Wavelength dependent energy transfer to semiconductors and dielectrics irradiated by ultrashort laser pulses Текст научной статьи по специальности «Медицинские технологии»

LMI-I-8

Wavelength dependent energy transfer to semiconductors and dielectrics irradiated by ultrashort laser pulses

T. Apostolova1,2

institute for Nuclear Research and Nuclear Energy, Cyclotron physics, Sofia, Bulgaria 2Institute for Advanced Physical Studies, New Bulgarian University, Sofia, Bulgaria

Femtosecond laser-induced energy absorption and optical breakdown of silicon and germanium is studied for laser wavelengths in the near- and mid-infrared spectral regions using the Time dependent Schrodinger equation in one electron approximation1'2. The dependence of the photoelectron density and deposited energy on the laser intensity and wavelength are obtained. For Si irradiated by mid-IR wavelengths and low laser field strength, material-specific threshold for the onset of energy absorption into the bulk is found, while for near-IR wavelengths the energy transfer to electrons occurs via multiphoton absorption. For high driving field strength, absorption of energy becomes wavelength independent and increases linearly with increase of the laser intensity. During the irradiation, part of the energy stored in the electronic system is transferred back to the radiation field via high harmonic generation. We obtain clean harmonic peaks generated during the irradiation with near-IR laser pulse, while quasi-continuous bremsstrahlung radiation is generated during the irradiation with mid-IR wavelengths. Dielectric breakdown thresholds are discussed in terms of the total laser energy coupled to ultrafast electron excitations in the materials and sufficient to cause melting of the solid and the onset of laser-induced DC currents after the end of the driving pulse.

References

[1] S. Lagomarsino et. al, Phys. Rev. B 93, 085128, 2016.

[2] T. Apostolova, et. al, Applied Surface Science, 427, 334, 2018.