Stepped mask interference laser exposure (SMILE)

We present a proof-of-concept of a novel fabrication setup for polarization converters – stepped mask interference laser exposure (SMILE). The SMILE setup enables the costeffective fabrication of polarization converters by means of standard laser interference lithography and dry etching processes. Key advantages of the proposed system include a large clear aperture diameter, limited only by the size of the lithography system, and a short fabrication time. Lloyd’s mirror interference lithography setup is modified by adding a mask with a circular sector opening. The mask and a substrate have independent rotation drives enabling the fabrication of segmented diffraction gratings with different grating line orientations. Each segment acts as a half-wave plate converting incident linear into radial polarization. Radial polarization is particularly beneficial in high-power laser applications, e.g. in material processing, as it provides higher cutting efficiency. Using SMILE we fabricated a segmented diffraction grating with a pitch below 500nm and a clear aperture diameter of 30mm. With an exposure time of 18s per segment, the resulting total processing time was below 5 minutes. 74 aktive Optische Elemente Meike Hofmann