In this paper, we introduce the use of an infinite-mode double-grating interferometer for investigating fluid dynamics that is induced by a thermal lens when an intense laser beam, we call it pump beam, passes through a liquid sample consisting strongly absorbing nanoparticles. In the passing of the pump beam through the sample, as absorption is occurred over the beam's trace, in normal temperature increases and density decreases. The density and temperature changes in the sample can be translated to a phase shift in the passing of a plane probe beam through the sample. By interfering two parts of the probe beam, one part passes from the thermal lens area and other one passes from another area of the sample in which these areas are away from each other, it is possible to determine the phase shift value. When propagation directions of the interfering beams are parallel, infinite-mode double-grating interference fringes are formed. At the infinite-mode, formation and evolution of the interference fringes directly reflect the changes of the density and temperature in the sample. The thermal convection is visually sensed and quantitatively determined by chasing the first produced infinite-mode interference fringe. In this work, measurement of the thermal convection velocity is reported by details. The measured value is comparable with the value obtained with other methods at the same conditions. The proposed method is reliable and very simple, also the convection process can be visualized in real-time.
کلید واژگان :infinite-mode double-grating interferometer, fluid dynamics, thermal lens, convection velocity, nano-particles
ارزش ریالی : 600000 ریال
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