| DATE: |
2012-03-08 10:00 - 12:00 |
| PLACE: |
PFtou, 2nd floor conf |
| TITLE: |
IMSS seminar |
| CONTACT: |
Naohiro Matsugaki 5647 |
| SPEAKER: |
Dr. Juergen Mohr (Karlsruhe Institute of Technology (KIT) ) |
| LANGUAGE: |
English |
| ABSTRACT: |
In the talk we will describe the processes to fabricate compound
refractive lenses (CRLs)
and grating structures and show the results of the characterization
experiments. In view of
application, the focus will be on synchrotron experiments but also on
experiments done with
conventional X-ray sources.
At the Karlsruhe Institute of Technology deep X-ray lithography, the
first step of the LIGA
process is used to fabricate high aspect ratio micro structures out of
polymer. By a
subsequent electroforming process, metallic micro structures are
realized. The structures are
characterized by dimensions in the micrometre range, aspect ratios of up
to 100, steep and
smooth sidewalls with roughness (Ra) in the range of 10 nm. These
features give rise to use
the LIGA process for fabricating X-ray optical structures like CRLs or
gratings for Talbot
interferometry.
Using an epoxy based resist material, compound refractive lenses (CRLs)
with parabolic
shaped elements have been fabricated for different energies up to 50
keV, focal lengths
down to a few millimetre and focal spot sizes of less than 100 nm.
These parabolic lenses are efficient up to apertures of a few hundred
micrometres. To
increase the aperture the absorbing material was further decreased by
transforming the
continuous parabolic into a truncated parabolic lens design with a size
of the refractive element
of approx. 10 ¦Ìm. By stabilizing more than ten thousands of these
structures with a height
of several millimetres by a lattice fence like arrangement, lenses with
an aperture of 1.5 mm x
1.5 mm could be achieved leading to spot sizes in the micron range.
Building a Talbot-interferometer system for X-ray phase imaging at
higher energies
requires the fabrication of gratings with a period in the micron range
out of gold with a height
of at least 100 ¦Ìm. In this case the lithographically fabricated SU8
(epoxy based resin)
structure is used as a template for the electroforming process.
Optimizing the resist material, the design and the process conditions
lead to the fabrication of
grating structures with an aspect ratio of more than 100 in a field of
view of 50 mm2. With such
gratings visibilities of 65% for 30 keV and 25% for 52 keV could be
measured at ID19 at ESRF. |
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