Optimum  grating  parameters  for  a  VUV  (vacuum  ultraviolet)  spectrometer

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Abstract

The  object  of  the  invention  is  to  provide manufacturing parameters for a  holographic  diffraction  grating  on  a  concave  or  toroidal  surface,  which  is used as the single optical element in a VUV spectrometer with a flat detector. The spectrometer geometry is also defined alongside the diffraction grating parameters. The invention from the research center Juelich (Germany) consists of a proprietary software  code  which  uses  various  numerical  methods  to  determine  the  optimal  grating parameters, with the aim of producing such gratings for VUV spectrometers with  a  minimal  line  width  for  a  pre-­‐defined  wavelength  and  at  the  same  time  achieving high spectrometer efficiencies.

Description of the Technology

The  invention  is  based  on  a  software  code  that  determines  manufacturing  parameters for an optimized holographic diffraction grating on a concave or toroidal surface,  together  with  the  geometry  of  the  corresponding  VUV  spectrometer  arrangement (entrance slit, grating and detector). The method described contains the  numerical  determination  of  the  full  parameter  set  for  the  grating  and  the  spectrometer. The offer focuses on providing optimum grating parameters for the production of spectrometers. Such parameters are made available through licensing.

Innovation and advantages of the offer

The method described above leads to accurate gratings with the ability to provide sharp spectrometric images at high efficiency and low stray light level. This could not be  achieved  by  mechanically  ruled  gratings  or  by  holographic  gratings  on  flat  surfaces.

Non-fusion applications

Beside the actual application domain – VUV spectrometry in Fusion, there are also applications licensed in extreme ultraviolet refractometry. A commercial spin-­‐off was created  outside  fusion  to  exploit  the  application  for  development  of  a  diffraction  grating for EUV reflectometry.

Fusion Heritage

The  method  was  developed  at  the  Forschungszentrum  Jülich  and  used  to  develop  diffraction gratings for the HEXOS spectrometer on W7-­‐X (1.2 M€, 20 ppy project). It was further used to develop the ITER VUV spectrometers (hardware to be delivered by Korea; 10 M€ project).
In the meantime, a commercial spin-­‐off was created outside fusion: Development of a diffraction grating for EUV reflectometry.

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