Study of the Negative Lensing Effect in Organic Solutions Induced by a CW He-Ne Laser

• Main Authors: Yuu-Sheng Tang, 湯羽生
• Other Authors: Tai-Huei Wei
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/n8a9mj

碩士 === 國立中正大學 === 物理學系暨研究所 === 103 === By measuring the total and axial transmittances of an ethanolic solution of chloroaluminum phthalocyanine (dubbed as ClAlPc-ethanol) with a 632.8 nm CW He-Ne laser, we investigate in this thesis, convection as well as thermal and mass diffusions of the solution and its constituents: the solvent and solute. To minimize the undesired convection induced by the gravitational force, we made the laser beam propagate downward perpendicularly to the optical table and then normally enter the 1 mm thick sample at two different concentrations (7e-4 M and 2 e-4 M). Considering the characteristic times for thermal diffusivity (Tth) and thermal diffusion (Td) are in the millisecond (ms) and sub-s orders respectively, we continue the transmittances measurements for 2s, which is considerably longer than Tth and Td. This is experimentally achieved by inserting a shutter in the light path and making it open for 2s. From the measured total transmittance as a function of time relative to the shutter opening time (denoted by T), we explain how the increase of total transmittance with T in terms of the electronic transition and the subsequent thermal and mass diffusions of the solute molecules. On the other hand, via he measured axial transmittance as a function of T, we interpret how the observed thermal lensing effect strengthens with T within Tth and then turns steady after T exceeds Tth in terms electronic transition, solution convection and thermal and mass diffusions of the solvent and solute. Combining the information obtained from the measured total and axial transmittances as functions of T, we study how the convection of the solution as well as thermal and mass diffusion of both the solute and solvent are induced by the temperature gradient induced in the absorptive solution.