Diffractive Optics developed for X-ray etching high efficiency mirrors and
super-mirrors used both for X and Neutron radiations

B. Vidal*, Hugues Trambly*, A. Yakchin*, Marc Cilia+, A. Erko**

* Laboratoire d'Optique Electromagnetique, CNRS URA 843, Facult des
Scinces de St Jerome,  Avenue    
E. Normandie Niemen,  F-13397 MARSEILLE CEDEX 20

+ FOM Institut, Postbus 41883, 1009 DB Amsterdam, The Netherlands

** BESSY II, Rudower Chausse 5, Geb 15.1, D-12489 BERLIN


Artificial periodic multilayers allows to produce High Reflectivity Mirrors
which are the basement of X-Ray Optics.  We will describe our sputtering
system with high degree of reproducibility both in regard to the layer
composition and the layer thicknesses.  We will explain improvement of our
magnetron sputtering.  These improvements are of three kind.  The first one is
a new extremely precise method of calculation of the exact deposition rate
using X-Ray diffraction.  The second one is using a cooling substrate.  The
third one is a in situ analysis of the R.F.  magnetron discharge using optical
emission spectroscopy in order to prevent any change in the deposition rate.
We will gives some results obtained in soft X-Ray Range around 1 Kev with a
high degree of reproducibility.  This extremely good reproducibility allows us
to perform non periodic structures as super-mirrors used both for neutron and
X rays.  The principle of neutron super-mirror can be applied to x-rays.
Bending super mirrors to focus x-rays at high energies can be used to provide
specific energy.  This W/Si super mirror showed a reflectivity of more than
30% for energies up to 65.5 Ke.  Such non periodic structures can be tested
with the appropriate radiation for which the super-mirror is designed but also
using classical X-ray diffractometer at 1.54 A (Cu Ka line)

The numerical study of propagation of electromagnetic waves in the resonance
domain can be adapted to the X-Rays and Neutron and the second allows
measurements to compare the validity of theoretical models Lamellar gratings
etched in a multilayer (LMG) are the basic type of Bragg-Fresnel optics.  In
this paper we describes important points in the fabrication, computer
simulation, and testing of the LM's.  They can be very interesting as a
spectroscopic device with a relatively high dispersion and efficiency.  We
develop a rigorous theory of diffraction combined with the layer-by-layer
differential integration numerical method.  The agreement with experimental
results obtained for a lamellar grating with several period and various etched
depths in a W/Si multilayer is very good.

The main result is an increasing of the effective extinction depth (text) in
short-period gratings which gives a possibility to increase the absolute
diffraction efficiency of the LGM practically from 30% to 60% in the first
order with a totally suppressed zero order.

Taking into account equation of focalisation, we use a convenient quick method
to achieve a picture of a special mask for optics designed.  First, we find a
profile of this mask with MATCAD.  Then, the data are transferred the photo
mask to etch the multilayer.  We will present some results of Bragg-Fresnel
lenses calculations.  The data will be applied for fabrication of optics based
on grooved W/Si and Ni/Ti multilayers mirrors and neutrons super mirrors.