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Alexandros Gerakis

Publications and source records attributed to Alexandros Gerakis.

5 recordsLinked to original sources

Non-resonant laser-driven narrowing of particle velocity distributions

Stark acceleration and deceleration based techniques for generating particle ensembles with low velocity spread are useful in many experimental applications. For a given velocity distribution of a particle ensemble, these techniques accelerate or decelerate a small subset of the total population, with a low velocity uncertainty. However, narrowing the original velocity distribution by accelerating or decelerating the ensemble particles near the mean velocity is fundamentally limited and not yet explored. We present a numerical study of particle dynamics using neutral cesium atoms as an example. We investigate different interaction regimes, identify key limitations, and propose an interaction regime in which optical Stark deceleration can be used to narrow the velocity distribution of a propagating ensemble about its mean velocity. These findings have potential implications for optical manipulation and control, controlled collisions, and matter interferometry.

physics.optics

Resolving Nonequilibrium Gas Kinetics in Supersonic Neutral Flows with Coherent Rayleigh Brillouin Scattering

We present a characterization of high-speed flows in nonequilibrium thermodynamic conditions using single-shot coherent Rayleigh-Brillouin scattering(CRBS). The technique is applied on a highly underexpanded jet using 200ns laser pulses, enabling simultaneous probing of multiple spatial locations. We map the jets average axial velocity and density distributions and resolve local velocity gradients, providing access to parameters relevant to turbulence characterization. The measurements are validated against numerical simulations, showing good agreement overall. We find that in most cases individual single-shot spectra exhibit substantial deviation from the bulk averaged lineshapes, reflecting the non-Maxwellian velocity distributions generated by shock-induced regimes. The results presented here establish single-shot CRBS as an important tool for direct measurements of flow velocity components, velocity gradients, and density in complex, unsteady supersonic environments.

physics.optics

Spark-Induced Shockwave Dynamics Revealed via Nonresonant Four-Wave Mixing

We report on the experimental detection of shockwave dynamics produced in a spark discharge, using a nonresonant four-wave mixing optical technique. In particular, we observe the spark-induced local density perturbation across a millimeter-range probe volume, centered on the discharge, via single-shot coherent Rayleigh-Brillouin scattering. We detect the emergence of shock-induced flow velocities, which appear as distinct features in the spectrum, and monitor their dynamic evolution from a few hundred nanoseconds to microseconds after the spark. Finally, we benchmark our measurements against simulations based on a one-dimensional compressible flow model. Our results pave the way for quantitative measurements of highly non-uniform transient flows in challenging environments featuring non-equilibrium gas kinetics.

physics.optics

High-energy chirped nanosecond pulsed laser system for particle diagnostics and manipulation

An upgraded high-energy nanosecond pulsed laser system tailored for optical particle diagnostics and manipulation capable of pulse energies beyond Joule-level is presented. In addition to the notable output energy increase, the laser system maintains its capability to generate laser pulses with customizable temporal profiles and variable durations ($1$ ns to $1$ $\mu$s) along with a chirping range of several GHz over the pulse duration. The expanded output energy range is anticipated to greatly broaden the laser system's application potential, both for thermodynamic diagnostics via coherent Rayleigh-Brillouin scattering, by substantially lowering the particle density detection thresholds, as well as for particle manipulation, by facilitating more efficient optical trapping potentials for particle acceleration and deceleration.

physics.optics

A dual color, frequency, pulse duration and shape agile laser system for particle spectroscopy and manipulation

A dual color, frequency and pulse duration agile laser system, capable of delivering laser pulses in arbitrary temporal profiles with ~1 ns to ~1 us pulse duration, chirping rates of ~27 MHz/ns with an achievable chirping range of several GHz across the pulse duration, and with energies ranging from a few nJ to hundreds of mJ per pulse has been developed. The flexibility and capability of this laser system provide a wide range of laser parameters that can be exploited to optimize operational conditions in various experiments ranging from laser diagnostics to spectroscopy and optical manipulation of matter. The developed system is successfully demonstrated to obtain coherent Rayleigh-Brillouin scattering (CRBS) in both single and dual color configuration, in an effort to expand the non-intrusive accessibility towards lower pressure regime for neutral gas and plasma diagnostics.

physics.optics