Refractive Index Dispersion Research Articles

Photonic eigenmodes and transmittance of finite-length 1D cholesteric liquid crystal resonators

Cholesteric liquid crystals exhibit a periodic helical structure that partially reflects light with wavelengths comparable to the period of the structure, thus performing as a one-dimensional photonic crystal. Here, we demonstrate a combined experimental and numerical study of light transmittance spectra of finite-length helical structure of cholesteric liquid crystals, as affected by the main system and material parameters, as well as the corresponding eigenmodes and frequency eigenspectra with their Q-factors. Specifically, we have measured and simulated transmittance spectra of samples with different thicknesses, birefringences and for various incident light polarisation configurations as well as quantified the role of refractive index dispersion and the divergence of the incident light beam on transmittance spectra. We identify the relation between transmittance spectra and the eigenfrequencies of the photonic eigenmodes. Furthermore, we present and visualize the geometry of these eigenmodes and corresponding Q-factors. More generally, this work systematically studies the properties of light propagation in a one-dimensional helical cholesteric liquid crystal birefringent profile, which is known to be of interest for the design of micro-lasers and other soft matter photonic devices.

Spectroscopic investigations of Tm3+ doped CdF2 single crystals and infrared laser potentialities

By use of standard Bridgman technique, CdF2 single crystals doped with Tm3+ have been obtained with good optical quality. XRD analysis has been performed confirming the cubic structure. An ordered sequence of spectroscopic measurements (including absorption, excitation, emission and fluorescence dynamics) was carried out at room temperature. By exploiting both UV–Visible and near-infrared absorption spectra, the JO phenomenological parameters are determined by taking into account the complete refractive index dispersion, which allowed us to compute the probabilities of all transitions. Under 355 nm wavelength excitation, the Stokes emission spectrum exhibits mainly an intense blue emission line around 450 nm which is associated to 1D2→3F4 excited state transition. Whereas, the anti-Stokes blue emission around 480 nm associated to 1G4→3H6 transition is obtained under infrared excitation according to a two photon absorption mechanism. For both blue emissions, the CIE chromaticity coordinates of CdF2:Tm3+ are located in the blue region.As trivalent Tm3+ ions are known for their emissions in the near- and mid-infrared spectral ranges suitable for efficient laser operation, we have systematically studied the fluorescence behavior of the eye safe emission (pointed at ∼1.8 μm) and associated to the 3F4 → 3H6 transition. Such transition exhibit a relatively high emission cross-section (σem = 0.22 × 10−20 cm2) and a positive gain cross-section at low pumping threshold with a metastable fluorescence lifetime decay.

Nonlocal bonding of a soliton and a blue-detuned state in a microcomb laser

Laser cavity-solitons can appear in a microresonator-filtered laser when judiciously balancing the slow nonlinearities of the system. Under certain conditions, such optical states can be made to self-emerge and recover spontaneously, and the understanding of their robustness is critical for practical applications. Here, we study the formation of a bonded state comprising a soliton and a blue-detuned continuous wave, whose coexistence is mediated by dispersion in the nonlinear refractive index. Our real-time dispersive Fourier transform measurements, supported by comprehensive theoretical analysis, reveal the presence of an elastic bonding between the two states, resulting in an enhancement of the soliton’s robustness.

Designing Strategy for High Refractive Index Polymers: From the Molecular Level to Bulk Structure Control

Abstract High refractive index polymers (HRIPs) are essential materials for many optical applications, including organic light-emitting diodes (OLEDs), charge-coupled devices (CCDs), complementary metal oxide semiconductors (CMOS), eyeglasses, and optical waveguides. Various molecular designs, synthetic routes, and material preparation methods have been reported to increase the refractive index (RI) of polymers; however, increasing the RI using only organic (and classical) components is difficult. Other properties, such as low or high Abbe numbers (RI dispersion), low birefringence, and high transparency, are also required for HRIPs depending on the intended wavelength usage, which ranges from visible to infrared (IR) light and X-ray applications. This review summarizes the recent developments in HRIPs, including their synthesis, properties, and applications, and provides future prospects for achieving HRIPs with the desired performances.

Effect of substrate temperature on the structural optical and electrical properties of new Cu2Cd0.8Mn0.2SnS4 photo-absorber layer for solar cells

We report for the first time the effect of substrate temperature on the structural, optical, and electrical properties of Cu2Cd0.8Mn0.2SnS4 new photovoltaic absorber layer. Cu2Cd0.8Mn0.2SnS4 thin films were deposited on soda lime glass (SLG) substrates by the spray pyrolysis method at different substrate temperatures. X-ray diffraction measurement revealed the formation of cernyite structure by Cu2Cd0.8Mn0.2SnS4 thin film. Also, an increase in crystal size from 7.23 to 14.35 nm and crystallinity improvement of Cu2Cd0.8Mn0.2SnS4 thin film with an increase in substrate temperature were achieved. The atomic force microscopy indicated an increase in surface roughness with substrate temperature. The elemental composition of the Cu2Cd0.8Mn0.2SnS4 thin films showed Cu-poor, S-poor, and Sn-poor conditions. The optical characterization showed that the absorption coefficient of Cu2Cd0.8Mn0.2SnS4 is in the order of 104 cm−1 and the bandgap decreased from 1.89 to 1.87 eV with an increase in substrate temperature. The refractive index dispersion parameters were discussed in terms of the Wemple-Didomenico and Sellmeier equations. Hall effect measurement indicated that the Cu2Cd0.8Mn0.2SnS4 films exhibit P-type conductivity. High hole mobility and the highest conductivity of 2.77 x104 cm2/Vs and 5.60 (Ω.cm)-1 respectively, were achieved at 400 °C substrate temperature. The Cu2Cd0.8Mn0.2SnS4 deposited at 400 °C is a potential candidate for use as a top absorber layer in the tandem solar cell.

Tunable ultra‐wideband NIR emission and irradiation resistance in novel Er3+/Tm3+/Pr3+ tri‐doped La2O3‐ Ga2O3‐Ta2O5 glasses synthesized using aerodynamic levitation method

AbstractGlasses with ultra‐wideband near‐infrared emission and superior irradiation resistance are important for the potential applications in optical communications under harsh environments. Here, transparent 35La2O3‐(65‐x)Ga2O3‐xTa2O5 (LGT) and Er3+/Tm3+/Pr3+ tri‐doped LGT glasses are fabricated using the levitation method. LGT glasses exhibit a wide glass‐formation region, low largest vibration energy, high refractive indices, and excellent mechanical properties. Additionally, Er3+/Tm3+/Pr3+ tri‐doped LGT samples with varying Pr3+ contents are characterized by possessing good thermal stability (Tg>849°C), wide transparent optical window, strong radiation resistance, excellent compatibility between low wavelength dispersion (vd>31.2), and large refractive index (nd>2.048). By optimizing the doping content of Er3+, Tm3+, and Pr3+ in an appropriate ratio, the ultra‐wideband near‐infrared luminescence ranging from 1250 to 1640 nm (FWHM = 251 nm) has been acquired under 808 nm pumping. Furthermore, decay curves are measured to reveal the fluorescence dynamics, and then the related emission mechanism is elaborated systematically. Meanwhile, the effects of gamma irradiation doses on microstructure, transmittance spectra, and fluorescence characteristics are studied. This work may offer a valuable reference for doping optimization and new design strategy of multifunctional materials.

In-depth opto-electrical analysis of Ni:CdS film towards the performance as Ag/Ni:CdS/FTO Schottky diode

Nickel doped cadmium sulfide (Ni:CdS) thin films are deposited onto glass and FTO substrate using spray pyrolysis technique. The effect of annealing temperature on the thin films and its morphological, microstructural, optical dispersion, linear-nonlinear and electrical, properties are extensively investigated by using various techniques such as field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM), X-ray diffraction (XRD) and ultraviolet visible (UV-VIS) diffuse reflectance spectroscopy. Morphological studies revealed that doped thin films surface is almost homogeneous and well-covered. Peaks associated with Ni, Cd and S elements are present in EDS analysis, which confirm the composition of the films. The energy band calculation using the Tauc plot from the recorded absorption spectra reveals the decrement in the energy gap from 3.75 eV to 3.61 eV and the refractive index is in the range of 2.57–2.62. The effect of annealing temperature on complex dielectric constant are also analyzed. Moreover, the dispersion of refractive index is calculated in terms of Wemple-DiDomenico approach. Third order susceptibility and nonlinear refractive index are calculated of Ni:CdS films. The designed Ag/Ni:CdS/FTO Schottky diode is tested under illumination conditions, and the empirical diode parameters, viz. ideality factor, barrier height, series resistance etc. are influenced by annealing temperature.

Bismuth vanadate layers alternated with nanoparticle-doped silicon dioxide layers for one-dimensional multilayer photonic crystals

Bismuth vanadate is one of most studied materials in the field of photocatalysis due to its high photocatalytic activity. The modulation of its optical properties can be engineered by fabricating photonic crystals in which bismuth vanadate is included. In the present study, bismuth vanadate in the monoclinic clinobisvanite structure has been included in a one-dimensional photonic crystal. Bismuth vanadate layers are alternated with layers on silicon dioxide doped with titanium dioxide nanoparticles and silver nanoparticles. The optical properties of the crystal have been studied by employing the transfer matrix method, taking into account all the refractive index dispersions of the selected materials. The transmission spectra have been studied as a function of the bismuth vanadate layers thickness and the filling factor of titanium dioxide and silver dioxide in the silicon dioxide layers.

Chirped optical solitons and stability analysis of the nonlinear Schrödinger equation with nonlinear chromatic dispersion

The present paper aims to investigate the chirped optical soliton solutions of the nonlinear Schrödinger equation with nonlinear chromatic dispersion and quadratic-cubic law of refractive index. The exquisite balance between the chromatic dispersion and the nonlinearity associated with the refractive index of a fiber gives rise to optical solitons, which can travel down the fiber for intercontinental distances. The effective technique, namely, the new extended auxiliary equation method is implemented as a solution method. Different types of chirped soliton solutions including dark, bright, singular and periodic soliton solutions are extracted from the Jacobi elliptic function solutions when the modulus of the Jacobi elliptic function approaches to one or zero. These obtained chirped optical soliton solutions might play an important role in optical communication links and optical signal processing systems. The stability of the system is examined in the framework of modulational instability analysis.

Accurate prediction of global-density-dependent range-separation parameters based on machine learning.

In this work, we develop an accurate and efficient XGBoost machine learning model for predicting the global-density-dependent range-separation parameter, ωGDD, for long-range corrected functional (LRC)-ωPBE. This ωGDDML model has been built using a wide range of systems (11 466 complexes, ten different elements, and up to 139 heavy atoms) with fingerprints for the local atomic environment and histograms of distances for the long-range atomic correlation for mapping the quantum mechanical range-separation values. The promising performance on the testing set with 7046 complexes shows a mean absolute error of 0.001 117 a0-1 and only five systems (0.07%) with an absolute error larger than 0.01 a0-1, which indicates the good transferability of our ωGDDML model. In addition, the only required input to obtain ωGDDML is the Cartesian coordinates without electronic structure calculations, thereby enabling rapid predictions. LRC-ωPBE(ωGDDML) is used to predict polarizabilities for a series of oligomers, where polarizabilities are sensitive to the asymptotic density decay and are crucial in a variety of applications, including the calculations of dispersion corrections and refractive index, and surpasses the performance of all other popular density functionals except for the non-tuned LRC-ωPBE. Finally, LRC-ωPBE (ωGDDML) combined with (extended) symmetry-adapted perturbation theory is used in calculating noncovalent interactions to further show that the traditional abinitio system-specific tuning procedure can be bypassed. The present study not only provides an accurate and efficient way to determine the range-separation parameter for LRC-ωPBE but also shows the synergistic benefits of fusing the power of physically inspired density functional LRC-ωPBE and the data-driven ωGDDML model.

Structural, electronic, optical and vibrational properties of CdSiP2 from first-principles

We report the results of a first-principles research of the structural, electronic, linear and nonlinear responses, and vibrational properties of CdSiP2 based on the density functional theory using pseudopotential plane-wave approach. We calculate the energy band structure, dielectric function, absorption coefficient, reflectivity, refractive index, SHG susceptibility, and phonon dispersion curves. In order to obtain accurate band gap value of CdSiP2, the GW approximation method is used to calculate the quasiparticle band structure and the corrected band gap value is in excellent agreement with experimental measurements. Furthermore, the corrected band gap can be used as scissor shift for linear and nonlinear optical properties calculations. The linear-response theory is used to derive the phonon dispersion curves and density of states. All zone-center phonon modes are calculated and LO-TO splitting of the infrared modes are identified. The results show a good agreement with available experimental data and other calculations.

Exploration of impact of thermal condition on microstructural-optical- electrical properties of Ni doped CdS thin films

In this study, Ni-doped cadmium sulfide films were deposited onto ITO substrate using spray-pyrolysis. The effects of annealing(450 °C) on the opto-electrical properties of deposited thin films were investigated.The band gap of films was estimated using absorption spectroscopy, and it decreased from 2.88 eV and 2.81 eV with annealing. The effect of annealing on refractive index and crystal size was also studied. Additionally,the dispersion of refractive index is calculated in terms of Wemple-DiDomenico approch. Third order susceptibility and nonlinear refractive index are calculated of Ni doped CdS films.The electrical properties of the films were characterized using the four-probe method, and the conductivity was found to increase with annealing temperature. The fabricated Ag/Ni:CdS/ITO Schottky diode was tested under illumination conditions, and the empirical diode parameters were influenced by annealing temperature. The morphological and elemental composition analysis of the Ni-doped CdS films was carried out using FESEM and EDS analysis.

Controlling refractive index and reducing the Global Warming Potential of Cerenkov gas radiators: a challenge in the era of diminishing fluorocarbon availability

Saturated fluorocarbons (SFCs) of the form CnF(2n+2) are chosen for their optical properties (high transparency in the near UV, adapted refractive index and low chromatic dispersion over wavelength ranges of interest) for use as Cherenkov radiators. The COMPASS and LHCb experiments currently use C4F10 and CF4 gas radiators. SFCs have high Global Warming Potentials (GWPs), however (in the range 5000–9000). There is thus an impetus to reduce their use and wastage through leaks in existing installations.Newer fluids of the form CnF2nO, including the 3M NOVEC® range, can offer similar optical performance to SFCs of the same order, n, but with GWPs equivalent to CO2. These GWPs are, however, geometry-specific: closed molecular rings having an oxygen atom as a link can have GWPs as high as those of SFCs, and should be avoided.While the optical constraints of RICH detectors can motivate a “special case” argument to retain the use of preferred SFCs, legislation and external market forces will limit their future availability, leaving “holes” in the CnFx spectrum that might not be filled by NOVEC equivalents. This situation might require the blending of low molar concentrations of heritage-stock higher-order SFCs and NOVEC vapours with transparent light gases such as nitrogen, and is the subject of this paper.While continuous optical measurement of refractive index in dynamically changing gas mixtures is very demanding, the monitoring of sound velocity has been historically shown to provide simple, reliable and continuous real time mixture information. Indeed the speed of sound is, in itself, a monitor of the speed of light and the Cherenkov threshold in a gas radiator.This ultrasonic (“sonar”) technique was first used for controlling the real-time blending C5F12 with N2 in the SLD CRID at the SLAC linear collider. The technique could become important again in future operation to meet the optical and low GWP constraints of future Cherenkov gas radiators. Some examples are explored in this paper.

Annealing Effect on Copper-Doped Sodium Borate Glasses (Na2O.4B2O3)

The annealing effect of an alkali borate type glass below its softening point was investigated according to the Na2O-B2O3 binary system. The samples were doped by introducing different amounts of copper oxide (CuO). The properties of elaborate glasses before and after annealing were studied. X-ray diffraction (XRD) as well as optical and infrared spectroscopy were used in this study. The results obtained show that annealing, that is, a heat treatment process, affects the structure of this type of glass by redistributing its structural units and partially correcting any defects, thereby reinforcing the structure. It was noticed that the BO3 units were reformed while the number of BO4 ones decreased, leading to an increase in the coefficient of thermal expansion, a decrease in both the refractive index and optical dispersion, the weakening of mechanical properties as well as a reduction in thermal conductivity and electric permittivity.

Mid-infrared analogue polaritonic reversed Cherenkov radiation in natural anisotropic crystals

Cherenkov radiation (CR) excited by fast charges can serve as on-chip light sources with a nanoscale footprint and broad frequency range. The reversed CR, which usually occurs in media with the negative refractive index or negative group-velocity dispersion, is highly desired because it can effectively separate the radiated light from fast charges thanks to the obtuse radiation angle. However, reversed CR at the mid-infrared remains challenging due to the significant loss of conventional artificial structures. Here we observe mid-infrared analogue polaritonic reversed CR in a natural van der Waals (vdW) material (i.e., α-MoO3), whose hyperbolic phonon polaritons exhibit negative group velocity. Further, the real-space image results of analogue polaritonic reversed CR indicate that the radiation distributions and angles are closely related to the in-plane isofrequency contours of α-MoO3, which can be further tuned in the heterostructures based on α-MoO3. This work demonstrates that natural vdW heterostructures can be used as a promising platform of reversed CR to design on-chip mid-infrared nano-light sources.

STABILITY OF SOME SILICONE LUBRICATING INTERLAYERS IN LIQUID-INFUSED COATINGS

One of the most actively developing research areas in materials science relevant to polyfunctional coatings is the creation of slippery liquid-infused porous surfaces (SLIPS) based on porous hydrophobic or hydrophilic materials filled with low-volatility viscous liquids (lubricants). In the present work, we have investigated the possibility of using two organosilicon liquids of different polarities, bis(trifluoromethylsulfonyl)imide dicationic ionic liquid and silicone oil, as lubricants for fabricating slippery coatings that reduce the adhesion of solid and liquid aqueous precipitations to aluminium oxide substrates. To calculate the stability of the films of such lubricants, we have employed the theory of van der Waals forces to study the refractive index dispersions and the dielectric properties of the liquids in the region of microwave relaxation. On the basis of experimentally obtained data, the dielectric permittivity spectra have been calculated as functions of imaginary frequency for the entire spectral range, as well as the contribution of the van der Waals forces to the stability of the disjoining pressure isotherms of the lubricant films on the hydrophobic and hydrophilic aluminium oxide substrates. The disjoining pressure isotherms obtained in this work have indicated that the ionic liquid used to prepare slippery coatings is a more durable lubricant than silicone oil, because its films retain their stability when the vapor phase is replaced by an aqueous medium over a wider range of thickness.

Structural and optical exploration of promising zinc (8-hydroxyquinoline) thin films for wide-scale optoelectronic applications

This research presents a detailed sequential study of the thickness effect on structural, morphological, and optical properties of vacuum thermally deposited zinc 8-hydroxyquinoline (ZnQ2) thin films. The FTIR results demonstrate that ZnQ2's molecular structure has a high degree of stabilization. On the other hand, the change in thickness affects the film's roughness. The film roughness decreases to 2.398 nm as the film thickness increase to 143 nm, and then roughness increases again at a thickness of 185 nm. The optical absorption features of the prepared films are explained. The optical energy gap has been calculated and found to be in the range of (2.79–2.87) eV. Furthermore, the refractive index dispersion has been analyzed. ZnQ2 thin film of thickness 87 nm achieved the highest linear optical susceptibility, nonlinear optical susceptibility, and nonlinear refractive index. The high peak located at photon energy 4.4 eV assures the validity of the material's proposal for optical switching applications. Besides, compared to many other organic complexes, ZnQ2 is a highly recommended candidate for efficient organic optoelectronic and optical switching applications.

Dynamics of Free Carrier Absorption and Refractive Index Dispersion in Si and Si/PolySi Microrings

We report pump-probe measurements of time resolved optical transmission spectra of Si and Si/poly-Si microrings after high free carrier densities have been generated by two-photon absorption of the pump pulse. From measurements, we can extract the recovery dynamics of free carrier absorption, refractive index dispersion, generated free carriers and finally the effective initial free carrier lifetimes. The method is validated by comparing modelling and simulations with measurements; the obtained results are in very good agreement with what predicted by the Shockley-Read-Hall recombination model for trap assisted recombination. We also propose a method for determining the empirical relations for free carrier absorption and refractive index dispersion in poly-Si waveguides.

Optical Properties of PT‐Based Relaxor Ferroelectric Crystals

AbstractDuring the last two decades, PT‐based relaxor ferroelectric crystals such as (1−x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–PT), (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT), and (1−x−y)Pb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–xPbTiO3 (PIN–PMN–PT or PIMNT) crystals, are widely studied due to their huge piezoelectric properties and super‐high electro‐mechanical coupling factors. They have excellent properties with compositions around the morphotropic phase boundary (MPB). It is gratifying that the PT‐based relaxor crystals are replacing traditional PZT piezo‐ceramics in many application fields. Most ferroelectrics with oxygen‐octahedral structure, which show outstanding electro‐mechanical properties, also have excellent optical performances. Ferroelectric single crystals with large electro‐optic (EO) modulation are widely applied in laser communication devices. For the practical applications, the knowledge of detailed optical parameters is desirable. This paper tries to show a global review on the optical properties of PT‐based relaxor ferroelectric crystals. In the present review, optical properties of the crystals are systematically summarized, including refractive index dispersion, transmittance, band gap, EO, acousto‐optic, and photorefractive properties. These properties change with the crystal composition, orientation, and poling condition. The purpose of the review is to provide a resource for the researchers who are concerned with basic physical investigation or optical device applications of the PT‐based relaxor ferroelectric crystals.

Optical properties and irradiation resistance of novel high-entropy oxide glasses La2O3–TiO2–Nb2O5–WO3–M2O3 (M=B/Ga/In)

A new class of high-entropy oxide glasses 20LaO3/2–20TiO2–20NbO5/2–20WO3–20MO3/2 (M = B/Ga/In) were designed and successfully fabricated by aerodynamic containerless processing. The results show that one can control the properties and increase the functionality of glass by changing the type of M. The Vicker's hardness reaches the highest value of 6.45 GPa for glass M = B. The best thermal stability and the glass forming ability, measured using the glass-transition temperature Tg and the temperature gap ΔT respectively, are found in glass M = In, with Tg = 740 °C and ΔT = 72 °C. The optical properties show that the as-prepared glasses exhibit good transparency and high refractive index. Especially for glass M = In, its transmittance reaches almost 78% from visible to IR region, and the value is nearly unchanged after electron beam irradiation, indicating good irradiation resistance of this high-entropy oxide glass. Furthermore, the glass M = In has the highest refractive index (nd = 2.46) and low wavelength dispersion (νd = 45.6). These results demonstrate that the conceptual design of high-entropy materials is adaptable to high performance oxide glasses, which should be promising host materials for optical applications such as smart phones with digital cameras and endoscopes.