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In this work, a thermally tunable optical resonator operating in the visible wavelength range is reported, which consists of a bilayer structure composed of a thin silver layer and a dielectric coating of [Fe(HB(1,2,4‐triazol‐1‐yl)3)2] switchable spin‐crossover (SCO) molecules. White light is coupled to the resonant structure using a prism and the resulting resonance spectra are investigated as a function of the incident angle and temperature. Switching the SCO molecules from the low‐spin to the high‐spin state gives rise to a substantial blueshift of the resonances reaching up to 30 nm (associated with a reflectance modulation of up to 70%), which can be linked, through transfer‐matrix simulations, to the variation of the optical thickness of the molecular layer. Interestingly, the study demonstrated that the large thermal tunability of the device also gives rise to a photothermal nonlinearity, which can be leveraged for achieving optical limiting applications. Overall, through the present study, it is shown that molecular SCO nanomaterials can be superior to commonly used thermo‐optical switches and well‐established optical phase‐change materials for applications requiring high broadband optical transparency in the visible spectral domain. [ABSTRACT FROM AUTHOR]

The hydrothermal technique was used to make nickel telluride nanorods (NiTe NRs) utilizing ascorbic acid and cetrimonium bromide (CTAB) as reducing agents. Temperature dependent magnetic study for NiTe NRs shows a ferromagnetism behavior. Under 532 nm laser excitation, the obtained materials had a better optical limiting property, with a two photon absorption coefficient of 6.6 × 10− 10 m/W and an optical limiting of 2.44 J/cm2 at 200 µJ. NiTe NRs modified electrode shows a excellent hydrogen peroxide electrocatalytic activity with reproducibility, repeatability and durability. It displays an outstanding sensitivity of 6.35 µAµM− 1 cm− 2 and a detection limit of 6 nM. In the presence of interfering species such as dopamine, uric acid, ascorbic acid, glucose, and folic acid, the electrode has a high level of selectivity. A real sample analysis for NiTe NRs sensor has been established in human serum and rat brain serum showed good recoveries. [ABSTRACT FROM AUTHOR]

In this work, thin films of molybdenum-doped CdO were prepared by spray technique from solutions with varied aging times. The structure of (1 1 1) preferentially grown films is cubic. Variation of crystallite size from 47 to 67 nm takes place with solution aging. Improvement in morphology is observed with aging. Increased transparency and Eg narrowing was realized with aging. The CdO:Mo film from 3-days aged solution exhibits a maximum transparency of 87%. With aging, resistivity decreases and a minimum value of 0.28 × 10–3 Ω-cm was realized with three days aging. Reverse saturable absorption (RSA) effect was realized from the Z-scan studies. Third order NLO susceptibility increases with solution aging. With a negative nonlinear refractive index and a high nonlinear absorption, it was confirmed that the aged films may be used as an optical limiter for laser radiation with self-defocusing. [ABSTRACT FROM AUTHOR]

Aurintricarboxylic (ATA) organic dye is a promising chemical compound candidate for several optical and electronic applications. However, this study aims to investigate the impact of molar concentrations and solvent type on the linear/nonlinear optical (NLO) properties of 5,5 ′ -[(3-carboxy-4-oxocyclohexa-2,5-dien-1-ylidene) methylene] bis (2-hydroxybenzoic acid) organic laser dyes. Three molar concentrations of organic dyes (2 × 1 0 − 3 , 4 × 1 0 − 3 , and 6 × 1 0 − 3 ) M were respectively dissolved in distilled water and dimethylsulfoxide (DMSO) at room temperature. The samples were investigated using 1H-NMR and UV/Visible spectrums. The bandgap ( E g ) of (2 × 1 0 − 3 M) ATA/water is 4.75 eV, but Eg of ATA/DMSO was 2.93 eV and 2.65 eV. The measurements were performed by employing a diode-pumped solid-state laser operating at a 457 nm wavelength and 112 mW of power. The Z -scan technique was applied to characterize open and close apertures, nonlinear refractive index (n), and nonlinear absorption coefficient (β). The obtained results predicted that both the n and β coefficients decreased with the reduction of molar concentrations. Additionally, DMSO exhibited better linear/NLO properties than water. The results revealed promising laser dye samples for image sensor and optical limiter applications. [ABSTRACT FROM AUTHOR]

An optical limiter (OL) is a nonlinear device that protects sensitive photodetectors or human eyes from high-intensity illumination. However, current OLs have low open-state transmittance and a limited turndown ratio in some cases. In this study, first it is demonstrated that combining the insulator-to-metal transition (IMT) of vanadium dioxide (VO2) with anti-reflection layers can enable both high and broadband open-state transmittance (>-0.9 dB at the peak wavelength) while preserving a large turndown ratio (>21.8 dB). Furthermore, optothermal simulation is conducted to analyze the performance of the VO2 OL under ultrafast laser irradiation. The result reveals that IMT of the VO2 OL occurs at 0.23 µs when the incident laser intensity is 90 kW cm-2. These benefits offer a promising alternative to OLs in technologies ranging from sensor protection to human eye defense. [ABSTRACT FROM AUTHOR]

Pristine NiO and 2% Cr doped NiO nanostructures are successfully synthesized by the modified auto–combustion method for the determination and improvement of linear and nonlinear optical behaviours, and for identifying them as suitable materials for optical limiting applications. Vibrational and linear optical properties of both nanostructures are investigated, and structural and morphological studies are carried out using XRD, FE-SEM, and HR-TEM. From the Kubelka-Munk model, the energy band gaps for pristine and doped samples are found to be 3.52 eV and 3.44 eV, respectively. Both pristine as well as Cr-doped NiO nanostructures reveal substantial nonlinear optical behaviour at the excitation wavelength of 532 nm, arising from the presence of strong reverse saturable absorption. The third order nonlinear absorption coefficients have values of the order of 10−10 m/W and 10−6 m/W, under pulsed (5 ns) and continuous wave laser excitations, respectively. These values confirm the suitability of these nanostructures for fabricating efficient optical limiting devices for safeguarding human eyes and optical sensors from hazardous laser radiation. [ABSTRACT FROM AUTHOR]

Titanium nitride nanoparticles have become a research interest due to their distinguished optical and photothermal properties. Furthermore, the search for nanoparticle solutions with tunable nonlinear optical properties for laser‐based applications is critical. More specifically, third order optical nonlinearities such as reverse saturable absorption, optical liming, and self‐focusing are important in the biomedical and electronics fields. The optical nonlinearities of titanium nitride plasmonic nanoparticles are investigated as a function of material concentration in water solutions. Furthermore, the effect of nanoparticle clustering on optical nonlinearities is investigated by fabricating micrometer‐sized clusters of ≈50 nm titanium nitride particles. These studies demonstrate that the nonlinear absorption coefficient increases linearly with concentration. However, clusters require higher concentrations compared to the freestanding nanoparticles to exhibit similar nonlinear absorption coefficient and optical density. Similarly, the optical limiting threshold for titanium nitride nanoparticles appears to be lower compared to the cluster solutions, which is impacted by the collective scattering of nanoparticles and high reverse saturable absorption. In addition, self‐focusing is observed in the continuous resonant regime. This study provides an in‐depth analysis of the nonlinear optical properties of titanium nitride, with relevant consequences for applications such as sensor protection and photothermal therapy. [ABSTRACT FROM AUTHOR]

All-optical limiting devices are based on materials enabling light to control light, possessing a nonlinear optical response, and are reviving their popularity. One-dimensional photonic crystals (1 D PhC) are an auspicious platform for achieving novel optical limiters functioning for remarkably low limiting threshold and high damage threshold over a wider regime. 1 D PhC, a periodic nanostructure with a refractive index distribution along one direction, has been widely investigated by researchers. However, their utility to limit the high-intensity radiation to protect sophisticated optical sensors and devices is scarce in the research field. An overview of the numerically simulated, mathematically modeled, theoretically proposed, and experimentally realized 1 D PhC reflective optical limiters are provided here. This review focuses on the limited but noteworthy scrutiny of 1 D photonic crystal-based optical limiters using rare earth metals, nanocomposites, semiconductors, and phase-changing materials as defect layers. A reliable 1D PhC reflective optical limiter is resistant to laser induced damages. Limiter mechanism relies on creation of nonlinear localized modes. 1D PhC optical limiter reflects high power incident beams for a broader frequency window. Reflection based limiters are applicable for arbitrary direction of incidence. [ABSTRACT FROM AUTHOR]

Nickel oxide (NiO) is one of the very few p-type semiconducting oxides, the study of which is gaining increasing attention in recent years due to its potential applicability in many emerging fields of technological research. Actually, a growing number of scientific works focus on NiO-based electrochromic devices, high-frequency spintronics, fuel cell electrodes, supercapacitors, photocatalyst, chemical/gas sensors, or magnetic devices, among others. However, less has been done so far in the development of NiO-based optical devices, a field in which this versatile transition metal oxide still lags in performance despite its potential applicability. This review could contribute with novelty and new forefront insights on NiO micro and nanostructures with promising applicability in optical and optoelectronic devices. As some examples, NiO lighting devices, optical microresonators, waveguides, optical limiters, and neuromorphic applications are reviewed and analyzed in this work. These emerging functionalities, together with some other recent developments based on NiO micro and nanostructures, can open a new field of research based on this p-type material which still remains scarcely explored from an optical perspective, and would pave the way to future research and scientific advances.

The phase transition behavior and damage mechanism of a single-layer VO 2 exposed to 1064-nm continuous laser irradiation were investigation. A performance-enhancing VO 2 -based optical limiter is developed, offering valuable insights for further optimization of such devices. [Display omitted] • The behavior and damage mechanism of a VO 2 optical limiter under 1064-nm continuous laser irradiation were investigated. • The temperature-dependent optical constants of VO 2 were obtained using the proposed dispersion calculation model. • A performance-enhancing VO 2 -based Fabry–Pérot optical limiter was developed. Optical limiters reduce transmittance under increasing incident optical power and protect sensitive components against high-intensity illumination. Vanadium dioxide (VO 2), which is known for its thermochromic properties, is a suitable material for fabricating optical limiters. However, research on its phase transition and damage mechanisms under continuous laser irradiation remains limited. In this study, the temperature-dependent optical constants that determine the performance of VO 2 were obtained using the proposed dispersion calculation model. The phase transition behavior and damage mechanism of a single-layer VO 2 optical limiter exposed to 1064-nm continuous laser irradiation were investigated. The results revealed that a higher laser power on the optical limiter triggered the partial oxidation of VO2 into V 2 O 5 within the damaged region, thus causing the transmittance before and after the phase transition in the damaged area to be higher than that in the undamaged area. Utilizing the calculation model results, a performance-enhancing VO 2 -based Fabry–Pérot optical limiter was developed. It exhibited a higher transmittance and a lower reflectance than single-layer VO 2 in the open state and a lower transmittance in the limiting state. These findings serve as valuable references for the further optimization of VO 2 -based optical limiters. [ABSTRACT FROM AUTHOR]

All optical analog to digital converters will play crucial roles in the future generation of all optical data processing. Cascading optical limiters is a suitable method for designing all optical analog to digital converters. In this paper an optical limiter was proposed using two nonlinear photonic crystal ring resonator, then by cascading 4 optical limiters an structure was proposed for realizing a 5-bit all optical converter. With the help of two examples the correct operation of the proposed structure was confirmed. The total foot print of the proposed structure is about 1796 mm2. [ABSTRACT FROM AUTHOR]

Optical limiters are nonlinear devices that feature decreasing transmittance with increasing incident optical intensity, and thus can protect sensitive components from high‐intensity illumination. The ideal optical limiter reflects rather than absorbs light in its active ("limiting") state, minimizing risk of damage to the limiter itself. Previous efforts to realize reflective (rather than absorbing) limiters were based on embedding nonlinear layers into relatively thick multilayer photonic structures, resulting in substantial fabrication complexity, reduced speed and, in some instances, limited working bandwidth. In this paper, these tradeoffs are overcome by using the insulator‐to‐metal transition (IMT) in vanadium dioxide (VO2) to achieve intensity‐dependent modulation of resonant transmission through aperture antennas. Due to the large change of optical properties across the IMT, low‐quality‐factor resonators are sufficient to achieve high on–off ratios in the transmittance of the limiter. As a result, our ultrathin reflective limiter (thickness ≈1/100 of the free‐space wavelength) is broadband in terms of operating wavelength (>2 µm at 10 µm) and angle of incidence (up to ≈50° away from the normal). Our analysis of the experimental results via opto‐thermal simulations provides insight into limiter performance and is a useful guidance for further engineering efforts. [ABSTRACT FROM AUTHOR]

A laser hazard evaluation compares the potential laser exposure to the maximum permissible exposure (MPE). Direct intrabeam viewing of a collimated laser beam produces a minimally sized retinal image. Viewing other laser sources often produces a larger retinal image known as an extended source. An optical limiter is designed to protect the eye from direct laser exposure through a combination of absorption and scattering, producing an extended source. Diode lasers in combination with diffusers also produce extended sources when viewed at a close distance. A substantial increase in the MPE is allowed for extended sources, based on the size of the retinal image. The larger retinal image produced by the optical limiter does not exhibit a Gaussian or top-hat profile, making it often difficult to judge its effectiveness. Therefore, it is necessary to define methods to quantify the reduction in hazard. The partial areas method that is currently used overestimates the reduction in hazard from a single extended source with a strong central peak. [ABSTRACT FROM AUTHOR]

Phthalocyanine compounds are a class of macrocyclic conjugated structures with 18 π-electrons. And have better photophysical properties. However, the π-π electron interactions lead to aggregation between phthalocyanine molecules, which affects optical limiting properties. In this work, the conjugated organic small molecule antiphenylenediamine (PDA) is grafted onto the phthalocyanine conjugate system through the azo condensation reaction, and the covalent organic framework polymer (PDA-InPc) was obtained. Then it is doped into the polymethyl methylmethacrylate (PMMA) matrix to produce a phthalocyanine solid device with different thickness (PMMA-PDA-InPc). The aggregation-free phthalocyanine covalent organic frameworks avoids intramolecular aggregation of the phthalocyanine units, and dispersing it in PMMA solid devices can also reduce intermolecular π-π stacking. As a result, the fluorescence lifetime of PMMA-PDA-InPc is τ 1 = 0.52 ns (A 1 = 95.71%) and τ 2 = 11.5 ns (A 2 = 4.29%), indicating that the phthalocyanine conjugated unit exists mainly as monomers (95.71%), while the proportion as aggregates is very small (4.29%). At the input laser energy of 9 μJ, the nonlinear absorption coefficient of PMMA-PDA-InPc device is (2.2 × 10−9 m/W), which is significantly better than PMMA-InPc device (1.0 × 10−9 m/W), indicating that PMMA-PDA-InPc has improved nonlinear absorption and reverse saturation absorption. This design idea of non-aggregated phthalocyanine covalent organic frameworks and its solid device expands a new idea for the development of useable phthalocyanine optical limiters. A novel phthalocyanine-based covalent organic frameworks (PDA-InPc) is developed by grafting conjugated p-phenylenediamine into the phthalocyanine system. The aggregation-free phthalocyanine covalent organic frameworks (PDA-InPc) avoids intramolecular aggregation of the phthalocyanine units. The PDA-InPc is doped in PMMA, and the resulting PMMA-PDA-InPc further reduce intermolecular π-π stacking. As a result, the PMMA-PDA-InPc presents a larger number of monomers, showing superior nonlinear absorption behaviors than the PMMA-InPc samples. The PMMA-PDA-InPc show superior laser stability, which would provide new ideas for the application of phthalocyanine based optical limiters. [Display omitted] • Phthalocyanine covalent frameworks (PDA-InPc) is developed by grafting p-phenylenediamine into the phthalocyanine system. • The aggregation-free of PDA-InPc avoids intramolecular aggregation of the phthalocyanine units. • The PMMA-PDA-InPc obtained by doping PDA-InPc in PMMA, further reduces the intermolecular π-π stacking. • The PMMA-PDA-InPc presents a larger number of monomers, showing superior nonlinear absorption behaviors. • The PMMA-PDA-InPc shows good laser stability, which provides new ideas for the design of phthalocyanine based optical limiters. [ABSTRACT FROM AUTHOR]

In the present work, silver nanoparticle was synthesis by pulse laser ablation by using (Q-switched Nd:YAG) pulse duration10ns and (E=80mJ, λ=532nm) of silver metal target in deionize-water and ethanol. The results of XRD explain that not found any impurity in diffraction peaks in the pattern and Ag nanoparticles have high quality from of crystalline, which evidences the presence of silver particles with FCC structure. The optical properties were studied with Ultraviolet- Visible (UV-Vis) spectrophotometer which showed blue-shaft with pulse number, and atomic force microscope (AFM) indicates the size in nanometer (nm) range abut(40-80)nm.

Laser excitation and intensity-dependent third-order nonlinear optical (NLO) absorption properties of 2-amino 5-nitropyridinium dihydrogen phosphate (2A5NPDP) in both pulsed (532 nm, 5 ns, 100 µJ) and continuous wave (532 nm, 50 mW) regime were studied by Z-scan experiment. Under CW laser excitation, 2A5NPDP exhibits saturable absorption (SA) ascribed to be of thermo-optic origin. Interestingly the sample show reverse saturable absorption (RSA) due to genuine two-photon absorption (2PA) process under nano pulsed laser excitation. Earlier thermodynamic properties such as thermal conductivity (51 W/m.K), specific heat capacity (3894 J/Kg.K) and thermal diffusivity (7.5 × 10−6 m2/s) were estimated theoretically from the DSC curves. Thus 2A5NPDP with excellent thermal stability and high NLO coefficients can be utilized as an energy-absorbing optical limiter and saturable absorber under nano pulsed and CW green laser excitation. [ABSTRACT FROM AUTHOR]

Highlights • FTIR results confirm the occurrence of intermolecular charge transfer (ICT) within the naphtyl-azo bonds. • SA type of behavior switches to RSA in increasing concentration of carmoisine dye. • Huge magnitude of χ (3) was calculated in the order of 10−5 esu due to ICT process within the dye molecules. • Optical limiting (OL) behavior revealed the low OL threshold at 0.01 kW/cm2. Abstract Unique nonlinear optics (NLO) properties i.e. intensity-dependent nonlinear absorption and refraction of carmoisine (food dye) is studied using a single beam z-scan technique. A switchover behavior from a saturable absorption (SA) to reverse saturable absorption (RSA) is observed by increasing concentration of carmoisine dye. The flip in the absorption response is attributed to the aggregated dye molecules under intense laser beam, which induces the formation of carmoisine dimers. In the UV–Vis absorption analysis, the appearance of two bands at higher concentration confirms the formation of carmoisine dimers. Fourier transform infrared spectroscopy (FTIR) suggests the intermolecular charge transfer (ICT) within the naphtyl-azo bonds. Huge magnitude of χ (3) is calculated in the order of 10−5 esu due to ICT process within the dye molecules. Optical limiting (OL) behavior is observed with low OL action threshold ∼0.01 kW/cm2 under continuous wave laser beam. The experimental findings shows that carmoisine dye has potential as an optical material for photonics applications such as an optical limiter under low-powered continuous wave laser. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Kufa - Physics is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper theeffect of ZnO dopant on the nonlinearoptical behavior of TiO2-PMMA Nano composites films was studied. TiO2-PMMA Nano composites films were prepared using solution casting method then doped with different amounts of ZnO nanoparticles. Z-Scan measurements were performed to obtain the nonlinear optical response of these samples at 1064nm using CW Nd-YAG laser. The addition of ZnO nanoparticle into the Nano composites showed a great enhancement in the nonlinear optical response and decreasing in limiting threshold (10 mW)as the dopants concentration increased.

Copyright of Al-Qadisiyah Journal of Pure Science is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We demonstrate a near 800-nm range all-optical limiter to stabilize pulse-by-pulse peak power fluctuations of near 800-nm optical pulses. The all-optical limiter proposed here relies on intensity-dependent spectral pattern change by self-phase modulation (SPM) under zero-dispersion condition by using a photonic crystal fiber (PCF). The experimental result shows the successful output power stabilization less than 0.36 dB against the 2.0 dB input power fluctuation. [ABSTRACT FROM AUTHOR]

In this work, based on nonlocal heat effect and Fresnel diffraction theory, the characteristics of closed Z-scan in materials with a large nonlinear phase shift have been studied and a formula for Z-scan transmittance is derived. Numerical computations show that the shapes of Z-scan curves are greatly affected by the values of thermal nonlinear phase shift. The Z-scan behavior is compared to the conventional thermal Z-scan theories, including the thermal thin lens and aberrant thermal lens model. We have used the Z-scan models to determine the nonlinear refraction of gold nanoparticle (AuNP) dispersed in cyclohexanone under irradiation of a low power CW laser at 532 nm. The Z-scan theory based on the conventional models does not fit the experimental data well. It is found that peak-to-valley features of the AuNPs colloid Z-scan curve behave the same as the derived Z-scan theory for large thermal nonlinear phase shift. This allows us to measure nonlinear refractive index up to -1.0 × 10-6 cm2/W in the tested samples. The optical limiting performance of the colloidal AuNPs is also investigated for device application. The results show that the optical limiting threshold of the AuNPs can be improved by making an appropriate choice of design geometry and increasing the AuNPs concentration of the colloids. [ABSTRACT FROM AUTHOR]

An extensive study on the behavior of l -Phenylalanine capped silver nanoparticles (Phe-Ag NPs) in the aqueous phase and in a sol–gel thin film showed different UV/Vis, Transmission Electron Microscope (TEM), Dynamic Light Scattering and Zeta potential profiles. Scanning Electron Microscope (SEM) images of the samples in the sol gel film showed Ag embedded in the SiO 2 matrix. Surface Enhanced Raman Spectra (SERS) confirmed that both in the aqueous media and in the sol gel film, the attachment of Phe to the Ag NP surface was through the benzene ring, with the sol–gel film showing a better enhancement. Photocatalytic degradation of crystal violet was measured spectrophotometrically using Phe-Ag NPs as a nanocatalyst under visible light illumination. Intensity-dependent nonlinear optical absorption of Phe-Ag measured using the open aperture Z-scan technique revealed that the material is an efficient optical limiter with potential applications. [ABSTRACT FROM AUTHOR]

Metal nanoparticle-decorated low dimensional materials can synergistically combine the nonlinear optical properties of metallic/inorganic nanostructures for enhancing the optical limiting performance. While many materials exhibit excellent optical limiting performance at a relatively higher fluence (>9 J/cm 2 ), there is a still a dearth of optical limiting materials for protecting low damage threshold (<1 J/cm 2 ) photonic devices. Although metal nanoparticle-decorated graphene hybrids are expected to resolve this issue, the rehybridization of metal d-orbitals and graphene p-orbitals often lead to undesirable changes in graphene’s electronic structure which adversely affect the nonlinear optical performance. Here, we demonstrate that d-orbitals of Au nanoparticles exhibit little or no rehybridization with graphene and result in an enhanced optical limiting behavior at a low fluence of ∼0.4 J/cm 2 , which is lower than most metal decorated graphene, carbon nanotube nanocomposites and metal nanoparticles. This optical limiting performance at a lower fluence is attributed to the excellent photo-absorption of Au nanoparticles combined with rapid thermalization of excited carriers by graphene. [ABSTRACT FROM AUTHOR]

• We have demonstrated a hydrothermal technique for the synthesis of pure and Co doped V 2 O 5. • Structural, spectral and analytical properties of the materials are analyzed. • Nanostructures show both two-photon and three-photon absorption mechanisms under pulsed excitation. • The above mechanism is shown only by a limited number of metal oxides. • The nanomaterials are useful for the fabrication of optical limiting devices for protecting human eyes and devices from harmful continuous and pulsed radiation. • Open aperture Z-scan measurements reveal that both V 2 O 5 and Co doped V 2 O 5 show excellent optical limiting behaviour. V 2 O 5 nanostructures doped with 1% Co have been successfully synthesized by simple hydrothermal method. Structural and morphological aspects, vibrational spectra and optical properties (linear and nonlinear) of pristine as well as Co-doped V 2 O 5 (V 2 O 5 :Co) nanoparticles are investigated. X-ray diffraction patterns indicate that both V 2 O 5 and Co doped V 2 O 5 are stabilized in an orthorhombic structure. Energy band gaps measured using the Tauc plot give 2.24 eV for V 2 O 5 and 2.16 eV for Co doped V 2 O 5. When excited using 5 ns laser pulses at 532 nm in the open aperture Z-scan configuration, pristine as well as Co-doped V 2 O 5 nanoparticles are found to show excellent nonlinear absorption, which arises from strong reverse saturable absorption occurring in the sample at this wavelength. The corresponding effective two-photon absorption coefficients are in the range of 10−11 to 10−12 m/W, and effective three-photon absorption coefficients are in the range of 10−22 to 10−23 m3/W2. When excited at the same wavelength using a continuous wave laser beam, the effective two-photon absorption coefficient gets enhanced to 10−6 m/W. These results confirm the suitability of V 2 O 5 and Co-doped V 2 O 5 nanoparticles for the fabrication of optical limiter devices for the protection of human eyes and sensitive optical detectors from hazardous laser radiation. [ABSTRACT FROM AUTHOR]

A new organic crystal belonging to chalcone family 1-[4-(methylsulfanyl) phenyl]-3-(2,4,5-trimethoxyphenyl) prop-2-en-1-One (4MSTP) with molecular formula C19H20O4S has been synthesized by Claisen Schimidt condensation method. 4MSTP was crystallized by slow evaporation technique using methanol solution at ambient temperature. Crystals of 4MSTP were characterized by Fourier transform infrared (FTIR) spectroscopy, NMR spectroscopy, single crystal and powder X-ray diffraction (XRD) technique, thermal analysis and UV-Vis spectroscopy. Nonlinear optical properties of 4MSTP crystals were investigated using Nd:YAG laser at 532 nm wavelength. The presence of functional groups were confirmed by FTIR and the structural elucidation was done using proton and carbon NMR spectral analysis. The X-ray diffraction peaks are indexed by the least square fit method. From the single crystal XRD study it is found that 4MSTP crystallizes in monoclinic system with a centro symmetric space group P21/c. The unit cell parameters of the crystal are: a = 19.2413(6) Å, b = 8.9504(3) Å, c = 10.3608(4) Å, α = 90°, β = 104.45°(2) and γ = 90°. Linear optical studies were carried out using UV visible spectral technique. The studies revealed that the 4MSTP crystals can be exploited for the nonlinear optical applications. TGA-DSC experiments indicated that the melting point of the material is 165.91 °C and the crystals showed absence of phase transition before melting point. Calculated excited state absorption (σex) is greater than the ground state absorption (σg) and thus the condition for Reverse Saturable Absorption (RSA) is achieved in 4MSTP. The open aperture Z-Scan curve showed minimum transmittance at the focus and hence 4MSTP crystals have maximum nonlinear absorption. The variation of nonlinear transmission with input intensity of laser showed that 4MSTP crystals can be used as an optical limiter. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we present a comparative study of the optical limiting and thermo-optical responses of silicon nanocrystals (SiNCs) prepared by laser ablation in the water and dimethyl sulfoxide (DMSO). We have investigated the nonlinear thermo-optical response of the samples by using the Z-scan technique. The experimental results showed that the thermo-optical response of the studied solvents (water and DMSO) was enhanced by the presence of silicon nanoparticles. Comparison of the thermo-optical measurement of the SiNCs in the water and DMSO elucidates the contribution of the physical properties of the carrier solvent on the nonlinear response. Low power optical limiting, with low limiting thresholds is obtained in the samples based on thermal defocusing phenomenon. It was noted that the silicon nanocrystals suspended in the DMSO had better limiting characteristics and its nonlinear refractive index was comparatively high. It is shown that the role of the surrounding liquid environment on the nonlinear optical properties of the SiNC colloids is important. [Copyright &y& Elsevier]

Abstract: An adaptive optical limiter composed of nonlinear medium sandwiched between phase grating and one piece of slab is discussed under the circumstances of weak lights and intense laser pulses. The effects of refractive indices mismatch between phase grating and nonlinear medium on diffraction efficiency are investigated, which provides guidance for compounding nonlinear medium and evaluating limiting performance. [Copyright &y& Elsevier]

Gold nanoparticle embedded polyaniline (PANI) was synthesized by in situ oxidative polymerization of monomer aniline. X-ray diffraction and Fourier transform IR techniques were used to establish the structure of the gold-PANI composite. UV-visible absorption studies have shown that, along with the normal absorption peak of polyaniline, the composite has an absorption peak characterized by surface plasmon resonance. The presence of surface plasmon resonance is a signature of the nano size of the gold particles embedded in the PANI. Energy-dispersive X-ray spectroscopy (EDS) has revealed the elemental composition of the composite sample quantitatively. Raman spectroscopy studies have strengthened the presence of plasmon resonance. Single-beam Z-scan results confirm the third-order optical nonlinearity associated with the nanocomposite. The present investigations show that gold nanoparticle embedded PANI composite can be of potential application in the fields of both linear and nonlinear optics. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Intelligent control techniques consist of knowledge-based expert or fuzzy logic control. One obvious drawback in many such applications is that fuzzy logic memberships are implemented at the lowest level. In high-bandwidth processes, this form of fuzzy logic membership implementation would require high speed and accuracy in the presence of strong nonlinearities and dynamic coupling. This paper presents a novel methodology called the Opto-fuzzy method to design a fuzzy logic membership using an optical hardware component. The proposed scheme is applied to triangular-shaped and half trapezoidal-shaped membership functions. [Copyright &y& Elsevier]

Optical limiting performance of gold nanoparticles (AuNPs) in castor oil is studied using a low power laser irradiation at 532 nm. Our results suggest that it is possible to tune the optical limiting threshold of the AuNPs by modifying the parameters of the set-up and gold nanoparticle concentration of the colloids. The closed Z-scan measurements reveal that non-local thermal nonlinear refraction process is responsible for the limiting action of the colloids. We have investigated the Z-scan behavior of the samples based on the non-local thermal nonlinear refraction process without using photo-thermal thin lens approximation. It is shown that this model is in good agreement with the experimental results and large enhancement factors are measured for values of nonlinear thermal refractive index and thermo-optical coefficients of the colloids at higher gold nanoparticle concentration compared to the measurement of castor oil. [ABSTRACT FROM AUTHOR]

Abstract: Undoped and Erbium (Er) doped zinc oxide (EZO) thin films were deposited on glass substrate by sol–gel method using spin coating technique with different doping concentration. EZO films were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), UV–VIS-NIR transmission and single beam z scan method under illumination of frequency doubled Nd:YAG laser. The deposited films were found to be well crystallized with hexagonal wurtzite structure having a preferential growth orientation along the ZnO (002) plane. A blue-shift was observed in the band gap of EZO films with increasing Er concentration. All the films exhibited a negative value of nonlinear refractive index (n 2) at 532nm which is attributed to the two photon absorption and weak free carrier absorption. Third order nonlinear optical susceptibility, χ (3) values of EZO films were observed in the remarkable range of 10−6 esu. EZO (0.4at.%) sample was found to be the best optical limiter with limiting threshold of 1.95KJ/cm2. [Copyright &y& Elsevier]

Concentration dependent optical properties of the various types of porphyrin compounds were studied using optical absorbance and Z-scan measurements. Enhanced absorbance width of the Soret and Q-bands have been observed by blending three different porphyrin molecules in Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. Moreover, new evidences have been found on the concentration dependance of the nonlinear absorption coefficient (β) of the VTPP in Nafion. [ABSTRACT FROM AUTHOR]