Fig. 1. Schematic diagram of the experimental setup. The laser pulses were focused by a fused silica lens F1 (f=21cm) into pure water and doped water. Filament in the cuvette was imaged by a CCD camera with ND and bandpass filters in front. The output emission was collected and directed to a fiber-coupled spectrometer. VA, variable attenuator; CCD, charge-coupled device.

Fig. 2. Top views of light channel (top row) and the corresponding longitudinal white light intensity distribution in gold-nanoparticle-doped water (bottom row) with input pulse energy of (a), (b) 5.49 μJ and (c), (d) 9.86 μJ and in pure water with pulse energy of (e), (f) 9.72 μJ.

Fig. 3. Starting position of multifilaments as a function of P/Pcr (input power divided by critical power) in gold-nanoparticle-doped water. Solid squares, experimental results; red line, simulations. We take Pcr=0.5MW for the critical power of self-focusing in doped water by considering the results in Table 1.

Fig. 4. Spectra obtained for the propagation of the laser pulse in gold-nanoparticle-doped water (green and dark yellow solid curves) as compared with those in pure water (pink and red solid curves) under (a) low and (b) high average input energy. The spectra are normalized to the intensity of the signal at 800 nm.