Upconversion emission obtained in Yb3+-Er3+ doped fluoroindate glasses using silica microspheres as focusing lens

An intensity enhancement of the green upconversion emission from a codoped Er3+-Yb3+ fluoroindate glass has been obtained by coating the glass surface with silica microspheres (3.8 mu m diameter). The microspheres focus an incoming beam (lambda approximate to 950 nm) on the surface of the fluoroindate glass. The green emission (lambda approximate to 545 nm) of the Er3+ ions located in the microsphere focus was measured with a microscope in reflection mode, being the peak intensity 4.5 times the emission of the bare substrate. The transversal FWHM of the upconversion spot was experimentally determined by deconvolution with the experimental Point Spread Function of the system, obtaining a value of 309 nm. This value is in good agreement with Finite-Difference Time-Domain simulations taking into account the magnification of the image due to the microsphere. (c) 2013 Optical Society of America