Optical characterization of thermal lens effect in ethanol and the influence of focusing lens and liquid cell size

A high power cw laser beam propagating in an absorbing medium spreads, distorted or deflected as a result of thermally self-induced refractive index gradients. In this paper, optical characteristic of thermal lens effect in liquid ethanol was studied experimentally. The thermal lens was induced by focusing of a high power He–Ne laser beam in ethanol (absorbing liquid). The thermal lens effect was investigated by Z-scan method. Depending on the focusing position of the beam in liquid cell, the results show both intensity increasing and decreasing on a screen, which is fixed at a specific position with respect to the cell. The results show such effects depend on the lens focal length, the liquid cell size, and the focusing position of the lens. According to the results there is a competition between focusing and defocusing of the transmitted beam if the position of the focusing region inside the sample cell is changed. Using a simple optical description, the experimental results were interpreted. ► Thermal lens effect produced by He–Ne laser beam in ethanol was studied. ► Different focusing lenses were used and the effect of focal length was inspected. ► The focal length and the position of focusing in the liquid affect the results. ► According to measurements, the results also depends on the liquid cell length