Model supporting the use of pressure in the hot slumping of glass substrates for X-ray telescopes

Thin glass foils are nowadays considered good substrates for lightweight focusing optics, especially for X-ray telescopes. The desired shape can be imparted to the foils by hot slumping, a process that replicates the shape of a slumping mould. During thermal slumping, when the glass and the mould come into contact, ripples in the glass surface appear spontaneously if the thermal expansions are mismatched. In our hot slumping setup, pressure is applied to ease the mould shape replication and to enhance the ripple relaxation. Starting from an existing model developed to explain the ripple formation in hot-slumped glass foils without pressure, we have developed a model that includes the pressure to support our experimental results

Modeling and measurement of the scattering properties of the source pinhole in the BEaTriX facility

The purpose of this brief technical note is to provide an assessment of the performance of the tungsten pinhole placed in front of the microfocus Incoatec X-ray source with Titanium anode in the BEaTriX X-ray facility. The pinhole is a part of the collimator kit by Amptek purchased years ago to collimate a solid-state detector, and consists of a small (1/2 inch) tungsten disk with a 2.2 mm thickness and a 450 μm diameter. The pinhole is placed at a 20 mm distance from the source and limits the beam along the short arm of the facility, avoiding so the X-ray incidence on the tube walls which might cause unwanted X-ray reflection/scattering or diffuse background. At the same time, the pinhole located near the X-ray source provides visual reference for the parabolic mirror alignment. Pinholes are crucial optical components, as they have to diaphragm an X-ray beam without degrading it. Due to the closeness of the lateral walls of the pinhole to the X-rays, the surface has to be properly ruggedized in order to avoid unwanted reflections or diffuse scattering when X-rays impinge on it in grazing incidence conditions. Should this condition not be fulfilled, the pinhole would cause a broadening of the X- ray source and a consequent worsening of the finally collimated X-ray beam in BEaTriX. In this short note, we will show measurements of the X-ray beam in the BEaTriX facility aiming at ascertaining the scattering properties of the pinhole surface. The conclusion is that the amount of scattered/reflected radiation off the pinhole is hardly detectable and that the pinhole appears perfectly suitable for the collimation of the X-ray beam in the short arm of BEaTriX

LAMP: a micro-satellite based soft X-ray polarimeter for astrophysics

The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite mission concept dedicated for astronomical X-ray polarimetry and is currently under early phase study. It consists of segmented paraboloidal multilayer mirrors with a collecting area of about 1300 cm^2 to reflect and focus 250 eV X-rays, which will be detected by position sensitive detectors at the focal plane. The primary targets of LAMP include the thermal emission from the surface of pulsars and synchrotron emission produced by relativistic jets in blazars. With the expected sensitivity, it will allow us to detect polarization or place a tight upper limit for about 10 pulsars and 20 blazars. In addition to measuring magnetic structures in these objects, LAMP will also enable us to discover bare quark stars if they exist, whose thermal emission is expected to be zero polarized, while the thermal emission from neutron stars is believed to be highly polarized due to plasma polarization and the quantum electrodynamics (QED) effect. Here we present an overview of the mission concept, its science objectives and simulated observational results

Slumped glass optics development with pressure assistance

Thin glass mirrors are a viable solution to build future X-ray telescopes with high angular resolution and large collecting area. This approach is very attractive for the optics implementation of future X-ray astronomy projects like the X-ray Surveyor Missions in USA, the XTP mission in China and the FORCE mission in Japan (all this projects could have an European participation). In the case of the X-ray Surveyor Mission, where a sub-arcsec angular resolution is requested, the use of actuators or post correction with sputtering deposition is envisaged. The hot slumping assisted by pressure is an innovative technology developed in our laboratories to replicate a mould figure. Our hot slumping process is based on thin substrates of Eagle XG glass to be thermally formed on Zerodur K20 moulds. This technology is coupled with an integration process able to damp low frequency errors. A continuous improvement in the reduction of the mid-frequency errors led to slumped glass foils with a potential angular resolution evaluated from the metrological data of a few arcsec. High frequency errors have been for a long time a critical point of our technology. In particular, the pressure assistance was leading to a partial replication of the mould micro-roughness, causing a non-negligible contribution to the Point Spread Function (PSF), in the incidence angle and X-ray energy range of operation. Therefore, we developed a new process to further reduce the micro-roughness of slumped glass foils, making now the technology attractive also for telescopes sensitive at higher X-ray energies. This paper provides the latest status of our research. <P /

Test plan of the BEaTriX paraboloidal mirror at PANTER

Scope of this technical note is the definition of a test plan for the X-ray characterization campaign of the BEaTriX paraboloidal mirror at PANTER. The collimating mirror is a core component of the 4.51 keV beamline of the BEaTriX expanded X-ray beam facility; indeed, the optical quality of the mirror will directly affect the collimation and the uniformity of the final beam that will be used to characterize the focusing performance of SPO MM for ATHENA. The mirror is made of HOQ 310 fused quartz, procured from Zeiss in a preliminary grinding and lapping state, and subsequently finished by a sequence of polishing at the Zeeko robotic machine installed at INAF-OAB. Improvement of the mirror figure has been achieved across several runs of IBF process, using the dedicated facility at INAF-OAB. At each polishing/figuring step, the mirror profile and surface roughness have been characterized using suitable metrology tools at MediaLario

Slumped glass foils as substrate for adjustable x-ray optics

Thin glass modular mirrors are a viable solution to build future X-ray telescopes with high angular resolution and large collecting area. In our laboratories, we shape thin glass foils by hot slumping and we apply pressure to assist the replication of a cylindrical mould figure; this technology is coupled with an integration process able to damp low frequency errors and produces optics in the Wolter I configuration, typical for the X-ray telescopes. From the point of view of the hot slumping process, the efforts were focused in reducing low-, mid- and high- frequency errors of the formed Eagle glass foils. Some of our slumped glass foils were used for the development of active X-ray optics, where piezoelectric actuators are used to correct the slumped glass foil deviations from the ideal shape. In particular, they were used for the Adjustable X-raY optics for astrOnoMy project (AXYOM) developed in Italy, and the X-ray Surveyor mission, as developed at the Smithsonian Astrophysical Observatory / Center for Astrophysics (SAO/CfA) in USA. In this paper we describe the optimisation of the hot slumping process, comparing the results with the requirements of the considered active optics projects. Finally, since the present configuration of the Pennsylvania State University (PSU) coating equipment is limited to 100 x 100 mm2, the slumped glass foils used for the SAO project were cut from 200 x 200 mm2 to 100 x 100 mm2, and a low-frequency change was observed. A characterisation of the profile change upon cutting is presented

Beyond Chandra (towards the X-ray Surveyor mission): possible solutions for the implementation of very high angular resolution X-ray telescopes in the new millennium based on fused silica segments

An important challenge for the X-ray astronomy of the new millennium is represented by the implementation of an X-ray telescope able to maintain the exquisite angular resolution of Chandra (with a sub-arcsec HEW, on-axis) but, at the same time, being characterized by a much larger throughput and grasp. A mission with similar characteristics is represented by the X-ray Surveyor Mission. The project has been recently proposed in USA and is being currently studied by NASA. It will host an X-ray telescope with an effective area of more than 2 square meters at 1 keV (i.e. 30 times greater than Chandra) and a 15-arcminutes field-of-view, with 1-arcsecond or better half-power diameter (versus the 4 arcmin diameter of Chandra). While the scientific reasons for implementing a similar mission are clear, being related to compelling problems like e.g. the formation and subsequent growth of black hole seeds at very high redshift or the identification of the first galaxy groups and proto-clusters, the realization of a grazing-angle optics system able to fulfil these specs remain highly challenging. Different technologies are being envisaged, like e.g. the use of adjustable segmented mirrors (with use of piezoelectric or magneto-restrictive film actuators on the back surface) or the direct polishing of a variety of thin substrates or the use of innovative correction methods like e.g. differential deposition, ionfiguring or the correction of the profile via controlled stress films. In this paper we present a possible approach based on the direct polishing (with final ion figuring correction of the profile) of thin SiO2 segmented substrates (typically 2 mm thick), discussing different aspects of the technology under implementation and presenting some preliminary results

Direct hot slumping of thin glass foils for future generation x-ray telescopes: current state of the art and future outlooks

To significantly improve the performances of the current X-ray observatories, the next generation of X-ray telescopes has to be characterized by a large effective area (Aeff { 2 m2 at 1 keV) and angular resolution better than 5 arcsec. The large dimension implied by these requirements forces the use of a modular approach, splitting the optics into segments. Moreover, lightweight materials, such as glass, have to be selected for the segmented optics in order to maintain a manageable weight for the optics. Since 2009 we are developing a direct hot slumping technique assisted by pressure, in which the glass optical surface is in contact with the mould and a pressure is applied in order to force the glass to copy the mould shape. A cold slumping step is used then to integrate the mirror segments into the final Wolter-I configuration. We present the state of the art of our hot slumping technology, comparing the results obtained with different glass types and mould materials. We also provide an overview of the possibilities of this technology also in view of future developments

Influence of folate-targeted gold nanoparticles on subcellular localization and distribution into lysosomes

The cell interaction, mechanism of cell entry and intracellular fate of surface decorated nanoparticles are known to be affected by the surface density of targeting agents. However, the correlation between nanoparticles multivalency and kinetics of the cell uptake process and disposition of intracellular compartments is complicated and dependent on a number of physicochemical and biological parameters, including the ligand, nanoparticle composition and colloidal properties, features of targeted cells, etc. Here, we have carried out an in-depth investigation on the impact of increasing folic acid density on the kinetic uptake process and endocytic route of folate (FA)-targeted fluorescently labelled gold nanoparticles (AuNPs). A set of AuNPs (15 nm mean size) produced by the Turkevich method was decorated with 0–100 FA-PEG3.5kDa-SH molecules/particle, and the surface was saturated with about 500 rhodamine-PEG2kDa-SH fluorescent probes. In vitro studies carried out using folate receptor overexpressing KB cells (KBFR-high) showed that the cell internalization progressively increased with the ligand surface density, reaching a plateau at 50:1 FA-PEG3.5kDa-SH/particle ratio. Pulse-chase experiments showed that higher FA density (50 FA-PEG3.5kDa-SH molecules/particle) induces more efficient particle internalization and trafficking to lysosomes, reaching the maximum concentration in lysosomes at 2 h, than the lower FA density of 10 FA-PEG3.5kDa-SH molecules/particle. Pharmacological inhibition of endocytic pathways and TEM analysis showed that particles with high folate density are internalized predominantly by a clathrin-independent process

Design and advancement status of the Beam Expander Testing X-ray facility (BEaTriX)

The BEaTriX (Beam Expander Testing X-ray facility) project is an X-ray apparatus under construction at INAF/OAB to generate a broad (200́60 mm2), uniform and low-divergent X-ray beam within a small lab (6́15 m2). BEaTriX will consist of an X-ray source in the focus a grazing incidence paraboloidal mirror to obtain a parallel beam, followed by a crystal monochromation system and by an asymmetrically-cut diffracting crystal to perform the beam expansion to the desired size. Once completed, BEaTriX will be used to directly perform the quality control of focusing modules of large X-ray optics such as those for the ATHENA X-ray observatory, based on either Silicon Pore Optics (baseline) or Slumped Glass Optics (alternative), and will thereby enable a direct quality control of angular resolution and effective area on a number of mirror modules in a short time, in full X-ray illumination and without being affected by the finite distance of the X-ray source. However, since the individual mirror modules for ATHENA will have an optical quality of 3-4 arcsec HEW or better, BEaTriX is required to produce a broad beam with divergence below 1-2 arcsec, and sufficient flux to quickly characterize the PSF of the module without being significantly affected by statistical uncertainties. Therefore, the optical components of BEaTriX have to be selected and/or manufactured with excellent optical properties in order to guarantee the final performance of the system. In this paper we report the final design of the facility and a detailed performance simulation