Nonlinear propagation and quasi self-confinement of light in plasmonic resonant media

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.

Light Confinement with Structured Beams in Gold Nanoparticle Suspensions

“…A transmittance peak followed by a minimum indicates a self-defocusing (repulsive) nonlinear optical response. The nonlinear absorption, characterized via open-aperture z-scan, was found to be negligible, consistently with the results from similar colloids containing larger gold nanoparticles [14]. Conversely, the linear UV-vis absorption, graphed in Figure 1b, showed a peak close to the laser wavelength λ = 532 nm.…”

“…In previous studies of gold nanocolloids [11,14,15], it was recognized how, even for NP mean diameter (40 nm) considerably larger than in this work, thermo-mediated self-defocusing dominated over potential self-focusing contributions due to optical trapping [14]. Therefore, it was expected that no NP redistribution would be caused by the incident beam, backing up the measured evidence of lacking nonlinear absorption [14,15].…”

“…It should be stressed that optical trapping forces, playing an important role in the nonlinear properties of other nanocolloids [5,25], are negligible in the present kind of samples [14][15][16]), owing to the dominant opto-thermal effect and the reduced size of the nanoparticles in the BGN; optical trapping on small particles, in fact, tends to be proportional to their volume [55].…”

“…A few applications of metallic nanocolloids in photonics exploit their nonlinear optical response, which entails, for instance, the generation of self-confined wavepackets [5,6,[11][12][13][14][15][16]. Since the Kerr-like (cubic) optical nonlinearity of nanocolloids can be either positive (focusing) or negative (defocusing) depending on the NP size and the wavelength of light, the generation of bright or dark spatial solitons has been pursued with them, as well, using pulsed or continuous-wave (CW) excitations [5,13].…”

Resonant Optical Nonlinearity and Fluorescence Enhancement in Electrically Tuned Plasmonic Nanosuspensions

“…[6][7][8][9][10][11][12] Recently, plasmonic nanosuspensions are found to have superior performance, as compared with their dielectric counterparts, in demonstrating tunable optical nonlinearities that support guiding and self-trapping of light beams. [13][14][15][16][17][18][19][20][21] Robust soliton-like propagation of light over a long distance of several centimeters has been observed due to an effective cubic-quintic-like plasmonic resonant nonlinearity, which would otherwise be impossible in such highly scattering media.…”