کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5428960 | 1397326 | 2012 | 9 صفحه PDF | دانلود رایگان |
The cavitation microbubbles in dilute gold colloids of different concentrations (2-10Â ppm) induced by a focused nanosecond-pulsed laser beam were measured and characterized at different wavelengths by using the passive and active ultrasound measurements. Three colloids with gold nanoparticles (GNPs) of different sizes (10, 45, and 75Â nm) were used for experiment. The results show that the lifespan of the microbubble is reduced as the concentration of GNP increases, particularly at the wavelength of 532Â nm, the surface plasmon resonance (SPR) of GNP. In contrast, at the off-resonant wavelength (e.g. 700Â nm), the lifespan reduction is relatively small. This wavelength-dependent cavitation is attributed to the Faraday-Tyndall effect, a strong light scattering by GNPs. A slight defocusing of the Gaussian beam in gold colloid was proposed. Hence, the waist of the focused beam increases to reduce the optical breakdown in gold colloid. For simplicity, a linear relation between the incremental waist radius of Gaussian beam and the concentration of GNP was assumed. According to this formulation, the theoretical results are consistent with the experimental ones. In addition, the dynamics of the microbubble in gold colloid measured by the active ultrasound method agree with the Rayleigh-Plesset model.
⺠The Faraday-Tyndall effect of gold colloid on laser induced microbubble is studied. ⺠Faraday-Tyndall effect of gold colloid causes the defocusing of laser beam. ⺠Lifespan of the microbubble is reduced as the concentration of GNP increases. ⺠Light scattering of laser beam at the surface plasmon resonance of GNP is the maximum.
Journal: Journal of Quantitative Spectroscopy and Radiative Transfer - Volume 113, Issue 17, November 2012, Pages 2234-2242