Spectroscopic properties of Ho~(3+), Tm~(3+) and Ho~(3+)/Tm~(3+) doped tellurite glasses for fiber laser applications

摘要

Several papers were reported on spectroscopic properties of rare earth doped different host glasses. A complete knowledge of fluorescence properties of rare earth ions in laser materials is necessary to achieve efficient, compact and cheap sources of laser radiation for NIR and mid-IR region. Tellurite glasses are potentially useful for generation of NIR and mid-IR laser radiation due to its special features such as lowest phonon energy (750 cm~(-1)) among oxide glasses, reasonably wide transmission region (0.35 - 5μm), good glass stability, good rare earth ion solubility, high linear and non-linear refractive index. In the present work, authors prepared Ho~(3+) and Tm~(3+) singly doped and Ho~(3+)/Tm~(3+) co-doped tellurite glasses using conventional melt-quenching method. Spectroscopic measurements and analysis of energy transfer process in Ho~(3+), Tm~(3+) and Ho~(3+)/Tm~(3+) co-doped glasses pumped with 785nm and 451 nm excitation wavelengths have been performed. There are some spectroscopic properties which are important in understanding and modeling of rare earth doped laser materials. Using Judd-Ofelt theory, radiative transition rates (A_(rad)), radiative lifetimes (τ_R) and branching ratios (β) were estimated for certain excited states of Ho~(3+) and Tm~(3+) doped tellurite glasses. The emission cross-sections and gain coefficients have been determined from the absorption spectra of Ho~(3+) and Tm~(3+) ions in tellurite glasses. The energy transfer process such as ion cross-relaxation, Tm~(3+)-Ho~(3+) energy transfer and energy transfer up-conversion were studied and identified to specific candidate for laser operation.