New generations of astronomical telescopes, whether space or ground-based, constantly express a higher demand for tighter angular resolutions, in particular with the recent bloom of X-ray telescopes and Imaging Atmospheric Cherenkov Telescopes (IACTs) for gamma-ray source detection. As astronomical telescopes always aim to detect further and fainter light signals from our Universe, it is crucial to reduce their level of scattered light to improve the focusing of the collected radiation and enhance their reflectivity. The Point Spread Function (PSF) is a key figure of merit for specifying the angular resolution of optical systems and the focusing accuracy in reflective optical systems and is chiefly determined by two factors: the deviation of the mirror shape from the nominal design and the surface finish. While the effects of the shape errors are usually well described by the geometrical optics, the surface finish is diffractive/interferential in nature and determined by a distribution of defects that cover several decades in the lateral scale. Surface roughness can have a highly damaging impact on telescope imaging performance in terms of reflectivity and scattering, particularly with X-ray telescopes. This was evaluated and established in the particular cases of the Lighweight Asymmetry and Magnetism Probe (LAMP) X-ray polarimeter or ESA-Advanced Telescope for High-ENergy Astrophysics (ATHENA) X-ray telescope. Indeed, we directly observed and characterized roughness or multilayer deposition defects on reflectivity in soft X-rays (250 eV) through LAMP samples’ surface topography and an X-ray reflectivity measurement campaign at the BEAR-Elettra Synchrotron (Trieste, Italy) on multilayer coatings of various composition (Cr/C, Co/C), deposited with different sputtering parameters on nickel, silicon, and glass substrates, using polarized X-rays in the spectral range 240 - 290 eV. Similarly, Silicon Pore Optics(SPO) used for ATHENA telescope optics were studied, their roughness degradation over multilayer deposition and photoresist deposition was also evaluated and related to their scattering properties. Surface properties are determined from various instruments such as reflectometers or scatterometers. However characterizing the surface topography of optical surfaces over large lateral scales (from meters to a few microns) provides an easy and complete way to describe and induce their properties. Indeed, from a full theoretical derivation based on the Huygens-Fresnel principle for electromagnetic wave propagation in the near and far-field approximation, we could reveal the direct dependence of the two-dimensional PSF with the surface topography of the reflective optical components of a telescope in single or multiple reflection and in near-normal incidence configuration for a monochromatic source. Hence, we could develop the PSF prediction formalism based on Physical Optics Real Computation Accounting for Surface Topography (PhOReCAST). PhOReCAST approach presents the advantage of being a simple, self-consistent and unifying method for directly evaluating the contribution of optical surface defects to the two-dimensional PSF of a single or multi-reflection system. It remains valid regardless of the shape and defect content of the optical surface: so it can be applied regardless of the classification of a spectral range as "geometry" or "roughness". From the optical design of the instrument, or geometrical shape of its optical components, reliable ray-tracing routines already exist and allow computing and displaying the PSF based on geometrical optics. However,those ray-tracing routines either lack real surface defect considerations (figure errors or microroughness) in their computation, or they include a scattering effect modeled separately that requires assumptions that are difficult to verify. As telescopes are typically arranged in multiple reflections and complex configurations, PhOReCAST allows for predicting and controlling the behavior of the multiple-scattered radiation within the telescope system; it also enables disentangling the effect of surface scattering from the PSF degradation caused by the shape deformation of the optical elements. The PhOReCAST formalism was numerically developed on Matlab and is able to reconstruct and extend roughness surface maps measured over a few mm2 field-of-view to a full surface mirror (up to a few m2). After being validated, PhOReCAST PSF prediction was successfully applied to numerous case studies in single and multiple reflections, usually extending the PSF to encircled energy consideration. In particular, PhOReCAST was used to estimate and model the aging properties of IACT coating candidates exposed to salt erosion in extreme environmental conditions. Hence, PhOReCAST is a promising tool for simulating and tolerancing a wide variety of complex telescopes, or more generally optical systems with tight angular resolutions.

New generations of astronomical telescopes, whether space or ground-based, constantly express a higher demand for tighter angular resolutions, in particular with the recent bloom of X-ray telescopes and Imaging Atmospheric Cherenkov Telescopes (IACTs) for gamma-ray source detection. As astronomical telescopes always aim to detect further and fainter light signals from our Universe, it is crucial to reduce their level of scattered light to improve the focusing of the collected radiation and enhance their reflectivity. The Point Spread Function (PSF) is a key figure of merit for specifying the angular resolution of optical systems and the focusing accuracy in reflective optical systems and is chiefly determined by two factors: the deviation of the mirror shape from the nominal design and the surface finish. While the effects of the shape errors are usually well described by the geometrical optics, the surface finish is diffractive/interferential in nature and determined by a distribution of defects that cover several decades in the lateral scale. Surface roughness can have a highly damaging impact on telescope imaging performance in terms of reflectivity and scattering, particularly with X-ray telescopes. This was evaluated and established in the particular cases of the Lighweight Asymmetry and Magnetism Probe (LAMP) X-ray polarimeter or ESA-Advanced Telescope for High-ENergy Astrophysics (ATHENA) X-ray telescope. Indeed, we directly observed and characterized roughness or multilayer deposition defects on reflectivity in soft X-rays (250 eV) through LAMP samples’ surface topography and an X-ray reflectivity measurement campaign at the BEAR-Elettra Synchrotron (Trieste, Italy) on multilayer coatings of various composition (Cr/C, Co/C), deposited with different sputtering parameters on nickel, silicon, and glass substrates, using polarized X-rays in the spectral range 240 - 290 eV. Similarly, Silicon Pore Optics(SPO) used for ATHENA telescope optics were studied, their roughness degradation over multilayer deposition and photoresist deposition was also evaluated and related to their scattering properties. Surface properties are determined from various instruments such as reflectometers or scatterometers. However characterizing the surface topography of optical surfaces over large lateral scales (from meters to a few microns) provides an easy and complete way to describe and induce their properties. Indeed, from a full theoretical derivation based on the Huygens-Fresnel principle for electromagnetic wave propagation in the near and far-field approximation, we could reveal the direct dependence of the two-dimensional PSF with the surface topography of the reflective optical components of a telescope in single or multiple reflection and in near-normal incidence configuration for a monochromatic source. Hence, we could develop the PSF prediction formalism based on Physical Optics Real Computation Accounting for Surface Topography (PhOReCAST). PhOReCAST approach presents the advantage of being a simple, self-consistent and unifying method for directly evaluating the contribution of optical surface defects to the two-dimensional PSF of a single or multi-reflection system. It remains valid regardless of the shape and defect content of the optical surface: so it can be applied regardless of the classification of a spectral range as "geometry" or "roughness". From the optical design of the instrument, or geometrical shape of its optical components, reliable ray-tracing routines already exist and allow computing and displaying the PSF based on geometrical optics. However,those ray-tracing routines either lack real surface defect considerations (figure errors or microroughness) in their computation, or they include a scattering effect modeled separately that requires assumptions that are difficult to verify. As telescopes are typically arranged in multiple reflections and complex configurations, PhOReCAST allows for predicting and controlling the behavior of the multiple-scattered radiation within the telescope system; it also enables disentangling the effect of surface scattering from the PSF degradation caused by the shape deformation of the optical elements. The PhOReCAST formalism was numerically developed on Matlab and is able to reconstruct and extend roughness surface maps measured over a few mm2 field-of-view to a full surface mirror (up to a few m2). After being validated, PhOReCAST PSF prediction was successfully applied to numerous case studies in single and multiple reflections, usually extending the PSF to encircled energy consideration. In particular, PhOReCAST was used to estimate and model the aging properties of IACT coating candidates exposed to salt erosion in extreme environmental conditions. Hence, PhOReCAST is a promising tool for simulating and tolerancing a wide variety of complex telescopes, or more generally optical systems with tight angular resolutions.

"NOVEL METHODS IN POINT SPREAD FUNCTION PREDICTION FROM SURFACE METROLOGY FOR SPACE AND GROUND-BASED TELESCOPES".

TAYABALY, KASHMIRA CHRISTELLE

Abstract

New generations of astronomical telescopes, whether space or ground-based, constantly express a higher demand for tighter angular resolutions, in particular with the recent bloom of X-ray telescopes and Imaging Atmospheric Cherenkov Telescopes (IACTs) for gamma-ray source detection. As astronomical telescopes always aim to detect further and fainter light signals from our Universe, it is crucial to reduce their level of scattered light to improve the focusing of the collected radiation and enhance their reflectivity. The Point Spread Function (PSF) is a key figure of merit for specifying the angular resolution of optical systems and the focusing accuracy in reflective optical systems and is chiefly determined by two factors: the deviation of the mirror shape from the nominal design and the surface finish. While the effects of the shape errors are usually well described by the geometrical optics, the surface finish is diffractive/interferential in nature and determined by a distribution of defects that cover several decades in the lateral scale. Surface roughness can have a highly damaging impact on telescope imaging performance in terms of reflectivity and scattering, particularly with X-ray telescopes. This was evaluated and established in the particular cases of the Lighweight Asymmetry and Magnetism Probe (LAMP) X-ray polarimeter or ESA-Advanced Telescope for High-ENergy Astrophysics (ATHENA) X-ray telescope. Indeed, we directly observed and characterized roughness or multilayer deposition defects on reflectivity in soft X-rays (250 eV) through LAMP samples’ surface topography and an X-ray reflectivity measurement campaign at the BEAR-Elettra Synchrotron (Trieste, Italy) on multilayer coatings of various composition (Cr/C, Co/C), deposited with different sputtering parameters on nickel, silicon, and glass substrates, using polarized X-rays in the spectral range 240 - 290 eV. Similarly, Silicon Pore Optics(SPO) used for ATHENA telescope optics were studied, their roughness degradation over multilayer deposition and photoresist deposition was also evaluated and related to their scattering properties. Surface properties are determined from various instruments such as reflectometers or scatterometers. However characterizing the surface topography of optical surfaces over large lateral scales (from meters to a few microns) provides an easy and complete way to describe and induce their properties. Indeed, from a full theoretical derivation based on the Huygens-Fresnel principle for electromagnetic wave propagation in the near and far-field approximation, we could reveal the direct dependence of the two-dimensional PSF with the surface topography of the reflective optical components of a telescope in single or multiple reflection and in near-normal incidence configuration for a monochromatic source. Hence, we could develop the PSF prediction formalism based on Physical Optics Real Computation Accounting for Surface Topography (PhOReCAST). PhOReCAST approach presents the advantage of being a simple, self-consistent and unifying method for directly evaluating the contribution of optical surface defects to the two-dimensional PSF of a single or multi-reflection system. It remains valid regardless of the shape and defect content of the optical surface: so it can be applied regardless of the classification of a spectral range as "geometry" or "roughness". From the optical design of the instrument, or geometrical shape of its optical components, reliable ray-tracing routines already exist and allow computing and displaying the PSF based on geometrical optics. However,those ray-tracing routines either lack real surface defect considerations (figure errors or microroughness) in their computation, or they include a scattering effect modeled separately that requires assumptions that are difficult to verify. As telescopes are typically arranged in multiple reflections and complex configurations, PhOReCAST allows for predicting and controlling the behavior of the multiple-scattered radiation within the telescope system; it also enables disentangling the effect of surface scattering from the PSF degradation caused by the shape deformation of the optical elements. The PhOReCAST formalism was numerically developed on Matlab and is able to reconstruct and extend roughness surface maps measured over a few mm2 field-of-view to a full surface mirror (up to a few m2). After being validated, PhOReCAST PSF prediction was successfully applied to numerous case studies in single and multiple reflections, usually extending the PSF to encircled energy consideration. In particular, PhOReCAST was used to estimate and model the aging properties of IACT coating candidates exposed to salt erosion in extreme environmental conditions. Hence, PhOReCAST is a promising tool for simulating and tolerancing a wide variety of complex telescopes, or more generally optical systems with tight angular resolutions.
VIGEVANO, LUIGI
SALA, GIUSEPPE
26-giu-2017
Novel methods in Point Spread Function Prediction from Surface Metrology for Space and Ground-based telescopes
New generations of astronomical telescopes, whether space or ground-based, constantly express a higher demand for tighter angular resolutions, in particular with the recent bloom of X-ray telescopes and Imaging Atmospheric Cherenkov Telescopes (IACTs) for gamma-ray source detection. As astronomical telescopes always aim to detect further and fainter light signals from our Universe, it is crucial to reduce their level of scattered light to improve the focusing of the collected radiation and enhance their reflectivity. The Point Spread Function (PSF) is a key figure of merit for specifying the angular resolution of optical systems and the focusing accuracy in reflective optical systems and is chiefly determined by two factors: the deviation of the mirror shape from the nominal design and the surface finish. While the effects of the shape errors are usually well described by the geometrical optics, the surface finish is diffractive/interferential in nature and determined by a distribution of defects that cover several decades in the lateral scale. Surface roughness can have a highly damaging impact on telescope imaging performance in terms of reflectivity and scattering, particularly with X-ray telescopes. This was evaluated and established in the particular cases of the Lighweight Asymmetry and Magnetism Probe (LAMP) X-ray polarimeter or ESA-Advanced Telescope for High-ENergy Astrophysics (ATHENA) X-ray telescope. Indeed, we directly observed and characterized roughness or multilayer deposition defects on reflectivity in soft X-rays (250 eV) through LAMP samples’ surface topography and an X-ray reflectivity measurement campaign at the BEAR-Elettra Synchrotron (Trieste, Italy) on multilayer coatings of various composition (Cr/C, Co/C), deposited with different sputtering parameters on nickel, silicon, and glass substrates, using polarized X-rays in the spectral range 240 - 290 eV. Similarly, Silicon Pore Optics(SPO) used for ATHENA telescope optics were studied, their roughness degradation over multilayer deposition and photoresist deposition was also evaluated and related to their scattering properties. Surface properties are determined from various instruments such as reflectometers or scatterometers. However characterizing the surface topography of optical surfaces over large lateral scales (from meters to a few microns) provides an easy and complete way to describe and induce their properties. Indeed, from a full theoretical derivation based on the Huygens-Fresnel principle for electromagnetic wave propagation in the near and far-field approximation, we could reveal the direct dependence of the two-dimensional PSF with the surface topography of the reflective optical components of a telescope in single or multiple reflection and in near-normal incidence configuration for a monochromatic source. Hence, we could develop the PSF prediction formalism based on Physical Optics Real Computation Accounting for Surface Topography (PhOReCAST). PhOReCAST approach presents the advantage of being a simple, self-consistent and unifying method for directly evaluating the contribution of optical surface defects to the two-dimensional PSF of a single or multi-reflection system. It remains valid regardless of the shape and defect content of the optical surface: so it can be applied regardless of the classification of a spectral range as "geometry" or "roughness". From the optical design of the instrument, or geometrical shape of its optical components, reliable ray-tracing routines already exist and allow computing and displaying the PSF based on geometrical optics. However,those ray-tracing routines either lack real surface defect considerations (figure errors or microroughness) in their computation, or they include a scattering effect modeled separately that requires assumptions that are difficult to verify. As telescopes are typically arranged in multiple reflections and complex configurations, PhOReCAST allows for predicting and controlling the behavior of the multiple-scattered radiation within the telescope system; it also enables disentangling the effect of surface scattering from the PSF degradation caused by the shape deformation of the optical elements. The PhOReCAST formalism was numerically developed on Matlab and is able to reconstruct and extend roughness surface maps measured over a few mm2 field-of-view to a full surface mirror (up to a few m2). After being validated, PhOReCAST PSF prediction was successfully applied to numerous case studies in single and multiple reflections, usually extending the PSF to encircled energy consideration. In particular, PhOReCAST was used to estimate and model the aging properties of IACT coating candidates exposed to salt erosion in extreme environmental conditions. Hence, PhOReCAST is a promising tool for simulating and tolerancing a wide variety of complex telescopes, or more generally optical systems with tight angular resolutions.
Tesi di dottorato
File allegati
File Dimensione Formato  
thesis_finalKT.pdf

accessibile in internet per tutti

Descrizione: PhD Thesis Kashmira Tayabaly
Dimensione 97.22 MB
Formato Adobe PDF
97.22 MB Adobe PDF Visualizza/Apri

I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10589/133575