Optical Effects Research Articles

Two-Photon and Three-Photon Circular Dichroism of Au38 Gold Nanoclusters Enantiomers.

While circular dichroism (CD) and optical activity (OA) are well established as optical effects used in characterization of chiral media, harmonic generation and multiphoton circular dichroism are increasingly seen as new, convenient ways of exploring chirality thanks to their operation in the near-infrared range of wavelengths. However, quantitative data about two-photon circular dichroism (2PCD) of organic and inorganic materials are scarce, and even less can be found about three-photon circular dichroism (3PCD). Here, we show that both 2PCD and 3PCD can be readily detected in chiral atomically precise gold nanoclusters via polarimetric Z-scan technique. We provide quantitative data on 2PCD and 3PCD of both enantiomers of Au38(PET)24 nanoclusters, which exhibit extraordinary chiroptical properties arising from the interplay of several levels of molecular organization. Interestingly, the corresponding two- and three-photon dissymmetry factors of Au38(PET)24 enantiomers are significantly enhanced in comparison to the one-photon CD by factors of 178 and 217, respectively.

Surface Plasmon-Driven Versatile Enhancement of Chemosensing.

Chemo-sensors have deeply integrated into various facets of our daily lives. To further satisfy the increasing performance demand, the current attempts are mainly centered on materials science approaches, usually involving time-& labor-consuming structure designing, synthesis, and modification. To date, it remains largely unexplored to enhance sensing material performance at the fundamental physical level by strategic exploitation of optical properties. In this work, we proposed a facile and versatile approach for improving the material performance by strategically utilizing the surface plasmon resonance─a characteristic property of optical devices. This approach is revealed to have a dual effect on fluorescence-based chemosensing: it amplifies the collection of fluorescence signals and simultaneously expedites the kinetics of chemical reactions. In this work, we developed a surface plasmon-driven fluorescence-based chemosensor that utilizes the 2,4,6-trisformyl phenol-diethylamine (TFP-I) fluorescent probe for the detection of hydrogen peroxide (H2O2) gas molecules. By harnessing the dual-effect induced by surface plasmons, we achieved outstanding sensing performance for H2O2 gas molecules, characterized by 0.0225 ppt sensitivity and an exceedingly low limit of detection. This study substantiates the applicability of the surface plasmon resonance-based optical effect in the realm of fluorescent chemical materials for sensing performance amplification. Beyond this, it pioneers the strategic harnessing of optical effects to manipulate the performance of chemical materials, particularly for the advancement of sensing capabilities.

Effect of bifocal soft contact lenses in combination with instillations of the combined drug (Phenylephrine 5% and Tropicamide 0.8%) on the anatomical and functional parameters of the eyes and progression of myopia in pediatric patients

AIM: The study aimed to assess the influence of combined optical and pharmacological effects on the anatomical and functional parameters of the eyes and changes in refraction in pediatric patients with progressive myopia. MATERIAL AND METHODS: Bifocal soft contact lenses (BSCL) Prima BIO Bifocal were prescribed to 43 pediatric patients. At the start of the study, the average age of the children was 10.42±0.26 years, and the average myopia was 3.43±0.19 D. The effect of a combination of optical and medicinal products on the visual apparatus of children was evaluated, namely, bifocal SCLs that form peripheral myopic defocus and instillations of a combined drug containing 0.8% tropicamide and 5% phenylephrine. The combined eye drops, which contained 0.8% tropicamide and 5% phenylephrine, was prescribed once a day at night for 1 month to 23 pediatric patients after wearing the lenses for 1 month (group 1). In group 2 (n=20), patients did not receive any additional treatment, except for optical exposure. RESULTS: The habitual tone of accommodation (HTA) slightly increased after 1 month of using BSCL. In group 1, the HTA decreased to the initial level after 6 and 12 months, whereas it remained high in group 2. Over the year, refraction increased by 0.39 D in group 1 and 0.18 D in group 2 (p 0.05). The annual progression gradient decreased by 2.3 times in group 1 and 5.2 times in group 2. Over the year, the anteroposterior axis increased by 0.13 mm in group 1 and 0.05 mm in group 2. Choroidal thickness increased by 19.09 and 24.77 µm, relative accommodation reserve increased by 0.98 and 1.24 D, and the accommodation amplitude increased by 1.28 and 1.05 D, respectively. CONCLUSION: BSCLs contribute to the reduction of the annual gradient of progression (AGP) and increase in accommodation and choroidal thickness. Instillations of the drug while using BSCL help reduce the habitual tone of accommodation (HTA).

Unraveling the structure-property relationship of novel thiophene and furan-fused cyclopentadienyl chromophores for nonlinear optical applications.

Development of organic nonlinear optical materials has become progressively more important due to their emerging applications in new-generation photonic devices. A novel series of chromophores based on innovative thiophene and furan-fused cyclopentadienyl bridge with various powerful donor and acceptor moieties were designed and theoretically investigated for applications in nonlinear optics. To unravel the structure-property relationship between this new push-pull conjugated systems and their nonlinear optical property, multiple methods, including density of states analysis, coupled perturbed Kohn-Sham (CPKS) method, sum-over-states (SOS) model, the two-level model (TSM), hyperpolarizability density analysis, and the (hyper)polarizability contribution decomposition, were performed to comprehensively investigated the nonlinear optical and electronic properties of this new π-system. Due to excellent charge transfer ability of new bridge and distinctive structure of donor and acceptor, the designed chromophores exhibit deep HOMO levels, low excitation energy, high dipole moment difference and large hyperpolarizability, indicating the appealing air-stable property and remarkable electrooptic performance of them. Importantly, THQ-CS-A3 and PA-CS-A3 shows outstanding NLO response properties with βtot value of 6953.9 × 10-30 and 5066.0 × 10-30 esu in AN, respectively. The influence of the push-pull strength, the heterocycle and the π-conjugation of new bridge on the nonlinear optical properties of this novel powerful systems are clarified. This new series of chromophores exhibit remarkable electro-optical Pockels and optical rectification effect. More interestingly, PA-CS-A3 and THQ-CS-A2 also show appealing SHG effect. This study will help people understand the nature of nonlinear optical properties of innovative heteroarene-fused based cyclopentadienyl chromophores and offer guidance for the rational design of chromophores with outstanding electrooptic (EO) performance in the future.

Efficient application of an all-fiber saturable absorber for the generation of heterogeneous and vector dissipative solitons in fiber lasers

A fully fiber-based structural saturable absorber (SA) incorporating graded-index multimode fiber, stepped-index multimode fiber, and graded-index multimode fiber (GIMF–SIMF–GIMF) has been fabricated and applied to a fiber laser. The modulation depth and saturation intensity are measured to be 1.32 % and 26.79 MW/cm2, respectively. A heterogeneous soliton with an adjustable optical spectrum interval with 4.6 nm and 3 nm is generated in the anomalous dispersion regime. The main pulse widths are approximately 41.80 ps and 35.56 ps. Additionally, a switchable single vector soliton and bound states of vector dissipative solitons are achieved in the normal dispersion regime. The pulse width of the single vector soliton is measured to be 6.16 ps, while the bound state exhibits a pulse width of 6.49 ps with a temporal separation of 15.22 ps. By employing external cavity compression, the minimum pulse widths for the single and bound states of vector dissipative solitons are reduced to 2.18 ps and 1.55 ps, respectively. These experimental results demonstrate that the GIMF–SIMF–GIMF SA exhibits unique nonlinear optical effects and offers promising potential for soliton generation applications.

Vibrational Spectroscopy of Perovskite Ferroelectrics

Ferroelectric and antiferroelectric materials are technologically important by the richness of applications such as piezoelectric, pyroelectric, electro-optic, elasto-optic, and nonlinear optic effects. Especially, oxides with a perovskite structure are very important. Its chemical formula is ABO3, where A is a cation with a larger ionic radius, and B is a cation with a smaller ionic radius. Various elements are available in A- and B-sites. For example, the large piezoelectricity of well-known Pb(ZrxTi1−x)O3 (PZT) solid solutions was found in a morphotropic phase boundary (MPB). The very high dielectric constant, colossal piezoelectric effect, and large electro-optic effect are induced by ferroelectric phase transitions. Such excellent functionalities are closely related to lattice dynamical instability. The vibrational spectroscopy, i.e., Raman scattering, Brillouin scattering, far-infrared, and terahertz time-domain spectroscopy, is a powerful tool for lattice dynamical anomalies. This paper intended a brief review of vibrational spectroscopy on ferroelectric phase transitions of advanced perovskite oxides.

Optical effects of graphene oxide attached to the hydrogel-inverse opal photonic crystals applicable to rapid semi-quantification of E.coli

Optical effects of graphene oxide attached to the hydrogel-inverse opal photonic crystals applicable to rapid semi-quantification of E.coli

Hydrogel‐Based Dynamic Structural Color with Optical Janus Effect for Imaging Encryption/Concealment

Hydrogel‐Based Dynamic Structural Color with Optical Janus Effect for Imaging Encryption/Concealment

Time-resolved exciton photoluminescence and its linear polarization of an ensemble of CdSe/CdS colloidal nanoplatelets

We present experimental and theoretical studies of the time-resolved photoluminescence and its linear polarization of an ensemble of CdSe/CdS colloidal nanoplatelets in the Faraday magnetic fields up to 6 T. The linearly polarized photoluminescence kinetics stems from the excitons resonantly excited with the linearly polarized light pulse and comprises both the structural contribution and the exciton optical alignment effect. The emission from the bright and dark exciton states is distinguished by their different intensity decay timescales with lifetime at cryogenic temperature of about 1–2ns and 100–200ns, respectively. The longitudinal spin relaxation time of the bright exciton was determined to be from 4 to 6ns depending on the magnetic field. The dark exciton spin relaxation time was estimated to be in the order of 20 to 100ns. The developed theory for the bright exciton polarization kinetics and the modeling of the data allowed us to conclude that spin dephasing times of the bright as well as of the dark exciton are shorter than 0.3ns. The origin of such a strong spin relaxation time anisotropy in the ensemble of nanoplatelets is discussed.

Exploring optical, electronic and NLO properties: Growth and characterization of rubidium hydrogen (+)- tartrate crystals

Rubidium, a highly reactive alkali metal, is used in several research areas, such as electronics for its light-emitting properties, and in making glass, ceramics, and in biomedical studies. Single crystals of Rubidium Hydrogen (+)-Tartrate (RHT) suitable for the X-ray analysis were obtained from water solution. The crystal structure of the RHT crystal was determined using single crystal XRD, revealing an orthorhombic system with a non-centrosymmetric space group, P212121. The lattice parameters were a = 7.9233 Å, b = 10.9883 Å, and c = 7.6527 Å, with a unit cell volume of 666.272 ų. The structural vibrations of the RHT compound were analysed using FT-IR and FT-Raman spectroscopy, while NMR provided further insights into its molecular structure. Theoretical investigations at the DFT/RB3LYP/LANL2DZ level were conducted to explore the molecular structure, vibrational spectra, and bonding interactions within the RHT compound's molecular system. Natural Bond Orbital (NBO) analysis of the RHT compound revealed significant charge transfer interactions and stabilization energies, particularly highlighting strong electron donor-acceptor correlations that contribute to the molecule's overall stability. The UV–Vis and HOMO-LUMO calculations were performed in the gas phase. Optical conductivity studies have been performed. The broad spectral curve in the photoluminescence spectrum reflects the optical effects and showed a significant intense peak at 281.22 nm and a moderately intense peak at 395.9 nm. First order hyperpolarizability studies reveals that nonlinear optical efficiency is 1.06 times better than urea and 58.19 times than KDP. Furthermore, Third Harmonic Generation (THG) studies using the Z-scan technique were also conducted to investigate the nonlinear properties.

Improved temporal characteristics for post-compressed pulses via application-tailored nonlinear polarization ellipse rotation.

Intense ultrashort laser pulses with high temporal quality are essential for fundamental science. Nonlinear polarization ellipse rotation (NER) is one way to ensure this high temporal quality, by suppressing weaker signals beyond the duration of the main pulse up to a few orders of magnitude. Post-compression schemes have revolutionized ultrafast lasers, enabling the generation of pulses with durations beyond the limit supported by laser gain media. However, high compression ratios lead to the formation of new pre- and post-pulses. Both NER and post-compression depend on the optical Kerr effect. This makes the combination of the two in a single setup both advantageous and straightforward. While NER cannot suppress the new pre- and post-pulses generated in post-compression, we show via simulations and experimental data that by combining the two, it is possible to shape the output spectrum and counteract temporal contrast degradation.

Theoretical and experimental study on optical polarization states in overhead optical cables under complex weather conditions such as real lightning

Abstract By analyzing the changes in three Stokes vectors, the trajectory of polarization state on the Poincaré sphere, and the polarization change rate, both theoretical and practical aspects of polarization state variations in signal light within optical fiber composite overhead power ground wires (OPGWs) during real thunderstorm conditions, were examined. Our findings reveal that lightning and mechanical vibrations both impact the polarization state of the signal light in OPGW. Theoretical models demonstrate that lightning induces polarization changes through the Faraday magneto-optic effect and exhibits nonlinear electro-optic effects, leading to a maximum polarization change rate of Mrad s−1. In contrast, mechanical vibrations cause long-term, low-intensity polarization rate changes, with a maximum polarization rate of Krad s−1, highlighting a significant optical birefringence effect. Digital signal processing algorithms for coherent receivers with over 100G polarization multiplexing provide valuable guidance for recovering polarization states.

“Chasing Rainbows” Beyond Kaposi Sarcoma’s Dermoscopy: A Mini-Review

The dermoscopic rainbow pattern (RP), also known as polychromatic pattern, is characterized by a multicolored appearance, resulting from the dispersion of polarized light as it penetrates various tissue components. Its separation into different wavelengths occurs according to the physics principles of scattering, absorption, and interference of light, creating the optical effect of RP. Even though the RP is regarded as a highly specific dermoscopic indicator of Kaposi’s sarcoma, in the medical literature, it has also been documented as an atypical dermoscopic finding of other non-Kaposi skin entities. We aim to present two distinct cases—a pigmented basal cell carcinoma (pBCC) and an aneurysmatic dermatofibroma—that exhibited RP in dermoscopy and to conduct a thorough review of skin conditions that display RP, revealing any predisposing factors that could increase the likelihood of its occurrence in certain lesions. We identified 33 case reports and large-scale studies with diverse entities characterized by the presence of RP, including skin cancers (Merkel cell carcinoma, BCC, melanoma, etc.), adnexal tumors, special types of nevi (blue, deep penetrating), vascular lesions (acroangiodermatitis, strawberry angioma, angiokeratoma, aneurismatic dermatofibromas, etc.), granulation tissue, hypertrophic scars and fibrous lesions, skin infections (sporotrichosis and cutaneous leishmaniasis), and inflammatory dermatoses (lichen simplex and stasis dermatitis). According to our results, the majority of the lesions exhibiting the RP were located on the extremities. Identified precipitating factors included the nodular shape, lesion composition and vascularization, skin pigmentation, and lesions’ depth and thickness. These parameters lead to increased scattering and interference of light, producing a spectrum of colors that resemble a rainbow.

Unusual Thermo-Enhanced Second Harmonic Generation in Organic Configurationally-Locked Polyene Crystals.

To modulate nonlinear optical (NLO) effects of crystalline material holds great application potential in the photoelectronic and optical fields. Organic configurationally-locked polyene represents an exciting NLO family with large second harmonic generation (SHG) effects, whereas it is a huge blank to switch and modulate their NLO property through external stimuli. For the first time, here present unusual thermo-enhanced SHG activities are presented in a polyene-based NLO compound, 2-{3-[2-(4-pyrrolidinphenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene}malononitrile (1), giving a record-high magnitude of SHG enhancement up to ≈170% during its isomorphic phase transition. Theoretical analysis discloses this behavior stems from the reduced degree of torsion in the π-conjugated structures in 1, as verified by dihedral angles between its pyrrolidine and phenyl planes. As the first study on thermo-enhanced SHG properties of organic crystals, this work affords a new avenue of modulating physical properties to fabricate high-performance photoelectronic and optical devices.

Distinct nonlinear absorption behaviors in Cu1.8S nanocrystals influenced by geometry features

Spherical and lamellar [Formula: see text] nanocrystals with radial dimension of about 40[Formula: see text]nm were synthesized by the thermal injection method. Combining the crystal and morphological analysis with the photo physical property, the lamellar [Formula: see text] nanocrystals displayed the typical features of 2D metal sulfides which can be ultrasonically exfoliated into single or few layers of [Formula: see text] nanosheets due to the fact that the atomic layers were bonded by interlayer van der Waals forces. While in the spherical [Formula: see text] nanocrystals, no exfoliation or morphological change occurred after sonication. The nonlinear optical properties of spherical and lamellar [Formula: see text] nanocrystals after sonication were investigated by the [Formula: see text]-scanning technique using a 532-nm nanosecond laser pulse. The lamellar [Formula: see text] nanocrystals showed saturation absorption, reaching a normalized transmittance of 1.58 at [Formula: see text] with a [Formula: see text] value of [Formula: see text] and [Formula: see text] value of [Formula: see text]. While the spherical [Formula: see text] nanocrystals exhibited optical limiting effects, reaching the normalized transmittance of 0.38, with a [Formula: see text] value of 8[Formula: see text]cm/GW. Distinct nonlinear absorption behaviors in [Formula: see text] nanocrystals with the similar lateral size were observed in the spherical and lamellar [Formula: see text] nanocrystals, showing significant geometry feature-dependent nonlinear absorption behaviors.

Effects of self-limiting oxide layer on optical and electronic properties of WTe2 for optoelectronic applications

The study focuses on the optical and electrical properties of Tungsten Ditelluride (WTe2), a type II Weyl semimetal, as well as the influence of its self-limiting oxide (SLO) layer that forms during natural oxidation. WTe2 exhibits promising applications in photodetection and energy harvesting due to its unique gapless linear dispersion and Berry-field-enhanced nonlinear optical effects. However, surface oxidation poses a challenge as it degrades the performance of WTe2. By employing spectroscopic ellipsometry and Raman spectroscopy, the progression of the oxide layer’s thickness and its impact on the optical constants of WTe2 were examined. The results revealed a rapid increase in oxide thickness within the first 24 h, and it reached saturation at ∼10 nm after 45 h of atmospheric exposure. Electrical properties were explored using Kelvin Probe Force Microscopy, uncovering a modification in surface potential and Fermi level following oxidation. Additionally, a SLO/WTe2 heterojunction device exhibited a wide region of positive and negative coexisting photocurrent, highlighting the potential for logical operations in ambient air. Finally, the mechanism of operation of the device is discussed. The electrical and optical properties of the pristine, partially oxidized and fully oxidized WTe2 are analyzed using density functional theory calculations. It shows that the SLO layer has a significant effect on the optical and electronic properties, which is instructive for future wavelength-modulated device optoelectronic logic operations.

Nanoscale phase transformation in SiC wafer by spatiotemporal tailored ultrafast laser pulses for multiple optical data encryption

Color center has shown great potential in optical data encryption due to its tunable optical performance. In this work, precise and controllable implantation of color centers within 4H-SiC wafers has been demonstrated by spatiotemporal tailored ultrafast laser irradiation. Distinct microstructures via micro-ablation, micro-cracking and internal phase transformation can be achieved by precisely regulating the spatial energy input in SiC wafer. The orientation of generated microstructures can be accurately controlled by tuning the laser polarization directions. Those color centers can be further customized by varying the defocusing distances and pulse durations. Wherein, nanoscale amorphous carbon layer with thickness ~ 100 nm was achieved by ultrafast laser induced internal phase transformation, which was ascribed to an enhanced near-field optical effect. Due to the thin-film interference, various colors can display from pink to light-green in those laser modified samples with different carbon nanolayer depths. With the highly flexible and precise modification in SiC crystal, multiple colors can therefore be implanted to encode optical information at small scale, allowing high density and complex information storage. This represents a significant advance in controlled phase transformation for nanoscale color centers fabrication, which is promising in multiple optical data encryption.

Coenhancement of optical transmission and Faraday effect with magnetic plasmonic nanopillars

Coenhancement of optical transmission and Faraday effect with magnetic plasmonic nanopillars

Plasmonic enhanced OLED efficiency upon silver-polyoxometalate core-shell nanoparticle integration into the hole injection/transport layer

Although organic light-emitting diodes (OLEDs) are considered a mature technology, further enhancements in their efficiency are of paramount importance for advancing their incorporation in high-quality displays and flexible, wearable, electronic devices. In this regard, we propose an innovative approach, focusing on strategic modifications to the hole transport layer (HTL) through the integration of core-shell nanoparticles. Silver nanoparticles (Ag-NPs) encapsulated in a tungsten polyoxometalate compound (POM) are embedded within the prototype poly(3,4-ethylenedioxythiophene)-poly(styrenesulphonate) (PEDOT:PSS) to form the modified HTL. Our work reveals the pivotal plasmonic role of Ag-NPs in enhancing OLED device performance based on commercially available conjugated polymers. Comprehensive analyses, including UV–Vis absorption spectroscopy, atomic force microscopy, photoluminescence spectroscopy, and electrical measurements, confirm the influence of the POM encapsulated Ag-NPs on improving the device efficiency. This is attributed to the synergistic influence of enhanced hole injection and conductivity and beneficial optical effects (i.e. the Localized Surface Plasmon Resonance (LSPR) and, likely, light scattering of the POM-Ag NPs in the core-shell configuration, depending on their diameter), contributing to enhanced carrier balance and exciton recombination rate. Comparison with POM gold NPs (POM-Au NPs) highlights the distinct advantages of POM-Ag NPs. Our work reveals the potential of this innovative approach to contribute to the evolution of high-performance OLEDs, ensuring a visually compelling and efficient future.

An improved calibration procedure for accurate plastic scintillation dosimetry on an MR-linac.

Plastic scintillation dosimeters (PSDs) are highly suitable for real-time dosimetry on the MR-linac. For optimal performance, the primary signal (scintillation) needs to be separated from secondary optical effects (Cerenkov, fluorescence and optical fiber attenuation). This requires a spectral separation approach and careful calibration. Currently, the 'classic' calibration is a multi-step procedure using both kV and MV X-ray sources, requiring an uninterrupted optical connection between the dosimeter and read-out system, complicating efficient use of PSDs. Therefore, we present a more time-efficient and more practical novel calibration technique for PSDs suitable for MR-linac dosimetry.
Approach: The novel calibration relies on prior spectral information combined with two 10x10 cm2field irradiations on the 1.5 T MR-linac. Performance of the novel calibration technique was evaluated focusing on its reproducibility, performance characteristics (repeatability, linearity, dose rate dependency, output factors, angular response and detector angle dependency) and IMRT deliveries. To investigate the calibration stability over time, prior spectral information up to 315 days old was used. To quantify the time efficiency, each step of the novel and classic calibration was timed.
Main results: The novel calibration showed a high reproducibility with a maximum relative standard deviation of 0.3%. The novel method showed maximum differences of 1.2% compared to the gold-standard calibration, while reusing old classic calibrations after reconnecting fibers showed differences up to 3.0%. The novel calibration improved time efficiency from 105 to 30 minutes compared to the classic method.
Significance: The novel calibration method showed a gain in time efficiency and practicality while preserving the dosimetric accuracy. Therefore, this method can replace the traditional method for PSDs suitable for MR-linac dosimetry, using prior spectral information of up to a year. This novel calibration facilitates reconnecting the detector to the read-out system which would lead to unacceptable dosimetric results with the classic calibration method.