Rowland ghost suppression in high efficiency spectrometer gratings fabricated by e-beam lithography

In this paper we report different methods to improve the stray light performance of binary spectrometer gratings fabricated by electron beam lithography. In particular, we report the optimization concerns about spurious stray light peaks, also known as "Rowland ghosts". As already known these Rowland ghosts arise from a non-optimized stitching process of special subareas needed in order to fabricate large area gratings. One approach to reduce the impact of the stitching errors is the technique of "multi-pass-exposure" (MPE). Furthermore, the potential of a direct improvement of the stitching accuracy via special calibration parameters is examined. In both cases the effects on the stray light performance were determined by angle resolved scattering measurements. The achieved results show that specific calibration parameters of an e-beam writer have a strong influence on the strength of the Rowland ghosts and that their recalibration combined with an adapted writing regime reduces the peaks significantly.