Revisiting ytterbium doped silica spectroscopy

Abstract

A thorough investigation of the spectroscopic properties of ytterbium-doped silica as a function of temperature (77-420 K) is carried out. Whitelight absorption and fluorescence collected under 915 nm excitation are used to calculate the temperature-dependent laser cross-sections. These datasets are made publicly available in this work. Factors influencing the acquisition and interpretation of Yb-doped glass spectroscopic data are discussed, including spectrum fitting ambiguities, site-selective excitation, lifetime decay versus spectral integration, vibronic features, and the validity of the McCumber theory over the studied temperature range. Site-selectivity affects the measurement of the emission lineshape at standard pump wavelengths of 915, 940, and 976 nm at room temperature. Lifetime measurements under 915 nm excitation vary by up to 10%, depending on the choice of bandpass or long pass filter employed and hence the spectral region integrated over. The McCumber transform yields reasonable agreement with measured spectra over the range of ∼200-420 K and then diverges rapidly at lower temperatures. Considering the measured cross-section data in the range applicable to contemporary fiber laser system operation, between 300-420 K, the cross-sections for some spectral regions change by more than 10%, including the absorption cross-section at 977 nm and the emission cross-section at 1030 nm. Some regions are essentially unchanged over the same temperature range, such as absorption at 940 nm and emission at 1045 nm. The provided data will be useful for future modeling and simulation efforts to consider the temperature-dependence of relevant quantities including, but not limited to, lifetime, cross-section, gain, and intensity saturation.