arXiv subjects

Francois Blanchard

Publications and source records attributed to Francois Blanchard.

4 recordsLinked to original sources

arXiv2026

Terahertz multispectral polarimetric imaging based on intensity measurement

A compact terahertz (THz) polarimetric spectrometer and imaging system is demonstrated using polarization-sensitive frequency-selective surfaces (PS-FSS) and rapid, intensity-based detection. Real-time Stokes parameter extraction enables angle-of-linear-polarization (AoLP) measurements and quantitative retrieval of the birefringence of a 1-mm-thick x-cut quartz crystal, used here as a benchmark anisotropic sample. The extracted birefringence is in good agreement with THz time domain spectroscopy-based measurements, validating the accuracy of the proposed THz polarimetric approach. Signal-to-noise ratios (SNR) up to 87 dB across 0.23-0.41 THz ensure reliable discrimination of the measured spectral components above the noise floor. Extending this approach to raster-scanned THz imaging using distinct PS-FSS orientations (0{\deg}, 45{\deg}, 90{\deg}, and 135{\deg}) enables simultaneous mapping of frequency-dependent Stokes parameters. The resulting degree of linear polarization (DoLP) and AoLP maps exhibit well-resolved polarimetric contrast, consistent with numerical simulations and independent visible polarimetric measurements. Operating entirely without field-resolved detection or mechanical delay stages, the system provides a robust and compact platform for THz polarimetric spectroscopy and imaging of anisotropic materials.

physics.optics↗

arXiv2019

Selective excitation of multipolar spoof plasmons using orbital angular momentum of light

The nature of light-matter interaction is governed by the spatial-temporal structures of a light field and material wavefunctions. The emergence of the light beam with transverse phase vortex, or equivalently orbital angular momentum (OAM) has been providing intriguing possibilities to induce unconventional optical transitions beyond the framework of the electric dipole interaction. The uniqueness stems from the OAM transfer from light to material, as demonstrated using the bound electron of a single trapped ion. However, many aspects of the vortex light-matter interaction are still unexplored especially in solids with extended electronic states. Here, we unambiguously visualized dipole-forbidden multipolar excitations in a solid-state electron system; spoof localized surface plasmon, selectively induced by the terahertz vortex beam. The results obey the selection rules governed by the conservation of the total angular momentum, which is numerically confirmed by the electromagnetic field analysis. Our results show light's OAM can be efficiently transferred to an elementary excitation in solids.

physics.optics↗

arXiv2015

High field response of gated graphene at THz frequencies

We study the Fermi energy level dependence of nonlinear terahertz (THz) transmission of gated multi-layer and single-layer graphene transferred onto sapphire and quartz substrates. The two samples represent two limits of low-field impurity scattering: short-range neutral and long-range charged impurity scattering, respectively. We observe an increase in the transmission as the field amplitude is increased due to intraband absorption bleaching starting at fields above 8 kV/cm. This effect arises from a field-induced reduction in THz conductivity that depends strongly on the Fermi energy. We account for intraband absorption using a free carrier Drude model that includes neutral and charged impurity scattering as well as optical phonon scattering. We find that although the Fermi-level dependence in the monolayer and five-layer samples is quite different, both exhibit a strong dependence on the field amplitude that cannot be explained on the basis of an increase in the lattice temperature alone. Our results provide a deeper understanding of transport in graphene devices operating at THz frequencies and in modest kV/cm field strengths where nonlinearities exist.

cond-mat.mes-hall↗

arXiv2003

Some properties of cellular automata with equicontinuity points

We investigate topological and ergodic properties of cellular automata having equicontinuity points. In this class surjectivity on a transitive SFT implies existence of a dense set of periodic points. Our main result is that under the action of such an automaton any shift ergodic measure converges in Cesaro Mean.

math.DS↗