fiber lasers

Laser action in a rare-earth-doped chalcogenide glass has been demonstrated by researchers at the Optoelectronics Research Centre in the University of Southampton (Southampton, England), working with colleagues from the Institut f?r Laser-Physik, Universitat Hamburg (Hamburg, Germany). The neodymium-doped gallium lanthanum sulfide (Nd:GaLaS) laser operated CW at a wavelength of 1.08 ?m when optically pumped with a Ti:sapphire laser at either 815 or 890 nm. Additionally, the grou¥has demonstr

Aug 1st, 1996

fiber lasers

Rare-earth-doped chalcogenide glass lases

Bridget R. Marx

Laser action in a rare-earth-doped chalcogenide glass has been demonstrated by researchers at the Optoelectronics Research Centre in the University of Southampton (Southampton, England), working with colleagues from the Institut f?r Laser-Physik, Universitat Hamburg (Hamburg, Germany). The neodymium-doped gallium lanthanum sulfide (Nd:GaLaS) laser operated CW at a wavelength of 1.08 ?m when optically pumped with a Ti:sapphire laser at either 815 or 890 nm. Additionally, the grou¥has demonstrated fabrication of GaLaS optical fibers, with core-clad fibers more than 200 m long being produced (see figure). Both of these demonstrations are believed by the researchers to be Ofirsts,O and the underlying developments represent significant steps toward the realization of fiber lasers operating at new wavelengths.

Chalcogenide glasses have interesting optical and acoustical properties that make them good candidates for rare-earth-doped laser hosts. Their transparency at longer wavelengths is higher than for silica glasses. In addition, the excited states of rare-earth ions set in chalcogenide glasses have a low nonradiative decay rate due to the low vibrational frequencies of the glass bonds. And their high refractive index increases the radiative decay rate. Such properties make possible new laser transitions and can increase the efficiency of those already used in other glass hosts. Nonetheless, the high coefficient of thermal expansion and strong temperature dependence of the refractive index lead to a strong thermal lensing effect that could limit laser output power.

The Southampton researchers found that the shorter Ti:sapphire pump-laser wavelength, although absorbed strongly, produced more thermal problems than the longer-wavelength pum¥laser. For pumping at 890 nm, best results were produced with 5% output coupling?the threshold was below

10 mW of pum¥power, and a maximum output of 2.7 mW at 1.08 ?m was obtained. Although fluorescence was seen from the three transitions, at 0.915, 1.08, and 1.36 ?m, only the 1.08-?m line was seen to lase.

In future work, the two groups hope to optimize the system by changing doping concentrations and configuration of the laser.

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