Ultrafast particle-plasmon enhancement by energy-band modification in nanostructured tungsten carbide.

Ultrafast optical excitation induced transient modification on the energy-band structures in tungsten, which resulted in the expansion and shift toward the Fermi-level of d-band. This process led to enhanced interband transitions at reduced photon energies. Meanwhile, enhanced interband excitation led to increased electron density above the Fermi level, resulting in enhanced optical scattering by localized surface plasmon resonance (LSPR). These mechanisms are responsible for balancing the direct heating of bulk electrons by optical pulses. The corresponding studies not only revealed the physics for the electronic dynamics in tungsten carbide, but also proposed that the modified electronic and electron-phononic interactions are one of the important responsible mechanisms for the enhanced laser-damage threshold of the hard-metal coating. Furthermore, the nanostructured hard-metal coating integrates functions of enhancement of the damage-threshold and anti-reflection coating, which is important for exploring new tools or materials in laser engineering.