Electrode modifications and characteristics of femtosecond laser-stimulated electrical discharges in nanoscale gaps

Femtosecond (FS) laser-stimulated discharges in nanoscale and microscale gaps between etched nanoprobe tip cathodes and gold film anodes were studied experimentally and by particle-in-cell simulation. Experimentally, for appropriate values of gap length, applied potential and laser irradiance, breakdown discharges could be reliably stimulated. Minor cathode tip damage could be observed for FS laser pulses that reliably stimulated discharges, suggesting that laser ablation of the cathode played on important role in stimulation of breakdown discharges in nanoscale gaps. Femtosecond (FS) laser stimulation of electrical discharges in 500 nm gaps excited with DC applied potential was simulated using a particle-in-cell and Monte Carlo collision model. Discharges were predicted to occur at a much lower applied potential with initial laser-ablated particles than for gaps without particles. The applied potentials and laser-ablated particle densities required for breakdown discharges in the simulations were well-correlated to experimental measurements. Threshold applied potential for anode melting was approximately correlated with experimental measurements. The simulations show that laser ablation of the cathode is a viable mechanism of FS laser discharge stimulation and that PIC simulation is able to make approximate predictions of threshold applied potential for anode melting.