Non-line-of-sight tracking of people at long range

A remote-sensing system that can determine the position of hidden objects has applications in many critical real-life scenarios, such as search and rescue missions and safe autonomous driving. Previous work has shown the ability to range and image objects hidden from the direct line of sight, employing advanced optical imaging technologies aimed at small objects at short range. In this work we demonstrate a long-range tracking system based on single laser illumination and single-pixel single-photon detection. This enables us to track one or more people hidden from view at a stand-off distance of over 50~m. These results pave the way towards next generation LiDAR systems that will reconstruct not only the direct-view scene but also the main elements hidden behind walls or corners

Contrast enhanced spectroscopic optical coherence tomography

A method of forming an image of a sample includes performing SOCT on a sample. The sample may include a contrast agent, which may include an absorbing agent and/or a scattering agent. A method of forming an image of tissue may include selecting a contrast agent, delivering the contrast agent to the tissue, acquiring SOCT data from the tissue, and converting the SOCT data into an image. The contributions to the SOCT data of an absorbing agent and a scattering agent in a sample may be quantified separately

Laser-induced electron interferences from atoms and molecules

Since discovering wave-particle duality, science has changed our perception of light and matter, especially at the subatomic level. Thanks to such discoveries, we have been able to develop and expand our scientific knowledge over the past two centuries, crossing those limits. For instance, let us take the famous double-slit experiment from T. Young (1801). This experiment has been extended after the twentieth-century quantum revolution, revealing electron and neutron diffraction used nowadays to measure the nuclei separation from complex structures. Similarly, the experiment of Michelson and Morley (1887), which follows T. Young foundations, got a fair success in astronomy, enabling high-resolution imaging of stars in the universe. In this thesis, we use light to generate electrons and produce interferences similar to the double-slit experiment, which is analyzed further to study the atomic properties. On the dynamics of an atom, that is, attoscience, we use ultrafast laser pulses to trigger motions on a femtoseconds time-scale. Together with the use of strong intense laser fields in the Mid-IR regime, the electron is ionized with zero-kinetic energy and subsequently accelerated by the laser ponderomotive energy. Strong field dynamics offer rich structures that are encoded in the photoelectron momentum distribution. Since we use two-color combined laser fields, we can gate and control those dynamics further down on the sub-cycle scale. More precisely, we show that with the help of a Reaction Microscope, we can extract both electron information and nuclear dynamics within extraordinary sub-cycle temporal resolution. Finally, the strong-field recollision model is investigated with molecules through the previously developed laser-induced electron diffraction (LIED) method. We show that backscattered electron interferences, issued from strong field at low impact parameters, embedded a particular molecular orientation that can be reproduced when the molecule is considered aligned with the laser field polarization. Those findings seem to encode a more profound property about wave diffraction in molecules until recently unexplored due to the imposed conditions given in conventional electron diffraction (CED).Desde que se descubrió la dualidad onda-partícula, la ciencia ha cambiado nuestra percepción de la luz y la materia, especialmente a nivel subatómico. Gracias a tales descubrimientos, hemos podido desarrollar y expandir nuestro conocimiento durante los últimos dos siglos, llegando ahora a estos infinitos límites de la ciencia. Por ejemplo, tomemos el famoso experimento de la doble rendija de T. Young (1801). Este experimento se ha ampliado después de la revolución cuántica del siglo XX, revelando la difracción de electrones y neutrones utilizada hoy en día para medir la separación de núcleos de estructuras complejas. De manera similar, el experimento de Michelson y Morley (1887), que sigue los fundamentos de T. Young, obtuvo un éxito considerable en astronomía, lo que permitió obtener imágenes de alta resolución de las estrellas del universo. En esta tesis, utilizamos la luz para generar electrones y producir interferencias de manera similar al experimento de doble rendija, que se analiza más a fondo para estudiar las propiedades atómicas. En la dinámica de un átomo, es decir, la attociencia, utilizamos pulsos de láser ultrarrápidos para desencadenar movimientos en una escala de tiempo de femtosegundos. Junto con el uso de campos láser intensos y fuertes en el régimen Mid-IR, OPCPA, el electrón se ioniza con energía cinética cero y, posteriormente, se acelera con la energía ponderomotriz del láser. La dinámica de campo fuerte ofrece estructuras ricas que están codificadas en la distribución de momento de fotoelectrones. Dado que usamos campos láser combinados de dos colores, podemos controlar esas dinámicas con precisiones de subciclo. Más precisamente, mostramos con la ayuda de un microscopio de reacción que podemos extraer tanto información de orbitales de electrones como dinámica nuclear dentro de una extraordinaria resolución temporal de subciclo. Finalmente, el modelo de recolisión de campo fuerte se investiga con moléculas, a través del método de difracción de electrones inducido por láser (LIED) desarrollado previamente. Mostramos que las interferencias de electrones retrodispersados, emitidas por un campo fuerte con parámetros de bajo impacto, incorporan una orientación molecular particular que se puede reproducir cuando la molécula se considera alineada con respecto a la polarización del campo láser. Esos hallazgos parecen codificar una propiedad más profunda sobre la difracción de ondas en moléculas hasta entonces inexplorada debido a las condiciones impuestas en la difracción de electrones convencional (CED).Depuis la découverte de la dualité onde-corpuscule, la science a changé notre façon de percevoir la lumière et la matière, notamment à l´échelle subatomique. C’est grâce à de telles découvertes que nous avons pu développer et élargir nos connaissances au cours des deux derniers siècles, atteignant desormais ces infimes limites de la science. Prenons par exemple la célèbre expérience de la double fente de T. Young (1801). Cette expérience a été étendue après la révolution quantique du XXe siècle, révélant la diffraction d´électrons et de neutrons utilisés aujourd’hui pour mesurer la séparation des noyaux formant des structures complexes. De même, l’expérience de Michelson et Morley (1887), qui fait suite aux fondations de T. Young, a connu un succès certain en astronomie, permettant l’imagerie à haute résolution des étoiles dans l’univers. Dans cette thèse, nous utilisons de la lumière pour générer des électrons, et ainsi produire des interférences similaires à l´expérience des fentes, qui sont par la suite analyser pour en connaître les propriétés atomiques. Sur la dynamique d’un atome, c’est-à-dire, attoscience, nous utilisons des impulsions laser ultra-rapides pour déclencher des mouvements sur une échelle de temps de la femtoseconde. Avec l’utilisation de champs laser intenses et puissants dans le régime Mid-IR, OPCPA, l’électron est ionisé avec une énergie cinétique nulle et ensuite accéléré par l’énergie pondéromotrice du laser. La dynamique des champs forts offre des structures riches qui sont encodées dans la distribution de quantité de mouvement des photoélectrons. Puisque nous utilisons des champs laser combinés à deux couleurs, nous pouvons contrôler ces dynamiques sur une échelle plus courte que la période du laser. Plus précisément, nous montrons à l’aide d’un microscope à réaction que nous pouvons extraire à la fois des informations sur les orbitales électroniques et la dynamique nucléaire avec une extraordinaire résolution temporelle. Enfin, le modèle de récollision en champ fort est étudié avec des molécules, grâce à la méthode de diffraction d’électrons induite par laser (LIED) précédemment développée. Nous montrons que les interférences électroniques rétrodiffusées, issues d’un champ fort avec faible paramètre d´impact, intègrent une orientation moléculaire particulière qui peut être reproduite lorsque la molécule est considérée alignée par rapport à la polarisation du champ électrique. Ces découvertes semblent encoder une propriété plus profonde de la diffraction d´ondes sur molécules jusqu’à alors inexplorée en raison des conditions imposées par la diffraction électronique conventionnelle (CED).Postprint (published version

Towards retrieving dispersion profiles using quantum-mimic Optical Coherence Tomography and Machine Learnin

Artefacts in quantum-mimic Optical Coherence Tomography are considered detrimental because they scramble the images even for the simplest objects. They are a side effect of autocorrelation which is used in the quantum entanglement mimicking algorithm behind this method. Interestingly, the autocorrelation imprints certain characteristics onto an artefact - it makes its shape and characteristics depend on the amount of dispersion exhibited by the layer that artefact corresponds to. This unique relationship between the artefact and the layer's dispersion can be used to determine Group Velocity Dispersion (GVD) values of object layers and, based on them, build a dispersion-contrasted depth profile. The retrieval of GVD profiles is achieved via Machine Learning. During training, a neural network learns the relationship between GVD and the artefacts' shape and characteristics, and consequently, it is able to provide a good qualitative representation of object's dispersion profile for never-seen-before data: computer-generated single dispersive layers and experimental pieces of glass.Comment: 11 pages, 5 figure

Terahertz near-field nanoscopy based on detectorless laser feedback interferometry under different feedback regimes

Near-field imaging techniques, at terahertz frequencies (1–10 THz), conventionally rely on bulky laser sources and detectors. Here, we employ a semiconductor heterostructure laser as a THz source and, simultaneously, as a phase-sensitive detector, exploiting optical feedback interferometry combined with scattering near-field nanoscopy. We analyze the amplitude and phase sensitivity of the proposed technique as a function of the laser driving current and of the feedback attenuation, discussing the operational conditions ideal to optimize the nano-imaging contrast and the phase sensitivity. As a targeted nanomaterial, we exploit a thin (39 nm) flake of Bi2Te2.2Se0.8, a topological insulator having infrared active optical phonon modes. The self-mixing interference fringes are analyzed within the Lang–Kobayashi formalism to rationalize the observed variations as a function of Acket's parameter C in the full range of weak feedback (C < 1)

Terahertz near-field nanoscopy based on detectorless laser feedback interferometry under different feedback regimes

Near-field imaging techniques, at terahertz frequencies (1-10 THz), conventionally rely on bulky laser sources and detectors. Here, we employ a semiconductor heterostructure laser as a THz source and, simultaneously, as a phase-sensitive detector, exploiting optical feedback interferometry combined with scattering near-field nanoscopy. We analyze the amplitude and phase sensitivity of the proposed technique as a function of the laser driving current and of the feedback attenuation, discussing the operational conditions ideal to optimize the nano-imaging contrast and the phase sensitivity. As a targeted nanomaterial, we exploit a thin (39 nm) flake of Bi2Te2.2Se0.8, a topological insulator having infrared active optical phonon modes. The self-mixing interference fringes are analyzed within the Lang-Kobayashi formalism to rationalize the observed variations as a function of Acket’s parameter C in the full range of weak feedback (C < 1)

Efficient Algorithms for Light Transmission, Focusing and Scattering Matrix Retrieval in Highly Diffusive 3D Random Media

Wavefront shaping provides an increasingly appealing avenue for imaging and other applications that require controlling electromagnetic waves passing through complex and disordered media. Indeed, these techniques allow researchers and engineers to exploit the properties of high-frequency waves, particularly optical ones, as they interact with these media to obtain nearly perfect transmission and a high degree of focusing. Here, we simulate the process of wave propagation in 3D random media using full-wave, integral equation-based computational electromagnetics schemes. We replicate many experimental observations relating to the existence of so-called open channels in non-absorbing random media and the distribution of their transmission coefficients. In addition, we develop new schemes for manipulating these waves, e.g. by focusing them onto one or multiple spots in the output plane. Furthermore, we leverage the computational methods to develop new schemes for characterizing random media, e.g. by computing their scattering and transmission matrices under a variety of conditions. Finally, we study the transmission properties of absorbing media and find a universal fluctuant pattern of their maximal transmission coefficients.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147580/1/hanguo_1.pd