Spatial Coherence and Stability in a Disordered Organic Polariton Condensate.

Long-range spatial coherence can be induced in incoherent thermal emitters by embedding a periodic grating within a material supporting propagating polaritons or dielectric modes. However, only a single spatially coherent mode is supported by purely periodic thermal emitters. While various designs have been proposed for the purpose of allowing arbitrary emission profiles, the limitations associated with the partial spatial coherence of thermal emitters are not known. Here, we explore superstructure gratings (SSGs) to control the spatial and spectral properties of thermal emitters. SSGs have long-range periodicity but employ a unit cell that provides multiple Bragg vectors to interact with light. These Bragg vectors allow simultaneous launching of polaritons with different frequencies/wavevectors in a single grating, manifesting as additional spatial and spectral modes in the thermal emission profile. However, SSGs still have a well-defined period, which allows us to assess the role that finite spatial coherence plays in thermal emitters. We find that the spatial coherence length defines the maximum possible SSG period that can be used. This provides a fundamental limit on the degree of spatial coherence that can be induced in a thermal emitter and has broader implications for the use of techniques such as inverse design for structure optimization.

Coherent light sources have been demonstrated based on a wide range of nanostructures, however, little effort has been devoted to probing their underlying coherence properties. Here, we report long-range spatial coherence of lattice plasmon lasers constructed from a periodic array of gold nanoparticles and a liquid gain medium at room temperature. By combining spatial and temporal interferometry, we demonstrate millimeter-scale (∼1 mm) spatial coherence and picosecond (∼2 ps) temporal coherence. The long-range spatial coherence occurs even without the presence of strong coupling with the lattice plasmon mode extending over macroscopic distances in the lasing regime. This plasmonic lasing system thus provides a platform for understanding the emergence of long-range coherence from collections of nanoscale resonators and points toward novel types of distributed lasing sources.

Scattering from small, random inhomogeneities in the ground (such as rocks and voids) diminishes the spatial coherence of seismic waves, much as turbulence in the atmosphere diminishes spatial coherence of propagating sound waves. In this paper, modeling of seismic spatial coherence for surface waves propagating over short distances (roughly 50 m to 1 km) and at relatively high frequencies (greater than approximately 1 Hz) is considered. The random inhomogeneities are distributed broadly in size and are described with a quasi‐wavelet (QW) model. For simplicity, we consider propagation of a 2‐D scalar wavefield. Scattering from an individual QW is first calculated using a single‐scattering approximation. Then, the contributions from all randomly placed QWs, including all size classes, are cross‐correlated to find the spatial coherence of the total wavefield. As an example, we consider modeling of seismic coherence at a site in the Mojave Desert with random basaltic inhomogeneities surrounded by sand. The impact of coherence loss on direction‐finding with geophone arrays is discussed.

Research in microfabrication is important to many areas of science and technology. An emerging set of microlithographic techniques, known as soft lithography, uses elastomeric elements for microcontact printing (μCP), molding, or near field photolithography. We describe the use of two soft lithographic techniques to build DFB lasers with narrow emission linewidths. This demonstrates the suitability of soft lithography for building structures that have (i) feature sizes (∼300 nm) significantly less than 1 μm, and (ii) long-range (∼1 mm) spatial coherence. The lasers use optically pumped gain material deposited on a DFB resonator formed from periodic relief on the surface of a transparent substrate. The required relief was generated on glass and polymer surfaces with μCP and replica molding respectively. μCP produced lines of gold on a glass slide; RIE using the gold as a resist generated periodic relief (600 nm period, 50 nm depth) on the glass surface. Polymer gratings with similar dimensions were formed by curing a polyurethane film against an elastomeric mold. The good performance of the lasers suggest the potential utility of soft lithographic techniques for low-cost fabrication of high-performance optoelectronic devices. Other types of resonators, including distributed Bragg reflector and quasi two-dimensional photonic bandgap based resonators can also be fabricated with the techniques demonstrated here.

Spatial and temporal coherence of acoustic field has very important effects on applications of underwater acoustics. In this paper, recent experimental results of low‐frequency signal coherence in shallow water are presented. For signals with low frequencies of 100∼500Hz in shallow water, the vertical correlation has no distinct depth dependence, but it has obvious range dependence. The horizontal correlation length is greater than 40 wavelengths, the temporal correlation length is greater than 510s at frequency of 475Hz and greater than 1800s at frequency of 150Hz. These experimental results show that low‐frequency acoustic field has strong spatial coherence and temporal stability in shallow water. [Work supported by the National Natural Science Foundation of China under Grant No.10734100]

Real- and momentum-space spectrally resolved images of microcavity polariton emission in the regime of condensation are investigated under nonresonant excitation using a laser source with reduced intensity fluctuations on the time scale of the exciton lifetime. We observe that the polariton emission consists of many macroscopically occupied modes. Lower-energy modes are strongly localized by the spatial polaritonic potential disorder on a scale of a few microns. Higher-energy modes have finite k vectors and are delocalized over 10– 15 m. All the modes exhibit long-range spatial coherence comparable to their size. We provide a theoretical model describing the behavior of the system with the results of the simulations in good agreement with the experimental observations. We show that the multimode emission of the polariton condensate is a result of its nonequilibrium character, the interaction with the local polaritonic potential, and the reduced intensity fluctuations of the excitation laser.

Quasi-2D halide perovskites are chemically synthesized realizations of quantum well stacks with giant exciton oscillator strengths, tunable emission spectra, and very large exciton binding energies. While these features render quasi-2D halide perovskites a promising platform for room-temperature polaritonics, bosonic condensation and polariton lasing in quasi-2D perovskites have so far remained elusive at ambient conditions. Here, we demonstrate room-temperature cavity exciton-polariton condensation in mechanically exfoliated crystals of the quasi-2D Ruddlesden-Popper iodide perovskite (BA)2(MA)2Pb3I10 in an open optical microcavity. We observe a polariton condensation threshold of 0.41 µJ cm−2 per pulse and detect a strong non-linear response. Interferometric measurements confirm the spontaneous emergence of spatial coherence across the condensate with an associated first-order autocorrelation reaching 0.6 with 1 ps coherence time and an effective de Broglie wavelength of 13 µm. Our results lay the foundation for a new class of room-temperature polariton lasers based on quasi-2D halide perovskites with great potential for hetero-integration with other van-der-Waals materials and combination with photonic crystals or waveguides.

Super-continuum (SC) lasers combine the broadband attributes of lamps with the spatial coherence and high brightness of lasers. By exploiting a modulational instability (MI)-initiated SC mechanism, an all-fiber-integrated SC laser with no moving parts is demonstrated using commercial off-the-shelf components in a simple architecture. The dominant mechanism for the long-wavelength expansion of the SC is based on the Raman effect in the fiber. Since the Raman effect is self-phase matched, the long-wavelength edge of the SC spectrum can fill the transparency band of the SC generation fiber for sufficient fiber length and/or peak power. On the other hand, the short-wavelength edge of the SC can be determined by nonlinear processes such as four-wave mixing, which may require phase matching and appropriate group velocity dispersion.

Manipulating bosonic condensates with electric fields is very challenging as the electric fields do not directly interact with the neutral particles of the condensate. Here we demonstrate a simple electric method to tune the vorticity of exciton-polariton condensates in a strong coupling liquid crystal (LC) microcavity with CsPbBr_{3} microplates as active material at room temperature. In such a microcavity, the LC molecular director can be electrically modulated giving control over the polariton condensation in different modes. For isotropic nonresonant optical pumping we demonstrate the spontaneous formation of vortices with topological charges of +1, +2, -2, and -1. The topological vortex charge is controlled by a voltage in the range of 1 to 10V applied to the microcavity sample. This control is achieved by the interplay of a built-in potential gradient, the anisotropy of the optically active perovskite microplates, and the electrically controllable LC molecular director in our system with intentionally broken rotational symmetry. Besides the fundamental interest in the achieved electric polariton vortex control at room temperature, our work paves the way to micron-sized emitters with electric control over the emitted light's phase profile and quantized orbital angular momentum for information processing and integration into photonic circuits.

We analytically investigate the spatial coherence properties of the signal\nemission from one-dimensional optical parametric oscillators. Because of the\nreduced dimensionality, quantum fluctuations are able to destroy the long-range\nphase coherence even far above threshold. The spatial decay of coherence is\nexponential and, for realistic parameters of semiconductor photonic wires in\nthe strong exciton-photon coupling regime, it is predicted to occur on an\nexperimentally accessible length scale.\n

We employ a time-dependent mean-field-hydrodynamic model to study the generation of bright solitons in a degenerate fermion–fermion mixture in a cigar-shaped geometry using variational and numerical methods. Due to a strong Pauli-blocking repulsion among identical spin-polarized fermions at short distances there cannot be bright solitons for repulsive interspecies interactions. Employing a linear stability analysis we demonstrate the formation of stable solitons due to modulational instability of a constant-amplitude solution of the model equations for a sufficiently attractive interspecies interaction. We perform a numerical stability analysis of these solitons and also demonstrate the formation of soliton trains by jumping the effective interspecies interaction from repulsive to attractive. These fermionic solitons can be formed and studied in laboratory with present technology.

This paper reports experimental findings on the flow of sand down a steep chute. Nearly all granular flow models have a maximum value for the friction and therefore predict that flows on steep slopes will accelerate at a constant rate until the interaction with the ambient fluid becomes important. This prediction has not been tested by previous work, which has focused on relatively low slope angles where steady, fully developed flows occur after short distances. We test this by investigating flows over a much greater range of slope angles (30–50${}^{\ensuremath{\circ} } $) and flow depths (4–130 particle diameters). We examine flows with two basal conditions, one flat and frictional, the other bumpy. The latter imposes a no-slip condition for slow, deep flows, but permits some degree of slip for high flow velocities. The data suggests that friction can be much larger than theories such as the $\ensuremath{\mu} (I)$ rheology proposed by Jop, Forterre & Pouliquen (Nature, vol. 441, 2006) suggest and that there may be constant velocity states above the angle of vanishing ${h}_{\mathit{stop}} $. Although these flows do not vary in time, all but the flows on the bumpy base at low inclinations accelerate down the slope. A recirculation mechanism sustains flows with a maximum mass flux of $20~\mathrm{kg} ~{\mathrm{s} }^{\ensuremath{-} 1} $, allowing observations to be made at multiple points for each flow for an indefinite period. Flows with Froude number in the range 0.1–25 and bulk inertial number 0.1–2.7 were observed in the dense regime, with surface velocities in the range 0.2–5.6 $\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $. Previous studies have focused on $I\lessapprox 0. 5$. We show that a numerical implementation of the $\ensuremath{\mu} (I)$ rheology does not fully capture the accelerating dynamics or the transverse velocity profile on the bumpy base. We also observe the transverse separation of the flow into a dense core flanked by dilute regions and the formation of longitudinal vortices.

view Abstract Citations (15) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Destabilization of Strongly Magnetized Jets Hardee, Philip E. ; Clarke, David A. Abstract Simulations of strongly magnetized slab jets in uniform expansion in an external atmosphere have been performed and compared to an unmagnetized expanding slab jet. A strongly magnetized super-Alfvénic jet with lower magnetosonic Mach number but with sonic Mach number equal to a purely fluid jet destabilizes in a much shorter distance than the fluid jet. A strongly magnetized sub-Alfvénic jet remains stable until the jet becomes super-Alfvénic. At the Alfvén point the jet is submagnetosonic and destabilizes abruptly. Results from a spatial stability analysis of the magnetized slab jet are compared to the numerical simulations. In general, predictions based on the theory are borne out by the simulations. In particular, the stability properties of a super-Alfvénic jet are confirmed to be a function of the magnetosonic Mach number, and the theoretical prediction of rapid jet destabilization at the Alfvén point transition between sub-Alfvénic and super-Alfvénic flow is confirmed. However, nonlinear effects associated with decreasing the jet density relative to the external density and with increasing the magnetic field strength can increase the destabilization-decollimation length and reduce decollimation, respectively. Some of the implications for three-dimensional jets are considered. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176037 Bibcode: 1995ApJ...449..119H Keywords: GALAXIES: INDIVIDUAL MESSIER NUMBER: M87; GALAXIES: JETS; HYDRODYNAMICS; INSTABILITIES; MAGNETOHYDRODYNAMICS: MHD full text sources ADS | data products SIMBAD (3) NED (1)

FEMALE :-Head: Eyes narrowly separated, bare. Antennae (Fig. 7) with flagellar segments in proportion of 20:15:15:15:15:185:15:16:33:33:36: 36:48. Antennal ratio 1.48 (1.44-1.53, n==4); distal sensorial pits in segments III-XV. The first eight flagellar segments yellowish, the last five brown. Palpal segments (Fig. 5) in proportion of 15:31:45:12:12; the third segment swollen, 2.48 (2.44-2.53, n=4) times as long as the greatest width; with a large deep sensory pit with a circular opening. The proboscis shorter than the head; the mandible with 15 (14-18, n-4) well developed teeth. Thorax: On slide mounted specimens the thorax appears to be uniformly yellowish brown; however, no pinned material was available for comparison. The legs are light brown; the femora with a subapical, and the tibia with a subbasal pale ring; all knees black. Hind tibial comb with four spines, (Fig. 6) the one nearest the spur the longest. Wing: Length of wing 1.36 (1.34-1.42, n-4) mm; the costa extending 0.58 (0.57-0.60, n=4) of the wing length. Wing pattern (Fig. 8) with markings distinct; the pale markings well separated. The second radial cell in a light spot, the distal pale spot broadly reaching the wing margin and nearly filling the apical portion of cell R5. A large round pale spot on vein M<; the distal pale spots in cells Ml and M2 broadly reaching the wing margin. The anal cell with one distal pale spot which fills the entire distal portion of the cell. Few macrotrichia present, these distributed evenly over the surface of the wing. The halter entirely clear. Abdomen: Two spherical spermathecae present; the ducts sclerotized for only a very short distance. The larger 0.079 (0.067-0.098, n=2) mm by 0.058 (0.055-0.060, n=2) mm; the smaller 0.065 (0.060-0.072, n=3) mm by 0.053 (0.048-0.055, n-3) mm. MALE:-Genitalia: The ninth sternite shallowly excavated; ninth tergite with apicolateral processes well developed, slightly divergent and with blunt ends; the caudal margin strongly indented and with a deep troughshaped notch. Basistyle with dorsal root well developed, blunt ended; the ventral root longer and tapering to a weakly curved point. Dististyle with the base swollen; nearly straight, with a slender, blunt, slightly curved tip. Aedeagus strongly arched; with ends of arms bent; tapering to a blunt tip. Parameres (Fig. 2) separate, with abruptly bent, knobbed bases and a sensible swelling medially, tapering to fine sharply bent simple tips.

Nonlinear and nonlocal effects are discussed in the interaction of laser fields with thermal Rydberg atoms in electromagnetically induced transparency configuration. We show that under the crucial approximation that the time variation in the dipole-dipole interactions due to atomic motions can be neglected in an ensemble average, an analytical form can be obtained for the nonlocal nonlinear atomic response of the thermal medium, and study it for different parameter cases. We further propose a generalized model to describe the modulational instability (MI) in absorptive nonlinear media, in order to understand the propagation dynamics in the thermal Rydberg medium. Interestingly, this model predicts that at short propagation distances, each wave component exhibits the MI effect in absorptive nonlinear media, unlike in the purely dispersive case.