High performance diffraction gratings made by e-beam lithography
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Gratings are essential components in different high performance optical set-ups such as spectrometers in space missions or ultrashort-pulse laser compression arrangements. Often such kinds of applications require gratings operating close to the technological accessible limits of today’s fabrication technology. Typical critical parameters are the diffraction efficiency and its polarization dependency, the wave-front error introduced by the grating, and the stray-light performance. Additionally, space applications have specific environmental requirements and laser application typically demand a high damage threshold. All these properties need to be controlled precisely on rather large grating areas. Grating sizes of 200 mm or even above are not unusual anymore. The paper provides a review on how such high performance gratings can be realized by electron-beam lithography and accompanying technologies. The approaches are demonstrated by different examples. The first example is the design and fabrication of the grating for the Radial-Velocity-Spectrometer of the GAIA-mission of the ESA. The second grating is a reflective pulse compression element with no wavelength resonances due to an optimized design. The last example shows a three level blazed grating in resonance domain with a diffraction efficiency of approximately 86 %.
KeywordsDiffraction Efficiency Effective Refractive Index Merit Function Electron Beam Lithography Grating Period
The authors like to thank their colleagues from the CMN-Optics of the Fraunhofer IOF and the IAP of the FSU-Jena for their contributions to the realization of the gratings. All gratings exposures presented here were done using the e-beam writer SB350 OS at the Fraunhofer IOF whose purchase has been supported by the European Union (FZK: B 408—04004). Parts of the technology development presented here where supported by the German Ministry of Science and Education in the frame of the project PhoNa (FZK: 03IS2101D).
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