Enhanced energy upconversion and super-resolved focused spot generation in Tm3+-Yb3+ codoped glass using silica microspheres

We report the enhancement of the blue upconversion emission in a Tm3+-Yb3+ codoped fluoroindate glass covered with silica microspheres. Each microsphere produces a photonic nanojet that concentrates the illuminating beam in a tiny region of the glass, increasing the intensity per unit area and so the upconversion emission by a factor of 3. Moreover, the mean size of the emission area has been reduced by a factor of root 3 due to the three-photon process involved in the blue emission band. The experimental values of the full width at half-maximum of the emission spots have been found to be in agreement with the theoretical values obtained from finite-difference time-domain simulations. (C) 2013 Optical Society of America