Figure 1

Spatial $xy$ dependence of the transmission change $\Delta T/T$ induced by a single gold nanoparticle with diameter $D\approx 10\mathrm{n}\mathrm{m}$ on a glass substrate. The laser, of wavelength $\lambda =532\mathrm{n}\mathrm{m}$ and power $P_i=10\mu \mathrm{W}$, is focused on a $0.34\mu \mathrm{m}$ FWHM focal spot centered at $(x_0,y_0)=(1\mu \mathrm{m},1\mu \mathrm{m})$. The sample position is scanned over a $2\times 2\mu {\mathrm{m}}^2$ area and modulated along the $y$ axis at $f=1.5\mathrm{k}\mathrm{H}z$. (a) The signal is detected at $f$. (b) The same for $2f$ detection. (c),(d) Cut along the $y$ direction for $x=x_0$ of the (a) and (b) data, respectively (points). The dashed lines are the computed profiles using $a_{bw}=0.34\mu \mathrm{m}$, ${\delta }_y=0.27\mu \mathrm{m}$, and ${\sigma }_{\mathrm{e}\mathrm{x}\mathrm{t}}$ as a parameter.Reuse & Permissions

Figure 2

(a) Spatial $xy$ dependence of the transmission change modulus $|\Delta T/T|$ measured at $\lambda =532\mathrm{n}\mathrm{m}$ over a $4\times 4\mu {\mathrm{m}}^2$ area for gold particles with average diameter $\overline{D}=20\mathrm{n}\mathrm{m}$ deposited on glass. Modulation and detection are performed at $f=1\mathrm{k}\mathrm{H}z$. Each peak pair along the modulation direction $y$ corresponds to a single particle. (b) Same probed area for $\lambda =633\mathrm{n}\mathrm{m}$. The large peak pair observed for both wavelengths is ascribed to scattering by dust or by a particle aggregate. Inset: extinction spectrum of the $\overline{D}=20\mathrm{n}\mathrm{m}$ colloidal solution. The arrows show the laser wavelengths $\lambda =532$ and 633 nm.Reuse & Permissions

Figure 3

Cubic root of the mean signal maximum $|\Delta T/T{|}_{\max }^{1/3}$ and single particle extinction cross section ${\sigma }_{\mathrm{e}\mathrm{x}\mathrm{t}}^{1/3}$ as a function of the average gold nanoparticle diameter $\overline{D}$ measured for $\lambda =532\mathrm{n}\mathrm{m}$ and $f$ detection (triangles). The lines are the computed ${\sigma }_{\mathrm{e}\mathrm{x}\mathrm{t}}^{1/3}$ using $g=1$ and ${ϵ}_m=1$, 1.6, and 2.25 (dotted, full, and dash-dotted lines, respectively) and $g=0$ and ${ϵ}_m=1.6$ (dashed line). Inset: histogram of the maximum signal amplitude distribution for the $\overline{D}=20\mathrm{n}\mathrm{m}$ sample. The dotted line is a Gaussian fit.Reuse & Permissions