Fabrication of Cylindrical Lenses by Combining Ultrashort Pulsed Laser and CO2 Laser

We report on the fabrication of cylindrical lenses by combining an ultrashort pulsed laser ablation process with a subsequent CO2 laser polishing step. Firstly, a 1030 nm ultrashort pulsed laser is used to ablate a designed geometry in fused silica in a layer-by-layer process. In a comprehensive parameter study, we find that the ablation height depends exponentially on the pulse-to-pulse distance and linear on both laser fluence and layer repetitions. This facilitates to precisely choose the step height of the multi-layer ablation process to about 1 mu m, which allows maintaining a high contour accuracy for fabricating and shaping 3D objects. In a subsequent step, a defocused 10.6 mu m CO2 laser is applied to solely polish the rough surface of the 3D objects, i.e. the CO2 laser does not shape the finally targeted object but rather fuses and thereby smoothens the surface. Microscopic measurements reveal an improvement of the surface roughness of about 0.6 mu m after the ablation process by two orders of magnitude after the CO2 laser smoothing process. The functionality of thus fabricated cylindrical lenses is tested using a HeNe laser. A typical beam profile for cylindrical lenses, which remarkably corresponds to the intensity profile of a Gaussian beam, is observed. This photonic process chain paves the way towards an all optical 3D micro-shaping technology with a high degree of geometrical freedom for medium sized volume production to single component rapid prototyping.