Controlling Three Laser-Excited Coherent Phonon Modes
in Boron Nitride Nanotubes To Produce Ultrashort Shaped Terahertz
Pulses: Implications for Memory Devices
posted on 2018-11-09, 00:00authored byBernd Bauerhenne, Eeuwe S. Zijlstra, Alan Kalitsov, Martin E. Garcia
The
excitation of lattice vibrations by ultrafast laser pulses
provides a tool to steer atomic-scale motions beyond usual thermodynamic
limitations. We simulate this process in armchair, chiral, and zigzag
boron nitride nanotubes (BNNTs). In particular, for ultrathin zigzag-type
tubes we show that three vibrational modes can be displacively excited.
Since the boron nitride bonds are polar, the three coherent phonon
oscillations emit terahertz (THz) radiation. In this work we focus
on the (5,0) zigzag BNNT, which is the thinnest stable one, and demonstrate,
by means of ab initio molecular dynamics simulations and optimization
algorithms, that the relative amplitudes of the three phonon modes
and therefore the corresponding shape of the emitted THz short pulse
can be controlled by laser-pulse trains. Our work could serve as a
basis for experimental studies using the coherent vibrations of BNNTs
as optical memory devices in nanophononics, since information could
be written in the phononic system by several femtosecond laser pulses
and could be read out by measuring the produced THz emission.