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 %
Here, we report on the approach of realizing an all-fused-silica PGP disperser (prism + grating + prism) by low temperature direct bonding. A surface relief grating with period 660nm and overall depth of approximately 2000nm is sandwiched between two equal prisms. Direct bonding of glass relies on the formation of covalent bonds between hydrophilic silicon-oxide surfaces. Compared to other joining technologies, like adhesive bonding or optical contacting, the established connection is stiff, shows no outgassing, is highly resistant against chemical and radiative degradation and the established optical interface is intrinsically impedance-matched. In summary, two prototypes were realized, optically characterized and successfully underwent environmental testing. The overall diffraction efficiency of the PGP is larger than 90%.
We report on subwavelength reflective gratings for hyperspectral applications operating in the 340 nm-1040 nm spectral range. The blazed grating period is 30 μm and is composed of 2D subwavelength binary structures with sizes in-between 120 nm and 350 nm. We demonstrate the manufacturing of gratings on 3” wafers by two lithography technologies (e-beam or nanoimprint) followed by dry etching process. These subwavelength gratings enable broadband efficiency which is in average 15%-20% above the efficiency requirement for next generation of spectro-imagers for Earth observation missions and a wavefront error that is much smaller than the 100 nm requirement for space application.
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