Dielectric micro-cavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate micro-lasers of simple shapes (Fabry-Perot, square, pentagon, and disk). Their lasing spectra consist mainly of almost equidistant peaks and the distance between peaks reveals the length of a quantized periodic orbit. To measure this length with a good precision, it is necessary to take into account different sources of refractive index dispersion. Our experimental and numerical results agree with the superscar model describing the formation of long-lived states in polygonal cavities. The limitations of the two-dimensional approximation are briefly discussed in connection with micro-disks.

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Er 3+ /Yb 3+ co-doped phosphate glass and Er 3+ :ZBLALiP fluoride glass microsphere lasers have been studied under pumping by a fiber taper at 1480 nm. Whispering Gallery Mode laser spectra were analyzed for different sphere diameters. Red-shift effect on the wavelengths of both fluorescence and laser spectra is experimentally observed when the pump power is increased, originating from thermal effects. We showed coupling effect between microspherical laser and an external cavity made by a metallic mirror. We observed line shift to lower wavelengths due to optical feedback effect.