Search for Hermite-Gauss mode rotation in cholesteric liquid crystals

Abstract

In theory, there are analogous transformations of light's spin and orbital angular momentum [Allen and Padgett, J. Mod. Opt. 54, 487 (2007)]; however, none have been observed experimentally yet. In particular, it is unknown if there exists for the orbital angular momentum of light an effect analogous to the spin angular momentum-based optical rotation; this would manifest itself as a rotation of the corresponding Hermite-Gauss mode. Here we report an experimental search for this effect in a cholesteric liquid crystal polymer, using strongly focussed, spin-orbit coupled light. We find that the relative phase velocities of the orbital modes constituting the Hermite-Gauss mode agree to within 10(-5).

Vacuum Faraday effect for electrons

“…The reason is that there is no intrinsic mechanism in a gyromagnetic medium to produce the required OAM state dependent dispersion, because selection rules forbid coupling of the OAM to the atomic electron degrees of freedom. This is consistent with results from a recent experiment in which no rotation was observed for a superposition of right and left handed OAM states (a Hermite-Gauss mode) propagating through cholesteric liquid crystals [7]. We note that a relative phase shift between right and left handed OAM components will appear as a rotation of the intensity pattern [8].…”

Enhanced optical activity using the orbital angular momentum of structured light

“…The published work proved that dipole transitions [engaging both electric-dipole (E1) and magnetic-dipole (M1) forms of coupling] could not produce discriminatory singlephoton absorption with twisted light. This conclusion was subsequently verified by experiments [21][22][23]. The theoretical studies were restrictive in that they did not allow for electric-quadrupole (E2) transition moments, which in their interaction with the radiation field are in general of a similar magnitude to the magnetic-dipole couplings.…”

Propagation of structured light beams after multiple reflections in a spiral phase plate

“…The optical vortices in the first column of Fig. For experiments requiring the maximal transfer of a single OAM state to a sample (e.g., electrons, 68 atoms, 69,70 molecules, 73,74 a crystal [75][76][77] etc. The other columns contain a superposition of OAM values, P m l m , with each OAM value separated by β, and with a different probability of detecting the individual OAM states.…”

“…67 It is due to the presence of OAM that a vortex core forms as the beam propagates into the far field, and it is due to a coherent superposition of OAM states that there is an intensity modulation as a function of azimuthal angle. One example is a 4f imaging system where the SPP (or other device used to generate an optical vortex) is placed at the object plane and the sample (e.g., electrons, 68 atoms, 69,70 molecules, 73,74 crystal, [75][76][77] etc.) ), an intensity profile such as a Gaussian intensity profile with OAM (e.g., r 2 ¼ 0, z ¼ 0.01 mm) is suitable.…”

“…66 As the thick-plate approximation 67 has been theoretically shown to give a more accurate description of the device compared to the thin-plate approximation for a standard SPP geometry, 67 this description will be used in understanding the propagation dynamics of optical vortices from immediately after the device to the far field of the device. [75][76][77] Hence, this paper starts with a discussion of the propagation dynamics of optical vortices from distances much shorter than the beam's Rayleigh range in the near field of the SPP to the far field. As the beam propagates into the far field of the device, a large optical vortex core develops and its intensity pattern rotates due to the Gouy phase.…”