Transcript The orbital characters of bands in BaFe1.85Co0.15As2

Room temperature polariton degenerate four wave mixing
oscillation by non-resonant excitation
Wei Xie, Liaoxin Sun, Hongxing Dong, Yanjing Ling, Jian Lu, Qiju Ren, Weihang Zhou, Saifeng Zhang, Xuechu Shen, Zhanghai Chen
Surface Physics Laboratory, Department of Physics, Fudan University, Shanghai 200433, P.R.China
Abstract
Using a laser beam to pump non-resonantly, polarition degenerate four wave mixing (DFWM) oscillation is reported in ZnO
one-dimensional whispering gallery microcavities at room temperature. We observe a directional elastic scattering of two cavity
polaritons above the threshold of DFWM effect in our system. The intensity of DFWM signal has a nonlinear increase when the
pump power is enhanced. We use rate equations to describe the evolution of the parametric scattering process and the theoretical
calculation agrees well with the experiment results.
Experiment and Discussion
FIG. 2. Room temperature
PL of the microwire for TE
and TM polarizations. The
emission intensity is color
scaled and increases from
black to yellow.
(a) PL in the (kYZ, energy)
dispersion plane. The dashed
and solid lines represent the
calculated dispersion of bare
cavity modes and excitons
respectively. The dotted lines
represent the polariton modes.
(b) PL in the (kXY, energy)
dispersion plane.
FIG. 1. (a) Scanning Electron Microscope (SEM) image of the typical
ZnO micro-rod. k is the wave vector of the emission photoluminescence
and the c-axis is the crystallographic axis of wurtzite ZnO rod.
(b) Angle-resolved micro-photoluminescence spectrum system
configuration.
FIG. 3. (a)(b) Room temperature polariton angleresolved PL spectrum in the one-dimensional ZnO
WG cavity by non-resonant excitation. The emission
intensity is color scaled in logarithm. (a) Polariton
lasing of both TE polarized excitation and emission.
(b) TE polarized emission of polariton DFWM effect
under TM (left) and TE (right) excitation, with the
excitation power higher than the lasing threshold.
Owing to the non-resonant excitation mechanism,
either TE or TM polarized excitation laser can induce
the DFWM oscillation in our system. (c) Sketch of the
Polariton DFWM effect. There are lower polariton
energy E versus the wave vector along c-axis k// and
the parametric polariton-polariton scattering process,
{(E, ko)N+1, (E, -ko)N+1}→{(E, k())N, (E, k(-))N}.
FIG. 4. (a) The process of the polariton DFWM effect
under four different excitation powers. The experimental
condition (except the excitation power) is the same as the left
one in fig. 3(b). The first two excitation powers are smaller
than the threshold of the polariton DFWM oscillation, while
the last two powers are above it. The open white circles B, B'
represent the right positions of directional parametric
scattering, and A, A', C, C' are the neighboring positions of
normal elastic scattering.
(b)(c)(d) The threshold phenomenon of the parametric
gain. (b) The centre intensity of the scattering source Io
dependence of the scattering intensity at position B (blue
circles) and B' (brown stars). (c) The scattering probability at
positions A, B, C VS the centre intensity of the scattering
source Io. From the different variation tendencies at positions
A, B (or C, B), it's easy to make a distinction between the
DFWM effect and normal elastic scattering in polaritons. (d)
is similar with (c).
Conclusion
References
We have observed one dimensional exciton-polariton dispersion and its condensation
when increasing pump power to the threshold in ZnO micro-rod at room temperature.
Polarition DFWM oscillation is presented when further increasing the pump power.
Our work will contribute to the further research on polariton dynamics and the
developing of novel polariton based devices.
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