Alexander K. Przhevuskii

Experimental determination of the upconversion rate in erbium-doped silicate glasses

A new experimental method for direct determination of the upconversion coefficient C(up) in Er-doped glasses is presented. This method is based on measurement of the dependence on pump power of the fluorescence quantum yield at 1.54 microm and of the excited-state absorption. Two methods are used for determination of the population of the excited Er ions. The first is based on the measurement of the variation in stimulated emission and on the variation in ground-state absorption for the (4)I(15/2)<-->(4)I(13/2) transition range. In the second, the excited-state absorption is measured for the (4)I(13/2) -->(4)F(7/2) transition. This method is successfully applied to Er-doped silicate glass fibers. The value of C(up) experimentally obtained is in good agreement with previously published results.

Characterization of non-linear upconversion quenching in Er-doped glasses: modeling and experiment

Non-linear upconversion quenching in highly Er-doped glasses has been studied with use of Monte-Carlo modeling and a new experimental steady-state technique. The experimental and simulated results exhibit that the upconversion coefficient depends on the following factors: (a) erbium content, (b) migration of excitation, (c) pump power, and (d) duration of pump pulse.

Monte-Carlo simulation of upconversion processes in erbium-doped materials

Abstract Nonlinear upconversion quenching in Er-doped materials has been studied with use of Monte-Carlo modeling. Structure models allowed one to consider homogeneous Er3+ ions space distributions as well as clustering. Two variants of the simulation algorithm have been developed which took into account an evolution of one excitation or evolutions of all excitations simultaneously. The obtained results provided quantitative data on the influence of the following factors on the upconversion efficiency: (a) erbium content, (b) migration of excitation, (c) pump power, and (d) duration of pulse pumping.

Classification of Stark structure in spectra of Nd-doped glasses

Abstract The absorption spectra of Nd3+ ions in more than 120 binary compositions of silicate, phosphate, germanate and borate glasses containing M2O (M  Li, Na, K, Rb, Cs), MO (M  Be, Mg, Ca, Sr, Ba) and M2O3 (M  Al, La) oxides as modifiers were investigated at 80 K. The study has revealed a number of cases when the absorption spectra of different glass-former-based glasses exhibit a striking similarity of spectral contours. Based on this result we introduce a concept of ‘spectrum type’ and classify all investigated spectra into types, the spectra of different glasses with similar contours being combined within one type. The spectrum variations with equimolar change of a modifier type and with alteration of a modifier (alkaline oxide) content were analyzed in terms of this classification. The analysis led to an inference about ‘the chemical composition’ of the second coordination sphere of Nd3+ ions for a number of types of neodymium centres. Recommendations for modelling of RE-doped glasses is proposed.

Spectral and luminescence properties of neodymium in chalcogenide glasses

Abstract Absorption and luminescence of chalcogenide glasses doped with neodymium were measured. Neodymium concentrations ≤2 wt% were achieved. Absorption spectra of the glass matrixes, matrixes with dopant (Nd3+) and impurities were measured. Luminescence spectra and the excited state lifetime of Nd3+ were also measured. It was shown that spectral properties of Nd3+ are similar regardless of which neodymium compound was used. However, these spectral properties differ when the base glass is either an oxide or a fluoride. It was found that the quantum yield of Nd3+ in the chalcogenide samples, approaches 100%. The viability of chalcogenide matrixes as laser hosts are discussed.

Study of polarized luminescence in erbium-doped laser glasses

A partial polarization of luminescence in laser phosphate and silicate erbium-doped glasses was found to take place for the fundamental laser transition 4I13/2→4I15/2 (λ=1.55 μm) under excitation by linearly polarized laser radiation (532 and 790–990 nm). The shape of the luminescence spectrum depends on the wavelength of the exciting light and on the composition of the glass matrix. The degree of polarization of the luminescence depends on the spectral range of both the excitation and the detection, attaining a maximum of ∼1%. The concentration dependence of the degree of polarization is studied.

Effect of pumping on spectral characteristics of Er-doped glasses

The fluorescence and absorption variation of spectra of Er- and Yb/Er-doped phosphate and silicate glasses under CW Ti- sapphire laser were investigated. On pumping, the differential spectra demonstrated variations of spectral profiles. The reason of these variations is heating effect under high pump power. These variations were explained by a redistribution of the populations of the Stark sublevels of the 4I15/2 ground and the 4I13/2 excited manifolds. The heating effect under pumping was taken into account for measurement of quantum yield and determination of absolute values of up-conversion coefficients. Several techniques that reduce the heating effect on fluorescence, excited state absorption, and ground state absorption spectra due to pumping were proposed.

Measuring the gain/loss spectra in high-concentration ytterbium-erbium-doped laser glasses

The gain/loss spectra of ytterbium-erbium-doped laser glasses have been investigated in the 1.5-µm region. A direct experimental method has been developed for determining the population of the excited metastable 4I13/2 level, the contour of the gain/loss spectrum, and its variation at various pumping levels. The experimental and calculated spectra are compared.

Steady-state characterization of up-conversion quenching in Er-doped glasses with the use of hypersensitive bands of ESA and GSA spectra

A steady-state method was used for characterization of up- conversion quenching in Er-doped glasses. This method is based on measurement of pumping dependencies of quantum yield and the population of the 4I13/2 metastable manifold. The population was determined from absorption spectra variation under the pump of semiconductor laser. The feature of the method consists in measurement of absorption spectra variation in short-wave spectral range of 300 - 520 nm. In this spectral region, a hypersensitive excited state absorption (ESA) band ((lambda) equals 478 nm) for 4I13/2 yields 4G9/2 transition was detected. The following parameters characterizing absolute intensity of ESA band were determined: line strength, integral cross- section, cross-section in maximum, and oscillator strength. This band was used for evaluation of the population of the 4I13/2 metastable manifold and up-conversion coefficients. The up-conversion coefficient, Cup equals 1.7 X 10-17 cm3s-1, was obtained for an Er3+ concentration of 6.8 X 1020 cm-3.

Effect of heating on spectral characteristics of Er-doped laser glasses

The absorption and fluorescence spectra of Er-doped phosphate and silicate laser glasses were investigated in a temperature range of 20 - 300 degree(s)C. On heating, the differential spectra demonstrated variations of spectral profiles. The effects of heating for silicate and phosphate glasses are similar. The contours of the absorption and luminescence bands varied nonmonotonically with the temperature. These variations were explained by a redistribution of the populations of the Stark sublevels of the 4I15/2 ground and the 4I13/2 excited terms. The heating resulted in 5 - 10% decrease of oscillator strengths of spectral bands. On the base of temperature variations of spectral profiles we proposed an energy levels model, which allowed to explain the thermal variation of spectrum of Er-doped laser at 1.54 micrometers . According to this model, the transitions in two range of lasing (1534 and 1542 nm) come from two Stark sublevels of the 4I13/2 excited manifold to two sublevels of the 4I15/2 ground manifold. The effective energy gaps between neighboring Stark components are equal to 50 cm-1 and 100 cm-1 for the 4I13/2 and the 4I15/2 states, respectively.