Search Results (72)

The linear and third-order nonlinear optical (NLO) properties of a water-soluble perylenediimide derivative, N,N′-di(2-(trimethylammonium iodide) ethylene) perylenediimide (TAIPDI), doped with semiconductor nanoparticles (NPs), were systematically investigated under femtosecond laser excitation. ZnO and TiO₂ NPs were synthesized using a pulsed laser ablation technique. Nanocomposite systems were prepared by incorporating different concentrations of ZnO and TiO₂ NPs into the TAIPDI dye solution. The optical properties were characterized using UV–visible absorption spectroscopy together with open- and closed-aperture Z-scan measurements at 800 nm. Linear absorption measurements revealed concentration-dependent modifications in the optical band gap, indicating electronic interaction between the dye molecules and the semiconductor NPs. Open-aperture Z-scan results demonstrated strong nonlinear absorption (NLA) behavior dominated by two-photon absorption and excited-state absorption processes. Closed-aperture measurements showed a negative nonlinear refractive (NLR) index, corresponding to self-defocusing behavior. Both the NLA coefficient and the NLR index increased with increasing NP concentration, resulting in a significant enhancement of the third-order nonlinear susceptibility of the nanocomposite systems. In addition, optical limiting measurements revealed a pronounced reduction in the limiting threshold with increasing nanoparticle concentration, demonstrating improved laser attenuation capability. These findings indicate that ZnO@TAIPDI and TiO₂@TAIPDI nanocomposites are promising candidates for applications in optical limiting, all-optical switching, and advanced photonic devices. Full article

The structural, mechanical, electronic, and optical properties of cubic double perovskite oxides A₂TiSiO₆ (A = Ca, Sr, Ba) were systematically investigated using first-principles density functional theory calculations. Structural optimization within the GGA–PBE framework confirms that all compounds crystallize in a stable cubic phase. The negative formation energies indicate thermodynamic stability and potential experimental synthesizability. Ab initio molecular dynamics (AIMD) simulations performed at 300 K further confirm the dynamical stability of all compounds under finite-temperature conditions. The Born–Huang stability criteria performed elastic constant analysis establishes mechanical stability and the derived mechanical moduli indicate the presence of rigid but brittle behavior with moderate amounts of elastic anisotropy. Calculation of the electronic band structure reveals that all the compounds are direct wide-bandgap semiconductors, with the HSE06 bandgaps of Ca₂TiSiO₆, Sr₂TiSiO₆ as well as Ba₂TiSiO₆ being 2.61, 2.50 and 2.37 eV, respectively. The optical property analysis has shown that they are strong in terms of their absorption in the visible–ultraviolet region, with high dielectric constants and good refractive indices, which makes them appropriate in optoelectronics and photovoltaic applications. On the whole, A₂TiSiO₆ double perovskites are promising for use as wide-bandgap materials in the development of superior optoelectronic devices. Full article

We investigated the influence of transition metal coordination on the optical dispersion and thermo-optic behavior of the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]). Refractive index measurements in the visible–near-infrared range (400–1000 nm), combined with temperature-dependent characterization (298–323 K), demonstrate that coordination with Al³⁺, Cd²⁺, Zn²⁺, and Mn²⁺ consistently increases the refractive index relative to the neat ionic liquid. All systems exhibit normal dispersion, following the hierarchy n(Al) > n(Cd) ≳ n(Zn) > n(Mn) > n([BMIM][SCN]), which reflects cooperative contributions from metal-centerd polarizability and coordination-induced modifications to density and electronic structure. Negative thermo-optic coefficients are measured for all samples, with [BMIM]₃[Al(SCN)₆] displaying the highest temperature sensitivity. Abbe diagrams and group-velocity dispersion analyses confirm a predictable index–dispersion trade-off and show that dispersion-related transport parameters are less temperature dependent than n(T). Collectively, these findings establish a structure–property framework for tuning refractive index, chromatic dispersion, and thermo-optic response via coordination chemistry, supporting the targeted design of thiocyanate-based ionic liquids for photonic components, thermal lenses, and dispersion-managed optical devices. Full article

The interaction between plasmonic nanoparticles and organic dye molecules plays an important role in varied photonic and optoelectronic applications. In this work, we systematically investigate the optical properties of a water-soluble perylenediimide derivative, N,N′-di(2-(trimethylammonium iodide) ethylene) perylenediimide (TAIPDI), in the presence of different concentrations of silver nanoparticles (AgNPs) under femtosecond (fs) laser excitation. The AgNPs were synthesized via the laser ablation technique. The influence of AgNP concentration on the linear, fluorescence, and nonlinear optical properties of the TAIPDI dye was explored through UV–visible absorption spectroscopy, fluorescence emission measurements, and open- and closed-aperture Z-scan techniques. The Ag NP–TAIPDI dye hybrid systems (Ag@TAIPDI nanocomposites) exhibited pronounced reverse saturable absorption and self-defocusing behavior, indicating a negative nonlinear refractive index. Both the nonlinear absorption coefficient and refractive index increased markedly with rising AgNP concentration, leading to a significant enhancement in the third-order nonlinear susceptibility. Fluorescence studies further revealed a concentration-dependent emission enhancement due to metal-enhanced fluorescence arising from surface plasmon resonance-induced local field amplification. The Ag@TAIPDI nanocomposites also demonstrated strong optical limiting performance, with the limiting threshold decreasing as the AgNP concentration increased. These findings highlight the synergistic role of plasmon–exciton coupling and thermal lensing in enhancing the nonlinear response of such nanocomposites. The results establish AgNPs–TAIPDI dye hybrid systems as promising materials for all-optical switching, optical limiting, and photonic device applications. Full article

Femtosecond laser processing has emerged as a promising post-deposition method for tailoring the properties of dielectric thin films, offering localized modification without thermal damage. This study investigates the effect of sub-ablative femtosecond laser irradiation on the nonlinear optical response of a TiO₂ single-layer coating deposited on soda-lime glass by electron-beam evaporation. The coating was modified using 35 fs pulses at 800 nm delivered at a repetition rate of 1 kHz and a fluence of 0.083 J/cm² while varying the number of pulses per spot. The effective nonlinear refractive index (n_2,eff) and effective nonlinear absorption coefficient (β_eff) were measured using the z-scan technique with femtosecond excitation. The as-deposited TiO₂ coating exhibited a negative effective nonlinear refractive index, signifying a self-defocusing nonlinear response, while femtosecond laser irradiation leads to pronounced changes in the effective nonlinear parameters. An increase in the magnitude of both effective nonlinear coefficients and a reversal of the sign of the effective nonlinear refractive index are experimentally observed after irradiation with higher pulse numbers. These findings provide experimental evidence that sub-ablative femtosecond laser processing can be used as a post-deposition tool to control the nonlinear optical response of TiO₂ thin films. Full article

Negative refraction of nanolight (e.g., polaritons, hybrid light, and matter excitation) provides a promising building block for nanophotonics, as it paves the way for developing cutting-edge nanoscale applications, such as super-resolution and subwavelength imaging. In the visible regime, negative refraction of surface plasmon polaritons has been extensively studied in conventional plasmonic and metamaterial systems; however, the inherent metallic losses remain a challenge that hinders their practical applications. Herein, we demonstrate negative refraction of low-loss and highly confined hyperbolic plasmon polaritons (HPPs) in a lateral heterojunction of a natural hyperbolic van der Waals material, molybdenum dioxide chloride (MoOCl₂). Owing to the exotic and ray-like propagating properties of HPPs, the negative refraction-inspired superlens can easily reach into the deep subwavelength scale, with spatial confinement of 800 nm near-infrared light wavelengths to below 150 nm focal spots. By elaborately adjusting the orientation directions of two-sided MoOCl₂, the mirror-symmetric superlensing effect can be tilted, and therefore, the focal spots are tuned and steered to deviate from the vertical interfacial lines. Our results applying the concepts of in-plane negative refraction with vdW materials achieve deep subwavelength light confinement and manipulation, offering new possibilities for constructing efficient and compact nanophotonic and opto-electronic devices. Full article

Background: Refractive errors are a common ophthalmological complaint, with a significant potential on the quality of life of our patients—myopia in particular has a growing incidence worldwide. Recent research focused on the ratio between the axial length of the eye (AL) and the corneal radius of curvature (CR), as it had proven valuable in refractive error diagnosis, and risk of progression and of complications. The objective of the study is to compare young emmetropic, hyperopic, and myopic eyes in terms of corneal biomechanics and ocular biometry, focusing on the AL/CR ratio. Methods: This cross-sectional study included 144 myopic eyes, 92 emmetropic eyes, and 47 hyperopic eyes. Measurements included cycloplegic autorefractometry (SE—spherical equivalent), Ocular Response Analyzer (CH—corneal hysteresis, CRF—corneal resistance factor), Aladdin biometry (AL, CR, ACD—anterior chamber depth, CCT—central corneal thickness, AL/CR ratio). Results: ACD, AL, and AL/CR were significantly higher and CCT, SE, CH, and CRF were lower in myopia. The AL/CR ratio correlated positively with AL and ACD and negatively with SE and CR in myopes and hyperopes, and correlated positively with AL and negatively with SE, CH, CRF, and CCT in emmetropes. Conclusions: The AL/CR ratio is significantly higher in myopes and significantly lower in hyperopes, compared to emmetropes, with differences also being in biomechanical properties (CH, CRF) and morphological ones (AL, CCT, ACD). This suggests the AL/CR ratio as a future potential biomarker for refractive errors, particularly for their risk of progression and complications. Full article

Metal hydrides are emerging hydrogen-storage materials that have attracted much attention for their stability and practicality. The novel magnesium-based metal hydride Mg₂CsH₉ was investigated using the CALYPSO software (version 7.0). First-principles predictive methods were then employed to investigate the structural, mechanical, electronic, optical, and hydrogen-storage properties of Mg₂CsH₉ and its alkali metal substitution structure Mg₂RbH₉. The negative formation energy, compliance with the Born stability criterion, and absence of imaginary modes in the phonon spectrum collectively confirm the thermodynamic, mechanical, and dynamic stability of Mg₂XH₉ (X = Cs, Rb), fulfilling the basic criteria for practical hydrogen-storage applications. Mg₂RbH₉ is particularly outstanding in terms of its hydrogen-storage capacity, with a gravimetric capacity of 6.34 wt% and a volumetric capacity as high as 92.70 g H₂/L, surpassing many conventional materials. The pronounced anisotropic characteristics of both compounds further enhance their practicality and adaptability to complex working conditions. An analysis of Poisson’s ratio revealed that the chemical bonding in both compounds is predominantly ionic. The details of the band structures and density of states indicate that Mg₂CsH₉ and Mg₂RbH₉ are semiconductors. Their optical properties confirm them as being high-refractive-index materials. Full article

The effects of cation substitution are the main emphasis of this investigation into the structural, mechanical, electronic, and optical properties of double perovskites K₂AgSbBr₆ and K₂NaScBr₆. Outwardly favorable tolerance and octahedral factors and negative formation energy confirmed structural stability and thermodynamic feasibility. Mechanical analysis showed that K₂AgSbBr₆ possesses greater volumetric stability and rigidity, while K₂NaScBr₆ exhibits greater ductility and isotropic characteristics. The electronic properties determined based on density functional theory (DFT) calculations indicate that K₂AgSbBr₆ has an indirect bandgap of 0.857 eV, making it suitable for applications using visible light, and K₂NaScBr₆ has a direct bandgap of 3.107 eV, making it ideal for UV-specific technologies. Optical analyses demonstrate complementary characteristics, particularly in terms of the dielectric function, absorption, reflectivity, energy loss function, refractive index, extinction coefficient, and optical conductivity. K₂AgSbBr₆ exhibits strong visible light absorptivity. Full article

Metamaterials represent artificially structured materials that exhibit unusual properties, such as a negative refractive index, negative permeability and permittivity, negative cloaking by Poisson ratios and optical effects, etc., which are inaccessible in natural materials. According to recent developments, novel devices and tools based on metamaterials are attracting great interest as they offer improved performance, functionality, sensitivity, biocompatibility, complex structures, and design freedom. Leveraging numerical design approaches, such as finite element analysis and finite difference time domain methods, researchers have tailored metamaterials to meet specific requirements in various areas through a range of manufacturing techniques. These materials can be broadly classified into optical, mechanical, thermal, electromagnetic, and acoustic categories based on their properties and intended use. The choice of fabrication method depends heavily on the specific application, the desired scale, and the complexity of the metamaterial design. These manufacturing methods can be broadly divided into top-down and bottom-up approaches, while each of them has advantages and limitations and offers valuable pathways for the development of the final product. This review offers a basic overview of metamaterials, covering their fundamental principles, fabrication and characterization techniques, and current design methodologies. It also explores their diverse applications, including specific case studies in medicine, while addressing existing limitations and challenges. Finally, this review highlights future perspectives, emphasizing the need for continued innovation in fabrication and characterization to unlock the full potential of metamaterials. Full article

An ultrathin film capable of exhibiting material properties across and around two different dimensions by bridging two-dimensionality frameworks, called a trans-dimensional (TD) material, can be an exceptional tool to tune various electronic and optoplasmonic properties of a system that are unattainable from either dimension. Taking an example of the planar periodic arrangement of single-walled carbon nanotube (SWCNT) TD films, we semi-analytically calculated their dynamical conductivities and dielectric responses as a function of the incident photon frequency and the SWCNT’s radius using the many-particles Green’s function formalism within the Matsubara frequency technique. The periodic array of SWCNTs has an anisotropic dielectric response, which is almost a constant and the same as that of the host dielectric medium in the perpendicular direction of the alignment of the SWCNT array due to the depolarization effect that SWCNTs have. However, the dielectric response functions depend on the incident photon energy in addition to the film’s thickness, the SWCNT’s sparseness, inhomogeneity, and the SWCNT’s diameter. The energy difference between the resonant absorption peak and the plasmonic peak varies with the thickness of the film. Varying the length of the CNTs, we also observed that the exciton–plasmon coupling strength increases with the increase in length of the SWCNTs. The metallic SWCNT-containing films have comparatively pronounced plasmon resonance peaks at low photon energy than semiconducting SWCNT-containing films. Both metallic and semiconducting SWCNT-consisting films have negative refraction for a wide range of energy, making them good candidates for metamaterials. Full article

In this study, Density Functional Theory (DFT) and Density Functional Tight-Binding (DFTB) calculations were used to study two different interfaces of Cu/VSe₂ as well as four nanodiodes of VSe₂ bulk including/excluding the Cu layer. We calculated the electronic and optical properties of two systems of two Cu/VSe₂ in which Cu atoms are positioned on the top and at the corner of the VSe₂ monolayer lattice. The electronic band structure calculations revealed that the metallic properties of the VSe₂ monolayer did not change with the interface of Cu atoms; however, the peak around the Fermi level (E_F) in Cu/VSe₂(Top) shifted downward to lower energies. The optical properties showed that in the visible range and the wavelengths related to the interband transition/intraband excitation of Cu atoms, the enhancement of Re(ω) values could be observed for both Cu/VSe₂(Top) and Cu/VSe₂(Corner) nanostructures, while in infrared/terahertz ranges, less/more negative values of Re(ω) were predicted. Through the effect of Cu atoms on the VSe₂ monolayer, the intensity of the peaks in the Im(ω) part of the dielectric constant was increased from 0.2 THz for Cu@VSe₂(Top) and 2.9 THz for Cu@VSe₂(Corner) instead of the zero constant line in the pure system of VSe₂. Refractive index ($n$) calculations indicated the higher indices at 5.4 and 4.6 for Cu/VSe₂(Top) and Cu@VSe₂(Corner), respectively, in comparison to the value of 2.9 for VSe₂. Finally, DFTB calculations predicted higher current values from I(V) characteristic curves of Au/Cu/VSe₂/Au and Ag/Cu/VSe₂/Ag nanodiodes concerning two other devices without the presence of the Cu layer. Full article

The increasing resolution requirements of imaging optical systems must be satisfied by expanding the aperture of the optical system according to Rayleigh’s criterion, and larger apertures of conventional refractive/reflective optics place a greater demand on manufacturing and transportation. Diffractive optics are applied to imaging optics to achieve lightweight design, but the image quality suffers due to their strong negative properties. Therefore, a wide-band imaging system based on the Schupmann achromatic model is proposed in this paper to solve the above problem, and the achromatic performance of the system is guaranteed by the Schupmann achromatic model. The aperture of the relay lens is reduced, since using harmonic diffractive optics as the primary lens results in a much more compact focus compared to the diffractive optics in the same wavelength band. This allows for the lightweight design of the optical system. An 80 mm aperture diffractive optical system covering the 400–900 nm band was designed and fabricated to verify the above theory. The actual resolution of the optical system was 76.196 lp/mm, and the achromatic task was accomplished. The design and experimentation of the wide-band achromatic imaging optical system confirms that the proposed theory is correct, and lays the foundation for the further application of large aperture diffractive telescopes. Full article

Silk fibroin (SF), the primary protein in silkworm silk, has emerged as a promising organic nonlinear optical material due to its unique combination of optical transparency, biocompatibility, and environmental sustainability. In this study, we investigate the nonlinear optical properties of SF thin films using the z-scan technique with femtosecond laser pulses (35 fs, 800 nm, 1 kHz). Our results reveal a strong self-defocusing effect (negative nonlinear refractive index) and significant multiphoton absorption, demonstrating SF’s tunable nonlinear response. Additionally, optical transmittance measurements confirm SF’s partial transparency in the deep UV region, enhancing its potential for second-harmonic generation (SHG) and efficient light frequency conversion. These findings address a key knowledge gap in nonlinear optics, positioning SF as a versatile biopolymer for advanced photonic applications. Full article

In this work, we present the exact equations for the back and effective focal lengths of a plano-concave thick lens. These equations are derived through a detailed ray-tracing approach, calculating the meridional ray’s path parallel to the optical axis while taking into account lens thickness, refractive index, and surface curvature. Our analysis bridges the gap between paraxial approximations and exact ray behavior, highlighting how traditional models (e.g., thin-lens equations) can be extended to thick lenses. Additionally, we review recent advancements in negative refraction and surface phase manipulation techniques to demonstrate how our equations compare to modern numerical methods and metacoating-enhanced designs. This work provides a comprehensive and exact framework for understanding the optical properties of plano-concave thick lenses, offering new insights into their application in precision optics. Full article