Influence of a Temperature Gradient Along the Light Propagation Direction on Thermal Diffusion in an Organic Solution

• Main Authors: Chia-Yu Fan, 范嘉宇
• Other Authors: Tai-Huei Wei
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/81759808205848117138

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-ps covering md, we found that when  was below a threshold th, the curves taken with various p-ps were indistinguishable and symmetrical about the beam waist. However, when  exceeded th, the curves taken with p-ps less than md skewed upward towards the side scanned after the beam and appeared higher than those obtained with p-ps 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.