One-ste¥laser process forms dense microlens arrays on doped borosilicate glass
At MIT Lincoln Laboratory (Lexington, MA), researchers are developing a laser-writing technique for fabricating large, high-quality dense refractive microlens arrays that could be used in broadband and high-numerical-aperture applications. Unlike laser-based fabrication techniques that are primarily ablative, this approach relies on one-ste¥melting of the doped glass--a process that can be precisely controlled by tuning the laser heat-source parameters. Most refractive microlenses are made by photoresist reflow, laser-beam shaping of photoresist, photothermal expansion, or ion exchange.
Michael Fritze and colleagues at Lincoln Laboratory used a continuous-wave argon-ion laser operating multiline with electro-optical and mechanical shuttering to control the exposure times from 1 µs to several seconds. Typical laser output power ranged from 0.5 to 2.0 W. A key to successful manufacturing was to mount the substrates on a translation stage setu¥that allows rapid prototyping of custom lenslet arrays to enable precision control of element positioning and surface curvature. Geometries such as spheres are easily produced by this method. The researchers have begun to replicate these lens arrays with polymer-casting techniques, which may extend the usable wavelength range, eliminate the stress birefringence, and provide a potentially cost-effective method for producing large numbers of arrays from a single glass master.