Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpin-to-Orbital Conversion of Angular Momentum in Harmonic Generation Driven by Intense Circularly Polarized Beam
101
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A new physical mechanism to achieve spin-to-orbital angular momentum conversion based on the interaction of an intense circularly polarized (CP) laser beam with a plane foil is presented and studied for the first time. It has been verified by both simulation and theoretical analysis that vortex harmonics carrying orbital angular momentum (OAM) are generated after a relativistic CP laser beam, even a Gaussian beam, impinges normally on a plane foil. The generation of this vortex harmonics is attributed to the vortex oscillation of the plasma surface driven harmonically by the vortex longitudinal electric field of the CP beam. During the process of harmonic generation, the spin angular momenta of fundamental-frequency photons are converted to OAM of harmonic photon because of the conservation of total angular momentum. In addition, if an initially vortex beam or a spiral phase plate is used, the OAM of harmonic photon can be more tunable and controllable.
rate research
Read More
We propose a scheme to generate gamma-ray photons with an orbital angular momentum (OAM) and high energy simultaneously from laser-plasma interactions by irradiating a circularly polarized Laguerre-Gaussian laser on a thin plasma target. The spin angular momentum and OAM are first transferred to electrons from the driving laser photons, and then the OAM is transferred to the gamma-ray photons from the electrons through quantum radiation. This scheme has been demonstrated using three-dimensional quantum electrodynamics particle-in-cell simulation. The topological charge, chirality and carrier-envelope phase of the short ultra-intense vortex laser can be revealed according to the pattern feature of the energy density of radiated photons.
We experimentally demonstrate a technique for the generation of optical beams carrying orbital angular momentum using a planar semiconductor microcavity. Despite being isotropic systems, the transverse electric - transverse magnetic (TE-TM) polarization splitting featured by semiconductor microcavities allows for the conversion of the circular polarization of an incoming laser beam into the orbital angular momentum of the transmitted light field. The process implies the formation of topological entities, a pair of optical half-vortices, in the intracavity field.
Spin and orbital angular momentum of an optical beam are two independent parameters that exhibit distinct effects on mechanical objects. However, when laser beams with angular momentum interact with plasmas, one can observe the interplay between the spin and the orbital angular momentum. Here, by measuring the helical phase of the second harmonic 2{omega} radiation generated in an underdense plasma using a known spin and orbital angular momentum pump beam, we verify that the total angular momentum of photons is conserved and observe the conversion of spin to orbital angular momentum. We further determine the source of the 2{omega} photons by analyzing near field intensity distributions of the 2{omega} light. The 2{omega} images are consistent with these photons being generated near the largest intensity gradients of the pump beam in the plasma as predicted by the combined effect of spin and orbital angular momentum when Laguerre-Gaussian beams are used.
A novel deflection effect of an intense laser beam with spin angular momentum is revealed theoretically by an analytical modeling using radiation pressure and momentum balance of laser plasma interaction in the relativistic regime, as a deviation from the law of reflection. The reflected beam deflects out of the plane of incidence with a deflection angle up to several milliradians, when a non-linear polarized laser, with the intensity $I_0sim10^{19}$W/cm$^2$ and duration around tens of femtoseconds, is obliquely incident and reflected by an overdense plasma target. This effect originates from the asymmetric radiation pressure caused by spin angular momentum of the laser photons. The dependence of the deflection angle of a Gaussian-type laser on the parameters of laser pulse and plasma foil is theoretically derived, which is also confirmed by three dimensional particle-in-cell simulations of circularly polarized laser beams with the different intensity and pulse duration.
A method of generating spin polarized proton beams from a gas jet by using a multi-petawatt laser is put forward. With currently available techniques of producing pre-polarized monatomic gases from photodissociated hydrogen halide molecules and petawatt lasers, proton beams with energy ~ 50 MeV and ~ 80 % polarization are proved to be obtained. Two-stage acceleration and spin dynamics of protons are investigated theoretically and by means of fully self-consistent three dimensional particle-in-cell simulations. Our results predict the dependence of the beam polarization on the intensity of the driving laser pulse. Generation of bright energetic polarized proton beams would open a domain of polarization studies with laser driven accelerators, and have potential application to enable effective detection in explorations of quantum chromodynamics.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
