Coherent light generators – Particular pumping means
Patent
1997-01-15
1998-10-13
Healy, Brian
Coherent light generators
Particular pumping means
372 39, 372 40, 372 70, 372 71, 372 51, 372 55, H01S 309
Patent
active
058223533
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the field of quantum electronics, and more particularly to lasers emitting at wavelengths of above 1.4 .mu.m.
DESCRIPTION OF THE PRIOR ART
Known are lasers using yttrium aluminum garnet (YAG) and yttrium aluminate (YAlO.sub.3) crystals doped with trivalent erbium ions (Er.sup.3+), in which, to reduce the threshold lasing energy at transitions between .sup.4 I.sub.11/2 and .sup.4 I.sub.13/2 levels at a wavelength of about 3 .mu.m, wavelength-selective filters isolating the active element from the pumping lamps and absorbing the pumping light with wavelengths below 645 to 545 nm are used. These filters interposed between the active medium and the pumping light source comprising one or several lamps are made in the form of filtering additives either to the liquid medium surrounding the pumping light source lamp(s) and/or the active element ( J. "Optics Letters", vol. 13, No. 11, 1988, J. Frauchiger et al.: "Laser Properties of Selectively Excited YAlO.sub.3 :Er",p.p.964-966), or to the material of the optical component isolating the active medium from the pumping light source (IEEE J. Quant. Electr., vol. QE-28, No. 11, 1992, J. Breguet et al.: "Comparison of Threshold Energy of Selectively Excited YAlO.sub.3 :Er and YAG:Er Lasers", p.p. 2563-2566).
The use of such lasers at the propagation of their radiation through humid atmosphere over large distances is a matter of some difficulty because a considerable absorption in atmospheric water vapors is observed at their lasing wavelength of about 3 .mu.m.
It is also known that lasing has been achieved in YAlO.sub.3 crystals doped with Er.sup.3 + ions in four-level operation at transitions between .sup.4 S.sub.3/2 and .sup.4 I.sub.9/2 levels at emission wavelengths between 1.6 and 1.8 .mu.m which coincides with the high atmospheric transmission region ( J. "Phys. D: Appl.Phys.", vol. 17, 1984, B.Dishler et al.: "Investigation of the laser materials YAlO.sub.3 :Er and LiYF.sub.4 :Ho", p.p. 1115-1124).
In such solid-state lasers using an active medium based on erbium-doped YAG and YAlO.sub.3 crystals the liquid medium isolating the pumping light source from the active medium comprises filters based on complex salts ( for example, NaNO.sub.3) and on various organic compounds ( IEEE J. Quant. Electr., vol. QE-23, No.2, 1987, M. Datwyler et al.: "New Wavelengths of the YAlO.sub.3 :Er Laser", p.p. 158-159). These filters have transmission bands in the spectrum of the said salts and organic compounds over the UV wavelength range, which cause the active medium degradation. They do not provide the desired useful life of lasers because of incomplete UV filtering, due to which the lasers have a low efficiency and a high threshold pumping energy the minimum value of which is 34 to 55 J.
In the U.S. Pat. No. 4,039,970, 1977, H01S 3/092 is described a solid-state laser with a light filter, which comprises an active medium doped with erbium ions and a pumping light source with an envelope made of a pumping light-transmitting material, which is isolated from the active medium by a gaseous and/or liquid medium and/or optical components intercepting and removing the pumping light short-wavelength component with wavelengths below 500 nm. Such a laser has an enhanced lasing threshold, 50 J, at the output mirror transmittance of 5%, but insufficient lasing efficiency, 3 mJ, at a wavelength of 1.663 nm and a pumping energy of 100 J.
In the EP 0,427,856 A1, H01S 3/092 document is described a solid-state laser comprising short-wavelength radiation absorbing volume filters with a small content (up to 1.5%) of rare-earth metals, including cerium (Ce). Such filters have a low optical density in the UV part of the spectrum. This causes the active medium degradation photo-induced by UV radiation resulting in the formation of color centers which absorb the pumping radiation over the Er.sup.3+ ion excitation range thus reducing the lasing efficiency and enhancing threshold pumping energy.
Known are lasers comprising protective coa
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Karlov Vasily N.
Semenov Alexei A.
Creighton Wray James
Healy Brian
Narasimhan Meera P.
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