Growth, spectra and continuous-wave 2.1 μm laser operation of a Ho3+-doped bismuth silicate crystal

Abstract

Single crystals of Ho³⁺-doped bismuth silicate (BSO) were grown by a modified Bridgman method. The spectroscopic properties for 2 μm laser operation via the ⁵I₇ → ⁵I₈ transition were investigated based on the absorption, emission and gain cross-section spectra of the as-grown crystal. Judd–Ofelt (J–O) theory was applied to calculate the J–O intensity parameters Ω_2,4,6, spontaneous emission probabilities, branching ratios and radiative lifetimes. The Ho³⁺:BSO crystal was in-band pumped at 1940.3 nm by a Tm fiber laser to produce an efficient continuous wave (CW) laser output at 2109.8 nm. The maximum output power obtained was 0.73 W, and the corresponding slope efficiency with respect to the absorbed power was 38.8% and the beam propagation factor M² of the Ho³⁺:BSO laser in horizontal and vertical directions was estimated to be 1.09 and 1.06, respectively.