The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured
optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through
consecutive aligned arrays of microscopic channels etched in silicon. Adaptability is achieved using a combination of
piezoelectric actuators, which bend the edges of the silicon chip, and a spider structure, which forms a series of levers
connecting the edges of the chip with the active area at the centre, effectively amplifying the bend radius. Test spider
structures, have been bent to a radius of curvature smaller than 5 cm, indicating that in complete devices a suitable focal
length using a tandem pair configuration could be achieved.
Finite Element Analysis (FEA) modelling has been carried out for the optimization of the spider MOA device design.
Prototype devices have been manufactured using a Viscous Plastic Processing technique for the PZT piezoelectric
actuators, and a single wet etch step using {111} planes in a (110) silicon wafer for both the silicon channels and the
spider structure. A surface roughness of 1.2 nm was achieved on the silicon channel walls.
Characterisation techniques have been developed in order to evaluate the device performance in terms of the bending of
the MOA channels produced by the actuators. This paper evaluates the progress to date on the development of spider
MOA's comparing FEA modelling with the results obtained for prototype structures.
The design of current X-ray telescope systems needs to reach a compromise between the resolution and sensitivity. A
new area of interest of adaptive optics is the development of actively controlled thin X-ray mirrors, where aberrations
would be corrected. Their assembly on an X-ray telescope would provide an instrument with both high resolution and
sensitivity.
The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing prototypes for the next
generation of X-ray telescopes. The overall aim is to produce X-ray mirrors using thin, below 1mm, structures,
comprising Ni mirror shells with bonded piezoelectric unimorph actuators, and with a target resolution of ~0.1 arcs. Such
an optic would enable the design of an X-ray telescope with both a greater resolution and collective area than the best
currently available by Chandra (0.5arcs) and XMM Newton (1650cm2) respectively.
Lead zirconate titanate, PZT-based piezoelectric actuators are being developed in this programme to fit precisely the
curved Ni mirror shell prototypes (100×300×0.4mm, radius of curvature 167mm). Viscous plastic processing has been
chosen for the fabrication of net-shaped piezoelectric unimorph actuators 75×32×0.18mm, with radius of curvature
conforming to those of the X-ray optic. Laser machining has been used for precisely controlling the actuator shape and
for the definition of the multi-segment electrodes. Accurate control of the thickness, surface finish and curvature are the
key factors to delivering satisfactory actuators. Results are presented concerning the fabrication and characterisation of
the piezoelectric actuators, and the integration procedure on the nickel optic.
The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured
optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through
consecutive aligned arrays of microscopic channels etched in silicon. The silicon channels have been produced both by
dry and wet etching, the latter providing smoother channel walls. Adaptability is achieved using piezoelectric actuators,
which bend the device and therefore change its focal distance. We aim to achieve a 5 cm radius of curvature which can
provide a suitable focal length using a tandem pair MOA configuration.
Finite Element Analysis (FEA) modelling has been carried out for the optimization of the MOA device design, consider
different types of actuators (unimorph, bimorph and active fibre composites), and different Si/piezoelectric absolute and
relative thicknesses. Prototype devices have been manufactured using a Viscous Plastic Processing Process for the
piezoelectric actuators and dry etched silicon channels, bonded together using a low shrinkage adhesive. Characterisation
techniques have been developed in order to evaluate the device performance in terms of the bending of the MOA
channels produced by the actuators. This paper evaluates the progress to date on the actuation of the MOAs, comparing
FEA modelling with the results obtained for different prototype structures.
Piezoelectric actuators are widely employed in adaptive optics to enable an actively controlled mirror surface and
improve the optical resolution and sensitivity. Currently two new prototype adaptive X-ray optical systems are under
development through the Smart X-ray Optics project in a UK based consortium. One proposed technology is micro-structured
optical arrays (MOAs) which uses aligned micro-channels structures obtained by deep silicon etching using
both dry and wet techniques and bonded piezoelectric actuators to produce a micro-focused X-ray source for biological
applications. The other technology is large scale optics which uses a thin shell mirror segment with 20-40 bonded piezo-actuators
for the next generation of X-ray telescopes with an aim to achieve a resolution greater than that currently
available by Chandra (0.5").
The Functional Materials Group of Birmingham University has the capability of fabricating a wide range of piezo-actuators
including, for example, unimorph, bimorph and active fibre composites (AFC) by using a viscous plastic
processing technique. This offers flexibility in customising the shapes (from planar to 3-D helix) and feature sizes (>20
μm) of the actuators, as well as achieving good piezoelectric properties. PZT unimorph actuators are being developed in
this programme according to the design and implementation of the proposed mirror and array structures. Precise
controls on the dimension, thickness, surface finishing and the curvature have been achieved for delivering satisfactory
actuators. Results are presented regarding the fabrication and characterisation of such piezo-actuators, as well as the
progress on the large optic and MOAs prototypes employing the piezo-actuators.
The next generation of X-ray telescopes will require both high resolution and high sensitivity to target the earliest
astronomical objects, to this end the UK based Smart X-ray Optics (SXO) project has been investigating the
application of active/adaptive optics to traditional grazing incidence X-ray optics and this has resulted in the
fabrication and testing of our first active X-ray prototype in November 2008. Results from these initial tests have
proved very encouraging for this advancing technology and have highlighted the prototype's ability to deform
its optical surface through piezoelectric actuation. We present a critical analysis of the first prototype system,
discussing metrology of the mandrel, the nickel replicated ellipsoidal optics and the prototype. The measured
actuator influence functions of the prototype are compared against finite element analysis simulations and the
observed characteristics are then described. The advances required in the current technology are then outlined
in relation to a second generation of active X-ray prototype, which is scheduled for X-ray testing in 2010.
The Smart X-ray Optics project is a UK based consortium of six institutions investigating active/adaptive X-ray
optics for both large and small scale applications. The large scale application is aimed towards future high
angular resolution, large X-ray telescopes for X-ray astronomy. The work presented here includes the modelling
and the testing of the large scale prototype optic. The prototype incorporates piezoelectric devices to a standard
X-ray shell to enable the surface to be actively deformed, aiming to achieve an angular resolution better than that
currently available (e.g. Chandra 0.5"). The initial design is based on a thin nickel ellipsoid segment on the back
of which a series of piezoelectric actuators have been bonded. Results from the initial testing of this prototype
in the X-ray beam line at the University of Leicester are presented and simulation of the X-ray performance, the
effect of the actuated piezoelectric devices on the detected image and further models are discussed.
The immediate future for X-ray astronomy is the need for high sensitivity, requiring large apertures and collecting
areas, the newly combined NASA, ESA and JAXA mission IXO (International X-ray Observatory) is specifically
designed to meet this need. However, looking beyond the next decade, there have been calls for an X-ray
space telescope that can not only achieve this high sensitivity, but could also boast an angular resolution of 0.1
arc-seconds, a factor of five improvement on the Chandra X-ray Observatory. NASA's proposed Generation-X
mission is designed to meet this demand; it has been suggested that the X-ray optics must be active in nature in
order to achieve this desired resolution. The Smart X-ray Optics (SXO) project is a UK based consortium looking
at the application of active/adaptive optics to both large and small scale devices, intended for astronomical and
medical purposes respectively. With Generation-X in mind, an active elliptical prototype has been designed by
the SXO consortium to perform point-to-point X-ray focussing, while simultaneously manipulating its optical
surface to improve its initial resolution. Following the completion of the large scale SXO prototype, presented
is an overview of the production and operation of the prototype, with emphasis on the X-ray environment and
preliminary results.
The Smart X-ray Optics (SXO) programme is developing advanced active-adaptive optics for X-rays. There are two
main themes: large optics for applications in astronomy and small scale optics for micro-probing of biological cells and
tissue samples using Ti or Cr Kα radiation (4.5keV and 5.4keV, respectively) in studies related to radiation induced
cancers. For the latter objective, microstructured optical arrays (MOAs) have been proposed. These consist of an array of
channels deep etched in silicon. They use grazing incidence reflection to focus the X-rays through consecutive aligned
arrays of channels, ideally reflecting once off a channel wall in each array. Bending the arrays allows variable focal
length. The adaptivity is achieved by flexing the arrays using PZT (Lead Zirconate Titanate)-based piezo actuators.
The array bending has been modelled using finite element analysis (FEA) and the results showed that for reasonable
efficiency, the wall roughness of the channels should not exceed 2nm.
This paper describes two techniques of fabrication the MOAs: dry etching and wet etching. The first method requires a
special equipment called "inductively coupled plasma" (ICP) using Bosch processes that are designed to produce
features with a high aspect ratio with vertical walls. The second method involves using an alkaline solution for etching
<110> silicon wafers. This type of wafer was selected because of the large wet etch ratio between the (111) and (100)
planes that leads to smooth vertical walls. For our application tetra-methyl-ammonium hydroxide (TMAH) was used as it
is fully compatible with CMOS integrated circuit processes.
The UK Smart X-Ray Optics consortium is developing novel reflective adaptive/active x-ray optics for small-scale laboratory applications, including studies of radiation-induced damage to biological material. The optics work on the same principle as polycapillaries, using configured arrays of channels etched into thin silicon, such that each x-ray photon reflects at most once off a channel wall. Using two arrays in succession provides two reflections and thus the Abbe sine condition can be approximately satisfied, reducing aberrations. Adaptivity is achieved by flexing one or both arrays using piezo actuation, which can provide further reduction of aberrations as well as controllable focal lengths. Modelling of such arrays for used on an x-ray microprobe, based on a microfocus source with an emitting region approximately 1μm in diameter, shows that a focused flux approximately two orders of magnitude greater than possible with a zone plate of comparable focal length is possible, assuming that the channel wall roughness is less than about 2nm.
The Smart X-ray Optics project is a UK based consortium of eight institutions investigating the application of
active/adaptive X-ray optics for both large and small scale. The work being undertaken at the University of
Leicester includes the modelling and testing of a large scale optic, suitable for an X-ray telescope. This will
incorporate piezoelectric devices to enable the surface to be actively deformed, aiming to achieve an angular
resolution better than that currently available (e.g. Chandra 0.5"). The test optic design is based on a thin
Nickel ellipsoid segment on the back of which will be bonded a series of piezoelectric actuators. Simulation of the
X-ray performance and the effect of the actuated piezoelectric devices on the detected image is described. Details
of the models produced for the piezoelectric actuation routine and the simulated annealing algorithm under development,
will be outlined. Planed testing of the ellipsoidal prototype and future objectives for implementation
of active X-ray optics in the design of an X-ray telescope will be discussed.
The Smart X-ray Optics (SXO) project is a UK based consortium consisting of several institutions investigating
the application of active/adaptive optics to both large and small scale grazing incidence x-ray optics. University
College London presents work relating to the large scale x-ray optics that is geared towards the next generation
of x-ray space telescopes. It is proposed that through the addition of piezoelectric actuators, an active x-ray
telescope with a resolution better than that currently achieved (e.g. Chandra 0.5") could be realised. An
immediate aim of the SXO project is to produce an operational active ellipsoidal segment prototype, with point-to-
point focusing and with the intention of being tested at the University of Leicester's x-ray beam source. Work
relating to the fabrication of the prototype will be presented, including shell replication via a nickel sulphamate
electroforming process, piezoelectric actuators and prototype assembly and operation. Results from finite element
analysis modelling will be discussed; these relate primarily to gravitational distortion effects and the plating tank
electrostatics.
The Smart X-ray Optics project is a UK based consortium consisting of several institutions to investigate the application
of active/adaptive optics upon both small and large scale grazing incidence x-ray optics. The work done at University
College London (UCL) focuses on the application of piezoelectric materials to large scale optics in order to actively
deform the mirror's surface. These optics are geared towards the next generation of x-ray telescopes and it is hoped that
the project will be able to achieve a resolution greater than that currently available by Chandra (0.5"). One of the aims of
the consortium is to produce a working prototype. The initial design is based on a thin nickel ellipsoid segment with an
x-ray reflective coating, on the back of which will be bonded a series of piezoelectric actuators.
Investigation into the specification of the design of an active x-ray optic prototype and suitable support test structure has
been undertaken. The dimensions and constraints upon the prototype, and the manufacturing process to produce a nickel
shell are discussed. Finite element analysis (FEA) of the physical characteristics of piezoelectric materials has shown the
ability to deform the nickel surface to correct for errors of several microns. FEA has also been utilised in the
specification of the prototype's support structure to ensure that gravitational sag upon the optic is kept to a minimum.
Laboratory experiments have tested a series of materials, different actuators and bonding methods, which could then be
applied to the prototype.
The UK Smart X-Ray Optics programme is developing the techniques required to both enhance the performance of
existing X-ray systems, such as X-ray telescopes, while also extending the utility of X-ray optics to a broader class of
scientific investigation. The approach requires the control of the inherent aberrations of X-ray systems using an
active/adaptive method. One of the technologies proposed to achieve this is micro-structured optical arrays, which use
grazing incidence reflection through consecutive aligned arrays of channels. Although such arrays are similar in concept
to polycapillary and microchannel plate optics, they are more flexible. Bending the arrays allows variable focal length,
while flexing parts of them provides adaptive or active systems. Custom configurations can be designed, using ray
tracing and finite element analysis, for applications from sub-keV to several-keV X-rays. The channels may be made
using deep silicon etching, which can provide appropriate aspect ratios, and flexed using piezo actuators. An exemplar
application will be in the micro-probing of biological cells and tissue samples using Ti Kα radiation (4.5 keV) in studies
related to radiation induced cancers.
This paper describes the progress made in a proof of concept study and recent results of a research program into large
active x-ray mirrors that is part of the UK Smart X-ray Optics project. The ultimate aim is to apply the techniques of
active/adaptive optics to the next generation of nested shell astronomical X-ray space telescopes.
A variety of deformable mirror technologies are currently available, the most promising of which for active X-ray
mirrors are probably unimorph and bimorph piezoelectric mirrors. In this type of mirror one or more sheets of
piezoelectric material are bonded to or coated with a passive reflective layer. On the back or between the piezoceramic
layer/layers are series of electrodes. Application of an electric field causes the piezoelectric material to undergo local
deformation thus changing the mirror shape. Starting in 2005 a proof of concept active mirror research program has
been undertaken. This work included modelling and development of actively controlled thin shell mirrors. Finite
element models of piezo-electric actuated mirrors have been developed and verified against experimental test systems.
This has included the modelling and test of piezo-electric hexagonal unimorph segments. Various actuator types and low
shrinkage conductive bonding methods have been investigated and laboratory tests of the use of piezo-electric actuators
to adjust the form of an XMM-Newton space telescope engineering model mirror shell have been conducted and show
that movement of the optics at the required level is achievable. Promising technological approaches have been identified
including moulded piezo-ceramics and piezo-electrics fibre bundles.
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