Phase-matching analysis in high-order harmonic generation with nonzero orbital angular momentum Laguerre-Gaussian beams

Abstract

Through high-order harmonic generation driven by intense ultrashort vortex infrared or midinfrared lasers, a nonzero orbital angular momentum can be imprinted onto extreme ultraviolet (XUV) or soft-x-ray (SXR) light pulses. Here we simulate the generation of vortex XUV harmonics in the gas medium as well as their propagation in vacuum till reaching the far field. We find that the intensity and phase of generated high harmonics are very sensitive to the position of gas jet with respect to the laser focus. The topological charge of the qth harmonic is found to be q times that of the driving Laguerre-Gaussian beam. Each harmonic in the far field appears as a single ring in the transverse plane with an invariant diameter which is scalable with the fundamental topological charge only when the gas jet is placed after the laser focus. The underlying phase-matching mechanism is analyzed by examining the spatial map of the coherence length and by calculating the evolution of harmonic emission in the medium. We anticipate this work to stimulate interest in generating intense vortex XUV or SXR attosecond pulses for probing dynamics of molecules where special molecular features are difficult to be detected with linear or circular XUV or SXR pulses.

Tailoring OAM spectrum of high-order harmonic generation driven by two mixed Laguerre–Gaussian beams with nonzero radial nodes

“…To simulate the vortex HHG driven by the mixed LG beams, we employ the general propagation theory in a gas medium, which has been established in Refs. [51,52]. Here we will only adopt some key equations, and will focus on the variation of spatial features of the mixed LG beams with the radial nodes.…”

“…We assume that the fundamental LG beams carrying orbital angular momentum (OAM) remain unchanged while propagating through an ionized gas medium, resembling their behaviors in free space. The propagation characteristics of the vortex high-harmonic field in the ionizing medium can be described by (in a Cartesian coordinate) [51,52,58] ∇…”

“…Willi et al [49] utilized two-color anti-spiral LG beams to generate HHG with specific OAM values, and they also coherently superimposed LG beams with different polarization states to generate the HHG and to control the OAM value. [50] Jin et al [51] simulated the phase-matching conditions of HHG driven by a single LG beam with the nonzero OAM. Recently, Guan et al [52] analyzed the macroscopic phase-matching mechanism for the OAM spectra of HHG by mixing two LG vortex modes and demonstrated that the OAM spectra can be readily tailored by varying the harmonic order, the position of the gas medium, and the energy ratio of two LG beams.…”

Research on multi-mode multiplexing OAM antenna system based on offset-fed beam bunching paraboloid

“…According to formula (1), the phases of each unit are calculated, and the phase shifts between adjacent units required for the first to the seventh OAM modes are shown in Table 1. Near-field phase distributions (Jin et al, 2020;Feng, Lin, and Long 2020) of this UCA are shown in Figure 3, where the observation plane of 300 mm × 300 mm large is set 300 mm away from the array aperture. Figure 4 (a) to (g) is the phase distribution diagrams of the first to the seventh-order vortex electromagnetic waves respectively.…”

A rotational-cavity optomechanical system with two revolving cavity mirrors: optical response and fast-slow light mechanism

“…Subsequently, Liu et al also accomplished the ground-state cooling of the rotating mirror in a double L-G cavity with atomic ensemble [58]. These studies on the ground cooling of the rotating mirror have provided many opportunities to further investigate macroscopic quantum phenomena in rotational cavity optomechanical systems, including bipartite quantum entanglement [57,[60][61][62] and tripartite quantum entanglement [63], macroscopic quantum coherence [64], OMIT phenomena [65][66][67][68][69][70], and its applications for the measurement of orbital angular momentum [65,71,72], higher order sideband generation [73,74] and phase-matching analysis [75]. However, compared to studies on conventional optomechanical systems, the research on the double-OMIT phenomenon in this type of rotating cavity optomechanical system is still essentially very limited.…”