Manipulation of the refractive index has been of growing interest lately. We consider parameters and possibilities of enhancing the absolute-value limit of the linear index in coherent atomic ...systems. Starting with a review of how two-level transitions – without and with added coherence effects – do not realistically allow for a significantly enhanced index at fixed atomic density, we discuss a possible way around this using wave mixing. This confirms that the only parameters, besides the medium optical depth/density, that can effectively change the value of the attainable index are the frequencies of the involved transitions.
•Density is the main route to modifying the refractive index in basic atomic systems.•Density is a major limitation in enhancing refractive index with linear dispersion.•Wave mixing gives more freedom in modifying the refractive index.•Frequency dependence via wave mixing can be used to enhance the refractive index.•There may be other possibilities via effects not usually considered in this context.
•On the basis of some experimental data, we have proposed an exponentially decreasing relation for calculating the refractive index of semiconductors from their energy gaps.•The new relation is ...applied to different groups of binary semiconductors and ternary compounds and also to calculate the dielectric constant of some III–V semiconductors.•The new relation is also applied to calculate the temperature variation of refractive index.•Our proposed relation provides a good estimate of refractive index over a wide range of energy gap of semiconductors.
An empirical relation based on energy gap and refractive index data has been proposed in the present study to calculate the refractive index of semiconductors. The proposed model is then applied to binary as well as ternary semiconductors for a wide range of energy gap. Using the relation, dielectric constants of some III–V group semiconductors are calculated. The calculated values for different group of binary semiconductors, alkali halides and ternary semiconductors fairly agree with other calculations and known values over a wide range of energy gap. The temperature variation of refractive index for some binary semiconductors have been calculated.
Clouds play a key role in Earth's radiative balance. Radiative transfer through liquid clouds depends on the optical properties of liquid water. Although these optical properties are known to be ...temperature dependent, radiative transfer simulations typically use properties based on measurements made at 298 K, even for supercooled liquid clouds at temperatures as low as 240 K. Here we report temperature‐dependent complex refractive indices (CRIs) of liquid water at 240, 253, 263, and 273 K from 1 to 15,000 cm−1 (0.7 to 10,000 μm). Imaginary parts of the CRI (k) are inferred from values reported in the literature for temperatures of 238 to 298 K and the real parts are obtained via Kramers‐Kronig transformation. Mie theory is used to calculate single scattering albedos and Legendre moments from the CRI, producing a set of optical constants suitable for radiative transfer calculations through supercooled liquid cloud at temperatures as low as 240 K. Ignoring the temperature dependence of complex refractive indices of liquid water is thereby found to result in biased‐high supercooled liquid‐cloud fluxes from 250 to 580 cm−1 and biased‐low fluxes from 710 to 940 cm−1.
Plain Language Summary
Clouds warm Earth's surface by trapping infrared light, that is, through the greenhouse effect. In cold, clean air, cloud droplets can stay liquid down to well below normal freezing temperature. Laboratory measurements have shown that the refractive indices of such “supercooled” liquid differ from those of warmer liquid. This has important consequences, since the refractive index influences a cloud's greenhouse effect. Here, we use a variety of laboratory measurements to infer the refractive indices of liquid water for temperatures of −33°C to 0°C (−28°F to 32°F).
Key Points
Temperature‐dependent complex refractive indices of liquid water are presented from 240 to 298 K and from 1 to 15,000 cm−1
Complex refractive indices of liquid water become more ice‐like as temperature decreases from 298 to 240 K
The temperature dependence of liquid‐water refractive indices has important consequences for radiative transfer through supercooled clouds
► Densities and refractive indices of two deep eutectic solvents were investigated. ► The systems are (choline chloride+ethylene glycol) and (choline chloride+glycerol). ► Their aqueous solutions ...were also studied. ► The measured data were correlated as functions of temperature and composition. ► The correlations give satisfactory results.
Deep eutectic solvents (DES) are new emerging alternatives to conventional ionic liquids that may find a number of interesting applications in industrial and chemical processes. In this study, the densities, ρ, and refractive indices, nD, of the DESs (choline chloride+ethylene glycol) and (choline chloride+glycerol) and their aqueous mixtures were investigated at atmospheric pressure over the temperature range 298.15–333.15K and across a complete composition range. The excess molar volumes, VE, and refractive index deviations, ΔnD, were also calculated from experimental results. The calculated excess molar volumes were negative at all temperatures over the entire range of composition considered, suggesting the presence of strong interactions between water and the DES in the mixtures. The refractive index deviations, on the other hand, were found positive in the entire concentration range. The calculated properties were fitted to a Redlich–Kister type equation to correlate them to the temperature and composition. The correlations used satisfactorily represent the densities and refractive indices of the pure DESs and their aqueous binary mixtures as functions of temperature and composition as indicated by the low overall average absolute deviations obtained in the calculations.
Abstract
Optical dispersion properties are indispensable in the thorough design of modern perovskite‐based photonics devices. Based on inverse temperature crystallization (ITC) method, here, CH
3
NH
...3
PbX
3
(CH
3
NH
3
═MA, X═Cl, Br, I) bulk single crystals are grown from precursor solution. X‐ray patterns indicate that the perovskite crystals have good crystallinity. MAPbCl
3
, MAPbBr
3
, and MAPbI
3
crystals are transparent above 427, 574, and 823 nm, respectively. Refractive indices of MAPbX
3
crystals are measured with different wavelength at 24 °C and reduced dramatically with the wavelength increase. Sellmeier dispersion equation fitted by least squares can be used to calculate the refractive index above the absorption edges. Refractive indices rank in the order of MAPbI
3
> MAPbBr
3
> MAPbCl
3
at the same wavelength. The halogen elements have great influence on refractive indices. These results play a vital role in studying MAPbX
3
nonlinear optical properties as well as in further designing photoelectric devices.
A novel surface plasmon resonance sensor (SPR) based on D-shaped photonic crystal fiber (PCF) is designed for sensing low refractive indexes, and its performance is investigated numerically by the ...finite element method (FEM). Indium tin oxide (ITO) is chosen as the plasmonic materials to expand the operating wavelength range of the PCF-SPR sensor to the infrared region. Spectral sensitivities of 2000–15000 nm/RIU for refractive indexes of 1.22-1.33 are validated in the wavelength range of 1200–2250 nm,and the maximum amplitude sensitivity up to 442.47 RIU−1 is obtained at 2,010 nm with a high resolution of 6.67×10−6RIU. Therefore, the sensor can effectively monitor subtle variations of low refractive indexes and, has enormous commercial value for biomedical and organic detection and related applications.
•A novel D-shaped PCF-SPR sensor based on the finite element method is proposed.•ITO is chosen as the plasmonic materials in order to operate the infrared range.•Maximum spectral sensitivities is 15000nm/RIU boasting a resolution of 6.67×10−6RIU.•The maximum amplitude sensitivity of 442.47RIU−1 is obtained at 2010nm.•The operating wavelength range is from 1200nm to 2250nm for low RIs of 1.22–1.33.
An industrial‐grade polyethylene naphthalate (PEN) substrate is explored as a simple, cost‐effective platform for high‐efficiency organic light‐emitting diodes (OLEDs). Its high refractive index, ...combined with the built‐in scattering properties inherent to the industrial‐grade version, allows for a significant enhancement in outcoupling without any extra structuring or special optical elements. Flexible, color‐stable OLEDs with efficiency close to 100 lm W−1 are demonstrated.
We present a modified method for measuring the refractive index (RI) based on the minimum deviation technique, which allows us to determine the RI of transparent triangular prisms with unknown apex ...angles. In the proposed method, the angles of light deviation are measured on three faces of the prism, and RI of the material and prism angles are determined from the solution of a system of equations. A high precision dynamic goniometer was used to implement the proposed method. A set of reference prisms made of optical glass were experimentally studied and the measurement errors were estimated. It is shown that the modified method can be used for high-precision measurements of the RI in cases when the prism angles are unknown, or their measurement is associated with technical difficulties. The method of measuring RI proposed in the article was implemented using the State Primary Standard of the Refractive Index Unit GET 138–2021 of the All-Russian Research Institute for Optical and Physical Measurements. This standard is intended for storing, reproducing, and transmitting the unit size of the RI of solid and liquid substances.
•Refractive index is the most important characteristic of optical materials.•The minimum deviation method is often used to measure the refractive index.•The proposed modified method allows not to measure the angles of the prism.•The use of a dynamic goniometer increases the accuracy of measurements.
Fiber optic SPR (Surface Plasmon Resonance) sensor based on MMF-FBG-MMF (Multi-mode Fiber–Fiber Bragg Grating–Multi-mode Fiber) structure has been proposed and applied to dual-parameter measurement– ...liquid refractive index and temperature. The fabrication method of this proposed sensor is simpler than other kinds of fiber optic SPR sensors. The basic sensing principle of fiber optic SPR sensors has been provided and the dual-parameter measurement system has been set up. The changes of NaCl resolution refractive index and temperature have been detected and analyzed. The refractive index sensitivity of the proposed sensor has reached 2556.8nm/RIU, and the temperature sensitivity has been improved to 172pm/°C.
We demonstrate the use of the electrooptic effect to control the propagation constant of the guided modes in silicate few mode fibers with internal electrodes. The electrooptic effect induces a ...perturbation of the fiber's refractive index profile that controls intermodal interference. To increase the electrooptic effect the silicate fibers are poled. The response time is in the nanosecond range.
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