Grating-assisted surface plasmons resonance in 2D microstructures induced by femtosecond vector fields

Two-dimensional near-wavelength microstructures have been fabricated on a copper film and a silicon wafer by femtosecond vector optical fields with different spatial polarization distribution, at a central wavelength of 800 nm, pulse duration of ∼70 fs, and a repetition rate of 1 kHz. Laser-induced ripples appear at the ablated region on silicon when the laser fluence is above the ablated threshold. When the number of the irradiated pulses increases, ripples with interspace larger than the wavelength could be observed, while the dimension of the ablated region has a slight variation. In the induced microstructures on a copper film, the microstructures in a ring have been observed under the irradiation of a few pulses. Under the irradiation of the multipulse femtosecond vector field, differently from the condition of the silicon, the induced microstructures on the metallic copper surface exhibit the anisotropic extending feature dependent on the polarization distribution of the vector field. The physics behind this unique feature is the anisotropic excitation and propagation of surface plasmon, caused by the coupling of the subsequent irradiation pulses with the existing microstructure. In this case, the surface plasmons resonance in the induced 2D microstructures is closely related to the induced grating structures on the surface.