Study On Heavily Erbium-doped Low-hydroxyl Fluorotellurite Glasses For2.7μm Laser Applications

Mid-infrared （MIR） laser has found wide applications in atmospheric opticalcommunication, remote mapping, molecular spectroscopy, molecular trace detection,MIR optical sensor, medical and biochemical therapy, industrial processing, defense,and so forth. Since MIR fiber lasers have low lasing threshold, high conversionefficiency, tunable output wavelength, high reliability, easy maintenance, and are easyto integrate with many kinds of optoelectronic systems simultaneously, they havebeen a research hotspot in the field of MIR lasers. To get MIR fiber laser, the keyissue is the preparation of laser glass materials. Among the gain media for MIR fiberlasers, erbium doped fluoride glasses become favorable candidates because of theirlow phonon energy, wide MIR transmission window and high laser damage threshold.They have received much attention because of the intense2.7m emission from the4I11/2→4I13/2transition of Er³⁺ions and its convenient976nm pump band. However,fluoride glasses have poor thermal and chemical stabilities and they are not suitablefor practical applications. Therefore, it is necessary to explore new glass materialswith better thermal and chemical stabilities for MIR fiber lasers.In this thesis, we focused on erbium doped fluorotellurite glasses for MIR lasers.Firstly, we fabricated a series of heavily erbium-doped low-hydroxylfluorotellurite glasses with molar composition of （85.7x）TeO2+xBaF2+（14.3y）Na₂CO₃+yEr₂O₃（x=38.1,28.6,19; y=4.8,6.7,7.6,8.6,9.5） bymelting-quenching method in high pressure pure oxygen atmosphere. The maximumdoping concentration of erbium ions was up to19mol%and larger than ever reported（<0.5mol%）. Meanwhile, the minimum absorption coefficient of OH at2.7m wasabout0.0702cm1. Under980nm excitation, intense emissions around2.7m fromthe4I11/2→4I13/2transition of Er³⁺ions were observed in these glasses. The efficientmid-infrared emission can be attributed to the existence of cross relaxation （CR）4I13/2→4I15/2(Er³⁺):4I13/2→4I9/2(Er³⁺) caused by high erbium concentration, low hydroxylcontent and low phonon energy. The stimulated emission cross section at2.7m of the glass （47.6TeO₂+38.1BaF₂+4.8Na₂CO₃+9.5Er₂O₃） was calculated as1.94×1020cm². We also characterized the thermal stability through DTA to determine thefiberized capacity of TBNE glasses. The onset crystallization temperature （Tx） and thetransition temperature （Tg） are358°C and492°C in TBNE-1e glass, respectively.The working temperature range ΔT=Tx Tgwas around134°C, therefore, whichmeans that TBNE-1e glass can be easily fiberized without surface crystallizationsduring fiber drawing.Secondly, we found that the crystallization occurred in fluorotellurite glasseswith low erbium concentration （<0.033mol%） and disappeared for high erbiumconcentration （>0.033mol%）. To clarify it, we investigated the crystallizationkinetics of our glass samples by measuring the XRD patterns and upconversionspectra of the glasses. We also observed the enhancement of upconversionfluorescence in erbium-doped transparent fluorotellurite glass-ceramics.