Dynamic measurement of thickness distribution in a soap film by using a phase-modulated large lateral shearing interferometer

Accurate measurement of soap film thickness distribution is a difficult and challenging task. In this paper, dynamic thickness distributions of a soap film were measured and visualized by using a phase-modulated large lateral shearing interferometer. A spatial light modulator (SLM) was utilized to modulate phase shifts of the incident laser, and film phases wrapped between 0 and $2\pi$ were calculated from a least square method. The continuities of soap film thickness in space and time were adopted to obtain precise phase distributions, and then thickness distributions were retrieved. During the experiment, film thickness distributions were reconstructed at a rate of about 12 ms per frame, and the entire process from the initial stage of the soap film formation to rupture was recorded by a high-speed camera. In this process, the overall thickness of the soap film became thinner and the absolute values of thickness gradient decreased, which can be explained by the drainage effect caused by gravity.