Coherent light generators – Particular active media – Insulating crystal
Patent
1993-03-22
1995-05-16
Scott, Jr., Leon
Coherent light generators
Particular active media
Insulating crystal
2523014R, H01S 316
Patent
active
054167892
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to crystals and more particularly to neodymium-doped gehlenite monocrystals. It can be used either in the field of microlasers for integrated optics, optical fibre telecommunications, medicine (microsurgery, skin treatment) and research on semiconductors, or in the field of power lasers making it possible to carry out material treatments (welding, perforating, marking, surface treatment), photochemical reactions, controlled thermonuclear fusion or the polarization of the atoms of a gas such as helium. These lasers emit in the infrared between 870 and 1130 nm. More particularly, the invention applies to lasers optically pumped by a laser diode and which can be wavelength tuned between 1050 and 1100 nm.
The most frequently used, commercial solid power lasers make use of a garnet of yttrium and aluminium Y.sub.3 Al.sub.5 O.sub.12 (YAG), doped by Nd.sup.3+. However, this material suffers from disadvantages. Thus, it has a crystallogenesis at a high temperature of 1900.degree. to 2000.degree. C., which makes it difficult and expensive, a segregation of the dopant, narrow absorption bands, etc. Therefore research has been carried out with a view to finding new matrixes and this has also been made necessary by the ever improving performance characteristics required for new lasers, namely very high efficiency, miniaturization, emission at various wavelengths, etc.
Numerous matrixes which can be doped by Nd.sup.3+ have been proposed in the literature. Among these matrixes, reference can be made to compounds such as melilite ALaGa.sub.3 O.sub.7, gehlenite AGa.sub.2 SiO.sub.7 and akermanite A MGe.sub.2 O, in which A represents the Ca.sup.2+, Sr.sup.2+2 or Ba.sup.2+ ions and M represents Be.sup.2+, Mg.sup.2+ or Zn.sup.2+ ions.
Compared with doped aluminium and yttrium garnet, these compounds have the major advantage of being producible by the Czochralski method, which is the most widely used in the laser industry and at temperatures roughly 500.degree. C. lower. In addition, there is no segregation of the luminescent dopant.
Under flash lamp optical pumping, a certain number of these compounds have the laser effect.
The document A. Keminskii et al. Phys. Star. Sol. (a), 97, 1986, pp 279-290, "Crystal structure, absorption, luminescence, properties, and stimulated emission of Ga gehlenite" describes the stimulated emission in a Ca.sub.2 Ga.sub.2 SiO.sub.7 monocrystal doped with neodymium ions.
The article by W. Ryba-Romanowski et al., J. Phys. Chem. Solids, 50, 1989, pp 685-692 "Relaxation of the .sup.3 F.sub.3/2 level of Nd.sup.3+ in BaLa.sub.1-x Nd.sub.x Ga.sub.3 O.sub.7 " describes the laser emission of a monocrystal of BaLa.sub.1-x Nd.sub.x Ga.sub.3 O.sub.7 with 0.ltoreq..times..ltoreq.0.2.
The article by D. J. Horowitz et al, J. Appl. Phys., vol. 43, No. 8, August 1972, "Laser action of Nd.sup.3+ in a crystal Ba.sub.2 ZnGe.sub.2 O.sub.7, pp 3527-3529 describes the laser effect of a Ba.sub.2 ZnGe.sub.2 O.sub.7 crystal doped with neodymium with a quantity of 2 mole %.
The article by M. Alan et al., J. Appl. Phys. 39, 1968, "Optical spectra and laser action of neodymium in a crystal Ba.sub.2 MgGe.sub.2 O.sub.7 ", pp 4728-4730 describes the laser effect of a crystal of Ba.sub.2 MgGe.sub.2 O.sub.7 doped with neodymium with approximately 2 mole %.
All these compounds have the advantage of a uniaxial quadratic structure, whereas the YAG crystal is cubic, so that a polarized emission can be obtained.
Unfortunately, all these compounds suffer from the disadvantage of containing a large amount of gallium, which is expensive. Moreover, it is unstable in oxidation state 3.sup.+ at high temperature, as a function of the working conditions and with the possibility of volatilization. Moreover, due to the volatilization of the gallium, the crystals obtained by Czochralski growth have inadequate quality characteristics when it is a question of obtaining the large dimensions required by the power laser industry.
Moreover, these compounds have a thermal conductivity making it difficult to d
REFERENCES:
patent: 4820445 (1989-04-01), Piekarczyk et al.
Finch et al; Czochralski Growth and Characterization of Single-Crystal Akelmante (Ca.sub.2 MgSi.sub.2 O.sub.7): Jour. Crystal Growth 23 (1974) pp. 295-298.
Finch et al.; Czochralski Growth of Single-Crystal Gehenite (Ca.sub.2 AlSiO.sub.7); Jour. Crystal Growth 54, (1981) pp. 482-484.
Kaminskii et al; "Crystal Structure, Absorption, Luminescence Properties, and Stimulated Emission of Ga Gehlenite"; Phys. Stat. Sol(A) vol. 82, No. 297, 1986.
J. Crystal Growth, vol. 54, No. 3, Sep. 1981, Amsterdam, NL pp. 482-484, C. B. Finch et al. "Czochralski Growth of Single-Crystal Gehlenite (Ca2Al2SiO7)" (see p. 482).
J. Crystal Growth, vol. 23, 1974, Amsterdam, NL, pp. 295-298, C. B. Finch et al., "Czochralski Growth of Single Crystal Akermanaite (Ca2 Mg2Si2O7)" (see p. 297).
Phys. Stat. Sol.(A), vol. 97, No. 297, 1986, Berlin, Allemagne, pp. 279-290, A. A. Kaminski et al., "Crystal Structure, Absorption, Luminescence Properties and Stimulated Emission of Ga Gehlenite".
Benitez Jean-Marie
Collongues Robert
LeJus Anne-Marie
Saber Driss
Vivien Daniel
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