Effect of electron cooling on the femtosecond laser induced electron-lattice dynamics in quartz: A RT-TDDFT calculation

Understanding the microscopic mechanism of interaction between ultrafast laser and quartz materials is vital for laser fabrication of quartz optical waveguide device. Recently, the time-dependent density functional theory (TDDFT) based on quantum mechanics becomes an effective theoretical tool to investigate the ultrafast photoexcitation dynamics in quartz. However, the role of electron cooling has not been involved in previous studies. In fact, the electron cooling as a key physical process significantly affects electron–lattice spatiotemporal evolution as well as the transient optical response of quartz. This paper employs the real-time TDDFT method to simulate the femtosecond laser irradiation of α-quartz at room temperature with a consideration of the electron cooling effect. It was found that the electron cooling increased the lattice temperature and atomic displacements within tens of femtoseconds through the electron–lattice energy transfer. Particularly, the bandgap of quartz presented a drastic reduction by up to 38%, which mainly originated from the rapid lattice structure evolution. This paper demonstrates that the electron cooling effect should not be ignored in the calculation of laser–quartz interaction because it stimulates the renormalization of electronic structure and lattice structures of quartz, which has a huge impact on optical and electrical properties of quartz materials.