Thermograms of melting of thin plates heated by laser radiation with modulated intensity

Analysis is made of thermograms taken from the surface of thin plates of refractory materials heated by laser radiation of modulated intensity. In a single-phase region (at temperature $T$ below the melting temperature $T_m$), the thermogram has a harmonic component with a constant amplitude and with a frequency equal to the modulation frequency of radiation. In a two-phase region (melting region), the harmonic component degenerates. At a temperature close to the melting temperature $T_m$, lower ($T<T_m$) and upper ($T>T_m$) variable-amplitude half-waves are observed, which alternate with short-duration regions of $T=T_m$. A longer-duration region of two-phase state ($T=T_m$) is located between time intervals with lower and upper half-waves. A one-dimensional model is constructed, which is used to obtain an approximate analytical description of oscillatory motion of melting front and of the time dependence of plate temperature which is in qualitative agreement with experimentally obtained thermograms. Possible reasons of quantitative differences between theory and experiment are identified. A fundamental possibility is demonstrated of influencing the duration of melting a thin plate in the presence of modulation of intensity of incident heat flux owing to the variation of modulation parameters, which may prove useful as regards the identification and investigation of phase transitions of low latent heat.