Dependence of Ultrafast Electron Emission Characteristics of Graphene Cold Cathode on Femtosecond Photoexcitation Polarization Angle.

Ultrafast electron pulses, generated through femtosecond photoexcitation in nanocathode materials, introduce high-frequency characteristics and ultrahigh temporal-spatial resolution to vacuum micro-nano electronic devices. To advance the development of ultrafast electron sources sensitive to polarized light, we propose an ultrafast pulsed electron source based on a vertical few-layer graphene cold cathode. This source exhibits selective electron emission properties for varying polarization angles, with high switching ratios of 277 (at 0°) and 235 (at 90°). The electron emission of the graphene evolves from cosine to sine as the polarization angle increases from 0° to 90°. The variation of electron emission current with polarization angle is intrinsically related to light absorption, local field enhancement, and photothermal conversion efficiency. A physical mechanism model and semiempirical expression were presented to reveal the MPP and PTE mechanisms at different polarization angles. This tunable conversion between mechanisms indicates potential applications in tunable ultrafast optoelectronic devices.