scholarly journals The white-light humidified optical particle spectrometer (WHOPS) – a novel airborne system to characterize aerosol hygroscopicity

2015 ◽  
Vol 8 (2) ◽  
pp. 921-939 ◽  
Author(s):  
B. Rosati ◽  
G. Wehrle ◽  
M. Gysel ◽  
P. Zieger ◽  
U. Baltensperger ◽  
...  
Keyword(s):  
Optical Properties ◽  
Ammonium Sulfate ◽  
White Light ◽  
Laboratory Experiments ◽  
Effective Index ◽  
Index Of Refraction ◽  
Hygroscopic Growth ◽  
Airborne Measurements ◽  
New Instrument ◽  
Effective Index Of Refraction

Abstract. Aerosol particles experience hygroscopic growth at enhanced relative humidity (RH), which leads to changes in their optical properties. We developed the white-light humidified optical particle spectrometer (WHOPS), a new instrument to investigate the particles' hygroscopic growth. Here we present a detailed technical description and characterization of the WHOPS in laboratory and field experiments. The WHOPS consists of a differential mobility analyzer, a humidifier/bypass and a white-light aerosol spectrometer (WELAS) connected in series to provide fast measurements of particle hygroscopicity at subsaturated RH and optical properties on airborne platforms. The WELAS employs a white-light source to minimize ambiguities in the optical particle sizing. In contrast to other hygroscopicity instruments, the WHOPS retrieves information of relatively large particles (i.e., diameter D > 280 nm), therefore investigating the more optically relevant size ranges. The effective index of refraction of the dry particles is retrieved from the optical diameter measured for size-selected aerosol samples with a well-defined dry mobility diameter. The data analysis approach for the optical sizing and retrieval of the index of refraction was extensively tested in laboratory experiments with polystyrene latex size standards and ammonium sulfate particles of different diameters. The hygroscopic growth factor (GF) distribution and aerosol mixing state is inferred from the optical size distribution measured for the size-selected and humidified aerosol sample. Laboratory experiments with pure ammonium sulfate particles revealed good agreement with Köhler theory (mean bias of ~3% and maximal deviation of 8% for GFs at RH = 95%). During first airborne measurements in the Netherlands, GFs (mean value of the GF distribution) at RH = 95% between 1.79 and 2.43 with a median of 2.02 were observed for particles with a dry diameter of 500 nm. This corresponds to hygroscopicity parameters (κ) between 0.25 and 0.75 with a median of 0.38. The GF distributions indicate externally mixed particles covering the whole range of GFs between ~1.0 and 3.0. On average, ~74% of the 500 nm particles had GFs > 1.5, ~15% had GF < 1.1 and the remaining ~1% showed values of 1.1 < GF < 1.5. The more hygroscopic mode sometimes peaked at GF > 2, indicating influence of sea-salt particles, consistent with previous ground-based particle hygroscopicity measurements in this area. The mean dry effective index of refraction for 500 nm particles was found to be rather constant with a value of 1.42 ± 0.04 (mean ± 1SD).

scholarly journals The white-light humidified optical particle spectrometer (WHOPS) – a novel airborne system to characterize aerosol hygroscopicity

2014 ◽  
Vol 7 (7) ◽  
pp. 7321-7366 ◽  
Author(s):  
B. Rosati ◽  
G. Wehrle ◽  
P. Zieger ◽  
M. Gysel ◽  
U. Baltensperger ◽  
...  
Keyword(s):  
Optical Properties ◽  
Ammonium Sulfate ◽  
White Light ◽  
Laboratory Experiments ◽  
Effective Index ◽  
Index Of Refraction ◽  
Hygroscopic Growth ◽  
Airborne Measurements ◽  
New Instrument ◽  
Effective Index Of Refraction

Abstract. Aerosol particles experience hygroscopic growth at enhanced relative humidity (RH) which leads to changes in their optical properties. We developed the white-light humidified optical particle spectrometer (WHOPS), a new instrument to investigate the particles' hygroscopic growth. Here we present a detailed technical description and characterization of the WHOPS in laboratory and field experiments. The WHOPS consists of a differential mobility analyzer, a humidifier/bypass and a WELAS (white-light aerosol spectrometer) connected in series to provide fast measurements of particle hygroscopicity at sub-saturated RH and optical properties on airborne platforms. The WELAS employs a white-light source to minimize ambiguities in the optical particle sizing. In contrast to other hygroscopicity instruments, the WHOPS retrieves information of relatively large particles (i.e. diameter D > 280 nm), therefore investigating the more optically relevant size ranges. The effective index of refraction of the dry particles is retrieved from the optical diameter measured for size-selected aerosol samples with a well-defined dry mobility diameter. The data analysis approach for the optical sizing and retrieval of the index of refraction was extensively tested in laboratory experiments with polystyrene latex size standards and ammonium sulfate particles of different diameters. The hygroscopic growth factor (GF) distribution and aerosol mixing state is inferred from the optical size distribution measured for the size-selected and humidified aerosol sample. Laboratory experiments with pure ammonium sulfate particles revealed good agreement with Köhler theory (mean bias of ~ 3% and maximal deviation of 9% for GFs at RH = 95%). First airborne measurements in the Netherlands observed GFs (mean value of the GF distribution) at RH = 95% between 1.74 and 2.67 with a median of 1.94 for particles with a dry diameter of 500 nm. This corresponds to hygroscopicity parameters (κ) between 0.21 and 0.93 with a median of 0.33. The GF distributions indicate externally mixed particles covering the whole range of GFs between ~ 1.0–3.0. On average ~ 74% of the particles were "more hygroscopic" with GFs > 1.5, ~ 15% were non- or slightly hygroscopic with GF < 1.1 and the remaining ~ 11% were "less hygroscopic" with 1.1 < GF < 1.5. The more hygroscopic mode sometimes peaked at GF > 2, indicating influence of sea salt particles, consistent with previous ground-based particle hygroscopicity measurements in this area. The mean dry effective index of refraction for 500 nm particles was found to be rather constant with a value of 1.42 ± 0.04.

scholarly journals NEGATIVE REFRACTION AND SUBWAVELENGTH FOCUSING USING PHOTONIC CRYSTALS

2004 ◽  
Vol 18 (25) ◽  
pp. 1275-1291 ◽  
Author(s):  
EKMEL OZBAY ◽  
KAAN GUVEN ◽  
ERTUGRUL CUBUKCU ◽  
KORAY AYDIN ◽  
B. KAMIL ALICI
Keyword(s):  
Optical Properties ◽  
Photonic Crystals ◽  
Negative Refraction ◽  
Numerical Study ◽  
Effective Index ◽  
Index Of Refraction ◽  
Far Field ◽  
Two Dimensional ◽  
Flat Lens ◽  
Effective Index Of Refraction

In this article, we present an experimental and numerical study of novel optical properties of two-dimensional dielectric photonic crystals (PCs) which exhibit negative refraction. We investigate two mechanisms which utilize the band structure of the PC to generate a negative effective index of refraction (n eff <0) and demonstrate the negative refraction experimentally. To the isotropic extend of n eff , different PC slab structures are employed to focus the radiation of a point source. It is shown experimentally that the PC can generate an image of the source with subwavelength resolution in the vicinity of the PC interface. Using a different PC, one can also obtain a far field focusing. In the latter case, we explicitly show the flat lens behavior of the structure. These examples indicate that PC-based lenses can surpass limitations of conventional lenses and lead to novel optics applications.

Optical Properties of Nanocomposite Thin-Films

2006 ◽  
Author(s):  
Anna Garahan ◽  
Laurent Pilon ◽  
Juan Yin ◽  
Indu Saxena
Keyword(s):  
Thin Films ◽  
Optical Properties ◽  
Maxwell’S Equations ◽  
Maxwell's Equations ◽  
Volume Fraction ◽  
Effective Index ◽  
Absorption Index ◽  
Index Of Refraction ◽  
Nanocomposite Thin Films ◽  
Effective Index Of Refraction

This paper aims at developing numerically validated models for predicting the through-plane effective index of refraction and absorption index of nanocomposite thin-films. First, models for the effective optical properties are derived from previously reported analysis applying the volume averaging theory (VAT) to the Maxwell's equations. The transmittance and reflectance of nanoporous thin-films are computed by solving the Maxwell's equations and the associated boundary conditions at all interfaces using finite element methods. The effective optical properties of the films are retrieved by minimizing the root mean square of the relative errors between the computed and theoretical transmittance and reflectance. Nanoporous thin-films made of SiO2 and TiO2 consisting of cylindrical nanopores and nanowires are investigated for different diameters and various porosities. Similarly, electromagnetic wave transport through dielectric medium with embedded metallic nanowires are simulated. Numerical results are compared with predictions from widely used effective property models including (1) Maxwell-Garnett Theory, (2) Bruggeman effective medium approximation, (3) parallel, (4) series, (5) Lorentz-Lorenz, and (6) VAT models. Very good agreement is found with the VAT model for both the effective index of refraction and absorption index. Finally, the effect of volume fraction on the effective complex index of refraction predicted by the VAT model is discussed. For certain values of wavelengths and volume fractions, the effective index of refraction or absorption index of the composite material can be smaller than that of both the continuous and dispersed phases. These results indicate guidelines for designing nanocomposite optical materials.

Variation of effective index of refraction in a double‐heterojunction laser (In1−xGaxP1−zAsz)

1977 ◽  
Vol 48 (5) ◽  
pp. 2091-2092 ◽  
Author(s):  
P. D. Wright ◽  
E. A. Rezek ◽  
M. J. Ludowise ◽  
N. Holonyak
Keyword(s):  
Effective Index ◽  
Index Of Refraction ◽  
Double Heterojunction ◽  
Effective Index Of Refraction

Efficient Focusing with an Ultra-Low Effective-Index Lens Based on Photonic Crystals

2005 ◽  
Vol 869 ◽  
Author(s):  
Eugen Foca ◽  
Helmut Föll ◽  
Frank Daschner ◽  
Vladimir V. Sergentu ◽  
Jürgen Carstensen ◽  
...  
Keyword(s):  
Refractive Index ◽  
Photonic Crystals ◽  
Effective Index ◽  
Index Of Refraction ◽  
Microwave Range ◽  
Optical Elements ◽  
New Approach ◽  
Concave Lens ◽  
Strong Focusing ◽  
Effective Index Of Refraction

AbstractThis work focuses on photonic crystals (PC) that can be ascribed an effective index of refraction > 1 or even > 0. We investigate the possibility to design optical elements (in this case a lens) based on this type of PC. A new approach for determining the effective refractive index of PCs with unusual index of refraction is used, which is simpler than earlier methods based on analyzing equi-frequency surfaces in k-space. An ultra-low refractive index PC is given a form approximating a concave lens and is proven theoretically and experimentally that it efficiently focuses the electromagnetic radiation in the microwave range. Strong focusing effects are found for both polarizations (TE and TM mode). Intensity gains as large as 35 for TM polarizations and 29 for TE polarizations are found. Measurements are in a good accordance with simulations.

Superlattice Optical Properties Measured by Variable Angle Spectroscopic Ellipsometry

1987 ◽  
Vol 102 ◽  
Author(s):  
P. G. Snyder ◽  
K. G. Merkel ◽  
B. N. De ◽  
J. A. Woollam ◽  
D. W. Langer ◽  
...  
Keyword(s):  
Spectroscopic Ellipsometry ◽  
Room Temperature ◽  
Optical Constants ◽  
Nondestructive Method ◽  
Effective Index ◽  
Index Of Refraction ◽  
Angle Of Incidence ◽  
Variable Angle ◽  
Superlattice Layer ◽  
Effective Index Of Refraction

ABSTRACTVariable Angle of incidence Spectroscopic Ellipsometry (VASE) is a sensitive, nondestructive method of determining optical constants, layer thicknesses, alloy compositions and other parameters. We model the VASE data for a sample containing a 20 period Al0 5Ga0 5As-GaAs superlattice, to obtain the effective index of refraction (n) and e tinction coefficient (k) of the superlattice layer. The room temperature VASE spectra contain strong, sharp features at the e-hh(1), e-lh(1) and e-hh(2) excitonic tran-sition energies. In addition, VASE was used to characterize more compli-cated layered structures, which also contained superlattices.

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