arXiv subjects

François Ramaz

Publications and source records attributed to François Ramaz.

8 recordsLinked to original sources

arXiv2023

Suppression of the Talbot effect in Fourier transform acousto-optic imaging

We report on the observation and correction of an imaging artifact attributed to the Talbot effect in the context of acousto-optic imaging using structured acoustic waves. When ultrasound waves are emitted with a periodic structure, the Talbot effect produces $π$ -phase shifts of that periodic structure at every half of the Talbot distance in propagation. This unwanted artifact is detrimental to the image reconstruction, which assumes near-field diffraction is negligible. Here, we demonstrate both theoretically and experimentally how imposing an additional phase modulation on the acoustic periodic structure induces a symmetry constraint leading to the annihilation of the Talbot effect. This will significantly improve the acousto-optic image reconstruction quality and allows for an improvement of the reachable spatial resolution of the image.

physics.class-ph↗

arXiv2019

Deep and persistent spectral holes in Tm-doped yttrium orthosilicate for imaging applications

With their optical wavelength in the near infrared (790-800nm) and their unique spectroscopic properties at cryogenic temperatures, thulium-doped crystals are at the center of many architectures linked to classical signal processing and quantum information. In this work, we focus on Tm-doped YSO, a compound that was left aside in the mid-1990s due to its rather short optical coherence lifetime. By means of time-resolved hole-burning spectroscopy, we investigate the anisotropic enhanced nuclear Zeeman effect and demonstrate deep, sub-MHz, persistent spectral hole burning under specific magnetic field orientation and magnitude. By estimating the experimental parameters corresponding to a real-scale ultrasound optical tomography setup using Tm:YSO as a spectral filter, we validate Tm:YSO as a promising compound for medical imaging in the human body.

physics.optics↗

arXiv2018

Ultrasound modulated optical tomography in scattering media: flux filtering based on persistent spectral hole burning in the optical diagnosis window

Ultrasound modulated optical tomography (UOT) is a powerful imaging technique to discriminate healthy from unhealthy biological tissues based on their optical signature. Among the numerous detection techniques developed for acousto-optic imaging, only those based on spectral filtering are intrinsically immune to speckle decorrelation. This paper reports on UOT imaging based on spectral hole burning in Tm:YAG crystal under a moderate magnetic field (200G) with a well-defined orientation. The deep and long-lasting holes translate into a more efficient UOT imaging with a higher contrast and faster imaging frame rate. We demonstrate the potential of this method by imaging calibrated phantom scattering gels.

physics.optics↗

arXiv2017

Controlling light in complex media beyond the acoustic diffraction-limit using the acousto-optic transmission matrix

Studying the internal structure of complex samples with light is an important task, but a difficult challenge due to light scattering. While the complex optical distortions induced by multiple scattering can be effectively undone with the knowledge of the medium's scattering-matrix, this matrix is generally unknown, and cannot be measured with high resolution without the presence of fluorescent or absorbing probes at all points of interest. To overcome these limitations, we introduce here the concept of the acousto-optic transmission matrix (AOTM). Taking advantage of the near scattering-free propagation of ultrasound in complex samples, we noninvasively measure an ultrasonically-encoded, spatially-resolved, optical scattering-matrix. We demonstrate that a singular value decomposition analysis of the AOTM, acquired using a single or multiple ultrasonic beams, allows controlled optical focusing beyond the acoustic diffraction limit in scattering media. Our approach provides a generalized framework for analyzing acousto-optical experiments, and for noninvasive, high-resolution study of complex media.

physics.optics↗

arXiv2013

Experimental study of z resolution in acousto-optical coherence tomography using random phase jumps on ultrasound and light

Acousto-Optical Coherence Tomography (AOCT) is a variant of Acousto Optic Imaging (also called Ultrasound modulated Optical Tomography) that makes possible to get resolution along the ultrasound propagation axis $z$. We present here new AOCT experimental results, and we study how the $z$ resolution depends on time step between phase jumps $T_ϕ$, or on the correlation length $Δz$. By working at low resolution, we perform a quantitative comparison of the $z$ measurements with the theoretical Point Spread Function (PSF). We present also images recorded with different $z$ resolution, and we qualitatively show how the image quality varies with $T_ϕ$, or $Δz$.

physics.optics↗

arXiv2012

Acousto-optical coherence tomography with a digital holographic detection scheme

Acousto-optical coherence tomography (AOCT) consists in using random phase jumps on ultrasound and light to achieve a millimeter resolution when imaging thick scattering media. We combined this technique with heterodyne off-axis digital holography. Two-dimensional images of absorbing objects embedded in scattering phantoms are obtained with a good signal-to-noise ratio. We study the impact of the phase modulation characteristics on the amplitude of the acousto-optic signal and on the contrast and apparent size of the absorbing inclusion.

physics.optics↗

arXiv2011

Theoretical study of Acousto-optical coherence tomography using random phase jumps on US and light

Acousto-Optical Coherence Tomography (AOCT) is variant of Acousto Optic Imaging (called also ultrasonic modulation imaging) that makes possible to get z resolution with acoustic and optic Continuous Wave (CW) beams. We describe here theoretically the AOCT e ect, and we show that the Acousto Optic tagged photons remains coherent if they are generated within a speci c z region of the sample. We quantify the z selectivity for both the tagged photon eld, and for the M. Lesa re et al. photorefractive signal.

physics.optics↗

arXiv2009

Detection of the tagged or untagged photons in acousto-optic imaging of thick highly scattering media by photorefractive adaptive holography

We propose an original adaptive wavefront holographic setup based on the photorefractive effect (PR), to make real-time measurements of acousto-optic signals in thick scattering media, with a high flux collection at high rates for breast tumor detection. We describe here our present state of art and understanding on the problem of breast imaging with PR detection of the acousto-optic signal.

physics.optics↗