Abstract
We study nonlinear propagation of light in colloidal suspension of metallic nanoparticles, in the regime of particles surface plasmon resonance. We show that the propagation exhibits features typical for purely defocusing media and the observed spatial confinement is not a real self-trapping, as for solitons, but rather than is caused by the phase modulation of the beam via nonlocal defocusing nonlinearity. We also show that the light-induced refractive index change in the suspension leads to stabilization of structured light beams. In particular, we demonstrate a stable nonlinear propagation of bright ring beams with complex states of polarization, including practically important radial and azimuthal states.
Highlights
Suspensions of nanoparticles have attracted great interest in the field of light-matter interaction due to their abilities to confine light beams and form solitons in both, short pulse [1, 2] and continuum wave regimes [3,4,5,6,7,8,9]. In the latter case the metallic nanoparticles are of particular interest because of their unique optical properties exhibiting surface plasmon resonance [7, 10,11,12]
The tailored combination of these parameters can dramatically affect optical properties of a suspension, typically in small focal volume of a tightly focused laser beam, by assembling particles via optical trapping [17, 18]. It was proposed [5, 16] that suspensions of gold nanoparticles illuminated with light of frequency near their surface plasmon resonance may change the local concentration of nanoparticles along a low-divergence beam by action of the polarizability-dependent gradient force acting on the particles
We show that thermo-optical response is, a dominating process preventing the refractive index increase and, making the true self-trapping of the beams practically impossible
Summary
Suspensions of nanoparticles have attracted great interest in the field of light-matter interaction due to their abilities to confine light beams and form solitons in both, short pulse [1, 2] and continuum wave (cw) regimes [3,4,5,6,7,8,9]. The tailored combination of these parameters can dramatically affect optical properties of a suspension, typically in small focal volume of a tightly focused laser beam, by assembling particles via optical trapping [17, 18] It was proposed [5, 16] that suspensions of gold nanoparticles illuminated with light of frequency near their surface plasmon resonance may change the local concentration of nanoparticles along a low-divergence beam by action of the polarizability-dependent gradient force acting on the particles. This leads to the modulation of the refractive index of the suspension within the beam, supporting nonlinear self-guiding of the latter. The experimentally observed apparent “self-focusing” of the beam is caused by the modulation of wavefront of the beam by spatially nonlocal defocusing nonlinearity
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