57 research outputs found
Enhanced Group Delay of the Pulse Reflection with Graphene Surface Plasmon via Modified Otto Configuration
In this paper, the group delay of the transverse magnetic (TM) polarized wave reflected from a modified Otto configuration with graphene surface plasmon is investigated theoretically. The findings show that the optical group delay in this structure can be enhanced negatively and can be switched from negative to positive due to the excitation of surface plasmon by graphene. It is clear that the negative group delay can be actively tuned through the Fermi energy of the graphene. Furthermore, the delay properties can also be manipulated by changing either the relaxation time of graphene or the distance between the coupling prism and the graphene. These tunable delay characteristics are promising for fabricating grapheme-based optical delay devices and other applications in the terahertz regime
Self-Retracting Motion of Graphite Microflakes
We report the observation of a novel phenomenon, the self-retracting motion
of graphite, in which tiny flakes of graphite, after being displaced to various
suspended positions from islands of highly orientated pyrolytic graphite,
retract back onto the islands under no external influences. Our repeated
probing and observing such flakes of various sizes indicate the existence of a
critical size of flakes, approximately 35 micrometer, above which the
self-retracting motion does not occur under the operation. This helps to
explain the fact that the self-retracting motion of graphite has not been
reported, because samples of natural graphite are typical larger than this
critical size. In fact, reports of this phenomenon have not been found in the
literature for single crystals of any kinds. A model that includes the static
and dynamic shear strengths, the van der Waals interaction force, and the edge
dangling bond interaction effect, was used to explain the observed phenomenon.
These findings may conduce to create nano-electromechanical systems with a wide
range of mechanical operating frequency from mega to giga hertzs
EZSpice
Cooking spices are crucial and necessary in our daily life. Without various spices, chefs as well as home cooks are unable to create multiple delicious dishes. Storing and looking for different types of spices in our kitchen is a headache, especially for those that are not frequently used. EZSpice was developed to solve this issue. EZSpice is an intelligent machine for the kitchen. EZSpice will dispense the desired spice with precise quantity for the consumer while they are cooking, using voice control and touch screen control.
With a simple greeting sentence “Hey EZSpice” or touching the screen, our intelligent spice dispensing machine will start serving you. With the voice commands from users, EZSpice will deliver the correct spice with the requested quantity. Given enough time of development, we believe that EZSpice will provide a convenient and affordable spice dispensing machine to the market
Optical bulk-boundary dichotomy in a quantum spin Hall insulator
The bulk-boundary correspondence is a key concept in topological quantum
materials. For instance, a quantum spin Hall insulator features a bulk
insulating gap with gapless helical boundary states protected by the underlying
Z2 topology. However, the bulk-boundary dichotomy and distinction are rarely
explored in optical experiments, which can provide unique information about
topological charge carriers beyond transport and electronic spectroscopy
techniques. Here, we utilize mid-infrared absorption micro-spectroscopy and
pump-probe micro-spectroscopy to elucidate the bulk-boundary optical responses
of Bi4Br4, a recently discovered room-temperature quantum spin Hall insulator.
Benefiting from the low energy of infrared photons and the high spatial
resolution, we unambiguously resolve a strong absorption from the boundary
states while the bulk absorption is suppressed by its insulating gap. Moreover,
the boundary absorption exhibits a strong polarization anisotropy, consistent
with the one-dimensional nature of the topological boundary states. Our
infrared pump-probe microscopy further measures a substantially increased
carrier lifetime for the boundary states, which reaches one nanosecond scale.
The nanosecond lifetime is about one to two orders longer than that of most
topological materials and can be attributed to the linear dispersion nature of
the helical boundary states. Our findings demonstrate the optical bulk-boundary
dichotomy in a topological material and provide a proof-of-principal
methodology for studying topological optoelectronics.Comment: 26 pages, 4 figure
Real-time Monitoring for the Next Core-Collapse Supernova in JUNO
Core-collapse supernova (CCSN) is one of the most energetic astrophysical
events in the Universe. The early and prompt detection of neutrinos before
(pre-SN) and during the SN burst is a unique opportunity to realize the
multi-messenger observation of the CCSN events. In this work, we describe the
monitoring concept and present the sensitivity of the system to the pre-SN and
SN neutrinos at the Jiangmen Underground Neutrino Observatory (JUNO), which is
a 20 kton liquid scintillator detector under construction in South China. The
real-time monitoring system is designed with both the prompt monitors on the
electronic board and online monitors at the data acquisition stage, in order to
ensure both the alert speed and alert coverage of progenitor stars. By assuming
a false alert rate of 1 per year, this monitoring system can be sensitive to
the pre-SN neutrinos up to the distance of about 1.6 (0.9) kpc and SN neutrinos
up to about 370 (360) kpc for a progenitor mass of 30 for the case
of normal (inverted) mass ordering. The pointing ability of the CCSN is
evaluated by using the accumulated event anisotropy of the inverse beta decay
interactions from pre-SN or SN neutrinos, which, along with the early alert,
can play important roles for the followup multi-messenger observations of the
next Galactic or nearby extragalactic CCSN.Comment: 24 pages, 9 figure
Real-time observation of vibrational quantum beat in condensed phase by 20 fs time-resolved spectroscopy
Interfacial electron transfer between Fe(II)(CN)<sub>6</sub><sup>4-</sup> and TiO<sub>2</sub> nanoparticles: direct electron injection and nonexponential recombination
Photoinduced electron-transfer (ET) dynamics in Fe(II)(CN)64- sensitized TiO2 nanoparticles in D2O solution are studied by subpicosecond tunable laser spectroscopy in the mid-infrared and visible region. The dynamics of the injected electrons are monitored by the mid-IR absorption of electrons in the semiconductor, and the corresponding dynamics of the adsorbate are monitored by the vibrational spectra of the CN stretching mode region and electronic absorption in the visible. After 400 nm excitation, the forward electron injection time from Fe(II)(CN)64- to TiO2 occurs in <50 fs, indicating a direct photoinduced charge-transfer process. The back ET from TiO2 to Fe(III)(CN)63- in the <1 ns time scale is found to be a non-single-exponential process. The best three-exponential fit to the data yields back ET time constants of 3 ps (35%), 40 ps (30%), and >1 ns (35%). Combining with previous measurements in the nanosecond to microsecond time scale (Lu et al. J. Am. Chem. Soc. 1993, 115, 4927 and Vrachnou et al. J. Chem. Soc., Chem. Commun. 1987, 868), the total back ET process is found to be highly nonexponential with time constants ranging from 3 ps to 3 ÎĽs
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