Ultrafast near infrared laser-induced field emission

Ultrafast electron pulses can be produced from sharp metallic tips illuminated by femtosecond near infrared laser pulses [1-3]; generation of ~5 pC from 120k-tip single-gate molybdenum FEA with 5 um pitch emitters by near infrared laser pulses was demonstrated recently, showing that the use of an array of metallic nanotips for high charge bunch generation and accelerator applications is also feasible but the small fraction of the emitter tip area limits the quantum efficiency. In a recent work, we are developing a submicron-pitch, high-density nanotip array device with a gate electrode [4-6], that can support surface-plasmon polaritons. From a theoretical analysis for a device with an asymmetric emitter position, a factor ~30 increased array quantum efficiency, within a factor of 60 in comparison with the UV-excited Copper photocathode, is demonstrated [4].

Figure 1. Laser-induced field emission experiment
Fig.1 Laser-induced field emission experiment
Fig.2 Laser intensity dependence of generated electron bunch charge
Fig.2 Laser intensity dependence of generated electron bunch charge
Fig.3 Enhancement of optical electic field at the metallic nano-tip: simulation
Fig.3 Enhancement of optical electic field at the metallic nano-tip: simulation
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We further investigated theoretically the laser-induced field emission from stacked-double gate devices, to explore the potential of such system to generate collimated field emission beams [4,7]. Using electromagnetic and particle tracking simulations, we showed that electron pulses with small rms transverse velocities are eciently produced from nanotip arrays by laser-induced field emission with the laser wavelength tuned to surface plasmon polariton resonance of the stacked double-gate structure. The result indicates the possibility of realizing a metal nanotip array cathode that outperforms state-of-the-art photocathodes.

Fig.4 Generation of collimated electron beams by near infrared laser-induced field emission from metallic nano-tip arrays: resonant enhancement of the laser-tip interaction via surface plasmon polariton resonance and collimation of the field emission beams by the on-chip stacked double-gate structure[4,7]
Fig.4 Generation of collimated electron beams by near infrared laser-induced field emission from metallic nano-tip arrays: resonant enhancement of the laser-tip interaction via surface plasmon polariton resonance and collimation of the field emission beams by the on-chip stacked double-gate structure[4,7]

[1] S. Tsujino, P. Beaud, E. Kirk, T. Vogel, H. Sehr, J. Gobrecht, and A. Wrulich Ultrafast electron emission from metallic nanotip arrays induced by near infrared femtosecond laser pulses, Appl. Phys. Lett. 92, 193501 (2008); Selected in Virtual Journal of Ultrafast Science -- June 2008, Volume 7, Issue 6. 

[2] S. Tsujino, F. le Pimpec, J. Raabe, M. Buess, M. Dehler, E. Kirk, J. Gobrecht, and A. Wrulich, Static and optical field enhancement in metallic nanotips studied by two-photon photoemission microscopy and spectroscopy excited by picosecond laser pulses, Appl. Phys. Lett. 94, 093508 (2009); Selected for the March 16, 2009 issue of Virtual Journal of Nanoscale Science & Technology; Selected for April 2009 issue (Volume 8, Issue 4) of Virtual Journal of Ultrafast Science. 

[3] A. Mustonen, P. Beaud, E. Kirk, T. Feurer, and S. Tsujino, Five picocoulomb electron bunch generation by ultrafast laser-induced field emission from metallic nano-tip arrays, Appl. Phys. Lett. 99, 103504 (2011); Selected for September 19, 2011 issue (Volume 24, Issue 12) of Virtual Journal of Nanoscale Science & Technology; Selected for October 2011 issue (Volume 10, Issue 10) of Virtual Journal of Ultrafast Science; highlighted in Nature Photonics, 5, 644-645 (November 2011). 

[4] A. Mustonen, P. Beaud, E. Kirk, T. Feurer, and S. Tsujino, Efficient light coupling for optically excited high-density metallic nanotip arrays, Scientific Reports, 2, 915 (2012). 

[5] A. Mustonen, V. Guzenko, C. Spreu, T. Feurer, and S. Tsujino, High-density metallic nano-emitter arrays and their field emission characteristics, Nanotechnology 25, 085203 (2014). 

[6] V. Guzenko, A. Mustonen, P. Helfenstein, E. Kirk, and S. Tsujino, High-density large-scale field emitter arrays for X-ray free electron laser cathodes, Microelectronic Engineering (2013). 

[7] P. Helfenstein, A. Mustonen, T. Feurer, and S. Tsujino, Collimated Field Emission Beams from Metal Double-Gate Nanotip Arrays Optically Excited via Surface Plasmon Resonance, Applied Physics Express 6, 114301 (2013). .