arXiv subjects

Francesco Chiadini

Publications and source records attributed to Francesco Chiadini.

9 recordsLinked to original sources

arXiv2026

Thermal Noise Reduction in Ternary Optical Coatings: From Ti::GeO$_2$-Based Ternary Systems to High Index Materials

Minimizing coating thermal noise is crucial for enhancing gravitational wave detector sensitivity, with a target Amplitude Spectral Density Reduction Factor (ASD RF) of $0.5$ relative to standard coatings. This study investigates the design of low-noise dielectric stacks using the 'Double Stack of Doublet' strategy, explored via ad-hoc optimization heuristics specifically developed for efficient parametric analysis of coating performance. We analyze the performance limits of ternary coatings based on SiO$_2$, Ti::SiO$_2$, and Ti::GeO$_2$, considering material property uncertainties and absorption constraints. Optimization results show that this system, even with relaxed absorbance constraint (1 ppm), falls short of the target, achieving a best ASD RF of $\sim 0.69$. Consequently, we explore alternative ternary 'Double Stack of Doublet' designs incorporating higher-refractive-index materials. Simulations demonstrate that incorporating alternative high-index materials offers a promising pathway, potentially enabling the achievement of the project target. We discuss the optimization strategies, performance trade-offs, design robustness, and implications of using high-index, potentially higher-loss materials for next-generation optical coatings.

physics.optics↗

arXiv2025

Comparative Analysis of Thermal Models for Test Masses in Next-Generation Gravitational Wave Interferometers

Accurate thermal modeling of Terminal Test Masses (TTMs) is crucial for optimizing the sensitivity of gravitational wave interferometers like Virgo. In fact, in such gravitational wave detectors even minimal laser power absorption can induce performance-limiting thermal effects. This paper presents a detailed investigation into the steady-state thermal behavior of TTMs. In particular, future scenarios of increased intracavity laser beam power and optical coating absorption are considered. We develop and compare two numerical models: a comprehensive model incorporating volumetric heat absorption in both the multilayer coating and the bulk substrate, and a simplified reduced model where the coating's thermal impact is represented as an effective surface boundary condition on the substrate. Our simulations were focused on a ternary coating design, which is a candidate for use in next-generation detectors. Results reveal that higher coating absorption localizes peak temperatures near the coating--vacuum interface. Importantly, the comparative analysis demonstrates that temperature predictions from the reduced model differ from the detailed model by only milli-Kelvins, a discrepancy often within the experimental uncertainties of the system's thermo-physical parameters. This finding suggests that computationally efficient reduced models can provide sufficiently accurate results for thermal management and first-order distortion analyses. Moreover, the critical role of accurately characterizing the total power absorbed by the coating is emphasized.

physics.app-ph↗

arXiv2021

Optimal Design of Coatings for Mirrors of Gravitational Wave Detectors: Analytic Turbo Solution via Herpin Equivalent Layers

In this paper, an analytical solution to the problem of optimal dielectric coating design of mirrors for gravitational wave detectors is found. The technique used to solve this problem is based on Herpin's equivalent layers, which provide a simple, constructive, and analytical solution. The performance of the Herpin-type design exceeds that of the periodic design and is almost equal to the performance of the numerical, non-constructive optimized design obtained by brute force. Note that the existence of explicit analytic constructive solutions of a constrained optimization problem is not guaranteed in general, when such a solution is found, we speak of turbo optimal solutions.

gr-qc↗

arXiv2020

Enhanced left/right asymmetry in reflection and transmission due to a periodic multilayer of a topological insulator and an anisotropic dielectric material

Very weak left/right asymmetry in reflection and transmission is offered by a layer of a topological insulator on top of a layer of an anisotropic dielectric material, but it can be enhanced very significantly by using a periodic multilayer of both types of materials. This is an attractive prospect for realizing one-way terahertz devices, because both types of materials can be grown using standard physical-vapor-deposition techniques.

physics.optics↗

arXiv2017

Bicontrollable Terahertz Metasurface with Subwavelength Scattering Elements of Two Different Materials

Transmission of a normally incident plane wave through a metasurface with bicontrollable subwavelength scattering elements was simulated using a commercial software. Some pixels comprising the $H-shaped scattering elements were made of a magnetostatically controllable material whereas the remaining pixels were made of a thermally controllable material, the metasurface designed to operate in the terahertz spectral regime. The co-polarized transmission coefficients were found to exhibit stopbands that shift when either a magnetostatic field is applied or the temperature is increased or both. Depending on spectral location of the stopband, either the magnetostatic field gives coarse control and temperature gives fine control or vice versa. The level of magnetostatic control depends on the magnetostatic-field configuration.

physics.optics↗

arXiv2017

Signatures of thermal hysteresis in Tamm-wave propagation

We numerically solved the boundary-value problem for Tamm waves (which may also be classified as Uller-Zenneck waves here) guided by the planar interface of a homogeneous isotropic dissipative dielectric (HIDD) material and a periodically multilayered isotropic dielectric material. The HIDD material was chosen to be VO${}_2$ which, at optical wavelengths, has a temperature-dependent refractive index with a hysteresis feature, i.e., the temperature-dependence of its refractive index varies depending upon whether the temperature is increasing or decreasing. A numerical code was implemented to extract solutions of the dispersion equation at a fixed wavelength for both $p$- and $s$-polarization states over the temperature range [50,80] degrees. A multitude of Tamm waves of both linear polarization states were found, demonstrating a clear demarcation of the heating and cooling phases in terms of wavenumbers and propagation distances. Thereby, the signatures of thermal hysteresis in Tamm-wave propagation were revealed.

physics.optics↗

arXiv2017

Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves

The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a dissipative plasmonic material. Correspondingly, the ESWs transmute from Dyakonov-Tamm surface waves into surface-plasmon-polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results.

physics.optics↗

arXiv2015

Compound surface-plasmon-polariton waves guided by a thin metal layer sandwiched between a homogeneous isotropic dielectric material and a structurally chiral material

Multiple compound surface plasmon-polariton (SPP) waves can be guided by a structure consisting of a sufficiently thick layer of metal sandwiched between a homogeneous isotropic dielectric (HID) material and a dielectric structurally chiral material (SCM). The compound SPP waves are strongly bound to both metal/dielectric interfaces when the thickness of the metal layer is comparable to the skin depth but just to one of the two interfaces when the thickness is much larger. The compound SPP waves differ in phase speed, attenuation rate, and field profile, even though all are excitable at the same frequency. Some compound SPP waves are not greatly affected by the choice of the direction of propagation in the transverse plane but others are, depending on metal thickness. For fixed metal thickness, the number of compound SPP waves depends on the relative permittivity of the HID material, which can be useful for sensing applications.

physics.optics↗

arXiv2015

Compound surface-plasmon-polariton waves guided by a thin metal layer sandwiched between a homogeneous isotropic dielectric material and a periodically multilayered isotropic dielectric material

Multiple p- and s-polarized compound surface plasmon-polariton (SPP) waves at a fixed frequency can be guided by a structure consisting of a metal layer sandwiched between a homogeneous isotropic dielectric (HID) material and a periodic multilayered isotropic dielectric (PMLID) material. For any thickness of the metal layer, at least one compound SPP wave must exist. It possesses the p-polarization state, is strongly bound to the metal/HID interface when the metal thickness is large but to both metal/dielectric interfaces when the metal thickness is small. When the metal layer vanishes, this compound SPP wave transmutes into a Tamm wave. Additional compound SPP waves exist, depending on the thickness of the metal layer, the relative permittivity of the HID material, and the period and the composition of the PMLID material. Some of these are p polarized, the others being s polarized. All of them differ in phase speed, attenuation rate, and field profile, even though all are excitable at the same frequency. The multiplicity and the dependence of the number of compound SPP waves on the relative permittivity of the HID material when the metal layer is thin could be useful for optical sensing applications.

physics.optics↗