Effect of ballistic electrons on ultrafast thermomechanical responses of a thin metal film**Project supported by the National Natural Science Foundation of China (Grant No. 11502085), the Natural Science Foundation of Hubei Province, China (Grant No. 2016CFB542), the Fundamental Research Funds for the Central Universities, China (Grant No. 2016YXMS097), and the Research Fund of State Key Laboratory of Mechanics and Control

Abstract

The ultrafast thermomechanical coupling problem in a thin gold film irradiated by ultrashort laser pulses with different electron ballistic depths is investigated via the ultrafast thermoelasticity model. The solution of the problem is obtained by solving finite element governing equations. The comparison between the results of ultrafast thermomechanical coupling responses with different electron ballistic depths is made to show the ballistic electron effect. It is found that the ballistic electrons have a significant influence on the ultrafast thermomechanical coupling behaviors of the gold thin film and the best laser micromachining results can be achieved by choosing the specific laser technology (large or small ballistic range). In addition, the influence of simplification of the ultrashort laser pulse source on the results is studied, and it is found that the simplification has a great influence on the thermomechanical responses, which implies that care should be taken when the simplified form of the laser source term is applied as the Gaussian heat source.