Reduction of phase singularities in speckle-shearing interferometry by incoherent averaging of speckle patterns

AbstractWe dispersed electrochemically etched Si into ultrabright ultrasmall nanoparticles, with brightness higher than fluorescein or rhodamine. The emission from single particles is readily detectable. Aggregates or films of the particles exhibit emission with highly nonlinear characteristics. We observe directed blue beams at ∼ 410 nm between faces of aggregates excited by femtosecond radiation at 780 nm; and at ∼ 610 nm from aggregates of red luminescent Si nanoparticles excited by radiation at 550-570 nm from a mercury lamp. Intense directed Gaussian beams, a pumping threshold, spectral line narrowing, and speckle patterns manifest the emission. The results are analyzed in terms of population inversion and stimulated emission in quantum confinement-induced Si-Si dimer phase, found only on ultrasmall Si nanoparticles. This microlasing constitutes an important step towards the realization of a laser on a chip.

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Moiré pattern of interference dislocations in condensate of indirect excitons

Nature Communications ◽

10.1038/s41467-021-21353-7 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

J. R. Leonard ◽

Lunhui Hu ◽

A. A. High ◽

A. T. Hammack ◽

Congjun Wu ◽

...

Keyword(s):

Long Range ◽

Direct Measurement ◽

Quantum Systems ◽

Matter Waves ◽

Moire Pattern ◽

Indirect Excitons ◽

Moiré Pattern ◽

Moiré Effect ◽

Phase Singularities ◽

Bose Einstein

AbstractInterference patterns provide direct measurement of coherent propagation of matter waves in quantum systems. Superfluidity in Bose–Einstein condensates of excitons can enable long-range ballistic exciton propagation and can lead to emerging long-scale interference patterns. Indirect excitons (IXs) are formed by electrons and holes in separated layers. The theory predicts that the reduced IX recombination enables IX superfluid propagation over macroscopic distances. Here, we present dislocation-like phase singularities in interference patterns produced by condensate of IXs. We analyze how exciton vortices and skyrmions should appear in the interference experiments and show that the observed interference dislocations are not associated with these phase defects. We show that the observed interference dislocations originate from the moiré effect in combined interference patterns of propagating condensate matter waves. The interference dislocations are formed by the IX matter waves ballistically propagating over macroscopic distances. The long-range ballistic IX propagation is the evidence for IX condensate superfluidity.

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Wavefront dislocations reveal the topology of quasi-1D photonic insulators

Nature Communications ◽

10.1038/s41467-021-23790-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Clément Dutreix ◽

Matthieu Bellec ◽

Pierre Delplace ◽

Fabrice Mortessagne

Keyword(s):

Local Density ◽

Topological Defects ◽

Wave Functions ◽

Topological Classification ◽

Local Density Of States ◽

Topological Phase Transition ◽

Interference Fringes ◽

Classical Wave ◽

Phase Singularities

AbstractPhase singularities appear ubiquitously in wavefields, regardless of the wave equation. Such topological defects can lead to wavefront dislocations, as observed in a humongous number of classical wave experiments. Phase singularities of wave functions are also at the heart of the topological classification of the gapped phases of matter. Despite identical singular features, topological insulators and topological defects in waves remain two distinct fields. Realising 1D microwave insulators, we experimentally observe a wavefront dislocation – a 2D phase singularity – in the local density of states when the systems undergo a topological phase transition. We show theoretically that the change in the number of interference fringes at the transition reveals the topological index that characterises the band topology in the insulator.

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Thermal stresses applied on helicopter blades useful to retrieve defects by means of infrared thermography and speckle patterns

Thermal Science and Engineering Progress ◽

10.1016/j.tsep.2020.100511 ◽

2020 ◽

Vol 18 ◽

pp. 100511

Author(s):

F. López ◽

S. Sfarra ◽

A. Chulkov ◽

C. Ibarra-Castanedo ◽

H. Zhang ◽

...

Keyword(s):

Infrared Thermography ◽

Thermal Stresses ◽

Helicopter Blades ◽

Speckle Patterns

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Image reconstruction through a multimode fiber with a simple neural network architecture

Scientific Reports ◽

10.1038/s41598-020-79646-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Changyan Zhu ◽

Eng Aik Chan ◽

You Wang ◽

Weina Peng ◽

Ruixiang Guo ◽

...

Keyword(s):

Neural Network ◽

Image Reconstruction ◽

Network Architecture ◽

Neural Network Architecture ◽

Training Time ◽

Modal Dispersion ◽

Multimode Fibers ◽

Speckle Patterns ◽

Hidden Layer ◽

Simple Neural Network

AbstractMultimode fibers (MMFs) have the potential to carry complex images for endoscopy and related applications, but decoding the complex speckle patterns produced by mode-mixing and modal dispersion in MMFs is a serious challenge. Several groups have recently shown that convolutional neural networks (CNNs) can be trained to perform high-fidelity MMF image reconstruction. We find that a considerably simpler neural network architecture, the single hidden layer dense neural network, performs at least as well as previously-used CNNs in terms of image reconstruction fidelity, and is superior in terms of training time and computing resources required. The trained networks can accurately reconstruct MMF images collected over a week after the cessation of the training set, with the dense network performing as well as the CNN over the entire period.

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SPECKLE STATISTICS IN THE PHOTON LOCALIZATION TRANSITION

International Journal of Modern Physics B ◽

10.1142/s0217979210064666 ◽

2010 ◽

Vol 24 (12n13) ◽

pp. 1950-1988 ◽

Cited By ~ 2

Author(s):

Azriel Z. Genack ◽

Jing Wang

Keyword(s):

Steady State ◽

Probability Distributions ◽

Speckle Pattern ◽

Frequency Variation ◽

Localization Transition ◽

Classical Waves ◽

Speckle Patterns ◽

The Many ◽

Photon Localization ◽

State Propagation

We review the statistics of speckle in the Anderson localization transition for classical waves. Probability distributions of local and integrated transmission and of the evolution of the structure of the speckle pattern are related to their corresponding correlation functions. Steady state and pulse transport can be described in terms of modes whose speckle patterns are obtained by decomposing the frequency variation of the transmitted field. At the same time, transmission can be purposefully manipulated by adjusting the incident field and the eigenchannels of the transmission matrix can be found by analyzing sets of speckle patterns for different inputs. The many aspects of steady state propagation are reflected in diverse, but simply related, parameters so that a single localization parameter encapsulates the character of transport on both sides of the divide separating localized from diffusive waves.

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