Rare-earth doped fluoride thin films grown by pulsed laser deposition as possible new optical active materials.

Crystalline Nd3+:LiYF4 films on pure LiYF4 monocrystalline substrates were obtained by ablating with 355 nm laser photons a Nd3+:LiYF4 bulk crystal. The films optical quality and response were studied as function of the laser ablation fluency, the substrate temperature, the bulk ion concentration and the presence or absence of an inert gas in the ablation/deposition chamber. The films surface was checked via a scanning electron microscope while their optical response was analyzed by recording polarized LIF spectra following excitation of the fundamental Nd3+ manifolds transition. Time resolved spectroscopy provided information on the Nd3+ concentration. All the results were compared with those obtained in the bulk crystal under the same experimental conditions. The film deposited on a substrate at T = 650 °C with 10 J/cm2 laser fluency, in presence of 1Pa of He, manifested the best quality. The fluorescence around the 1050 nm, important for a possible laser action, was favoured in the film in the same way as in the bulk so making it promising as a microlaser active material. Experiments are in progress to grow good optical quality Tm3+:LiYF4 thin films for 2 µm microlaser sources.