Gubarev, Mikhail

NASA Technical Reports Server

Supporting Technologies for High 
Resolution Optics
Decadal Telescope TIM, June 17 2016
Mikhail Gubarev, MSFC
On behalf of the X-ray Astronomy Group
https://ntrs.nasa.gov/search.jsp?R=20160007984 2019-08-31T02:29:01+00:00Z
• Jeff Kolodziejczak
• Brian Ramsey
• Steve O’Dell
• Jacki Roche
• Bill Arnold
• Charlie Griffith
• Tom Kester
• Darell Engelhaupt
• Kiranmayee Kilaru
• Carolyn Atkins
• Scott Smith
• Danielle Gurgew
Team:
Decadal Telescope TIM, June 17 2016
• X-rays reflected at very shallow angles
• Typical configuration uses combination of parabola and 
hyperbola to reduce aberrations
X-ray optics permits detailed imaging and background 
reduction
• Typically many such mirrors are concentrically nested to 
increase effective area
Introduction
Chandra – x-ray mirror system
The challenge is to develop the optical fabrication 
technology capable of producing x-ray optics but 
with an order of magnitude lighter mirrors and at an 
affordable price. Decadal Telescope TIM, June 17 2016
Material Density 
(g/cm3)
CTE
(10-6 / K-1)
Elastic Modulus
GPa
Yield Strength
MPa
Fused Silica 2.2 0.5 72 48*
Beryllium 1.8 12 318 240
BeAL-162MET 2.1 24 69 276
AlSi 2.8 13.9 193 314
Duralcan F3S.30S
AlSi+SiC(30% by vol)
2.8 14.6 120 210
Mechanical Properties of Potential Mirror Substrate Materials
*Maximal achievable value. The ‘working’ value is typically much less and depends on the surface/subsurface condition.
Ideally, the mirror shell has low 
density, low coefficient of expansion 
(CTE), high modulus of elasticity and 
high yield strength. It should also be 
a material that is not too difficult to 
figure and polish.
Substrates can be plated with the 
nickel phosphorous alloy: 
- Be + NiP (CATS-ISS telescope)
- BeAl +NiP
- AlSi + NiP
Direct Fabrication
Companies are confident they can deliver the Be, BeAl and AlSi substrates 
fabricated with necessary tolerances
Additional Benefits of metal substrate: 
• Less joints – less epoxy error
• Thermal design could be simplified, the support structure from the same 
material
Decadal Telescope TIM, June 17 2016
Zeeko machine
- The machine utilizes a “bonnet” 
technique in which an inflated rubber 
hemispherical diaphragm supports the 
polishing medium. 
- there are different “bonnet” sizes (20 
mm, 40 mm and 80 mm radii of 
curvature) 
- This computer-controlled deterministic 
polishing processes leads to a high 
convergence rate. 
- The control software had to be 
developed in order to figure x-ray optics
Correction of figure through deterministic 
material removal
Tool offset
surface
bonnet
Decadal Telescope TIM, June 17 2016
Process development
 Parametric model is created
 The process operational parameters are optimized 
 Algorithm for optimal correction of the surface errors are verified
Example of measured wear function
Decadal Telescope TIM, June 17 2016
before after
Figure error (St. Dev.) 500 nm 10.7 nm
Slope error (> 2 cm) cm(RMS) 6.32 arcsec 0.30 arcsec
Low frequency (> 7 cm) slope error (RMS)   2.66 arcsec 0.09 arcsec
Mid frequency (2-7 cm) slope error (RMS) 5.73 arcsec 0.29 arcsec
Mandrel Experiments- before and after
ART-XC mandrel installed on the Zeeko
machine for figuring experiments
Decadal Telescope TIM, June 17 2016
• Differential Deposition
- Kiranmayee Kilaru (USRA, MSFC)
- Carolyn Atkins (UAH)
- David Windt (Reflective X-ray 
Optics, LLC) 
Correction of figure through 
Diferential Deposition
Principle of Differential Deposition
Decadal Telescope TIM, June 17 2016
Horizontal and Vertical Coating systems at MSFC
X-ray mirror held in a 
rotating and 
translating collet
Mask
9
Sputtering target
Mask
Segmented glass 
optic 
Decadal Telescope TIM, June 17 2016
10
Recent X-ray test results: Angular resolution is improved  from 17 to 20 arc secs to ~ 5 arc secs HPD.
• Variation of sputtered beam profile along the length of mirror, particularly for short focal length mirrors –
Improvements in mechanical set-up to maintain constant target-to-substrate distance for tapered-shells
• Thorough characterization of the overlap areas in the case of customized correction for each meridian
• Improvements in the mask to shell alignment system
• Stress effects – Quantify and control stress – so far simulations and metrology agree well and there is no evidence for 
stress induced distortion for these full-shell optics
Sources of errors
Decadal Telescope TIM, June 17 2016
Thin-film stress (In-situ stress measurement)
• Stress is a leading technological challenge in thin-film coatings regardless of their application.
• The intrinsic stress in the thin-film single and multilayer reflective coatings will deform the optic’s figure and compromise
their ability to render sharply-focused, high-resolution images.  
• We have developed a method for the in-situ, high-resolution measurement of the stress during film growth 
In-situ measurement has helped identify a mechanism for reducing the stress in iridium by three orders of magnitude
“Mechanical stress measurement during thin film fabrication”, NASA, 
United States Patent Application #14,645,994, (2015), D. Broadway
Decadal Telescope TIM, June 17 2016
 Working on demonstration of x-ray optics fabricated directly.
 Working towards the in-situ metrology of X-ray mirrors inside the differential 
deposition vacuum chambers and during polishing
 Combine the direct fabrication with Differential Deposition Technique
 Incorporate the in-situ stress measuring system into coating chambers
Future work
Decadal Telescope TIM, June 17 2016
Summary
 MSFC develops the direct fabrication technology for full shell x-ray optics made 
from metal substrates;
 Post-fabrication and post-assembly figure correction provides an additional 
venue to meet the requirements;
 Differential Deposition technique has potential for development of sub-arc-
second x-ray optics;
 Use of in-situ stress measurement system could significantly reduce x-ray optics 
deformation when single or multi- layers are used to boost reflectivity.
Decadal Telescope TIM, June 17 2016


Supporting Technologies for High Resolution Optics

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