Experimental investigation of thermal effects in laser-nanofluid interaction by moiré technique.

Interaction of a CW laser with a nonlinear medium leads to some thermal phenomena. Thermal lensing, which changes the distribution of the refractive index of the medium in the interacting area, is the most important phenomenon among them. Moiré deflectometry is a known technique for measuring the profile of refractive index. In this work, by using nonscanning moiré deflectometry, the refractive index profile in the interaction region of a graphene oxide nanofluid sample and a green CW laser is measured. Using the thermal diffusion equation, the thermo-optical coefficient is calculated. The obtained thermo-optical coefficient value is in good agreement with value from other methods. Having the thermo-optical coefficient and three-dimensional profile of the refractive index, the three-dimensional distribution of temperature is obtained. Although this method is inexpensive and simple, it is applicable for liquid, solid, and gas samples.