Focusing performances of Transmission Phase Fresnel Zone Plates

P. Troussel, S. Bac, J. M. Dalmasso, M. Pichet, M. Ollivier,
R. Sauneuf, C. Reverdin

CEA, 94195 Villeneuve saint Georges Cedex, France

M. Idir

Laboratoire  de Spectroscopie  Atomique  et  Ionique
Universit-Paris Sud, 91405 Orsay Cedex, France

G.  Soullie

CEA  B3,  Service CEM, BP12,  91680  Bruyres  le Chatel, France


The  high spatial resolution capability and the high efficiency
of  the  Fresnel zone plates (FZP) explain why they are choosen
in  many  applications  for focusing x-ray  radiation  (1).  An
amplitude   FZP   consist  of  concentric  annuli   alternately
transparent  and opaque. J. Kirz (1) has shown that  a  maximum
theoretical  focusing efficiency of approximately  10%  can  be
obtained,  due to the total x-ray absorption within the  opaque
zones.  To  improve  this efficiency (40%) and  to  reduce  the
influence  of  the different diffraction orders,  he  has  also
shown  that  it  is  possible  to  use  a  FZP  in  which   the
opaque  zones  are only slightly absorbing; the  phase  of  the
transmitted radiation through these zones can then be  adjusted
to contribute to the focusing. It is currently known as a Phase
Zone  Plate  (PZP). We present an experimental and  theoretical
study concerning a gold PZP, made by lithography technique (2),
which is used to focus x-rays in the 1-4 keV range.

The performances of our PZP were at first evaluated on the SB3
beamline  of  the  SUPER-ACO Synchrotron  source  (LURE/Orsay),
equipped with a double crystal monochromator and a theta-2theta
goniometer (3). Efficiency measurements at the zeroth  and  the
first order diffraction orders have been realized between  1400
eV  and 3200 eV, and a focusing efficiency as high as 23 %  has
been  obtained at 1900 eV photon energy, which is in real  good
agreement with our calculation based on the thickness indicated
by  Heidenhain  (0.5  nm).  At this photon  energy,  the  ratio
between  the zeroth and the first orders efficiencies  is  very
low  (28%).  Energy  distribution of the  synchrotron  beam  is
given: a spatial resolution better than a few microns has  been
obtained.

We, in a second time, obtained images of grids illuminated by
a  classical x-ray tube. An intense radiation line is  selected
by  a  multilayer mirror with a very narrow bandwidth  (E/DE =
100).  In  this  way,  the chromatic aberration,  which  has  a
noticeable effect on the spatial resolution, is suppressed.
We very soon expect to get at the first order focus the 0.4 um
spatial  resolution, which corresponds to the width of the  PZP
outmost ring.

1.  J. Kirz, Phase zone plates for X-rays and the extreme UV,
JOSA, Volume 64, Number 3, (1974).

2. HEIDENHAIN BELGIEN Bellekouter, 30, B-1790 Affligem.

3. M. Idir, Etude experimentale et theorique d'optiques
focalisantes de type Bragg-Fresnel graves sur des multicouches
adaptes aux domaines X et X-UV, Thesis, Universite Pierre et
Marie Curie (Paris VI) (1994).