We present our development of high-efficiency reflective grating development by holographic processing. Its primary objective is to carry out exoplanet science studies in the ultraviolet (UV) wavelength region using space-borne telescopes. While the final development goal is aspheric grating, in this study, we manufactured planar grating samples with laminar and blazed grooves for our first step in order to establish processing conditions and to evaluate characteristics of each grating. Geometry of the manufactured gratings is 30×30×10 mm, and their groove density is 2400/mm. It was confirmed by Atomic Force Microscope (AFM) evaluation that laminar and blazed grooves were constructed on the surface of each grating. The measured absolute diffraction efficiency achieved by the brazed grating is 40.2% and 44.1% at wavelengths of 122 nm and 131 nm, respectively. These values are higher than values of the laminar grating by factor of ∼1.5.
T. Imazono, M. Koike, T. Kawachi, N. Hasegawa, M. Koeda, T. Nagano, H. Sasai, Y. Oue, Z. Yonezawa, S. Kuramoto, M. Terauchi, H. Takahashi, N. Handa, T. Murano
We have developed an objective soft x-ray flat-field spectrograph installed in electron microscopes (EMs). The
spectrograph has two attractive features. One is that it is designed to cover a wide energy range of 50-4000 eV by using
four varied-line-spacing holographic gratings (VLSHGs) optimized for 50–200 eV, 155–350 eV, 300–2200 eV, and
2000–4000 eV. The gratings dedicated for the respective energy ranges can be accommodated in the single spectrograph.
This advantage comes from that the positions of the source points and image planes are assumed as the common
parameters in the design of all gratings. Therefore, it allows to easily change the energy range by only choosing an
appropriate grating and its position. The other is the application of a newly invented W/B4C multilayer coating. It has
been adopted to the grating for the 2000–4000 eV range to overcome the considerable decrease of the diffraction
efficiency in the energy range above ~2 keV. The novel coating makes it possible to enhance uniformly the diffraction
efficiency at a constant incidence angle in the whole energy range.
A versatile soft x-ray flat-field grating spectrograph to be installed to a conventional transmission electron microscope
has been developed. A holographic spherical grating of a 1200-lines/mm effective groove density which places emphasis
on the low energy region of 50-200 eV is designed by an aspheric wavefront recording system. Laminar and blazed types
master (LM and BM) gratings and their respective replica (LR and BR) gratings are fabricated by holographic exposure
and ion-beam etching methods. Absolute diffraction efficiencies in the 50-300 eV range at the angle of incidence of 86.0
degrees were measured using a synchrotron radiation. The first order diffraction efficiencies are 6.1-7.5% (or 12%) for
LM (or BM) and 7.4-9.6% (or 13%) for LR (or BR) gratings at near 55 eV, and over 5% (or 8%) in the 50-200 eV range
for LM and LR (or BM and BR) gratings. The replica gratings show the comparable first-order diffraction efficiencies
with their respective laminar and blazed types of master gratings.
A new type of monochromators that incorporates two kinds of Monk-Gillieson monochromators has been designed and constructed for the purpose of realizing an evaluation beamline for characterizing soft X-ray optical elements in a wide wavelength range of 0.7-25 nm. One of the monochromators is a conventional type equipped with three varied-line-spacing plane gratings, allowing a choice of two inclusion angles. The other is a new type that employs a scanning mechanism based on Surface Normal Rotation (SNR). The SNR scheme provides high throughput at short wavelengths and simple scanning mechanism by means of a grating rotation about its normal. The monochromators is operated in the SNR and conventional modes over the ranges of 0.7-2.0 nm and 2.0-25 nm, respectively. The system was installed on a beamline of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. In this paper we describe the optical and mechanical designs of the monochromators, and a practical method of wavelength calibration. Also experimental data are shown which demonstrate the performance and versatility of the new type of Monk-Gillieson monochromators.
A Varied-Line-Spacing (VLS) plane grating for the Monk-Gillieson mounting monochromator was fabricated with aspheric wavefront holographic recording following a new design concept. Ray-tracing results show that the holographic VLS grating affords high resolving power as a total optical system of a soft x-ray grazing incidence monochromator. Effects of errors in the recording parameters are also estimated, and the adjustment procedure to compensate for them was proposed. An 800-L'mm holographic laminar VLS grating has been tested in a new monochromator installed at a bending magnet source of the Photon Factory, and the resolving power of -..5OOO was obtained in the vicinity of nitrogen K-edge. It was found that the holographic grating has a relatively high reflectivity with a low scattered light level.
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