Fig. 1. SEM image and size distribution of the gold nanocages (inset).

Fig. 2. Linear absorption spectra of gold nanocages.

Fig. 3. Electric field distributions of gold nanocages with incident wavelength of (a) 600 nm and (b) 300 nm.

Fig. 4. Open-aperture Z-scan curves for (a) gold nanocages at 550 nm and 300 μJ, (b) gold nanocages at 550 nm and 800 μJ, (c) gold nanocages at 600 nm and 300 μJ, (d) gold nanocages at 600 nm and 800 μJ, (e) gold nanocages at 650 nm and 300 μJ, and (f) gold nanocages at 650 nm and 800 μJ. The dots are experimental data, while the solid lines are the generated theoretical fit.

Fig. 5. Solid lines are the linear absorption spectra. The dots are saturation strength $I_s$ and nonlinear absorption coefficient $\beta$ versus wavelength when $I_0$ is (a) $4.95\times {10}^{13}\mathrm{W}/{\mathrm{m}}^2$ and (b) and (c) $1.32\times {10}^{14}\mathrm{W}/{\mathrm{m}}^2$.

Table 1. Nonlinear Optical Parameters of Gold Nanocages