Fig. 1. Schematic of the experimental setup. A linearly polarized 1064 nm probe beam is sent through a soliton channel created by a pump beam of tunable wavelength from 700 to 960 nm in a suspension of gold nanorods. The polarizer before the dichroic mirror is to establish a linearly polarized light for the probe beam. BE, beam expander; DCM, dichroic mirror; FL, focusing lens; M, mirror; PBS, polarizing beam splitter; PM, powermeter. The insert shows the guidance of an infrared probe beam of 1064 nm wavelength through a 4-cm-long cuvette of gold nanoparticle suspension by a soliton-induced waveguide formed typically at a visible wavelength of 532 nm.

Fig. 2. Beam profiles of a 740 nm laser soliton beam passing through a suspension of gold nanorods (average diameter 50 nm, average length 145 nm) in water (top panels) and toluene (bottom panels) at different powers. (a) Input beam profile at 10 mW. (b)–(d) Output beam profiles pumped at 10, 157, and 620 mW, respectively. (e) Input beam profile at 10 mW. (f)–(h) Output beam profiles pumped at 10, 50, and 157 mW, respectively. Note the significant decrease in threshold power for self-trapping in toluene solution.

Fig. 3. Threshold power for self-trapping and transmission spectrum of the pump beam through a gold nanorod (average diameter 50 nm, average length 145 nm) suspension in toluene. (a) Soliton-formation power as a function of pump wavelength. (b) Transmission spectra (left axis) of the pump beam for two different input powers: 1 mW (solid circles) for linear propagation and threshold power for soliton formation (open triangles) as shown in (a), and calculated parallel extinction cross sections (dashed line, right axis) of a single nanorod as a function of wavelength and measured white-light extinction spectrum (solid line, arbitrary units, right axis).

Fig. 4. (a) Real part of the polarizabilities calculated for a single nanorod (diameter 50 nm, length 145 nm) suspended in toluene as a function of wavelength. The perpendicular component (dashed line) stays positive, while the parallel one (solid line) changes from negative to positive as the wavelength is tuned through the LSPR at 865 nm. The two vertical arrows mark the locations of LSPR for rods in water (790 nm) and toluene (865 nm). (b) Calculated parallel (solid line) and perpendicular (dotted line) extinction cross sections of a single nanorod as a function of wavelength.

Fig. 5. (a) Calculated potential energy for rotation along the z axis (the beam propagation direction) as a result of the soliton beam acting on a single gold nanorod in toluene at the beam center for two soliton wavelengths: 740 nm (solid line) and 960 nm (dotted line). The soliton beam is assumed to have a power of 100 mW and a Gaussian beam radius of 10 μm. The inset shows the definition of the orientation angle β. Note that the rotational potential energies in the x and y directions (not shown here) are typically 3 orders of magnitude smaller. (b) Schematic illustration of perpendicular and parallel orientations of the nanorods for two soliton wavelengths of 740 and 960 nm, respectively.

Fig. 6. (a) Transmittance of a 1064 nm probe beam guided by a 740 nm soliton beam as a function of the pump power for probe polarization perpendicular (crosses) and parallel (open circles) to the polarization of the soliton beam. The input power of the probe beam is fixed at 5.0 mW. (b) Relative percentage difference between the perpendicular and parallel transmittances.