Prospects of Holmium-doped fluorides as gain media for visible solid state lasers

Abstract

In this paper we report on the suitability of Ho3+:LiLuF4 and Ho3+:LaF3 as active media for solid state lasers emitting in the green spectral region. The ground state absorption spectra were measured and employed to calculate the emission cross section spectra via the reciprocity method. These allowed to derive the gain characteristics for various inversion ratios. The decay dynamics of the 5F4,5S2 multiplet, which would act as upper laser level, were investigated to estimate the quantum efficiency. Measurements of the excited state absorption were conducted which showed that stimulated emission is the dominating effect around 550 nm. Laser operation was demonstrated in the green spectral region by employing Ho3+:LaF3 as gain medium. Laser oscillation occurred in a self-pulsed regime with a maximum average output power of 7.7 mW, a repetition rate of 5.3 kHz, and a pulse duration of 1.6 μs. To the best of our knowledge this constitutes the first green laser emission of a Ho3+-doped crystal at room temperature.