Figure 2

Trapping efficiency measurements versus separation distance.

(a) Trapping efficiency, Q, as a function of the relative distance, z, between the trapping laser beam focus and various substrates. Relative distance is the measured distance with respect to the zero position. Solid line: exponential fit to the data obtained with the nanostructured silicon substrate, coated with Cu/Au. Trapping data were obtained with the CW laser setup. (b) Trapping efficiency, Q, as a function of the relative distance, z, between the trapping laser beam focus and the nanostructured silicon substrate, coated with Cu/Au, obtained with three different laser systems for the same wavelength (1070 nm). The laser systems are: CW laser at 1070 nm; femtosecond laser at 1070 nm (140 fs); optical parametric oscillator (OPO) at 1070 nm (200 fs). The x-error corresponds to the Rayleigh length of the trapping laser beam and the y-error to the standard deviation of the trapping efficiency measurement.