arXiv subjects

Tiago E. C. Magalhães

Publications and source records attributed to Tiago E. C. Magalhães.

4 recordsLinked to original sources

arXiv2026

Dynamics of confined acoustic phonon modes in nanocrystalline silicon membranes

We report femtosecond time-resolved measurements of confined acoustic phonons in free-standing nanocrystalline silicon membranes and compare them with the crystalline silicon counterpart. While the latter exhibit well-resolved higher-order modes, a strong suppression of these modes is observed in nanocrystalline samples. The suppression is strongly frequency dependent and becomes more pronounced as the phonon wavelength approaches the characteristic grain size. Analysis of the phonon lifetimes reveals an additional frequency-dependent scattering mechanism in nanocrystalline silicon, with a scattering rate that scales approximately as $f^2$, where $f$ is the phonon frequency. The measured sound velocity is consistent with previous reports for nanocrystalline silicon and indicates an effective elastic response arising from multiple crystallographic orientations. These results establish coherent phonons as a sensitive probe of microstructure-dependent scattering in nanocrystalline materials and indicate that grain boundaries act as an effective spectral filter for high-frequency acoustic phonons.

physics.optics↗

arXiv2022

PyWolf: A PyOpenCL implementation for simulating the propagation of partially coherent light

We present PyWolf, an open-source software capable of performing numerical simulations of partially coherent light propagation from two-dimensional light sources. PyWolf computes the evolution of a user-defined cross-spectral density function in the Fresnel and far field approximations, which enables the retrieval of second-order optical quantities of interest such as the spectral degree of coherence and spectral density for a given frequency. The open-source tool kit PyOpenCL is used to increase the computation speed. We present examples of propagation of different source models and optical systems to validate our implementation. Performance results for the computation speed when using parallel computation through PyOpenCL is shown. Source models and propagation systems can be easily added to PyWolf, which has a graphical user interface built with PyQt5. This software can be of great utility for partially coherent light simulation problems that are difficult to treat analytically.

physics.optics↗

arXiv2021

Observation of atmospheric gravity waves using a Raspberry Pi camera module on board the International Space Station

We identified and computed the horizontal wavelengths of atmospheric gravity waves in clouds using a visible camera installed on a window of the Columbus module of the International Space Station (ISS) and controlled by a Raspberry Pi computer. The experiment was designed in the context of the Astro Pi challenge, a project run by ESA in collaboration with the Raspberry Pi Foundation, where students are allowed the opportunity to write a code to be executed at the ISS. A code was developed to maximize the probability of capturing images of clouds while the ISS is orbiting the Earth. Several constraints had to be fulfilled such as the experiment duration limit (3 hours) and the maximum data size (3 gigabytes). After receiving the data from the ISS, small-scale gravity waves were observed in different regions in the northern hemisphere with horizontal wavelengths in the range of 1.0 to 4.7 km.

physics.ao-ph↗

arXiv2020

Spatial coherence characterization of light: an experimental study using digital micromirror devices

We present spatial coherence measurements of partially coherent light in the far-field of incoherent sources with an experimental setup based on the Thompson-Wolf and Partanen-Turunen-Tervo experiments, to be performed in the context of a possible solar coherence measurement space instrument. The optical setup consists of a telescope to collimate light from a source, to diffract it by a digital micromirror device implementing a Young double-aperture interferometer in retroreflection mode, and finally to image the source into a two-dimensional sensor. Two multimode optical fibers with different diameters were used as incoherent sources and the results obtained for the spectral degree of coherence are compared to those expected from the van Cittert-Zernike theorem.

physics.ins-det↗