Search Results (14)

In this study, we have compared different Rydberg atom-based microwave electrometry techniques under the same experimental conditions and using the same Rydberg states ($68S_{1/2}$, $68P_{3/2}$, and $67P_{3/2}$). The comparison was carried out for the following techniques: (i) auxiliary microwave field, (ii) microwave amplitude modulation, and (iii) polarization spectroscopy. Our results indicate that all three techniques have a similar minimum measurable microwave electric field. A slightly better result can be obtained by performing polarization spectroscopy using a Laguerre–Gauss coupling laser beam. Full article

The research on high-order transverse modes in lasers is a subject as old as the laser itself and has been largely abandoned. However, recently several studies have demonstrated an interest in using, instead of the usual Gaussian beam, a radial Laguerre–Gauss LG_p0 beam, as, for instance, one can observe a strong improvement, for a given power, in the longitudinal and radial forces in optical tweezers illuminated by a LG_p0 beam instead of the usual Gaussian beam. Since in most commercial lasers, the delivered laser beam is Gaussian, we therefore think it opportune to consider the problems of forcing a laser to oscillate individually on a higher-order transverse LG_p0 mode. We propose a comprehensive analysis of the effects of an intra-cavity phase or amplitude mask on the fundamental mode of a plano-concave cavity. In particular, we discuss the best choice of parameters favouring the fundamental mode of a pure radial Laguerre–Gauss LG_p0 model. Full article

We investigate the dynamic excitation of surface plasmon polaritons (SPPs) using vector Laguerre–Gauss (LG) beams, which offer unique properties for manipulating the polarization and spatial distribution of light. Our study demonstrates the efficient coupling of SPPs with LG beams, characterized by their azimuthal and radial indices $(m,p)$, as well as polarization distribution type. Numerical simulations reveal that the vector nature of LG beams enables selective excitation of SPPs, depending on the polarization type of the beam. Experimental verification of our simulations is achieved using a gold circular Bragg grating and a spatial light modulator that generates vector LG beams. Leakage radiation imaging demonstrates the potential of vector LG beams for dynamic SPP excitation and manipulation. This study opens novel ways for the control of SPPs in plasmonic devices, such as modulators, and nanophotonic circuits. Full article

Usually, optical tweezers for trapping atoms or nanoparticles are based on the focusing of a Gaussian laser beam (GB). The optical trap is characterised by its longitudinal stability (LS), expressed as the ratio of the backward axial gradient and the forward scattering forces. Replacing the GB with a LG_p0 beam (one central peak surrounded by p rings) does not improve the LS because the on-axis intensity distribution is the same whatever the mode order p. However, it has been recently demonstrated that a restructured LG_p0 beam can improve greatly the LS. In this paper, we consider the restructuring of a LG_p0 beam when passing through a simple binary diffracting optical element called a circular π-plate (CPP). For a particular radius of the dephasing zone of the CPP, it is found that the LS is multiplied by a factor corresponding to a relative increase of about 220% to 320%. Full article

Combined with vortex light and airglow, some different physical phenomena are presented in this paper. Based on the ground-based airglow imaging interferometer (GBAII) made by our group, a liquid crystal on silicon (LCoS) device on one arm of a wide-angle Michelson interferometer (MI) of the GBAII is replaced by the reflector mirror to become the GBAII-LCoS system. LCoS generates a vortex phase to convert a Gaussian profile airglow into a vortex light pattern. After the Gaussian profile vortex light equation is obtained by combining the Gaussian profile airglow with the Laguerre–Gauss light, three different physical phenomena are obtained: the simulated Gaussian vortex airglow beam exhibits a hollow phenomenon with the introduction of the vortex phase, and as the topological charge (TC) l increases, the hollow range also increases; after adding the vortex factor, the interference fringe intensity can be ‘broadened’ with the optical path difference (OPD) and TC l increases, which match the field broadening technology for solid wide-angle MI; the ‘Four-point algorithm’ wind measurement for the upper atmosphere based on the vortex airglow is derived, which is different from the usual expressions. Some experimental results are presented: We obtained the influence modes of vortex light interference and a polarization angle from 335° to 245°. We also obtained a series of interference images that verifies the rotation of the vortex light, onto which is loaded a set of superimposed vortex phase images with TC l = 3 into LCoS in turn, and the interference image is rotated under the condition of the polarization angle of 245°. The controlled vortex interference image for different TC and grayscale values are completed. Full article

Most laser applications are based on the focusing of a Gaussian laser beam (GLB). When the latter is subject to a phase aberration such as the optical Kerr effect (OKE) or spherical aberration (SA), it is recognised that the focusing performance of the GLB is degraded. In this paper, it is demonstrated that high-order radial Laguerre–Gauss LG_p0 beams are more resilient than the GLB when subject to the OKE or SA. This opens up opportunities to replace with advantages the usual GLB with a high-order LG_p0 beam for some applications. Full article

The connections between Laguerre–Gauss and Bessel–Gauss beams, and between Hermite–Gauss and cosine-Gauss beams are investigated. We review different asymptotic expressions for generalized Laguerre and Hermite polynomials of large radial/transverse order. The amplitude variations of generalized Laguerre–Gauss beams, including standard and elegant Laguerre–Gauss beams as special cases, are compared with Bessel–Gauss beams. Bessel–Gauss beams can be well-approximated by elegant Laguerre–Gauss beams. For non-integral values of the Laguerre function radial order, a generalized Laguerre–Gauss beam with integer order matches the width of the central lobe well, even for low radial orders. Previous approximations are found to be inaccurate for large azimuthal mode number (topolgical charge), and an improved approximation for this case is also introduced. Full article

Traditional ideas about linearly polarized paraxial beam propagation along the optical axis of a uniaxial crystal suggest that at the crystal exit face, after propagation through the polarizer, the beam will form an intensity distribution in the form of a conoscopic pattern. Any violation of axial propagation was considered as a perturbation of the conoscopic pattern and was not taken into account. Nevertheless, this process opens up a wide variety of transformations of polarization singularities caused by weak perturbations. In this article, the behavior of linearly polarized low-order Laguerre–Gauss beams in a uniaxial crystal is considered. The existence of a fine structure of radiation on the output face of a uniaxial crystal and the dependence of this fine structure on the parameters of the crystal and the beam are shown. Full article

Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that the effect of projectile coherence cannot be ignored, even when the projectile-target interaction is within the perturbative regime. This has led to a surge in studies that examine the effects of the projectile’s coherence length. Heavy-ion collisions are particularly well-suited to this because the projectile’s momentum can be large, leading to a small deBroglie wavelength. In contrast, electron projectiles that have larger deBroglie wavelengths and coherence effects can usually be safely ignored. However, the recent demonstration of sculpted electron wave packets opens the door to studying projectile coherence effects in electron-impact collisions. We report here theoretical triple differential cross-sections (TDCSs) for the electron-impact ionization of helium using Bessel and Laguerre-Gauss projectiles. We show that the projectile’s transverse coherence length affects the shape and magnitude of the TDCSs and that the atomic target’s position within the projectile beam plays a significant role in the probability of ionization. We also demonstrate that projectiles with large coherence lengths result in cross-sections that more closely resemble their fully coherent counterparts. Full article

We investigate the concept that the value of the spin-orbit coupling is the energy efficiency of energy transfer between orthogonal components. The energy efficiency changes as the beam propagates through the crystal. For a fundamental Gaussian beam, its value cannot exceed 50%, while the energy efficiency for Hermite–Gaussian and Laguerre–Gaussian beams of higher orders of the complex argument can reach a value close to 100%. For Hermite–Gauss and Laguerre–Gauss beams of higher orders of real argument, the maximum energy efficiency can only slightly exceed 50%. It is shown that zero-order Bessel–Gauss beams are able to achieve an energy efficiency close to 100% when generating an axial vortex in the orthogonal component in both monochromatic and polychromatic light, while for a polychromatic Laguerre–Gauss or Hermite–Gauss beam of a complex argument, the energy efficiency reduced to a value not exceeding 50%. The spin angular momentum is compensated by changing the orbital angular momentum of the entire beam, which occurs as a result of the difference in the topological charge of the orthogonally polarized component by 2 units. Full article

Light beams carrying Orbital Angular Momentum (OAM), also known as optical vortices (OV), have led to fascinating new developments in fields ranging from quantum communication to novel light–matter interaction aspects. Even though several techniques have emerged to synthesize these structured-beams, their detection, in particular, single-shot amplitude, wavefront, and modal content characterization, remains a challenging task. Here, we report the single-shot amplitude, wavefront, and modal content characterization of ultrashort OV using a Shack-Hartmann wavefront sensor. These vortex beams are obtained using spiral phase plates (SPPs) that are frequently used for high-intensity applications. The reconstructed wavefronts display a helical structure compatible with the topological charge induced by the SPPs. We affirm the accuracy of the optical field reconstruction by the wavefront sensor through an excellent agreement between the numerically backpropagated and experimentally obtained intensity distribution at the waist. Consequently, through Laguerre–Gauss (LG) decomposition of the reconstructed fields, we reveal the radial and azimuthal mode composition of vortex beams under different conditions. The potential of our method is further illustrated by characterizing asymmetric Gaussian vortices carrying fractional average OAM, and a realtime topological charge measurement at a 10Hz repetition rate. These results can promote Shack-Hartmann wavefront sensing as a single-shot OV characterization tool. Full article

Polarization is measured very often to study the interaction of light and matter, so the description of the polarization of light beams is of both practical and fundamental interest. This review discusses the polarization properties of structured light in multimode graded-index optical fibers, with an emphasis on the recent advances in the area of spin-orbit interactions. The basic physical principles and properties of twisted light propagating in a graded index fiber are described: rotation of the polarization plane, Laguerre–Gauss vector beams with polarization-orbital angular momentum entanglement, splitting of degenerate modes due to spin-orbit interaction, depolarization of light beams, Berry phase and 2D and 3D degrees of polarizations, etc. Special attention is paid to analytical methods for solving the Maxwell equations of a three-component field using perturbation analysis and quantum mechanical approaches. Vector and tensor polarization degrees for the description of strongly focused light beams and their geometrical interpretation are also discussed. Full article

In this paper, we characterize the helical beam structure through an analysis of the spiral character of the phase distribution inside a light beam. In particular, we show that a line connected with the 2π phase jump in the Laguerre–Gauss beam can be described by a Fermat’s spiral. We propose a numerical fitting method to determine the parameters of a spiral equation for the phase distribution of the helical beam. Next, we extend the procedure to a vortex beam created by the spiral phase plate and apply it to experimental phase maps, which allows us to recover the phase shift introduced into the object beam in the optical vortex scanning microscope. Full article

Optical modes bearing optical vortices are important light systems in which to encode information. Optical vortices are robust features of optical beams that do not dissipate upon propagation. Thus, decoding the modal content of a beam is a vital component of the process. In this work, we present a method to decode modal superpositions of light beams that contain optical vortices. We do so using shear interferometry, which presents a simple and effective means of determining the vortex content of a beam, and extract the parameters of the component vortex modes that constitute them. We find that optical modes in a beam are easily determined. Its modal content can be extracted when they are of comparable magnitude. The use of modes of well-defined topological charge, but not well-defined radial-mode content, such as those produced by phase-only encoding, are much easier to diagnose than pure Laguerre–Gauss modes. Full article