitudinal mode intervals), under which good single longitudinal mode characteristics are capable of being obtained, were not clear. Therefore, the problems occur in that, in cases where an etalon, which yields good single longitudinal mode characteristics when being located within a certain resonator, is utilized directly in a different resonator, good single longitudinal mode characteristics cannot be obtained.
Also, the problems occur in that, though good single longitudinal mode characteristics are capable of being obtained, a beam profile becomes bad, and the output becomes low. Thus the conditions of the etalon and the resonator, which simultaneously satisfy the requirements for the single longitudinal mode characteristics, the beam profile, and the output, were not clear.
The inventors conducted extensive research and found that, in cases where each of the thickness of the etalon, the reflectivity of the etalon, and the inclination of the etalon is set at a large value, the single longitudinal mode characteristics become good, but the beam profile becomes bad, and the output becomes low. Also, it was found that, in cases where each of the thickness of the etalon, the reflectivity of the etalon, and the inclination of the etalon is set at a small value, the beam profile becomes good, the output becomes high, but the single longitudinal mode characteristics become bad.
Further, it was found that, in cases where a resonator length is set at a large value (i.e., the resonator longitudinal mode intervals are set to be small), the single longitudinal mode characteristics become bad. Furthermore, it was found that, in cases where the resonator length is set at a small value, the single longitudinal mode characteristics become good, and the beam profile and the output are not much affected by the resonator length.
As for a solid laser, which utilizes Nd:YAG as a solid laser medium and produces a laser beam having a wavelength of a 0.9 &mgr;m band, the inventors have already found the conditions of the etalon, under which good, reliable single longitudinal mode characteristics, a good beam profile, and a high output are capable of being obtained simultaneously. The conditions of the etalon are disclosed in Japanese Unexamined Patent Publication No. 8(1996)-186316. However, as for the solid laser, which produces a laser beam having a wavelength of the 1 &mgr;m band, appropriate conditions of the etalon have not yet been clarified.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a single-longitudinal-mode solid laser, which produces a laser beam having a wavelength of a 1 &mgr;m band and which exhibits good, reliable single longitudinal mode characteristics, a good beam profile, and a high output.
The present invention provides a single-longitudinal-mode solid laser capable of producing a laser beam having a wavelength of a 1 &mgr;m band, the solid laser comprising:
i) a solid laser medium doped with neodymium,
ii) a resonator, and
iii) a Fabry-Pérot type of etalon, which is located within the resonator and brings an oscillation mode to a single longitudinal mode,
wherein a thickness of the etalon, a reflectivity of the etalon, an inclination of the etalon, and a resonator longitudinal mode interval are adjusted so as to satisfy the relationships represented by the formulas:
1.2%≦R
N
≦15% and 0.5°≦&thgr;≦2.0°
in which R
N
represents an effective reflectivity of the etalon with respect to wavelengths &lgr;=&lgr;
0
±&Dgr;&lgr;c deviating by a resonator longitudinal mode interval &Dgr;&lgr;c from a resonance wavelength &lgr;
0
of the etalon, and &thgr; represents an inclination of an optical axis of the etalon with respect to an optical axis of the resonator.
The single-longitudinal-mode solid laser in accordance with the present invention should preferably be modified such that the thickness of the etalon, the reflectivity of the etalon, the inclination of the etalon, and the resonator longitudinal mode interval are adjusted so as to satisfy the relationships represented by the formulas:
3.0%≦R
N
≦10% and 0.80°≦&thgr;≦1.5°
in which R
N
represents the effective reflectivity of the etalon, and &thgr; represents the inclination of the optical axis of the etalon with respect to the optical axis of the resonator.
Effects of the single-longitudinal-mode solid laser in accordance with the present invention will be described hereinbelow.
The Fabry-Pérot type of etalon is a wavelength selecting device utilizing multiple interference of light.
FIG. 3
is a graph showing relationships among an effective reflectivity of an etalon, an etalon longitudinal mode, and a resonator longitudinal mode. In
FIG. 3
, a curve “a” indicates the wavelength characteristics of an effective reflectivity R
eff
of the etalon. As illustrated in
FIG. 3
, the effective reflectivity R
eff
of the etalon changes periodically, and the etalon longitudinal mode occurs at points, at which the effective reflectivity R
eff
becomes equal to 0 at a wavelength interval &Dgr;&lgr;e (FSR: free spectral range).
In
FIG. 3
, a curve “b” indicates a gain spectrum of a solid laser medium. Ordinarily, the resonator longitudinal mode occurs at a plurality of points falling within an oscillation wavelength width W in the gain spectrum. Therefore, in cases where the etalon is not utilized, the laser undergoes oscillation in a multiple longitudinal mode. In cases where the etalon is inserted into the resonator, the loss, to which each of the longitudinal modes of the resonator is subjected, is modulated in accordance with the effective reflectivity R
eff
of the etalon. Also, oscillation occurs only in the mode, which is subjected to the smallest loss among the plurality of the resonator longitudinal modes falling within the wavelength width W.
In the manner described above, with the etalon, the oscillation mode is brought to the single longitudinal mode. However, heretofore, it was not clear how the loss modulation with the effective reflectivity R
eff
of the etalon and the inclination of the etalon are to be set in order for all of the three requirements with respect to good, reliable single longitudinal mode characteristics, a good beam profile, and a high output to be satisfied.
The inventors conducted extensive research in order to clarify how the loss modulation with the effective reflectivity R
eff
of the etalon and the inclination of the etalon are to be set in order for all of the three requirements with respect to good, reliable single longitudinal mode c
Hyuga Hiroaki
Okazaki Yoji
Fuji Photo Film Co. , Ltd.
Ip Paul
Sughrue & Mion, PLLC
Vy Hung T
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