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3Emission of energetic electrons from a nanotip under combined exposure to intense terahertz and femtosecond laser fields
S.B. Bodrov, A.A. Murzanev, A.V. Romashkin, A.N. Stepanov*, A.E. Fedotov
Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia
The creation of short-pulse point sources of electrons with an energy of several keV is of interest for a wide range of problems: from the creation of bunches of seed electrons for free electron lasers to projection electron microscopes with high time resolution. In this work, to solve this problem, we used an approach based on irradiation of a submicron metal tip with a combination of femtosecond laser and picosecond terahertz radiation.
A polycrystalline tungsten needle with a radius of curvature of the tip rtip = 170 nm was placed on a three-coordinate motorized stage in a vacuum chamber (p ~ 5-10-5 Torr) and irradiated with focused femtosecond laser (t = 100 fs, F = 10 Hz, intensity up to 3*1012 W/cm2) and terahertz (tthz ~1 ps, Emax ~ 300 kV/cm) pulses with field polarization directed along the needle axis. Electrons emitted from the needle were recorded using a microchannel plate.
Figure 1 presents experimentally obtained results on the efficiency of electron emission at different laser radiation intensities depending on terahertz fields. The results presented show that adding optical radiation to the THz field significantly increases the emission efficiency especially in low THz field region. Note that the maximum emitted charge of the electron bunch was several picoculombs, similar to work [1]. By placing the grid in front of the MCP and applying an adjustable negative voltage to it, measurements were taken of the energy distribution function of electrons emitted from the needle. It was shown that the maximum electron energy increases linearly with increasing terahertz field (Fig. 2), reaching 3 keV at the maximum THz fields used.
Thus, the experimental studies performed indicate that a submicron metal needle irradiated with femtosecond optical and THz pulses can be a point source of short electron bunches with a charge of the pico-coulomb level and an electron energy of several kiloelectronvolts.
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Fig. 1. Electron emission as a function of THz field, optical energies are presented in the inset. Fig. 2. Dependence of the maximum energy of emitted electrons on the amplitude of the THz field.
The study was supported by a grant from the Russian Science Foundation № 24-62-00032, https://rscf.ru/project/24-62-00032/
[1] N.A. Abramovsky, S.B. Bodrov, A.M. Kiselev, A.A. Murzanev, A.V. Romashkin, A.N. Stepanov, Generation of electron bunches of the picoculomb level from a metal needle under the influence of femtosecond radiation from a titanium-sapphire laser, High Temperature, 58,
938-941, (2020).
