Effects of laser parameters on heat distribution in a cylindrical sample

Abstract

The coherence and high power in the focal area make laser sources a very convenient source for controlled heating of small samples. The distribution of heat and temperatures produced by laser heating can also be used to control reaction rates. In this paper we investigate the effects of laser parameters like power, profile and mode structure on the heating of a cylindrical sample of aqueous dipeptide solution and observe the amount of hydrolysis produced. The experiment involves heating of the sample from the top by a continuous-wave CO2 laser which hydrolyses and evaporates the solution resulting in production of amino acids. We do a theoretical modelling of the experiment where we investigate conditions of optimal hydrolysis versus evaporation. We also do a numerical simulation of the experiment where we solve the heat conduction equation for the cylindrical sample with a laser source and find the distributions of temperatures. We determine the volumes of different temperature zones and plot contours of these zones in the sample. Steady state conditions are assumed with no convection. Heat losses from the boundary of the sample are included in our model. We estimate an effective temperature which determines the rate of hydrolysis.