CONVECTIVE AND FREE-SURFACE INSTABILITIES PROVOKED BY HEATING BELOW AN INTERFACE

This paper discusses a new phenomenon, the so-called heartbeat apparently observed for the first time in 1981. The optical heartbeat is formed under certain conditions by the oscillations of a thermal lens produced when a continuous-wave (CW) laser beam propagates below a liquid-free surface. The contents of the paper are divided into two parts: first, a discussion of the mechanisms leading to the observed phenomena is presented; second, the laminar/turbulent transition is examined in some detail to illustrate several universal features of the optical heartbeat. The physical properties connected with the phenomena under discussion include convective heat transfer, which is associated with convective Benard and Marangoni instabilities possibly coupled to laser irradiation effects.