Two optical techniques are described for measurement of a liquid film's surface. Bothtechniques make use of the total internal reflection which occurs at a liquid-vapor interface dueto the refractive index difference between a liquid and a vapor. The fIrst technique is used forfilm thickness determination. A video camera records the distance between a light source andthe rays which are reflected back from the liquid-vapor interface. This distance can be shown tobe linearly proportional to film thickness. The second technique measures surface wavevelocities. Two photosensors, spaced a fIxed distance apart, are used to record the time varyingintensity of light reflected from the liquid-vapor interface. The velocity is then deduced from thetime lag between the two signals.
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