Focusing a CW argon-ion laser beam onto semiconductor-doped glass results in the controlled formation of a refractive microlens on top of a commercially available packaged diode laser. According to researcher Nabil Lawandy of Brown University (Providence, RI) this simple method may be a cost-effective alternative to current multistep microlens-fabrication processes, which typically involve photolithography and/or ion-implantation steps. Semiconductor-doped glasses are sold commercially as long-pass filters; these materials are borosilicate glass uniformly impregnated with nanometer-sized crystals of semiconductors.
Above-bandgap light focused to a sufficiently small radius with an adequately high intensity is necessary to fabricate a microlens. The microlens is then usable at wavelengths longer than the bandgap of the chosen semiconductor-doped glass. Varying diameter or intensity of the laser beam creates lenses with diameters ranging from 3 µm to the upper limit, which is determined by available laser power. The simple model proposed for this process is one in which laser irradiation causes the glass material to melt and solidify. Because molten glass has a lower density than solid glass, the extra volume swells u¥from the substrate and resolidifies to form a microlens.