Improvement of the angular resolution of glass/plastic thin-foil mirrors for large area X-ray telescopes via active control

Progetto: Research project

Dettagli progetto


The improvement of the angular resolution of focusing optics for X-rays to levels of 1 arcsec or betteris one of the frontiers of the instrumentation development for future X-ray telescopes in space.However, such a level can be reached only with thick mirrors (like Chandra’s) in order to preservetheir accurate figure. The next generation of X-ray telescopes will also require a high effective area,i.e., a number of thin mirrors to be assembled to maintain the optic mass within acceptable limits.For the same reason, the mirrors have to be made of a lightweight material like thermally formedglass foils. However, this makes the mirrors prone to deform, at the expense of the achievable angularresolution. Even though studies based on the hot slumping of thin glass (at INAF/OAB) or plastic(UNIPA and INAF/OAPA) foils are on-going to solve this problem a true leap forward can beachieved by adopting thin mirrors with adjustable profile via actuators, in a fashion similar to theconcept of adaptive optics in on-ground optical telescopes. There is no atmospheric seeing to correct,because X-ray optics operate in space. Rather, it is the unavoidable fabrication errors that haveto be corrected by applying appropriate voltages to a matrix of actuators. Active X-ray mirrors arein use at Synchrotron beam-lines, where the focal spot has to be on the order of 0.1 arcsec.In this project, we are proposing the study and the realization of prototypes of thin X-ray mirrors with adjustable shapevia different concepts of actuators. Other research groups are investigating this approach (noticeablyat the Center for Astrophysics, Boston) on thin glasses, with encouraging results. However, theyessentially rely on profile measurement to assess the mirror shape correction, and in real cases theoptical surface is seldom accessible to off-situ metrology because of the dense mirror nesting. Inaddition, no metrology is possible for optics already operated in orbit; the sole available informationto correct possible unpredictable deformation caused by, e.g., the telescope launch would be optical.For this reason, in this project we will study the shape optimization of X-ray mirrors, made ofglass/plastic formed foils, via an piezoelectric actuation system, mostly driven by X-ray images takenintra-focus; in this X-ray setup, the mirror shape can be reconstructed and the needed correctioncan be imparted to the mirrors via a dedicated electronic providing the appropriate voltages to theactuators, an approach so far unexplored by the other research groups. A team of skilled instituteswill carry out this research, complementing the existing facilities and skills in an effective synergy:• INAF/OAB will provide the facilities and the skills in glass foil forming and integration, surfaceand profile metrology, piezoelectric actuators, thin film characterization, Finite Element Analysis,X-ray data interpretation, and imaging quality prediction.• UNIPA/DiFC will provide the facilities and the skills in plastic foils forming, thin film depositionand characterization, control electronic development.• INAF/OAPA will provide the 35 m long X-ray testing facility (XACT) to perform the intrafocusmeasurements, and the computation skills to elaborate the voltage convergence algorithm.The project foresees to manufacture some active optic prototypes, made of single or multipleshells, to serve as demonstrators of the effectiveness of the approach. If financed and successful,this project will expectedly improve the imaging quality of future, large X-ray telescopes by morethan a factor of ten, leadin

Layman's description

The aim of this research project is to study the application of a system of piezoelectric actuators to grazing-incidence X-ray telescope optic prototypes made of a lightweight material: thin glass or plastic foils, in order to increase their angular resolution.

Key findings

Data di inizio/fine effettiva10/23/1310/22/15