Numerical modeling of laser-induced heating effect in optical thermometry

The laser-induced heating effect leads to obvious inaccuracy in optical thermometry, since this heating effect adjusts the fluorescence intensity ratio from two adjacent thermally coupled energy levels, and is difficult to measure with some equipment. It is necessary to accurately evaluate this heating effect and understand its formation mechanism. To overcome this problem, a 3D heat transfer model was developed by using finite element methods. Three physical processes are considered in this work: energy absorption from CW or pulsed lasers, heat conduction inside the matrix materials and heat transfer to the ambient air. It was found that the heating effect induced by lasers is dependent on the pump power and the spot radii of the lasers. Higher laser power and a narrower laser spot led to greater heat energy, resulting in higher temperatures. A fairly high temperature increment of 25.60 K was observed when a CW laser was used as an excitation source. The excitation modes of the laser also affect the heating effect. The thermal effect was suppressed by using a pulsed laser due to its shorter interaction time; however, it still cannot be ignored in the application of optical temperature sensors.