arXiv subjects

Patrick Mounaix

Publications and source records attributed to Patrick Mounaix.

3 recordsLinked to original sources

arXiv2025

Terahertz Fourier Ptychographic Imaging

High-resolution imaging in the terahertz (THz) spectral range remains fundamentally constrained by the limited numerical apertures of currently existing state-of-the-art imagers, which restricts its applicability across many fields, such as imaging in complex media or nondestructive testing. To address this challenge, we introduce a proof-of-concept implementation of THz Fourier Ptychographic imaging to enhance spatial resolution without requiring extensive hardware modifications. Our method employs a motorized kinematic mirror to generate a sequence of controlled, multi-angle plane-wave illuminations, with each resulting oblique-illumination intensity image encoding a limited portion of the spatial-frequency content of the target imaging sample. These measurements are combined in the Fourier domain using an aberration-corrected iterative phase-retrieval algorithm integrated with an efficient illumination calibration scheme, which enables the reconstruction of resolution-enhanced amplitude and phase images through the synthetic expansion of the effective numerical aperture. Our work establishes a robust framework for high-resolution THz imaging and paves the way for a wide array of applications in materials characterization, spectroscopy, and non-destructive evaluation.

physics.optics↗

arXiv2024

Broadband THz emission of long pulses from photomixing process with optical chirped pulses

Terahertz (THz) generation via photomixing on photoconductive antenna using twin delayed chirped pulses provides a long THz pulse with a narrow bandwidth. To generate a long pulse with broad bandwidth, we propose a new method that combines two long optical pulses with opposite chirps. The pulses exhibit temporal distributions of their instantaneous frequencies with opposite slopes. As a result, interaction between the beat frequency evolving over time and a photoconductor produces a broad THz spectrum with temporal variations. In our experimental setup, we generate a 12 ps-long pulse with a 1 THz bandwidth spectrum, featuring a frequency ramp of 90 GHz/ps, resembling a chirped THz pulse. This approach signifies a major advancement toward integrating photomixer technology, particularly in THz ranging applications.

physics.optics↗

arXiv2024

Fourier Synthetic Aperture-based Time-resolved Terahertz Imaging

Terahertz microscopy has attracted attention owing to distinctive characteristics of the THz frequency region, particularly non-ionizing photon energy, spectral fingerprint, and transparency to most nonpolar materials. Nevertheless, the well-known Rayleigh diffraction limit imposed on THz waves commonly constrains the resultant imaging resolution to values beyond the millimeter scale, consequently limiting the applicability in numerous emerging applications for chemical sensing and complex media imaging. In this theoretical and numerical work, we address this challenge by introducing a new imaging approach, based on acquiring high-spatial frequencies by adapting the Fourier synthetic aperture approach to the terahertz spectral range, thus surpassing the diffraction-limited resolution. Our methodology combines multi-angle terahertz pulsed illumination with time-resolved field measurements, as enabled by the state-of-the-art time-domain spectroscopy technique. We demonstrate the potential of the approach for hyperspectral terahertz imaging of semi-transparent samples and show that the technique can reconstruct spatial and temporal features of complex inhomogeneous samples with subwavelength resolution.

physics.optics↗