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Master thesis

Ultrafast electron dynamics in nano-objects

Electrons are particles, but they also behave like a wave. The electron waves are “coherently” extended in a metal on a scale of tens of femtoseconds and nanometers. Our main goals are to temporally and spatially control these coherent electron waves in nano-objects, and thus to sow the seeds for future ultrafast quantum devices.

During the last decade, we have been working on investigating laser-induced electron emission from a metallic tip with nanometer sharpness (we call it a nanotip). Applying strong DC fields on the nanotip drives electron emission from its apex, which is called a field emission. Since the emitted electrons are propagating radially, one can magnify nanoscopic information to the macroscopic scale, and display them on a two-dimensional detector. This field emission microscopy, as it’s called, is one of our main tools. Illuminating such a metallic nanotip with femtosecond laser pulses creates nano-sized optical electric fields at the tip apex, and induces ultrafast field emission from the apex. By varying the laser polarization with respect to the tip axis, the spatial distribution of the nano-optical fields on the tip apex can be changed, and subsequently their emission sites [1]. The animation shows an example of a laser-induced field emission from a tungsten nanotip in laser fields with rotating polarization. In effect, we can achieve an ultrafast pulsed coherent electron source with emission site selectivity on a scale of ten nanometers [1]. Using this technique, we can manipulate electron emissions within their coherence time and area, which then enables us to control coherent electron emission in time and space. In a demonstration, we realized optical control of Young’s electron interference [2]. The underlying electron dynamics is on a scale of femtoseconds. By using an electron energy analyzer, those electron dynamics in a tungsten tip have been revealed over a wide range of optical fields [3-5].

We would like to develop a technique for spatio-temporal optical control of coherent electron waves. At present, we are envisioning multiple projects. These projects are briefly listed below.

  1. Ultrafast electron dynamics in a low-dimensional nano-objects (Tukuba University)
  2. Optical control of coherent electron waves (Tokyo University)
  3. Optical control of quantum entanglement (Tokyo University)
  4. Development of an ultrafast spin switch (Hong Kong University of Sci. and Tech.)
  5. Development of atomic resolution field emission microscopy (NAIST)
  6. Ultrafast molecular dynamics (CERN and Helsinki University)

We also have active collaborations with researchers in multiple disciplines (shown in the round brackets) and can provide you opportunities to visit some foreign countries.

If you are interested in our projects and would like to hear more details, please contact:

Dr. Hirofumi Yanagisawa, DFG project leader,

(office: w132, Am Coulombwall 1, 85748 Garching)

hirofumi.yanagisawa@mpq.mpg.de

Office Phone: 08928914110

References:
[1] Hirofumi Yanagisawa et al., Phys. Rev. Lett. 103, 257603 (2009)

[2] Hirofumi Yanagisawa et al., Sci. Rep. 7:12661 (2017)

[3] Hirofumi Yanagisawa et al., Phys. Rev. Lett. 107, 087601 (2011)

[4] Hirofumi Yanagisawa et al., Sci. Rep. 6:35877 (2016)

[5] Hirofumi Yanagisawa et al., APL Photonics 1, 091305 (2016).

24th November 2017

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