35 research outputs found
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Cold, Optically Dense Samples of Atomic Rubidium
Cold and optically dense gases of atomic rubidium are produced using buffer gas cooling in combination with rapid, high-ïŹow vapor injection. The observed rubidium density is 3 Ă 10cm at a gas temperature of âŒ20 K, leading to an optical density of the order of 200.Physic
Manufacturing Large-scale Materials with Structural Color
Living organisms frequently use structural color for coloration as an alternative mechanism to chemical pigmentation. Recently there has been a growing interest to translate structural color into synthetic materials as a more durable and less hazardous alternative to conventional pigments. Efforts to fabricate structurally colored materials take place in different fronts, from 3D printing to spray-coating and roll-to-roll casting. Stability, performance, and quality of the color, the environmental impact of the materials or their manufacturing methods are some of the heavily researched topics we discuss. First, we highlight recent examples of large-scale manufacturing technologies to fabricate structurally colored objects. Second, we discuss the current challenges to be tackled to create perfect appearances which aim at the full color gamut while caring for environmental concerns. Finally, we discuss possible scenarios that could be followed in order to involve other manufacturing methods for creating structurally colored objects
Effects of multiple scattering on angle-independent structural color in disordered colloidal materials
Disordered packings of colloidal spheres show angle-independent structural
color when the particles are on the scale of the wavelength of visible light.
Previous work has shown that the positions of the peaks in the reflectance
spectra can be predicted accurately from a single-scattering model that
accounts for the effective refractive index of the material. This agreement
shows that the main color peak arises from short-range correlations between
particles. However, the single-scattering model does not quantitatively
reproduce the observed color: the main peak in the reflectance spectrum is much
broader and the reflectance at low wavelengths is much larger than predicted by
the model. We use a combination of experiment and theory to understand these
features. We find that one significant contribution to the breadth of the main
peak is light that is scattered, totally internally reflected from the boundary
of the sample, and then scattered again. The high reflectance at low
wavelengths also results from multiple scattering but can be traced to the
increase in the scattering cross-section of individual particles with
decreasing wavelength. Both of these effects tend to reduce the saturation of
the structural color, which limits the use of these materials in applications.
We show that while the single-scattering model cannot reproduce the observed
saturations, it can be used to design materials in which multiple scattering is
suppressed and the color saturated, even in the absence of absorbing
components
Motile dislocations knead odd crystals into whorls
The competition between thermal fluctuations and potential forces governs the stability of matter in equilibrium, in particular the proliferation and annihilation of topological defects. However, driving matter out of equilibrium allows for a new class of forces that are neither attractive nor repulsive, but rather transverse. The possibility of activating transverse forces raises the question of how they affect basic principles of material self-organization and control. Here we show that transverse forces organize colloidal spinners into odd elastic crystals crisscrossed by motile dislocations. These motile topological defects organize into a polycrystal made of grains with tunable length scale and rotation rate. The self-kneading dynamics drive super-diffusive mass transport, which can be controlled over orders of magnitude by varying the spinning rate. Simulations of both a minimal model and fully resolved hydrodynamics establish the generic nature of this crystal whorl state. Using a continuum theory, we show that both odd and Hall stresses can destabilize odd elastic crystals, giving rise to a generic state of crystalline active matter. Adding rotations to a materialâs constituents has far-reaching consequences for continuous control of structures and transport at all scales.The National Science Foundation (NSF) under award no. DMR-2011854.
NSF DMR-1905974, NSF EFRI NewLAW 1741685 and the Packard Foundation.
NSF grants DMR-1420073 (NYU-MRSEC) and DMR-2004469.
ARN grant WTF and IdexLyon Tore.
The National Science Foundation Graduate Research Fellowship under grant no. 1746045. D.B.
The Chicago-France FACCTS programme.
âla Caixaâ Foundation (ID 100010434), fellowship LCF/BQ/PI20/11760014 and from the European Unionâs Horizon 2020 research and innovation programme under Marie SkĆodowska-Curie grant agreement no. 847648.
NSF DMR-1828629 and US NSF grant no. DMR-201185
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Full-Spectrum Photonic Pigments with Non-iridescent Structural Colors through Colloidal Assembly
Structurally colored materials could potentially replace dyes and pigments in many applications, but it is challenging to fabricate structural colors that mimic the appearance of absorbing pigments. We demonstrate the microfluidic fabrication of âphotonic pigmentsâ consisting of microcapsules containing dense amorphous packings of coreâshell colloidal particles. These microcapsules show non-iridescent structural colors that are independent of viewing angle, a critical requirement for applications such as displays or coatings. We show that the design of the microcapsules facilitates the suppression of incoherent and multiple scattering, enabling the fabrication of photonic pigments with colors spanning the visible spectrum. Our findings should provide new insights into the design and synthesis of materials with structural colors.Engineering and Applied Science
Atom lasers: production, properties and prospects for precision inertial measurement
We review experimental progress on atom lasers out-coupled from Bose-Einstein
condensates, and consider the properties of such beams in the context of
precision inertial sensing. The atom laser is the matter-wave analog of the
optical laser. Both devices rely on Bose-enhanced scattering to produce a
macroscopically populated trapped mode that is output-coupled to produce an
intense beam. In both cases, the beams often display highly desirable
properties such as low divergence, high spectral flux and a simple spatial mode
that make them useful in practical applications, as well as the potential to
perform measurements at or below the quantum projection noise limit. Both
devices display similar second-order correlations that differ from thermal
sources. Because of these properties, atom lasers are a promising source for
application to precision inertial measurements.Comment: This is a review paper. It contains 40 pages, including references
and figure
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Structural Color From Colloidal Glasses
When a material has inhomogeneities at a lengthscale comparable to the wavelength of light, interference can give rise to structural colors: colors that originate from the interaction of the material's microstructure with light and do not require absorbing dyes. In this thesis we study a class of these materials, called photonic glasses, where the inhomogeneities form a dense and random arrangement. Photonic glasses have angle-independent structural colors that look like those of conventional dyes. However, when this work started, there was only a handful of colors accessible with photonic glasses, mostly hues of blue.
We use various types of colloidal particles to make photonic glasses, and we study, both theoretically and experimentally, how the optical properties of these glasses relate to their structure and constituent particles. Based on our observations from glasses of conventional particles, we construct a theoretical model that explains the scarcity of yellow, orange, and red photonic glasses. Guided by this model, we develop novel colloidal systems that allow a higher degree of control over structural color. We assemble glasses of soft, core-shell particles with scattering cores and transparent shells, where the resonant wavelength can be tuned independently of the reflectivity. We then encapsulate glasses of these core-shell particles into emulsion droplets of tunable size; in this system, we observe, for the first time, angle-independent structural colors that cover the entire visible spectrum. To enhance color saturation, we begin experimenting with inverse glasses, where the refractive index of the particles is lower than the refractive index of the medium, with promising results. Finally, based on our theoretical model for scattering from colloidal glasses, we begin an exploration of the color gamut that could be achieved with this technique, and we find that photonic glasses are a promising approach to a new type of long-lasting, non-toxic, and tunable pigment
Manufacturing Large-scale Materials with Structural Color
Living organisms frequently use structural color for coloration as an alternative mechanism to chemical pigmentation. Recently there has been a growing interest to translate structural color into synthetic materials as a more durable and less hazardous alternative to conventional pigments. Efforts to fabricate structurally colored materials take place on different fronts, from 3D printing to spray-coating and roll-to-roll casting. Stability, performance, and quality of the color, the environmental impact of the materials or their manufacturing methods are some of the heavily researched topics we discuss. First, we highlight recent examples of large-scale manufacturing technologies to fabricate structurally colored objects. Second, we discuss the current challenges to be tackled to create perfect appearances which aim at the full color gamut while caring for environmental concerns. Finally, we discuss possible scenarios that could be followed in order to involve other manufacturing methods for creating structurally colored objects.ISSN:0009-429
Absence of red structural color in photonic glasses, bird feathers, and certain beetles
Colloidal glasses, bird feathers, and beetle scales can all show structural colors arising from short-ranged spatial correlations between scattering centers. Unlike the structural colors arising from Bragg diffraction in ordered materials like opals, the colors of these photonic glasses are independent of orientation, owing to their disordered, isotropic microstructures. However, there are few examples of photonic glasses with angle-independent red colors in nature, and colloidal glasses with particle sizes chosen to yield structural colors in the red show weak color saturation. Using scattering theory, we show that the absence of angle-independent red color can be explained by the tendency of individual particles to backscatter light more strongly in the blue. We discuss how the backscattering resonances of individual particles arise from cavity-like modes and how they interact with the structural resonances to prevent red. Finally, we use the model to develop design rules for colloidal glasses with red, angle-independent structural colors.Physic
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Disordered packings of core-shell particles with angle-independent structural colors
Making materials that display angle-independent structural color requires control over both scattering and short-range correlations in the refractive index. We demonstrate a simple way to make such materials by packing core-shell colloidal particles consisting of high-refractive-index cores and soft, transparent shells. The core-shell structure allows us to control the scattering cross-section of the particles independently of the interparticle distance, which sets the resonance condition. At the same time, the softness of the shells makes it easy to assemble disordered structures through centrifugation. We show that packings of these particles display angle-independent structural colors that can be tuned by changing the shell diameter, either by using different particles or simply by varying the concentration of the suspension. The transparency of the suspensions can be tuned independently of the color by changing the core diameter. These materials might be useful for electronic displays, cosmetics, or long-lasting dyes.Engineering and Applied Science