The mechanisms through which electrons are ejected from atoms (or molecules) and subsequently driven to high-energies in a strong oscillating electric field are generally well understood, enabling a variety of techniques from attosecond pulse generation to imaging via time-resolved electron scattering. Analogous processes are at play in strong-field emission and acceleration of electrons from solids and, for nano-scale targets, brief electron bursts from particles with dimensions much less than the wavelength of the drive field hold great promise for ultrafast imaging and other applications. For long wavelength drivers, the enhanced local field near nano-particles or nano-tips can fundamentally change the energy transfer process and allow for the creation of very high energy electrons. As an extreme example of the long-wavelength limit, we have used intense single-cycle THz pulses to drive electron emission from unbiased, nano-tipped tungsten wires. Energies easily exceeding 5 keV are observed, substantially greater than those previously attained at higher THz and infrared frequencies. The large electron energies reflect electric field enhancement factors as large as 3000 in the vicinity of the sharpest tips. Despite large differences in the magnitude of the respective local fields, we find that the maximum electron energies are only weakly dependent on the tip radius, for 10nm < R < 1μm. Due to the single-cycle nature of the field, the high-energy electron emission should be confined to a single burst, potentially enabling applications in ultrafast imaging.
Robert R. Jones and Sha Li, "High-energy electron emission from THz-irradiated nano-tips (Conference Presentation)," Proc. SPIE 10530, Ultrafast Phenomena and Nanophotonics XXII, 105300A (Presented at SPIE OPTO: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2292915.5751516118001.
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