Colloidal suspensions offer as a promising platform for engineering polarizibilities and realization of large and tunable nonlinearities. Previous studies of Gaussian beams propagation in various colloidal suspensions predicted in a number of remarkable optical phenomena and applications, including initiation and regulation of chemical reactions, sorting different species of nanoparticles and imaging through highly scattering media. As compared to the conventionally used Gaussian beams, optical vortices that are characterized by the doughnut-shaped intensity profile and a helical phase front offer even more degrees of freedom for, in particular, optical trapping or imaging applications. In our earlier work, we predicted, using the linear stability analysis and numerical simulations, that the perturbations with an orbital angular momentum of a particular charge will be amplified and lead to the formation of a necklace beam with a particular number of peaks, or “beads.” Here, we performed detailed experimental studies of such necklace beam formation that show an excellent agreement with the analytical and numerical predictions. This work might bring about new possibilities for dynamic optical manipulation and transmission of light through scattering media as well as formation of complex optical patters in colloids.
Colloidal metamaterials are a robust and flexible platform for engineering of optical nonlinearities and studies of light filamentation. To date, nonlinear propagation and modulation instability of Gaussian beams and optical vortices carrying orbital angular momentum were studied in such media.
Here, we investigate the propagation of necklace beams and the conservation of the orbital angular momentum in colloidal media with saturable nonlinearity. We study various scenarios leading to generation of helical necklace beams or twisted beams, depending on the radius, power, and charge of the input vortex beam. Helical beams are build of two separate solitary beams with circular cross-sections that spiral around their center of mass as a result of the equilibrium between the attraction force of in-phase solitons and the centrifugal force associated with the rotational movement. A twisted beam is a single beam with an elliptical cross-section that rotates around it's own axis. We show that the orbital angular momentum is converted into the rotational motion at different rates for helical and twisted beams.
While earlier studies reported that solitary beams are expelled form the initial vortex ring along straight trajectories tangent to the vortex ring, we show that depending on the charge and the power of the initial beam, these trajectories can diverge from the tangential direction and may be curvilinear. These results provide a detailed description of necklace beam dynamics in saturable nonlinear media and may be useful in studies of light filamentation in liquids and light propagation in highly scattering colloids and biological samples.
The emergence of metamaterials also has a strong potential to enable a plethora of novel nonlinear light-matter interactions and even new nonlinear materials. In particular, nonlinear focusing and defocusing effects are of paramount importance for manipulation of the minimum focusing spot size of structured light beams necessary for nanoscale trapping, manipulation, and fundamental spectroscopic studies. Colloidal suspensions offer as a promising platform for engineering polarizibilities and realization of large and tunable nonlinearities. We will present our recent studies of the phenomenon of spatial modulational instability leading to laser beam filamentation in an engineered soft-matter nonlinear media as well as in negative index metamaterials. We will also discuss the possibilities of guiding, manipulating, and processing radio-and microwave-frequency radiation using photonic structures built of filaments in air. In particular, we introduce so-called virtual hyperbolic metamaterials formed by an array of plasma channels in air as a result of self-focusing of an intense laser pulse, and show that such structure can be used to manipulate microwave beams in a free space. Generation of virtual hyperbolic metamaterials requires a regular and spatially invariant distribution of plasma channels. Therefore, we discuss the generation of such large regular arrays of filaments and consider the interactions between multiple filaments, multiple filament formation, and phase-controlled structured filaments.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.