GEOMETRICAL INTERPRETATION OF A LASER-INDUCED THERMAL LENS

Spatial characteristics of a thermal lens induced by a Gaussian beam i n an absorbing liquid are studied using a nonlinear geometrical optics approximation. We show that the thermal lens in the vicinity of the s ample cell is a focal point of light and a ring-of-light foci located in a plane displaced with respect to the focal point. The distance bet ween the focal point and the ring-of-light foci decreases when the lig ht power is increased. Experiments performed on an ethanol solution of iodine confirm the existence of this microscopic structure. The dista nce between the focal point and the ring of foci was measured for samp les of different absorption coefficients. A good agreement between the ory and experiment was obtained.