科研之友
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摘要
The application of recently developed diffraction theory for cw transverse photothermal deflection spectroscopy (normal deflection only) to the measurements of thermophysical and mass-diffusion properties of gases is presented. Compared with the traditional ray-optics theory, the diffraction theory has one more term in the phase signal. This term quantitatively exhibits the probe-beam size effect on the phase signal. Experimental results demonstrated that even if the ratio of the probe-beam radius to the thermal diffusion length of a deflecting medium was as low as about 0.22, the probe-beam size effect could not be ignored when measuring the distance between the probe beam and a solid sample using the phase signal. With the measured distance, the thermal diffusivity alpha(g) and the temperature coefficient of the refractive index dn/dT of pure gases (O-2, N-2, and CO2) and binary gas mixtures (CO2-O-2 and CO2-O-2) were precisely measured, resulting in good agreement with literature values. Furthermore the measured dn/dT values of the pure gases had one more significant figure than the literature ones. The concentration dependences of alpha(g) and dn/dT were employed for the determination of mass-diffusion coefficients of CO2-O-2 and CO2-N-2, and the results were consistent with literature values.
