Description

We report a first-principle calculation for the wavelength-dependence of a laser excitation process on a silicon surface.

Although  lower frequency laser is reflected by a lower density plasma, it can penetrate thicker plasma sheet. 

Therefore, the depth of the laser processing depends on the width of the plasma at the surface and laser wavelength. 

The time-dependent density-functional theory (TDDFT) and Maxwell’s equations are simultaneously employed to elucidate the effect of laser propagation on laser-matter interaction under ultrafast pulse lasers (FWHM:12 fs).

Our numerical approach employing TDDFT can describes the non-linear electron excitation process in the first-principle level. 

The transient response of the excited electron is included in the Maxwell's Eq. as the electronics current in multi-scale treatment.

With this simulation method, we can access the reflectivity modulated by the plasma and  position dependence of the electron excitation.

We assume three laser frequencies, 0.4, 0.775, and 1.55 eV.

Although the reflectivity increases around the peak laser intensity of 1x1013 W/cm2 in all frequencies,

a lower-frequency laser field facilitates deeper melting and ablation in silicon, despite a lower critical plasma density. 

Such a deeper excitation by a longer wavelength is because of the penetration of the laser field through the plasma on the surface. 

The plasma-formation depth is saturated at approximately half the wavelength in silicon.

Contributing Authors

  • Tomohito Otobe
    Kansai Photon Science Institute, QST
Tomohito Otobe
Kansai Photon Science Institute, QST
Track: Laser Nanomanufacturing
Session: Basics Physics of Laser Nanoprocessing
Day of Week: Monday
Date/Time:
Location:

Keywords

  • First-Principle Calculation
  • Laser Excitation
  • Silicon Surface