Generation of optical apertures with ns-laser micromachining of metal layers

Optical apertures are simple standard components in optics and laser physics. Today, they are produced by using microstructure technology (etching process), electrical discharge machining or laser drilling in foils. In some applications, when diffraction effects on apertures or aperture arrays in the micrometer range are specifically exploited, it becomes apparent that the precision of technologies such as laser drilling is insufficient and high-precision microstructure technology is too cost-intensive for some applications [1,2,3]. As an example, we observe this when measuring the phase of laser beams by diffraction at a scanning pinhole. Based on this problem, a cost-effective process was developed in the presented project. We use cost effective diode-pumped ns-lasers and investigate the direct ablation of thin metal layers on glass substrates. We compare different metal layers and layer systems which we apply via sputtering. It is known that laser drilling with ns-pulses achieved worse results than fs-lasers, especially in the micrometer range, due to temperature input and molten material. However, especially for very thin metal layers, this effect is not be too strong and good results should be achievable down to the sub-micrometer range [4]. In tests we optimize the parameters mechanical layer stability, highest optical density at minimum layer thickness, smallest achievable ablation structure and especially important the tolerance range of the process window. This provides a low-cost micro processing stage for the direct and reproducible production of diffractive optical structures. We are also investigating the direct production of complex elements such as diffraction gratings and DOEs. For both, the technology could be a kind of rapid prototyping for customized applications. Another initial application we are investigating is the micro structuring of coated fibers for SPR-sensors [5].