Atkins, C.

Broadway, D.

Gubarev, M.

Kilaru, K.

Ramsey, B.

NASA Technical Reports Server

SCIENCE & TECHNOLOGY
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Technology developments toward 
sub-arc-second x-ray optics
M. Gubarev1, B. Ramsey1, D. Broadway1, 
K. Kilaru2, C. Atkins3
1 Marshall Space Flight Center, Huntsville, AL
2 Universities Space Research Association, Huntsville, AL
3 University of Alabama, Huntsville, AL
https://ntrs.nasa.gov/search.jsp?R=20140004251 2019-08-29T14:33:26+00:00Z
SCIENCE & TECHNOLOGY
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Differential Deposition
Challenge is to control the figure errors for spatial scale range between 0.5 mm to 0.5 m 
Figure correction - Differential Deposition
Advantages:
- Covers the full spatial scale range.
- Applicable to full shell and segmented 
optics
- Can be used to correct the surface 
deformations due to mounting and 
assembly
- Technique is used for synchrotron optics
From:
A preferential coating technique for fabricating large, high quality optics S.G. Alcock, S. Cockerton, NIM A 616, 2010
SCIENCE & TECHNOLOGY
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Differential Deposition
Collet to hold the mirror –
translation and rotation
Magnetron
-Proof of concept on miniature optics 
completed. 
-Chambers for full scale optics are just 
being commissioned ( coating rates, 
beam profiles etc). 
-Expect to be coating shells in a few 
weeks (both full shells and segmented 
optics). We can accommodate up to 50 
cm diameter full shells, but we will start 
with 15 cm ones
SCIENCE & TECHNOLOGY
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Stress Measurement in Coatings 
Our Method: We exploit the known spherical 
deformation due to stress and calculate the 
substrate curvature by measuring the sag of the 
coated wafer (just one point).
Micro Cantilever
Multi-Beam Array
SCIENCE & TECHNOLOGY
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Film Stress
The stress can be controlled by varying the Ar
pressure 
The deposition rate has to be taken into account.
In-situ stress monitoring during the deposition process 
is being pursued.
SCIENCE & TECHNOLOGY
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Stress Measurement in Coatings 
o The probe tip can detect changes as small as 5nm under ideal conditions (i.e. in very low 
noise environment)
o Typical background noise during a two hour deposition process is about 0.5 micron.  This 
corresponds to a minimum stress that can be measured of a few MPa for a substrate 
thickness of 350 micron
o However, the signal to noise can be improved for a given stress value by decreasing the 
thickness of the wafer.
o Largest source of noise is due to thermal expansion of critical components resulting from 
temperature variation in the lab and during the deposition process.  
o The unwanted effects are being mitigated through the fabrication of water cooled 
components
o Stress measurements as low as a few Pascals may be in reach.
SCIENCE & TECHNOLOGY
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Deterministic Polishing
- Thin-wall-full-shell “Chandra-like” optics;
- Goal is 1-2 mm thick, meter-class full shell mirrors;
- Take advantage of modern robotic polishing/grinding 
machines;
- Metrology/fabrication support fixtures are under 
development.
5-mm thick, 0.6 m diameter  glass shell after grinding 
Zeeko machine at MSFC NASA logo polished into the 50 mm diameter glass flat
SCIENCE & TECHNOLOGY
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Sub-Micro-Rad Metrology 
0 10 20 30 40 50
-150
-100
-50
0
50
100
150
Axial Position, mm
S
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Red – Zygo interferometer, Black - MBLTP
MBLTP: Ten signal and one 
reference beams on the detector
Multi-beam Long Trace Profilometer developed at MSFC
To achieve the sub-arc-sec x-ray optics the resolution of the 
figure metrology has to be at sub micro-rad level
State-of-the-art for Long Trace Profilometer (LTP) is 0.2 
microrad
LTP measures the surface slope directly using a single laser 
beam. The change of laser spot position on the detector is 
directly proportional to the change in the surface slope.
Multi-Beam Long Trace Profiler (MBLTP) is developed to 
increase the speed of measurements
SCIENCE & TECHNOLOGY
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Can Bendable X-ray Optics be Applied for Astrophysical 
Applications?
In synchrotron world the diffraction-limited angular resolution 
has been achieved using bendable x-ray optics:
-The use of torque bending 
- Metrology and, hence, fabrication of perfect flat surface ( better than 
0.5 micro-rad rms) is straightforward. The substrates are affordable, but 
they are relatively thick – few mm.
Approach is to start the x-ray mirror fabrication process with 
naturally-flat, thin silicon wafers and form them through torque 
bending and differential deposition into very-light-weight, sub-
arcsecond-resolution mirrors ready to be installed into a 
telescope structure. 
150 µm thick wafer cylindrically bent to 0.25 m dia
Wafer bender
To date:
-The stresses and the resulting surface deformations in Si-wafers 
have been simulated. The deformations are low frequency and in the 
range correctable by differential deposition.
- The simulation results for the deformations are confirmed by 
experiment
-The bender is designed and a model has been printed.
- The experiments to form the parabolic surface on the flat substrate 
by differential deposition are in progress. 
SCIENCE & TECHNOLOGY
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THANK YOU
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Technology Developments Toward Sub-arc-second X-ray Optics

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