Abstract:
Angular momentum (AM) is an inherent property of electromagnetic fields. A light
beam can possess both spin angular momentum (SAM) and orbital angular momentum
(OAM). SAM and OAM are results of transverse spin and orbital energy/momentum
flows of the light beam respectively. Transverse spin momentum flow originates from
the rotating electric field vector of a circularly polarized light beam. SAM can have two
orthogonal states corresponding to left and right-handedness of circular polarization.
On the other hand, transverse orbital momentum flow is a result of the azimuthal phase
gradient present in optical vortex beams. Systematic control of the spatial phase of a
vortex beam can result in an infinite number of orthogonal states of OAM. AM carrying
beams can be easily generated in the laboratory by engineering polarization and spatial
phase of the Gaussian output of a LASER source. One of the commonly used and easy
to prepare OAM carrying beams is Laguerre-Gaussian (LG) beam. AM of the light
beam has been utilized as an extra degree of freedom to enhance optical information
transfer. Interaction of AM carrying light beams with matter not only provides a fundamental
understanding of light-matter interaction but has been harnessed in applications
such as quantum memory gadgets, optical trapping, directional coupling and more. The
effects of optical AM interaction with matter are small at large scale and can be neglected.
But it is important to consider them at scales comparable to the wavelength of
the light beam and has been utilized in nanophotonics based applications.
Herein, we have studied the interaction of AM carrying beams with a single plasmonic
nanowire (NW). Our study aims at how transverse spin and orbital momentum
flows control the scattering of AM carrying beams from an individual NW and generation
of plasmons in the NW. We show the optical Spin-Hall effect in the scattering
of a light beam from NW caused by spin flow, the detection of OAM states using a
single NW at the subwavelength scale and OAM controlled surface plasmon polaritons
generation in a plasmonic NW. In order to experimentally probe the above concepts,
we have utilized a home-built dual-channel Fourier plane microscopy setup and corroborated
the measurement with finite element based numerical simulations. Structured
light beams such as Hermite-Gaussian and Laguerr-Gaussian beams are generated using
spatial light modulator working in off-axis hologram configuration for experimental
observations. Using the developed experimental methods, we have also explored nonlinear optical effects such as second-harmonic generation and two-photon excited
fluorescence from organic mesowire using conventional optical Gaussian beams.
