| Summary: | 碩士 === 國立中正大學 === 物理學系暨研究所 === 101 === Using a 10 Hz, frequency doubled, Q-switched and mode-locked Nd:YAG laser, we have investigated, with the Z-scan the technique, short pulse induced outward solute migration in a 1 mm thick ethanolic solution of chloroaluminum, dubbed as ClAlPc-ethanol. Knowing the mass diffusion time constant to be md = 0.3 s, we placed a shutter in the light path to select 19 ps pulses, delivered by the abovementioned laser, at time intervals of p-p = 0.1 s n with n denoting any integers. By comparing the Z-scan curves obtained with pulses of equal energy and different p-ps covering md, we found that when was below a threshold th, the curves taken with various p-ps were indistinguishable and symmetrical about the beam waist. However, when exceeded th, the curves taken with p-ps less than md skewed upward towards the side scanned after the beam and appeared higher than those obtained with p-ps considerably larger than md which were symmetrical about the beam waist. Accordingly, we concluded that a 19 ps pulse with energy above the threshold th can induce the outward solute migration.
In this study, we repeated the same Z-scan measurements with a temperature gradient along the light propagation direction added to the same sample. This is fulfilled by separately controlling the temperature of both the front and rear surfaces of the sample with a temperature controller (Instec HCS402). The purpose of this study is to verify the influence of convection on short pulse induced solute migration. As a result, we found that a temperature gradient (or convection) either parallel or antiparallel to the light propagation direction equivalently weakens the outward solute migration.
We qualitatively explained the observed results by appealing to the three fundamental laws of fluid dynamics (mass conservation, momentum conversation and energy conservation) and thermodynamics. We intend to quantitatively explain the experimental results in the future.
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