13:30 〜 15:30
▲ [20p-P1-6] Femtosecond laser trapping dynamics of dielectric nanoparticles in viscous medium
キーワード：laser trapping, femtosecond laser, dielectric nanoparticles
We have studied laser trapping dynamics of nanoparticles using a femtosecond (fs) laser (800 nm, 80 MHz, 100 fs). Hydrophobic 50 nm-sized polystyrene nanoparticles (PS NPs) are trapped at the focus, followed by their ejection perpendicular to laser polarization direction. It always takes place into one and the opposite directions in an alternative manner, which has been studied by examining the dependence of pulse width, repetition rate, laser power, laser polarization, and surface property of material on trapping and ejection of fs laser1-3. Here, we report femtosecond laser trapping dynamics based on tuning the solvent viscosity, which affects the gathering, assembling, and ejection processes of NPs upon the irradiation of fs laser pulses.
The threshold of laser power for the ejection first decreased and then saturated with the increase in solvent viscosity (Figure 1a). Possibly, high viscosity enables the stable formation of PS NPs assembly by suppressing its dissociation and finally the single large transient assembly is ejected. This viscosity dependence is compensated with the suppressed diffusion to the trapping site in more viscous medium.
Hydrophilic 50 nm-sized bare silica NPs are trapped more efficiently by fs laser than by cw laser4, giving no ejection even at 300 mW. Interestingly, a single assembly of silica NPs was ejected in viscous solvent at 400mW (Figure 1b), although the number of trapped NPs by fs laser became less than that by cw laser. We discuss the trapping and ejection dynamics considering how gathering of NPs and their assembly formation during the fs pulse as well as the assembly dissociation after the pulse depends on viscous medium, and point out the crucial role of the assembly formation in ejection behavior.
The threshold of laser power for the ejection first decreased and then saturated with the increase in solvent viscosity (Figure 1a). Possibly, high viscosity enables the stable formation of PS NPs assembly by suppressing its dissociation and finally the single large transient assembly is ejected. This viscosity dependence is compensated with the suppressed diffusion to the trapping site in more viscous medium.
Hydrophilic 50 nm-sized bare silica NPs are trapped more efficiently by fs laser than by cw laser4, giving no ejection even at 300 mW. Interestingly, a single assembly of silica NPs was ejected in viscous solvent at 400mW (Figure 1b), although the number of trapped NPs by fs laser became less than that by cw laser. We discuss the trapping and ejection dynamics considering how gathering of NPs and their assembly formation during the fs pulse as well as the assembly dissociation after the pulse depends on viscous medium, and point out the crucial role of the assembly formation in ejection behavior.