Multilayer mirrors (MLM) with narrow spectral bandwidth are important for X-ray spectroscopy and imaging
experiments in order to improve the spectral resolution. To overcome the bandwidth limit of conventional
multilayers, single order lamellar multilayer grating (LMG) is one of the most promising methods. Driven by the
high resolution spectroscopy for the plasma diagnosis at E=~1keV, single order LMG based on MoSi2/Si multilayer
is developed. The multilayer period is 5.0 nm, with the Si thickness ratio of 0.6. An LMG with 600 nm grating
period and 1:2 line-to-space ratio is designed. As it works at the single order diffraction regime, the 0th order peak
reflectance (in theory) of the LMG is 45.4% at E=1.2 keV, which is the same as the multilayer mirror. The
bandwidth can be reduced by 3 times compared to the planar multilayer. To demonstrate this LMG structure,
MoSi2/Si multilayers have been deposited using direct current magnetron sputtering. Deep reactive ion etching
technique is under optimization in order to produce the multilayer grating structure with a high aspect-ratio of
around 5.
The high resolution extreme ultraviolet spectroscopy mission based on the normal-incidence multilayered diffraction grating technology, which provides high effective area and spectral resolution, can carry out a survey of local Galactic stellar and white dwarf targets. Compared to grazing-incidence systems, this approach allows previous observatory-class science to be delivered in a low-cost package. The instrument has already been proven in two sub-orbital space flights. However, the multilayer used before is periodic one and the working band-pass is limited. In this paper, the spectroscopic properties of a normal-incidence multilayered diffraction grating were simulated with three kinds multilayers for the wavelength range between 17.5nm and 25.0nm, which includes lines of Fe VIII to XIII that will be strongest in the cooler (solar like) coronae, plus some weaker lines of O, Si, S and Ar. The highest efficiency at central wavelength of band-pass can be obtained if the periodic multilayer is adopted. The most flat response efficiency can be achieved if we utilized a non-periodic multilayer. The simulation results demonstrated that the choice of the multilayer is dependent on the requirement to the spectroscopy mission and should be considered carefully.
We present a short review of our activities carried out in Tongji University (Shanghai, China) in the field of theory and technology of soft X-ray multilayer diffraction gratings. Diffraction gratings are widely used to study the structure and dynamics of a matter in laboratory and space by spectral analysis techniques. Combining multilayer and grating structures into a single unit allows to increase essentially both the spectral resolution and the efficiency of the diffraction optics. The unified analytical theory of soft X-ray diffraction from multilayer gratings operating in the single-order regime is briefly discussed. The single-order regime occurs when incident wave excites the only diffraction order and it is characterized by ultimately high diffraction efficiency tending to the reflectivity of conventional multilayer mirror. Our first experiments in fabrication of the blazed multilayer gratings by anisotropic etching of a silicon crystal with small roughness of the facet surfaces are described.
A novel and simple design method based on pole-zero diagram is proposed for optical interleaver based on Michelson
Gires-Tournois interferometer (MGTI) with arbitrary cascaded reflectors. Digital filter model which is equivalent to the
MGTI optical interleaver is derived firstly. Then on the basis of it, the transfer functions of two output ports of the
interleaver are simplified and all the design parameters of the interleaver can be obtained conveniently by the use of the
mature design principle of elliptic filter and pole values. The two output spectrums obtained has the wide flat passband
(and stopband) width and high isolation simultaneously. Compared with other existing design methods, the proposed
method is simpler and more efficient, especially for interleavers with GTE composed of much more reflectors. Design
examples of the interleaver with different cascaded G-T etalon structure are given.
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