09:30 〜 11:30
▲ [21a-P5-4] Femtosecond laser-induced acoustic wave emission from gold nano-colloidal suspensions; shape dependence
キーワード：femtosecond laser,gold nanoparticles,acoustic wave emission
In recent studies, photoacoustic (PA) wave emission from gold nano-particles induced by nanosecond laser irradiation was reported and the mechanism was attributed to non-radiative relaxation dynamics of surface plasmon resonance. However, thermal instability and shape deformation of gold nano-particles which result in decay of PA signal intensity were reported. In this study, an enhanced PA signal intensity from gold nano-colloidal suspensions with different particle shapes under the condition of tightly-focused femtosecond-pulsed laser (800 nm, 1 kHz, 35 fs) irradiation was investigated. PA signal intensity from gold nano-colloidal suspensions in a glass tube was measured by ultrasound transducers at frequencies of 5, 10, and 25 MHz. Sample suspensions were with gold nano-spheres (diameter = 20 nm) with an absorption peak at 520 nm, and gold nano-rods (35 x 12 nm) with absorption peaks at 520 nm and 800 nm which corresponds to transverse and longitudinal surface plasmon resonance, respectively. The experimental results revealed a linear-dependence of the relative PA amplitude at 5 MHz to various shapes of gold nano-particles at different laser power. The longitudinal absorption band of gold nano-rods at the wavelength of 800 nm, which coincides with the wavelength of the femtosecond laser, leads to higher PA signal generation. On the other hand, gold nano-spheres without effective absorption at the laser wavelength generate lower PA signal intensity. No significant shape deformation of gold nano-rods and nano-spheres was observed before and after the experiments under our experimental conditions. Hence, thermal stability and increase in acoustic wave emission from femtosecond laser-irradiated gold nano-particles was demonstrated.