arXiv subjects

T. Peter Rakitzis

Publications and source records attributed to T. Peter Rakitzis.

14 recordsLinked to original sources

arXiv2026

A plasma photocathode for spin-polarized electron beams via state-selected hydrogen halide photofragments

Spin-polarized electron beams are essential tools for probing fundamental symmetries and for the search beyond the Standard Model. While plasma-based accelerators are a promising pathway towards higher-energy frontiers, they have so far failed to deliver a competitive polarized source: existing proposals are challenging to realize and achievable polarizations remain far below conventional sources. Here, we introduce a photocathode-like scheme, applied to a gas of pre-polarized hydrogen and halogen atoms. A VUV and a visible laser pulse excite the halogen atoms to create a two-component ionization medium, consisting of low-threshold excited halogen atoms and high-threshold polarized hydrogen. Particle-in-cell simulations show witness beams with tens of pC charge retaining up to 97% of the initial polarization, rivaling state-of-the-art conventional sources.

physics.plasm-ph↗

arXiv2026

Pinching injection in wakefields for spin-polarized electron beams

Pinching of the driver beam in plasma wakefield acceleration is generally considered an unwanted effect that needs to be mitigated. Here, we propose that this effect can be utilized for the injection of spin-polarized electron beams from hydrogen halide targets into wakefields. Particle-in-cell simulations show that the electron spin is preserved on a level of 50% for a wide range of parameters due to the injection geometry. The presented injection scheme provides a possible pathway to alleviate some of the restrictions associated with pre-polarized hydrogen halide targets.

physics.plasm-ph↗

arXiv2025

Spin manipulation and nuclear polarization enhancement in particle beams with static magnetic fields

A theoretical study of spin dynamics in non-relativistic particle beams with interacting angular momenta traversing static, spatially varying magnetic fields is presented. The computational framework evaluates sinusoidal magnetic field configurations, calculating key observables such as average spin projections and state populations during the interaction. It is demonstrated that such fields can effectively enhance nuclear polarization in partially, incoherently polarized hydrogen and deuterium atomic beams, as well as coherently rotationally state-selected hydrogen deuteride molecular beams. This enhancement is attributed to transitions induced within the hyperfine regime of these systems. The study spans frequency ranges from GHz scales for atoms to hundreds of kHz for molecules, corresponding to magnetic field variations on spatial scales from submillimeters to meters.

physics.chem-ph↗

arXiv2025

High-energy polarized electron beams from the ionization of isolated spin polarized hydrogen atoms

We propose a laser-based method for the preparation of high-energy polarized electrons, from the ionization of isolated spin-polarized hydrogen (SPH) atoms. The SPH atoms are prepared from the photodissociation of HCl, using two consecutive UV pulses of ps duration. By appropriately timing and focusing the pulses, we can spatially separate the highly polarized SPH from other unwanted photoproducts, which then act as the target for the acceleration lasers. We show how elastic collisions define number density $n$ and polarization P regimes ($10^{16}\leq$ $n$ $\leq 10^{18}$ cm$^{-3}$, 0.99 $\geq$ P $\geq$ 0.40) for the pre-polarized targets, and use particle-in-cell simulations to demonstrate the method's feasibility.

physics.atom-ph↗

arXiv2025

Spatial Wavefunctions of Spin

We present an alternative formulation of quantum mechanical angular momentum, based on spatial wavefunctions that depend on the Euler angles $ϕ, θ, χ$, and have an additional internal projection $n$. The wavefunctions are Wigner D-functions, $D_{n m}^s (ϕ, θ, χ)$, for which the body-fixed projection quantum number $n$ has the unusual value $n=|s|=\sqrt{s(s+1)}$, or $n=0$. We show that the states $D_{\sqrt{s(s+1)},m}^s (ϕ, θ, χ)$ of elementary particles with spin $\sqrt{s(s+1)}$ give a gyromagnetic ratio of $g=2$ for $s>0$, and we identify these as the spatial angular-momentum wavefunctions of known fundamental charged particles with spin. All known Standard-Model particles can be categorized with either value $n=\sqrt{s(s+1)}$ or $n=0$, and all known particle reactions are consistent with the conservation of its projection in the internal frame, and with internal-frame Clebsch-Gordan coefficients of unity. Therefore, we make the case that the $D_{n m}^s (ϕ, θ, χ)$ are useful as spatial wavefunctions for angular momentum. Some implications and new predictions related to the quantum number $n$ for fundamental particles are discussed, such as the proposed Dirac-fermion nature of the neutrino, the explanation of some Standard-Model structure, and some proposed dark-matter candidates.

quant-ph↗

arXiv2024

The Vector-Model Wavefunction: spatial description and wavepacket formation of quantum-mechanical angular momenta

In quantum mechanics, spatial wavefunctions describe distributions of a particle's position or momentum, but not of angular momentum $j$. In contrast, here we show that a spatial wavefunction, $j_m (ϕ,θ,χ)=~e^{i m ϕ} δ(θ- θ_m) ~e^{i(j+1/2)χ}$, which treats $j$ in the $|jm>$ state as a three-dimensional entity, is an asymptotic eigenfunction of angular-momentum operators; $ϕ$, $θ$, $χ$ are the Euler angles, and $cos θ_m=(m/|j|)$ is the Vector-Model polar angle. The $j_m (ϕ,θ,χ)$ gives a computationally simple description of particle and orbital-angular-momentum wavepackets (constructed from Gaussian distributions in $j$ and $m$) which predicts the effective wavepacket angular uncertainty relations for $Δm Δϕ$, $Δj Δχ$, and $ΔϕΔθ$, and the position of the particle-wavepacket angular motion on the orbital plane. The particle-wavepacket rotation can be experimentally probed through continuous and non-destructive $j$-rotation measurements. We also use the $j_m (ϕ,θ,χ)$ to determine well-known asymptotic expressions for Clebsch-Gordan coefficients, Wigner d-functions, the gyromagnetic ratio of elementary particles, $g=2$, and the m-state-correlation matrix elements, $ $. Interestingly, for low j, even down to $j=1/2$, these expressions are either exact (the last two) or excellent approximations (the first two), showing that $j_m (ϕ,θ,χ)$ gives a useful spatial description of quantum-mechanical angular momentum, and provides a smooth connection with classical angular momentum.

quant-ph↗

arXiv2022

Chirality sensing employing PT-symmetric and other resonant gain-loss optical systems

Molecular chirality detection and enantiomer discrimination are very important issues for many areas of science and technology, prompting intensive investigations via optical methods. However, these methods are hindered by the intrinsically weak nature of chiro-optical signals. Here, we investigate and demonstrate the potential of gain materials and of combined gain-loss media to enhance these signals. Specifically, we show that the proper combination of a thin chiral layer with a gain-loss bilayer can lead to large enhancements of both the circular dichroism (CD) response and the dissymmetry factor, g, compared to the chiral layer alone. The most pronounced enhancements are obtained in the case of a Parity-Time (PT) symmetric gain-loss bilayer, while deviations from the exact PT symmetry lead to only moderate deterioration of the CD and g response, demonstrating also the possibility of tuning the system response by tuning the gain layer properties. In the case of PT-symmetric gain-loss bilayers we found that the largest CD enhancement is obtained at the system lasing threshold, while the g-enhancements at the anisotropic transmission resonances of the systems. Our results clearly demonstrate the potential of gain materials in chirality detection. Moreover, our gain-involving approach can be applied in conjunction with most of the nanophotonics/nanostructures-based approaches that have been already proposed for chirality sensing, further enhancing the performance/output of both approaches.

physics.optics↗

arXiv2021

A Nanosecond-Resolved Atomic Hydrogen Magnetometer

Spin polarized atomic ensembles can be used for the precise measurement of magnetic field. Conventional atomic magnetometers have demonstrated high sensitivities, albeit at low detection bandwidth, fundamentally limited by the Larmor precession frequency of the atoms. Here, we introduce a new type of atomic magnetometer which can realize sensitive detection with high temporal resolution. The magnetometer is based on monitoring the effect of the magnetic field on the hyperfine coherences of spin-polarized hydrogen atoms produced from the rapid photodissociation of hydrogen chloride (HCl). This scheme extends the magnetic measurement bandwidth to an upper frequency limit set by the hyperfine interaction. The use of HCl as the source for polarized atoms allows for large spin densities in the range of $10^{19}$ - $10^{20} cm^{-3}$, many orders of magnitude higher than those achieved with conventional alkali-atomic magnetometers. A spin-projection noise-limited magnetometer smaller than 100 μm can detect with nanosecond temporal resolution a magnetic field as low as 1 nT. This novel magnetometer opens new possibilities for precise measurement of ultrafast magnetic fields, with applications in biology, surface science and chemistry.

physics.atom-ph↗

arXiv2021

Depolarization of Spin-Polarized Hydrogen via Collisions with Chlorine Atoms at Ultrahigh Density

Recently, the production of ultrahigh-density (~10^{19}cm^{-3}) spin-polarized deuterium (SPD) atoms was demonstrated, from the photodissociation of deuterium iodide, but the upper density limit was not determined. Here, we present studies of spin-polarized hydrogen (SPH) densities up to 10^{20} cm^{-3}, by photodissociating 5 bar of hydrogen chloride with a focused 213 nm, 150 ps laser pulse. We extract the depolarization cross-section of hydrogen and chlorine atom collisions, which is the main depolarization mechanism at this high-density regime, to be σ_{HCl} = 7(2) x 10^{-17}cm^2. We discuss the conditions under which the ultrahigh SPH and SPD densities can be reached, and the potential applications to ultrafast magnetometry, laser-ion acceleration, and tests of polarized nuclear fusion.

physics.atom-ph↗

arXiv2021

Magnetometry with spin polarized Hydrogen from molecular photo-dissociation

In a recent publication [arXiv:2010.14579], we introduced a new type of atomic magnetometer, which relies on hydrohalide photo-dissociation to create high-density spin-polarized hydrogen. Here, we extend our previous work and present a detailed theoretical analysis of the magnetometer signal and its dependence on time. We also derive the sensitivity for a spin-projection noise limited magnetometer, which can be applied to an arbitrary magnetic field waveform.

physics.atom-ph↗

arXiv2020

Simulation of Polarized Beams from Laser-Plasma Accelerators

The generation of polarized particle beams still relies on conventional particle accelerators, which are typically very large in scale and budget. Concepts based on laser-driven wake-field acceleration have strongly been promoted during the last decades. Despite many advances in the understanding of fundamental physical phenomena, one largely unexplored issue is how the particle spins are influenced by the huge magnetic fields of plasma and, thus, how highly polarized beams can be produced. The realization of laser-plasma based accelerators for polarized beams is now being pursued as a joint effort of groups from Forschungszentrum Jülich (Germany), University of Crete (Greece), and SIOM Shanghai (China) within the ATHENA consortium. As a first step, we have theoretically investigated and identified the mechanisms that influence the beam polarization in laser-plasma accelerators. We then carried out a set of Particle-in-cell simulations on the acceleration of electrons and proton beams from gaseous and foil targets. We could show that intense polarized beams may be produced if pre-polarized gas targets of high density are employed. In these proceedings we further present that the polarization of protons in HT and HCl gas targets is largely conserved during laser wake-field acceleration, even if the proton energies enter the multi-GeV regime. Such polarized sources for electrons, protons, deuterons and $^{3}$He ions are now being built in Jülich. Proof-of-principle measurements at the (multi-)PW laser facilities PHELIX (GSI Darmstadt) and SULF (Shanghai) are in preparation.

physics.acc-ph↗

arXiv2018

Polarized Proton Beams from Laser-induced Plasmas

We report on the concept of an innovative source to produce polarized proton/deuteron beams of a kinetic energy up to several GeV from a laser-driven plasma accelerator. Spin effects have been implemented into the PIC simulation code VLPL to make theoretical predictions about the behavior of proton spins in laser-induced plasmas. Simulations of spin-polarized targets show that the polarization is conserved during the acceleration process. For the experimental realization, a polarized HCl gas-jet target is under construction using the fundamental wavelength of a Nd:YAG laser system to align the HCl bonds and simultaneously circular polarized light of the fifth harmonic to photo-dissociate, yielding nuclear polarized H atoms. Subsequently, their degree of polarization is measured with a Lamb-shift polarimeter. The final experiments, aiming at the first observation of a polarized particle beam from laser-generated plasmas, will be carried out at the 10 PW laser system SULF at SIOM/Shanghai.

physics.plasm-ph↗

arXiv2018

Ultrahigh-density spin-polarized H and D observed via magnetization quantum beats

We measure nuclear and electron spin-polarized H and D densities of at least 10$^{19}\, cm^{-3}$ with $\sim$10 ns lifetimes, from the photodissociation of HBr and DI with circularly-polarized UV light pulses. This density is $\sim$6 orders of magnitude higher than that produced by conventional continuous-production methods, and, surprisingly, at least 100 times higher than expected densities for this photodissociation method. We observe the hyperfine quantum beating of the H and D magnetization with a pick-up coil, i.e., the respective 0.7 and 3 ns periodic transfer of polarization from the electrons to the nuclei and back. The $\rm{10^{19}\,cm^{-3}}$ spin-polarized H and D density is sufficient for laser-driven ion acceleration of spin polarized electrons, protons, or deuterons, the preparation of nuclear-spin-polarized molecules, and for the demonstration of spin-polarized D-T or D-$\rm{^3He}$ laser fusion, for which a reactivity enhancement of $\rm{\sim50\%}$ is expected.

physics.chem-ph↗

arXiv2014

Evanescent-wave and open-air chiral sensing via signal-reversing cavity-enhanced polarimetry

Sensing chirality is of fundamental importance to many fields, including analytical and biological chemistry, pharmacology, and fundamental physics. Recent developments have extended optical chiral sensing using microwaves, fs pulses, superchiral light, and photoionization. The most widely used methods are the traditional methods of circular dichroism and optical rotation (OR). However, chiral signals are typically very weak, and their measurement is limited by larger time-dependent backgrounds and by imperfect and slow subtraction procedures. Here, we demonstrate a pulsed-laser bowtie-cavity-enhanced polarimeter with counter-propagating beams, which solves these background problems: the chiral signals are enhanced by the number of cavity passes; the effects of linear birefringence are suppressed by a large induced intracavity Faraday rotation; and rapid signal reversals are effected by reversing the Faraday rotation and subtracting signals from the counter-propagating beams. These advantages allow measurements of absolute chiral signals in environments where background subtractions are not feasible: we measure optical rotation from chiral vapour in open air, and from chiral liquids in the evanescent wave (EW) produced by total internal reflection at a prism surface. EW-OR of (+)-maltodextrin and (-)-fructose solutions confirm the Drude-Condon model for Maxwell's equations in isotropic optically active media. In particular, the effective optical rotation path length, near index matching, is equal to the Goos-Hänchen shift of the EW. The limits of this polarimeter, when using a continuous-wave laser locked to a stable high-finesse cavity, should match sensitivity measurements for linear birefringence ($3\times 10^{-13}$ rad), which is several orders of magnitude more sensitive than current chiral detection limits, transforming the power of chiral sensing in many fields.

physics.chem-ph↗