scholarly journals Optical properties of elongated conducting grains

2021 ◽  
Vol 503 (3) ◽  
pp. 4544-4550
Author(s):  
X M Huang ◽  
Qi Li ◽  
Aigen Li ◽  
J H Chen ◽  
F Z Liu ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cross Sections ◽  
Interstellar Extinction ◽  
Wavelength Dependence ◽  
Dipole Approximation ◽  
Dust Particles ◽  
Absorption Cross ◽  
Microwave Background ◽  
Rayleigh Approximation ◽  
Aspect Ratios

ABSTRACT Extremely elongated, conducting dust particles (also known as metallic ‘needles’ or ‘whiskers’) are seen in carbonaceous chondrites and in samples brought back from the Itokawa asteroid. Their formation in protostellar nebulae and subsequent injection into the interstellar medium have been demonstrated, both experimentally and theoretically. Metallic needles have been suggested to explain a wide variety of astrophysical phenomena, ranging from the mid-infrared interstellar extinction at $\sim \,$3–8$\, {\rm \mu m}$ to the thermalization of starlight to generate the cosmic microwave background. To validate (or invalidate) these suggestions, an accurate knowledge of the optics (e.g. the amplitude and the wavelength dependence of the absorption cross sections) of metallic needles is crucial. Here we calculate the absorption cross sections of iron needles of various aspect ratios over a wide wavelength range, by exploiting the discrete dipole approximation, the most powerful technique for rigorously calculating the optics of irregular or nonspherical grains. Our calculations support the earlier findings that the antenna theory and the Rayleigh approximation, which are often taken to approximate the optical properties of metallic needles, are indeed inapplicable.

scholarly journals On the absorption properties of metallic needles

2020 ◽  
Vol 498 (3) ◽  
pp. 3560-3564
Author(s):  
C Y Xiao ◽  
Qi Li ◽  
Aigen Li ◽  
J H Chen
Keyword(s):  
Cross Sections ◽  
Theoretical Calculations ◽  
Experimental Studies ◽  
Interstellar Extinction ◽  
Wavelength Dependence ◽  
Dipole Approximation ◽  
Absorption Cross ◽  
Absorption Properties ◽  
Aspect Ratios ◽  
Iron Whiskers

ABSTRACT Needle-like metallic particles have been suggested to explain a wide variety of astrophysical phenomena, ranging from the mid-infrared interstellar extinction to the thermalization of starlight to generate the cosmic microwave background. These suggestions rely on the amplitude and the wavelength dependence of the absorption cross-sections of metallic needles. On the absence of an exact solution to the absorption properties of metallic needles, their absorption cross-sections are often derived from the antenna approximation. However, it is shown here that the antenna approximation is not an appropriate representation, since it violates the Kramers–Kronig relation. Stimulated by the recent discovery of iron whiskers in asteroid Itokawa and graphite whiskers in carbonaceous chondrites, we call for rigorous calculations of the absorption cross-sections of metallic needle-like particles, presumably with the discrete dipole approximation. We also call for experimental studies of the formation and growth mechanisms of metallic needle-like particles as well as experimental measurements of the absorption cross-sections of metallic needles of various aspect ratios over a wide wavelength range to bound theoretical calculations.

scholarly journals Improved One- and Multiple-Photon Excited Photoluminescence from Cd2+-Doped CsPbBr3 Perovskite NCs

Nanomaterials ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 151
Author(s):  
Ivan D. Skurlov ◽  
Wenxu Yin ◽  
Azat O. Ismagilov ◽  
Anton N. Tcypkin ◽  
Haohang Hua ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cross Sections ◽  
Nonlinear Optical ◽  
Metal Halide ◽  
Photon Absorption ◽  
Absorption Cross ◽  
Trap States ◽  
Metal Halide Perovskite ◽  
Halide Perovskite ◽  
Optical Applications

Metal halide perovskite nanocrystals (NCs) attract much attention for light-emitting applications due to their exceptional optical properties. More recently, perovskite NCs have begun to be considered a promising material for nonlinear optical applications. Numerous strategies have recently been developed to improve the properties of metal halide perovskite NCs. Among them, B-site doping is one of the most promising ways to enhance their brightness and stability. However, there is a lack of study of the influence of B-site doping on the nonlinear optical properties of inorganic perovskite NCs. Here, we demonstrate that Cd2+ doping simultaneously improves both the linear (higher photoluminescence quantum yield, larger exciton binding energy, reduced trap states density, and faster radiative recombination) and nonlinear (higher two- and three-photon absorption cross-sections) optical properties of CsPbBr3 NCs. Cd2+ doping results in a two-photon absorption cross-section, reaching 2.6 × 106 Goeppert-Mayer (GM), which is among the highest reported for CsPbBr3 NCs.

scholarly journals Snowfall retrieval at X, Ka and W bands: consistency of backscattering and microphysical properties using BAECC ground-based measurements

2018 ◽  
Vol 11 (5) ◽  
pp. 3059-3079 ◽  
Author(s):  
Marta Tecla Falconi ◽  
Annakaisa von Lerber ◽  
Davide Ori ◽  
Frank Silvio Marzano ◽  
Dmitri Moisseev
Keyword(s):  
Cross Sections ◽  
Liquid Water ◽  
Microwave Radiometer ◽  
Dipole Approximation ◽  
Liquid Water Path ◽  
Microphysical Properties ◽  
Aspect Ratios ◽  
Atmospheric Radiation Measurement ◽  
Using Data ◽  
Biogenic Aerosols

Abstract. Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using co-located ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Ze, measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these combined observations, power-law Ze–S relationships are derived for all three frequencies considering the influence of riming. Using microwave radiometer observations of liquid water path, the measured precipitation is divided into lightly, moderately and heavily rimed snow. Interestingly lightly rimed snow events show a spectrally distinct signature of Ze–S with respect to moderately or heavily rimed snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are performed by using the particle size distribution provided by the in situ video disdrometer and retrieved ice particle masses. The latter are carried out by using both the T-matrix method (TMM) applied to soft-spheroid particle models with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for rimed aggregates. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multi-frequency Ze–S relations if a proper spheroid aspect ratio is selected. The latter may depend on the degree of riming in snowfall. A further analysis of the backscattering simulations reveals that TMM cross sections are higher than the DDA ones for small ice particles, but lower for larger particles. The differences of computed cross sections for larger and smaller particles are compensating for each other. This may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations under study.

Model study on effect of hematite and goethite on optical properties of inhomogeneous desert dust aerosols

2020 ◽  
Author(s):  
Josef Gasteiger ◽  
Andreas Gattringer ◽  
Bernadett Weinzierl
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Dipole Approximation ◽  
Dust Particles ◽  
Desert Dust ◽  
Dust Aerosols ◽  
Irregular Shapes ◽  
Model Study ◽  
Absorbing Material ◽  
Individual Particles

<p><span>Desert dust aerosols occur as complex ensembles of particles with irregular shapes. Furthermore, these particles consist of a variety of different minerals which often coexist next to each other within individual particles. While in recent years the nonsphericity of particles is considered more and more in optical models of desert dust, the mineralogical inhomogeneity is still rarely considered though it can have a significant effect on light scattering and absorption. </span></p><p><span>Is this study, we discuss optical properties of irregularly-shaped inhomogeneous dust particles which were modelled with a Discrete Dipole Approximation code. We </span><span>show</span><span> how absorbing inclusions embedded in a non-absorbing material affect</span><span> absorption</span> <span>and scattering </span><span>by a particle as compared to the case when all the absorbing material is homogeneously distributed inside the particle. Hematite and goethite were selected as the material of the absorbing inclusions since these minerals are known to be responsible for most of the light absorption in desert dust aerosols.</span></p>

scholarly journals Optical properties of laboratory grown sea ice doped with light absorbing impurities (black carbon)

2017 ◽  
Author(s):  
Amelia A. Marks ◽  
Maxim L. Lamare ◽  
Martin D. King
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Sea Ice ◽  
Black Carbon ◽  
Penetration Depth ◽  
Cross Sections ◽  
Absorption Cross ◽  
Light Penetration ◽  
Irradiance Data ◽  
Snow Model

Abstract. Sea ice radiative-transfer models are of great importance for prediction of future sea ice trends but they are limited by uncertainty in models and requirement for evaluation of modelled irradiance data against measured irradiance data. Presented here are the first results from the Royal Holloway sea ice simulator used to evaluate the output of the TUV-snow radiative-transfer model against the optical properties from the simulated sea ice. The sea ice simulator creates a realistic sea ice environment where both optical (reflectance and light penetration depth (e-folding depth)) and physical (temperature, salinity, density) properties of a ∼ 30 cm thick sea ice can be monitored and measured. Using albedo and e-folding depth data measured from simulated sea ice, scattering and absorption cross-sections of the ice are derived using the TUV-snow model. Absorption cross-sections for the ice are highly wavelength dependent, suggesting the addition of a further absorbing impurity in the ice matching the absorption spectrum of algae. Scattering cross-sections were wavelength independent with values ranging from 0.012 and 0.032 cm2 kg−1 for different ice created in the simulator. Reflectance and light penetration depth (e-folding depth) of sea ice is calculated from the derived values of the scattering and absorption cross-section using the TUV-snow model within error of the experiment. The model is also shown to replicate ice optical properties for sea ice with an extra layer doped with black carbon, well within error of the experiment. Particulate black carbon at mass ratios of 75, 150 and 300 ng g−1 in a 5 cm ice layer lowers the albedo by 97 %, 90 %, and 79 % compared to clean ice at a wavelength of 500 nm.

Optical Limiting in Modified meso-alkynyl Porphyrins

1997 ◽  
Vol 479 ◽  
Author(s):  
Nansheng Tang ◽  
Weijie Su ◽  
Douglas M. Krein ◽  
Daniel G. McLean ◽  
Mark C. Brant ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cross Sections ◽  
Absorption Maximum ◽  
Optical Limiting ◽  
Absorption Cross

AbstractWe characterize the optical properties of modified meso-alkynyl porphyrins by a number of techniques. Our data show that extending the conjugation and incorporating metal in the center of the ring in these molecules serve the objective of tuning the absorption maximum wavelength. We evaluate the optical limiting performance by determining the effective reversesaturable- absorption (RSA) lifetime and the change in the absorption cross-sections. The ultimate optical limiting performance of these molecules is tested in both picosecond and nanosecond regimes.

Scalable Fabrication and Optical Characterization of Nm Si Structures

1994 ◽  
Vol 358 ◽  
Author(s):  
Saleem H. Zaidi ◽  
An-Shyang Chu ◽  
S. R. J. Brueck
Keyword(s):  
Optical Properties ◽  
Cross Sections ◽  
Porous Si ◽  
Aspect Ratios ◽  
Electromagnetic Resonance ◽  
Interferometric Lithography ◽  
Spectral Linewidth ◽  
Resonance Enhancement ◽  
Koh Etching

ABSTRACTObservations of efficient room temperature photoluminescence (PL) from porous Si have generated a great deal of interest in the optical properties of nm-scale Si structures. The stochastic character of porous-Si fabrication results in a distribution of crystal sizes and shapes. We report on a scalable (to large areas) and manufacturable (to high volumes) fabrication technology for uniform, nm-linewidth Si structures providing an important testbed for controlled studies of these optical properties. Large areas ( ∼ 1 cm2) of extreme sub-μm structures (to ∼ 5 nm) are re-producibly fabricated. Both walls (1-D confinement) and wires (2-D confinement) are reported. The fabrication process includes: interferometric lithography, highly anisotropic KOH etching, and structure dependent oxidation. For the walls, nearly perfect <111> crystal planes form the sidewalls and very high width/depth aspect ratios (> 50) have been achieved. Raman scattering results on the walls demonstrate three regimes: 1) lineshapes and cross sections similar to bulk Si for line widths, W > 200 nm; 2) electromagnetic resonance enhancement of the cross section ( to - 100x) for W from 50-200 nm; and 3) highly asymmetric lineshapes and splittings from W < 30 nm. Photoluminescence is observed for the thinnest samples (W < 10 nm) and is as intense as that observed from porous Si with a spectral linewidth ∼ 50 % smaller than that of porous Si.

scholarly journals Snowfall retrieval at X, Ka and W band: consistency of backscattering and microphysical properties using BAECC ground-based measurements

2018 ◽  
Author(s):  
Marta Tecla Falconi ◽  
Annakaisa von Lerber ◽  
Davide Ori ◽  
Frank Silvio Marzano ◽  
Dmitri Moisseev
Keyword(s):  
Cross Sections ◽  
Dipole Approximation ◽  
Microphysical Properties ◽  
Aspect Ratios ◽  
Millimeter Wavelengths ◽  
W Band ◽  
Atmospheric Radiation Measurement ◽  
Using Data ◽  
Biogenic Aerosols

Abstract. Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using high-quality collocated ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Ze, measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these coupled observations power-law Ze-S relationships are derived for all considered frequencies and distinguishing fluffy from rimed snowfall. Interestingly fluffy-snow events show a spectrally distinct signature of Ze-S with respect to rimed-snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are also performed by using the particle size distribution provided by the in-situ video-disdrometer. The latter are carried out by using both the T-matrix method (TMM) for soft-spheroids with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for complex-shape snowflakes. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multi-frequency Ze-S relations if a proper spheroid aspect ratio is selected. The latter may depend on the snowfall type. A further analysis of the backscattering simulations reveals that TMM cross-sections are higher than the DDA ones for small ice particles, but lower for larger particles. These differences may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations, the errors of computed cross-sections for larger and smaller particles compensating each other.

scholarly journals Поглощение электромагнитного излучения аморфным углеродом, модифицированным металлами

2021 ◽  
Vol 47 (2) ◽  
pp. 18
Author(s):  
С.Г. Ястребов ◽  
И.Е. Истомин ◽  
M. Singh
Keyword(s):  
Electromagnetic Wave ◽  
Radio Frequency ◽  
Electromagnetic Radiation ◽  
Amorphous Carbon ◽  
Cross Sections ◽  
Theoretical Study ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Structural Studies ◽  
Absorption Cross

This article presents a theoretical study of the scattering and absorption of an electromagnetic wave from the gigahertz to the red range for a model of amorphous carbon modified by metals. On the basis of structural studies of this material, a cylindrical anisotropic nanoparticle - a nanotube responsible for its absorbing and antireflection properties - was selected as a candidate. A model of such a particle was developed and the scattering and absorption cross sections of an electromagnetic wave were calculated within the framework of the theory of the discrete dipole approximation. A pair of nanotubes allowed us to explain the contribution of the interaction of immediate neighbors to scattering and absorption. The constructed model explains the effect of absorption of radio-frequency electromagnetic radiation, observed experimentally in amorphous carbon modified with metals.

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