Comparison of calculated and measured temperature fields in laser-heated thin film systems

Clarke, Andrew James

Abstract

Thermal modelling of the laser processing of nanoparticulate ITO films has been carried out with models of varying complexity. The results from a simple semi-analytical 1D model and numerical 1D, 2D and 2D-axisymmetric models are reported for continuous wave HeCd laser and nanosecond pulsed XeCl laser irradiation. These results are compared to thermal camera measurements to determine the validity of the models under the different laser regimes.

For continuous wave laser heating, it is shown that heat flow out of the laser irradiated volume significantly affects the predicted peak temperature rise. Models with fewer dimensions overestimate the temperature change, by a factor of over 100 times in the worst cases, due to the lack of lateral heat conduction. Consequently, meaningful temperatures are only calculated with 2D-axisymmetric or 3D models. When considering nanosecond pulsed lasers, the energy absorbed does not have enough time during the pulse to diffuse away from the volume in which it was deposited. Because of this, lateral heat flow is less important during heating and all the numerical models converge to the same predicted peak temperature rise. This allows much less computationally taxing models to be solved whilst obtaining the same result.

The optical properties of the film are shown to be significant in determining the rate of laser induced heating and resultant temperature rise. However, for continuous wave irradiation, the models were insensitive to changes in the thermal parameters of the film and the peak temperature is controlled by the thermal parameters of the substrate. The opposite is true for the nanosecond pulsed lasers, with the thermal parameters of the film drastically affecting the temperature rise and the substrate parameters only contributing to the cooling which occurred over longer timescales. The differing sensitivity of the models to these parameters has been attributed to the rates of heating under the different laser regimes.

Citation

Clarke, A. J. (2017). Comparison of calculated and measured temperature fields in laser-heated thin film systems. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4221782

• Thesis Type: Thesis
• Deposit Date: Aug 27, 2019
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4221782
• Additional Information: Department of Physics and Mathematics, The University of Hull
• Award Date: Aug 1, 2017