The surprising recent
observation of highly emissive triplet-states
in lead halide perovskites accounts for their orders-of-magnitude
brighter optical signals and high quantum efficiencies compared to
other semiconductors. This makes them attractive for future optoelectronic
applications, especially in bright low-threshold nanolasers. While
nonresonantly pumped lasing from all-inorganic lead-halide perovskites
is now well-established as an attractive pathway to scalable low-power
laser sources for nano-optoelectronics, here we showcase a resonant
optical pumping scheme on a fast triplet-state in CsPbBr
3
nanocrystals. The scheme allows us to realize a polarized triplet-laser
source that dramatically enhances the coherent signal by 1 order of
magnitude while suppressing noncoherent contributions. The result
is a source with highly attractive technological characteristics,
including a bright and polarized signal and a high stimulated-to-spontaneous
emission signal contrast that can be filtered to enhance spectral
purity. The emission is generated by pumping selectively on a weakly
confined excitonic state with a Bohr radius ∼10 nm in the nanocrystals.
The exciton fine-structure is revealed by the energy-splitting resulting
from confinement in nanocrystals with tetragonal symmetry. We use
a linear polarizer to resolve 2-fold nondegenerate sublevels in the
triplet exciton and use photoluminescence excitation spectroscopy
to determine the energy of the state before pumping it resonantly.
The honeycomb phononic crystal displays good performance in reducing vibration, especially at low frequency, but there are few corresponding experiments involving this kind of phononic crystal and the influence of geometric parameters on the bandgap is unclear. We design a honeycomb phononic crystal, which is assembled by using a chemigum plate and a steel column, calculate the bandgaps of the phononic crystal, and analyze the vibration modes. In the experiment, we attach a same-sized rubber plate and a phononic crystal to a steel plate separately in order to compare their vibration reduction performances. We use 8×8 unit cells as a complete phononic crystal plate to imitate an infinite period structure and choose a string suspension arrangement to support the experiment. The results show that the honeycomb phononic crystal can reduce the vibrating plate magnitude by up to 60 dB in a frequency range of 600 Hz-900 Hz, while the rubber plate can reduce only about 20 dB. In addition, we study the effect of the thickness of plate and the height and the radius of the column in order to choose the most superior parameters to achieve low frequency and wide bandgap.
Our work investigates a tunable multilayer composite structure for applications in the area of low-frequency absorption. This acoustic device is comprised of three layers, Helmholtz cavity layer, microperforated panel layer, and the porous material layer. For the simulation and experiment in our research, the absorber can fulfill a twofold requirement: the acoustic absorption coefficient can reach near 0.8 in very low frequency (400 Hz) and the range of frequency is very wide (400–3000 Hz). In all its absorption frequency, the average of the acoustic absorption coefficient is over 0.9. Besides, the absorption coefficient can be tunable by the scalable cavity. The multilayer composite structure in our article solved the disadvantages in single material. For example, small absorption coefficient in low frequency in traditional material such as microperforated panel and porous material and narrow reduction frequency range in acoustic metamaterial such as Helmholtz cavity. The design of the composite structure in our article can have more wide application than single material. It can also give us a novel idea to produce new acoustic devices.
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