Searcharxiv⌕ Search

arXiv subjects

O. Raz

Publications and source records attributed to O. Raz.

9 recordsLinked to original sources
arXiv2026

All-Optical Single-Shot Temporal Characterization of SASE FEL Pulses Using Double-Blind Holography

X-ray Free-electron lasers (XFELs) deliver ultrashort and ultrabright radiation in a photon-energy range spanning from extreme ultraviolet to hard X-rays. Supporting pulse durations down to hundreds of attoseconds, these sources are unique in enabling imaging of matter with unprecedented temporal and spatial resolution. However, schemes that produce such ultrashort pulses typically rely on Self-Amplified Spontaneous Emission (SASE), a stochastic process that introduces significant temporal and spectral jitter, therefore requiring single-shot characterization methods for post sorting the acquired data. Although various methods have been developed for pulse characterization and delay tagging, they often come with experimental and computational complexity. Moreover, no existing method currently combines both single-shot pulse reconstruction and delay tagging at the attosecond time scale. To close this gap, we present a single-shot all-optical method based on Double-Blind Holography (DBH). By recording the spectral interference between an extreme ultraviolet (XUV) FEL source and a high-harmonic generation (HHG)-based source, we achieve simultaneous waveform reconstruction and delay tagging of sub-10 fs FEL pulses with attosecond precision.

physics.optics↗
arXiv2024

Water-based Quantum Dots Liquid Scintillator for Particle Physics

Liquid scintillators are typically composed from organic compounds dissolved in organic solvents. However, usage of such material is often restricted due to fire safety and environmental reasons. Because of this, R\&D of water-based liquid scintillators is of extreme relevance; yet, no such scintillators have been made commercially available as yet. Here, we investigate an alternative, water-based quantum dots liquid scintillator. Pre-determined and controllable optical properties of the quantum dots, as well as the existence of large libraries of established protocols for their dispersion in aqueous solutions, make them an attractive option for nuclear and particle physics applications. We characterize the optical properties of water-based quantum dots liquid scintillator and find that most of its optical properties are preserved upon quantum dots' phase transfer into water, through the addition of an oleic acid hydrophilic layer. Using the developed scintillator, the time and charge responses from atmospheric muons are measured, highlighting the practical viability of water-based quantum dots liquid scintillators for nuclear and particle physics, special interest on neutrino physics.

physics.ins-det↗
arXiv2021

The power of reciprocal knowledge sharing relationships for startup success

Purpose: The purpose of this paper is to examine the innovative capabilities of biotech start-ups in relation to geographic proximity and knowledge sharing interaction in the R&D network of a major high-tech cluster. Design-methodology-approach: This study compares longitudinal informal communication networks of researchers at biotech start-ups with company patent applications in subsequent years. For a year, senior R&D staff members from over 70 biotech firms located in the Boston biotech cluster were polled and communication information about interaction with peers, universities and big pharmaceutical companies was collected, as well as their geolocation tags. Findings: Location influences the amount of communication between firms, but not their innovation success. Rather, what matters is communication intensity and recollection by others. In particular, there is evidence that rotating leadership - changing between a more active and passive communication style - is a predictor of innovative performance. Practical implications: Expensive real-estate investments can be replaced by maintaining social ties. A more dynamic communication style and more diverse social ties are beneficial to innovation. Originality-value: Compared to earlier work that has shown a connection between location, network and firm performance, this paper offers a more differentiated view; including a novel measure of communication style, using a unique data set and providing new insights for firms who want to shape their communication patterns to improve innovation, independently of their location.

cs.SI↗
arXiv2020

Mpemba effect in driven granular Maxwell gases

Mpemba effect refers to the counterintuitive result that, when quenched to a low temperature, a system at higher temperature may equilibrate faster than one at intermediate temperatures. This effect has recently been demonstrated in driven granular gases, both for smooth as well as rough hard-sphere systems based on a perturbative analysis. In this paper, we consider the inelastic driven Maxwell gas, a simplified model for a granular gas, where the rate of collision is assumed to be independent of the relative velocity. Through an exact analysis, we determine the conditions under which a Mpemba effect is present in this model. For mono-dispersed gases, we show that the Mpemba effect is present only when the initial states are allowed to be non-stationary, while for bi-dispersed gases, it is present for steady state initial states. We also demonstrate the existence of the strong Mpemba effect for bi-dispersed Maxwell gas wherein the system at higher temperature relaxes to a final steady state at an exponentially faster rate leading to smaller equilibration time.

cond-mat.stat-mech↗
arXiv2010

Near-threshold high-order harmonic spectroscopy with aligned molecules

We study high-order harmonic generation in aligned molecules close to the ionization threshold. Two distinct contributions to the harmonic signal are observed, which show very different responses to molecular alignment and ellipticity of the driving field. We perform a classical electron trajectory analysis, taking into account the significant influence of the Coulomb potential on the strong-field-driven electron dynamics. The two contributions are related to primary ionization and excitation processes, offering a deeper understanding of the origin of high harmonics near the ionization threshold. This work shows that high harmonic spectroscopy can be extended to the near-threshold spectral range, which is in general spectroscopically rich.

physics.atom-ph↗
arXiv2008

The Square Cat

We present a simple, two dimensional example of a "cat" -- a body with zero angular momentum that can rotate itself with no external forces. This model is used to explain why this problem is known to be a gauge theory and to illustrate the importance of non-commutative operators. We will also show a comparison between the free-space "cat" in Newtonian mechanics and the same problem in Aristotelian mechanics at low Reynolds number; this simple example shows the analogy between (angular) momentum in Newtonian mechanics and (torque) force in Aristotelian mechanics. We will end by pointing out a topological invariant common to our model in free space and at low Reynolds number.

physics.class-ph↗
arXiv2007

A geometric theory of swimming: Purcell's swimmer and its symmetrized cousin

We develop a qualitative geometric approach to swimming at low Reynolds number which avoids solving differential equations and uses instead landscape figures of two notions of curvatures: The swimming curvature and the curvature derived from dissipation. This approach gives complete information for swimmers that swim on a line without rotations and gives the main qualitative features for general swimmers that can also rotate. We illustrate this approach for a symmetric version of Purcell's swimmer which we solve by elementary analytical means within slender body theory. We then apply the theory to derive the basic qualitative properties of Purcell's swimmer.

physics.flu-dyn↗
arXiv2007

Swimming, Pumping and Gliding at low Reynolds numbers

Simple, linear equations relate microscopic swimmers to the corresponding gliders and pumps. They have the following set of consequences: The swimming velocity of free swimmers can be inferred from the force on the tethered swimmer and vice versa; A tethered swimmer dissipates more energy than a free swimmer; It is possible to swim with arbitrarily high efficiency, but it is impossible to pump with arbitrarily high efficiency and finally that pumping is geometric. We also solve several optimization problems associated with swimming and pumping: The problem of optimal anchoring for a certain class of swimmers that includes the Purcell swimmer and the three linked spheres and the optimal geometries of helices considered as swimmers and pumps.

physics.flu-dyn↗