Ultra-low threshold glass thin film random lasers

Multiple scattering of light in several materials can lead to diffusion and localization of photons resulting in random lasing and it has attracted much interest recently. In a low dimensional scattering medium with gain, random lasers can operate with low threshold and higher efficiency. In this work we report the fabrication and operation of a 2-dimensional, tunable random laser requiring very low threshold pump power. Nanoporous glass thin films of high refractive index (~2) were grown using ultrafast laser ablation of tellurite glass doped with Er³⁺ ions. The films were characterized for their thickness, effective refractive index, porosity and, scattering strength. The lasing characteristics of the films were carried out using a continuous wave pump laser at 980 nm Low threshold random lasers were obtained with wide tunability in the wavelength region of 1512-1612 nm in a stable and easily reproducible planar slab waveguide structure. The tunability was obtained by varying the angle of collection of laser output from the film surface. Figures la shows the transmittance spectra of the film used for laser experiments and lb show the spectrum of the laser obtained at an angle of collection of 43°. The lasing at various other wavelengths was obtained by the use of films doped with other rare earth ions as well.