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

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

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 hydro-halide molecules, 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 for the prepolarized targets, and use particle-in-cell simulations to demonstrate the method's feasibility.

High density Spin Polarized Hydrogen (SPH) atoms, which can be prepared using UV dissociation of hydro-halide molecules, can be attractive as potential targets for laser ionization/acceleration schemes aiming to create high energy and high current polarized electron beams. However, for these SPH targets to be of practical use, they have to be spatially isolated from the halide atoms which accompany hydrogen in the parent hydro-halide molecule. We show how the UV dissociation dynamics of hydro-halides and the dissociation geometry and timing can be combined to prepare a variety of isolated SPH targets aimed to accommodate laser acceleration schemes.

We study the photo-induced oxidation of acetylene in two different spectral areas, around 220 and 320 nm. In both spectral areas, the dominant reaction pathways involve the rupture of the acetylene C - H bond, thus primarily generating C2H and H fragments. The released fragments react in O2 presence resulting in glyoxal and other molecular species formation. We observe strong variations in the photooxidation rates, which point to the increased participation of excited, predissociation states, in the oxidation process. Such effects of increased excited state participation in photooxidation should be observed in a variety of photo-induced reactions, affecting the reaction spectral response and eventually the reaction cycles in terrestrial or planetary environments.

The angular distribution of the ions coming from Coulomb explosion following femtosecond ionisation of methyl iodide is studied in the spectral range of 600 to 1450 nm. Under these conditions, iodine and methyl fragment ions are generated, both via dissociative ionisation and via Coulomb explosion following the double ionisation of the parent ion. However, the dependence of the angular distribution of the fragment ions on the ionisation wavelength is completely different for those two mechanisms: dissociative ionisation fragments are being ejected with high anisotropy, irrespectively of the wavelength, while the angular distribution of the Coulomb explosion fragments changes from anisotropic, for an excitation wavelength close to 600 nm, to isotropic close to 950 nm, and remain isotropic up to 1450 nm.

When high intensity pulses are used to ionize an atom or molecule, the electrons produced can be driven back to the ionic core by the laser’s electric field, where they can collide with the ion, resulting to a plethora of phenomena such as high harmonic generation, non-sequential double ionization and more. Here, we consider ionization using an asymmetric $$\omega $$ /2 $$\omega $$ pulse, and we study the dependence of the kinetic energy distribution of the returning electrons on the relative phase $$\phi $$ and electric field amplitude ratio $$\gamma $$ between the two components of the asymmetric pulse. We find that for a specific combination of $$\gamma $$ and $$\phi $$ , the kinetic energy of the vast majority of the returning electrons which return to the ion, follows a sharp, nearly monochromatic distribution. We examine the effect of small variations of the asymmetric pulse parameters $$\gamma $$ and $$\phi $$ , as well as the effect of pulse duration and multiple returns of the electron to the ionic core. We find that the kinetic energy distribution remains narrow for a variety of such conditions, demonstrating the experimental feasibility of the process. This way, $$\omega $$ /2 $$\omega $$ asymmetric pulses can offer control over a variety of rescattering-related processes, such as high-harmonic generation, for which we give an example. (a) Evolution of the kinetic energy distribution of the returning electrons as a function of the phase $$\phi $$ between the $$\omega $$ and 2 $$\omega $$ components of the asymmetric field. The amplitude ratio $$\gamma $$ between the $$\omega $$ and 2 $$\omega $$ components of the asymmetric field is 0.45. (b) Evolution of the HHG spectra as a function of $$\phi $$ . The ratio $$\gamma $$ is 0.45 as in part (a)

Spin-polarized hydrogen: production by photodissociation A laser-based scheme to produce spin-polarized hydrogen (SPH) at much higher densities than conventional methods could create new opportunities in physics. In a review of the topic, Alexandros Spiliotis and coworkers from the University of Create and FORTH Institute of Electronic Structure and Laser in Greece describe how the use of circularly polarized, pulsed ultraviolet laser light can produce SPH with a density of 10(19) cm(-3) by photodissociation of hydrogen halide molecules. This high-density production approach brings many benefits including the prospect of ultrafast magnetometry and the generation of high energy beams of spin-polarized electrons, protons or deuterons by laser-plasma acceleration. Furthermore, spin-polarized nuclear fusion is expected to be more efficient than conventional fusion. Recently, our group produced spin-polarized hydrogen (SPH) atoms at densities of at least 10(19) cm(-3) from the photodissociation of hydrogen halide molecules with circularly polarized UV light and measured them via magnetization-quantum beats with a pickup coil. These densities are approximately 7 orders of magnitude higher than those produced using conventional methods, opening up new fields of application, such as ultrafast magnetometry, the production of polarized MeV and GeV particle beams, such as electron beams with intensities approximately 10(4) higher than current sources, and the study of polarized nuclear fusion, for which the reaction cross sections of D-T and D-He-3 reactions are expected to increase by 50% for fully polarized nuclear spins. We review the production, detection, depolarization mechanisms, and potential applications of high-density SPH.

Recently, the production of ultrahigh-density (∼1019cm−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 1020cm−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 σH-Cl=7(2)×10−17cm2. 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.

We introduce a novel and sensitive ns-resolved atomic magnetometer, which is at least three orders of magnitude faster than conventional magnetometers. We use the magnetic field dependence of the hyperfine beating of high-density spin-polarized H atoms, produced from the rapid photodissociation of HCl gas with sub-ns laser pulses and measured with a pick-up coil, to demonstrate ns-resolved magnetometry, and project sensitivity of a few nT for a spin-projection-limited sensor with 10 nl measurement volume after 1 ns measurement time. The magnetometer will allow ultrafast continuous B-field measurements in many fields, including spin chemistry, spin physics, and plasma physics.

We perform velocity map imaging in the electrons generated from the ionization of CH3I molecules at 800 nm, in the intensity range 3.1 x 10(13) W/cm(2)<= I <= 6 x 10(13) W/cm(2). The photoelectron spectra reveal a Freeman resonance at a peak intensity of approximate to 3.5 x 10(13) W/cm(2). The photoelectron kinetic energy dependence on the laser intensity, as well as the observation of the 8-th photon channel closing offers absolute intensity calibration in our experiment, which allows for the accurate determination of the ponderomotive potential induced by the laser field and ultimately the determination of the Rydberg state involved in the Freeman resonance.

We present a compact polarimeter, which can perform sensitive measurements of optical rotation in vapor. The operation of the polarimeter is based on a Cavity Ring-Down scheme which employs two signal reversals, which increase sensitivity and reduce noise, allowing the realization of sensitive measurements in the presence of spurious birefringence. We describe the operation of the polarimeter, give the basic equations for the signal analysis and retrieval of optical rotation angle, and present measurements that demonstrate a sensitivity of ∼80 μdeg/pass.

The possibility to exploit spin physics in fusion science opens new impressive panorama and challenging fields to be explored. In addition to the fundamental interesting topics the PREFER collaboration is trying with synergetic efforts to make the well known behaviour of spin–dependent nuclear reactions available for feasability studies and experimental tests for fusion programs. In this contribution the main challenges of the different collaborating groups will be put in evidence, and recent developments with the respective references will be provided.

An improved optical cavity-based polarimetry method is employed to measure the optical activity of lysozyme in water solution, in the concentration range of 0-2 mg/ml. We employ a signal reversing technique, which gives the absolute optical rotation, without needing to remove the sample for a null measurement. We report an absolute sensitivity limit on the order of 0.1 mdeg, corresponding to a detection limit of< 50 mu g/ml for a sample volume lower than 50 mu L, thus surpassing the sensitivity of existing commercial polarimeters. We discuss how these sensitivity levels can be further improved using existing methods and technologies.

We measure the magnetization quantum beats of spin-polarized hydrogen (SPH) and spin-polarized deuterium (SPD) with a pickup coil, from the UV photodissociation of HCI, HBr, and DI, in the 5-5000 mbar pressure range. The pressure-dependent depolarization rate is linear at low pressures and reaches a plateau at higher pressures. The high-pressure depolarization rate is observed to be proportional to the halogen nuclear electric quadrupole coupling constant. We also investigate how the presence of an inert gas, SF6 or N-2, affects the depolarization rate. The results are explained using a model in which depolarization occurs predominantly through an HY-H intermediate species (Y = Cl, Br, I).

We report on the concept of an innovative laser-driven plasma accelerator for polarized proton (or deuteron) beams with a kinetic energy up to several GeV. In order to model the motion of the particle spins in the plasmas, these have been implemented as an additional degree of freedom into the Particle-in-Cell simulation code VLPL. For the experimental realization, a polarized HCl gas-jet target is under construction, where the degree of proton polarization is determined 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.

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 particle-in-cell (PIC) simulation code VLPL (Virtual Laser Plasma Lab) 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 circularly 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.

The use of nuclear polarized fuel, i.e. polarized D, T or $^3$He, for coming fusion reactors promises to increase their energy output and to optimize the complete fusion process in various ways. But before these advantages can be utilized, several questions must be answered and technical issues must be overcome. Among others, the members of the PREFER collaboration started to investigate the different challenges of 'polarized fusion'.

The use of nuclear polarized fuel, i.e. polarized D, T or 3He, for coming fusion reactors promises to increase their energy output and to optimize the complete fusion process in various ways. But before these advantages can be utilized, several questions must be answered and technical issues must be overcome. Among others, the members of the PREFER collaboration started to investigate the different challenges of “polarized fusion”.

We review the development of cavity ring-down polarimetry, which is a cavity-based method using pulsed lasers, for enhancing chiral-optical-rotation signals by the number of the cavity passes (typically 102–104), while suppressing non-chiral backgrounds, and isolating the chiral signals from the backgrounds through signal reversals. The advantages of this method is demonstrated in measurements of optical rotation of chiral samples in an evanescent wave near the surface of a prism. We also discuss the future prospects for perming cavity-based polarimetry with continuous lasers, for which the opticalrotation sensitivity should surpass current commercial instruments by several orders of magnitude.