156 research outputs found
Ultrafast polariton population build-up mediated by molecular phonons in organic microcavities
No full textA key prerequisite for low-threshold polariton lasing in organic or inorganic microcavity systems is the efficient population of the lower polariton ground state. Here, we report the observation of a resonant phonon-mediated relaxation process which gives rise to nonthermal polariton population with sub 100 fs build-up times. This mechanism is manifested by discrete maxima of the angular-resolved photoluminescence intensity, with corresponding shortening of the photoluminescence rise time at respective phonon resonances. The realization of enhanced relaxation rates in disordered J-aggregate systems is important for developing room temperature organic laser sources with less fabrication complexity than their crystalline counterparts
Phonon-driven resonantly-enhanced polariton luminescence in organic microcavities
No full textCharacteristic low-threshold polariton lasing of organic and inorganic microcavity systems can only be achieved with efficient population of the lower polariton ground state. In this regard, the key role undertaken by vibronic replicas and molecular phonon it has been shown experimentally and theoretically predicted by various works. We report here, direct observation of critical enhancement of polariton population density in strongly coupled J-aggregate based organic microcavities. The process highlighted in our study is manifested by discrete maxima of the angular-resolved photoluminescence intensity and interpreted by the mediation of molecular vibrations quanta characteristic of the active material. By measuring the reduced time scale of vibrations driven relaxation dynamics, manifested by sub 100fs buildup times, we emphasized the efficiency of the mechanism to overcome losses channel in disordered J-aggregate systems. Hence, the realization of amplified polariton population with improved relaxation rates paves the way for the observation of low threshold lasing, primary step for developing room temperature organic laser sources and ultra-fast optoelectronic devices with less fabrication complexity than their crystalline counterparts
I potenziali oscillatori dell'ERG fotopico in pazienti con epilessia trattati con Vigabatrin.
No full textVisualization and quantum control of light-accelerated condensates by terahertz multi-dimensional coherent spectroscopy
No full textCharacterizing and controlling high-order correlation of quantum systems is key for developing quantum devices and switching technologies. Although conventional static and ultrafast spectroscopy gives access to collective excitations characterizing quantum states, more exotic correlations cannot be easily separated from other contributions. Here we develop density matrix simulations to show that seventh-order-wave-mixing peaks with distinct temperature and field dependences in two-dimensional terahertz nonlinear spectra reveal light-induced correlations in non-equilibrium superconducting states. Above critical terahertz driving, these emerging peaks split from conventional peaks along the second axis introduced by pump-probe relative phase in two-dimensional frequency space. They are photo-generated by correlations between two-photon fluctuations and interacting quasi-particle and quasi-particle/Higgs superconductor excitations. By photo-inducing persistent symmetry breaking via light-wave propagation, we also demonstrate seventh-order-wave-mixing sensing of Higgs collective modes. Our theory suggests to use multi-dimensional spectroscopy for quantum sensing of light-driven superconductivity and paves a path for quantum operations by few-cycle-THz-periodic photocurrent modulation.This article is published as Mootz, Martin, Liang Luo, Jigang Wang, and llias E. Perakis. "Visualization and quantum control of light-accelerated condensates by terahertz multi-dimensional coherent spectroscopy." Communications Physics 5, no. 1 (2022): 47.
DOI: 10.1038/s42005-022-00822-5.
Copyright 2022 The Author(s).
Attribution 4.0 International (CC BY 4.0).
Posted with permission.
DOE Contract Number(s): AC02-07CH11358; SC0019137; AC02-07CH11358
Ultrafast bipolar conductivity driven by intense single-cycle terahertz pulses in a topological insulator Bi2Se3
No full textWe present the measurement of ultrafast terahertz (THz) conductivity of a 50 nm thick topological insulator Bi2Se3 at low temperature 5 K by using a THz pump and THz probe spectroscopy scheme. The THz conductivity driven by a single-cycle intense THz pump exhibits a bipolar lineshape and frequency-dependent relaxation dynamics due to the separated surface and bulk charge carriers with distinctly different scattering rates and relaxation times. We also demonstrate THz pump field-dependent excitation of the surface and bulk spectral weights, which suggests one of the optimal THz excitation conditions for generating the most charge carriers from the topology-protected surface state relative to the bulk. This also allows THz control of surface and bulk transport channels in a selective way.This is a manuscript of an article published as Luo, L., X. Yang, C. Vaswani, X. Liu, I. E. Perakis, M. Dobrowolska, J. K. Furdyna, and J. Wang. "Ultrafast bipolar conductivity driven by intense single-cycle terahertz pulses in a topological insulator Bi2Se3." Journal of Optics 23, no. 10 (2021): 104003.
DOI: 10.1088/2040-8986/ac0316.
Copyright 2021 IOP Publishing Ltd.
DOE Contract Number(s): AC02-07CH11358; SC0019137.
Posted with permission
On Certain Indices for Ordinal Data with Unequally Weighted Classes
No full textIn this paper, some new indices for ordinal data are introduced. These indices have been developed so as to measure the degree of concentration on the “small” or the “large” values of a variable whose level of measurement is ordinal. Their advantage in relation to other approaches is that they ascribe unequal weights to each class of values. Although, they constitute a useful tool in various fields of applications, the focus here is on their use in sample surveys and specifically in situations where one is interested in taking into account the “distance” of the responses from the “neutral” category in a given question. The properties of these indices are examined and methods for constructing confidence intervals for their actual values are discussed. The performance of these methods is evaluated through an extensive simulation study.
A feasibility study for the provision of electronic healthcare tools and services in areas of Greece, Cyprus and Italy
No full textBackground:
Through this paper, we present the initial steps for the creation of an integrated platform for the provision of a series of eHealth tools and services to both citizens and travelers in isolated areas of thesoutheast Mediterranean, and on board ships travelling across it. The platform was created through an INTERREG IIIB ARCHIMED project called INTERMED.
Methods:
The support of primary healthcare, home care and the continuous education of physicians are the three major issues that the proposed platform is trying to facilitate. The proposed system is based on state-of-the-art telemedicine systems and is able to provide the following healthcare services: i) Telecollaboration and teleconsultation services between remotely located healthcare providers, ii) telemedicine services in emergencies, iii) home telecare services for "at risk" citizens such as the elderly and patients with chronic diseases, and iv) eLearning services for the continuous training through seminars of both healthcare personnel (physicians, nurses etc) and persons supporting "at risk" citizens.
These systems support data transmission over simple phone lines, internet connections, integrated services digital network/digital subscriber lines, satellite links, mobile networks (GPRS/3G), and wireless local area networks. The data corresponds, among others, to voice, vital biosignals, still medical images, video, and data used by eLearning applications. The proposed platform comprises several systems, each supporting different services. These were integrated using a common data storage and exchange scheme in order to achieve system interoperability in terms of software, language and national characteristics.
Results:
The platform has been installed and evaluated in different rural and urban sites in Greece, Cyprus and Italy. The evaluation was mainly related to technical issues and user satisfaction. The selected sites are, among others, rural health centers, ambulances, homes of "at-risk" citizens, and a ferry.
Conclusions:
The results proved the functionality and utilization of the platform in various rural places in Greece, Cyprus and Italy. However, further actions are needed to enable the local healthcare systems and the different population groups to be familiarized with, and use in their everyday lives, mature technological solutions for the provision of healthcare services
Critical speeding up of nonequilibrium electronic relaxation near nematic phase transition in unstrained Ba(Fe1-xCox)(2)As-2
No full textThe origin of the anisotropic, paramagnetic phase associated with electronic nematicity in the iron pnictides is yet to be resolved. Furthermore, the detwinning technique used to study the nematic order in single crystals is known to introduce extra anisotropy into the sample, which can smear out the transition and even modify intrinsic characteristics associated with “spontaneous” Ising, Z2, symmetry breaking. Here we use a strain- and stress-free twinned sample to show that there is a significant reduction in the energy relaxation times of the hot electrons following nonequilibrium femtosecond laser excitation on both the high- and low-temperature sides of the nematic phase transition. This femtosecond critical speeding-up behavior provides an alternative way to study complex, electronically driven nematicity, neither invoking external strain nor measuring a small anisotropy in twinned crystals. Particularly, a detailed analysis of the observed ultrafast decay time and the amplitude associated with an initial electronic relaxation provides compelling implications on the physical origin of nematicity in iron pnictides: (1) nematic fluctuations strongly influence the dynamics of electron cooling, and (2) spin fluctuations determine the part of amplitude arising from the nematicity. Finally, we discuss ultrafast coherent phonon generation which may contribute to the measured transition temperature in our ultrafast measurements.This article is published as Patz, A., T. Li, L. Luo, X. Yang, S. Bud'ko, P. C. Canfield, I. E. Perakis, and J. Wang. "Critical speeding up of nonequilibrium electronic relaxation near nematic phase transition in unstrained Ba (Fe 1− x Co x) 2 As 2." Physical Review B 95, no. 16 (2017): 165122. DOI: 10.1103/PhysRevB.95.165122. Posted with permission.</p
The Ising Model in a Transverse Magnetic Field: a Test-Bed for Many-Body Theories
No full textedited by D.J. Ernst, (Nova Science, Publ. Commack, New York, 2000)
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