Excited state absorption of pump radiation as a loss mechanism in solid-state lasers

The characteristics of optical pumping dynamics occurring in laser-pumped rare earth-doped, solid-state laser materials were investigated by using a tunable alexandrite laser to pump Y3Al5O12:Nd3+ in an optical cavity. It was found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process will be an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths