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Nanostructured materials employed as passive nonlinear absorptive limiters offer protection to the human eyes and optical sensors from damage by pulsed laser radiation. However, such materials are prone to laser induced damage, which can be avoided or minimized by employing a robust shell layer. Here, we report the optical limiting properties of nine-atom silver quantum clusters grafted in TiO2 nanotube matrix (Ag9QCs-TNT). Nonlinear absorption revealed from open-aperture Z-scan measurements on Ag9QCs-TNT using both 5 ns (532 nm) and 100 fs (800 nm) laser pulses is larger than those observed from its pristine counterparts (Ag9QCs and TNT). The optical limiting threshold value obtained for Ag9QCs-TNT under fs excitation is smaller by a factor of five compared to that under ns excitation, indicating its ability to passively limit high intensity laser radiation for potential device applications.

Purpose: To report the intermediate-term safety and efficacy of Aurolab aqueous drainage implant (AADI) in patients with glaucoma. Methods: Retrospective review of patients who underwent AADI between January 2013 and December 2016. Patients aged >16 years and with a minimum follow-up of 6 months were included. Success was defined as complete when the intraocular pressure was ≥6 and ≤21 mmHg without antiglaucoma medication and as qualified if those requiring additional antiglaucoma medications were included. Results: The study included 55 patients (55 eyes) with a mean age ± standard deviation (SD) of 47.3 ± 18.1 years with a mean follow-up of 16.7 ± 11.4 months. Mean intraocular pressure reduced from 30.8 ± 11.1 mmHg to 13.1 ± 4.7, 14.1 ± 4.8, 15.7 ± 2.5 (P < 0.001) mmHg at 6 months, 1 year, and 2 years, respectively. The mean number of antiglaucoma medications reduced from 3.4 ± 1 to 0.8 ± 1.2, 0.7 ± 1.1, 0.8 ± 1 (P < 0.001) at 6 months, 1 year, and 2 years, respectively. The cumulative probability of complete and qualified success was 62% and 100% at 6 months, 54% and 92% at 1 year, and 43% and 88% at 2 years, respectively. Four patients failed during the follow-up period. Postoperative complication occurred in 28 eyes (51%), of which 17 eyes (31%) required intervention. Conclusion: AADI is a safe and effective treatment for the control of intraocular pressure in patients with glaucoma.

The field of NLO grew substantially over the years, facilitating a deeper understanding of light-matter interaction and providing solutions for several technological problems. Efficient nonlinear optical interactions have become essential for many applications in advanced photonics. Obtaining materials with stronger nonlinear properties is an important step towards applications. Nanoparticles and nanocomposites have become important materials for nonlinear optics in recent years because of their interesting surface effects and properties such as quantum confinement, plasmon oscillations etc., The remarkable NLO properties displayed by nanomaterials have motivated the design and fabrication of nanoscale photonic and optoelectronic devices. In this chapter we will outline the physical origins of optical nonlinearity in material media, and discuss the nonlinear optical properties reported for advanced nanomaterials in recent years. Experimental techniques will be explained and results obtained in different nanomaterials will be overviewed.

Laser surface structuring is a versatile physical method to alter the surface morphology and subsequent surface properties of solid materials. In this work, we report the role of ambient conditions in nanosecond laser (Nd:YAG laser, τ = 7 ns) surface texturing of silicon, and the optical and morphological characterization of textured samples. We performed multiscale texturing (5 mm × 5 mm) on silicon by keeping the target in air as well as in water. The significant differences in the morphological and optical properties of textured samples indicate that the ambience (air or water) has a crucial role in laser material processing. 3D topographical analysis shows that nanosecond laser texturing performed in air offers more roughness to the silicon surface, which results in much reduced optical reflection (R ≈ 10% in the visible region) from the textured surface. Laser texturing has numerous applications in material science, industry, and biomedical fields and our results indicate that materials with specific surface roughness and reflectivity can be fabricated by changing the ambient conditions of laser texturing.

We report on enhanced nonlinear optical absorption and optical limiting in β-MnO2 sponge-like nanowire network decorated with Ag nanoparticles excited by nanosecond laser. A simple two-step process is used to prepare the samples. The structure, morphology and the elemental analysis of the prepared samples are studied using x-ray diffraction, field emission scanning electron microscopy and energy-dispersive x-ray spectroscopy. Nonlinear optical absorption properties of the samples in solution is studied using the open aperture Z-scan technique employing 5 ns laser pulses at 532 nm. Nonlinear transmission measurements show that β-MnO2 exhibit weak saturable absorption at low fluence and large optical limiting at high fluence, while upon decoration with Ag particles, Ag/β-MnO2 shows strong saturable absorption at low fluence and enhanced optical limiting at higher fluence with an optical limiting threshold value three times lower than that of bare β-MnO2 nanowires. The results indicate that these materials are potentially useful for constructing saturable absorbers and optical limiters.

We report the nonlinear optical properties of graphene oxide (GO), reduced graphene oxide (rGO), sulfonated graphene oxide (S-rGO), and sparingly sulfonated water soluble graphene (WSG), measured under ultrafast (100 fs) and short pulse (300 ps, 50 ns) laser excitations at 800 nm, employing the open aperture Z-scan technique. The samples exhibit typical third order nonlinear optical behaviour including two-photon absorption (2 PA), reverse saturable absorption (RSA), and saturable absorption (SA). A significant variation in the nature of nonlinear absorption is seen when the laser pulse duration is changed. For example, RSA is prominent under nanosecond (ns) excitation, 2 PA is prevalent under femtosecond (fs) excitation, and SA is dominant under picosecond (ps) excitation. For comparison purposes the measurements are repeated using 5 ns laser pulses at 532 nm. RSA is enhanced in WSG in the nanosecond excitation domain, which can be attributed to the covalent bonding between p-phenyl-SO3H groups and sp2 graphitic planes. WSG exhibits a switching behaviour from SA to RSA upon increasing the excitation intensity under fs excitation. Results show that these graphene derivatives are potentially useful for saturable absorber and optical limiter device applications.

PURPOSE To compare the effect of mannitol in reducing intraocular pressure (IOP) in vitrectomized and nonvitrectomized eyes. MATERIALS AND METHODS Prospective comparative case study. Eyes with IOP≥40 mm Hg were included. Eyes which are vitrectomized and silicon oil filled were classified as group 1, and nonvitrectomized open-angle eyes were classified as group 2. Mannitol (20%, 1 g/kg) was administered intravenously over 30 minutes, and IOP was recorded at 30 minutes interval till 2 hours and at the third and fourth hour from the start of mannitol. RESULTS Thirty eyes (patients) were recruited in each group. Mean (SD) IOP reduced from 48.5±5.2 to 43.7±8 at 30 minutes, 40.7±8.4 at 60 minutes, 37.3±9.6 at 90 minutes, 35.6±10.4 at 2 hours, 34±10.7 at 3 hours, and 33±11.2 mm Hg at 4 hours in group 1, and from 48.9±6.5 to 43.2±8.6 at 30 minutes, 40.2±7.8 at 60 minutes, 36.7±7.3 at 90 minutes, 35.1±7.7 at 2 hours, 34.2±8.8 at 3 hours, and 35.7±9.4 mm Hg at 4 hours in group 2. There was a significant reduction in IOP at each time point compared with baseline in both the groups (P

A series of MnxZn1-xO (x=0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in ebeam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters

Development of tunable photonic devices having molecular dimensions is an active research area in nonlinear optics which continues to evolve and impact many technologies. Here, we demonstrate the tailoring of nonlinear optical properties of nitrochalcone derivatives by engineering the donor-acceptor configurations on either end of the molecules, to control the intramolecular charge transfer process. The central π-bridge in chalcones provides delocalized electrons which lead to the nonlinear polarizability observed in these molecules. Optical nonlinearity is studied by means of second harmonic generation (SHG) and open aperture Z-scan measurements. Samples show optical limiting behaviour in the nanosecond excitation regime due to excited state absorption (ESA) and two-photon absorption (2PA) phenomena. Our study highlights the importance of structure-property correlations in molecular designs.

We demonstrate pyrolytic synthesis of nitrogen-doped multiwalled carbon nanotubes (NCNTs) incorporated with graphite-encapsulated FeCoCr alloy nanoparticles (FeCoCr@CN sample) and report their non-linear optical absorption (NLA) behaviour. The NCNTs present in the FeCoCr@CN sample were bamboo-type with box-shaped compartments. The improved electrical conduction in NCNTs, due to high degree of graphitization associated with optimum defect-concentration in the graphitic layer covering the FeCoCr-nanoparticles and nanotube structure, provides the non-linear absorption conditions required for their application in optical limiting devices. Our results emphasize the excellent optical limiting performance of our samples which originates mainly due to excited state absorption (ESA) and free carrier absorption (FCA) processes. The defect induced modification of the electronic properties of the graphitic carbon framework (due to nitrogen-doping) culminates the enhanced ESA of the laser beam. In addition, the choice of metallic FeCoCr-alloy nanoparticles provide two fold advantage in enhancing NLA: (i) it induces high graphitization on its surface than that expected due to the individual constituent metals, thereby enhancing the ESA effect, and (ii) being metallic, it leads to NLA via FCA. Our results highlight the superior NLA performance of our FeCoCr@CN sample, making it an excellent choice for its direct industrial use as laser shields.

Ultrafast optical nonlinearity in chitosan (CS) films doped with multi-walled boron nitride nanotubes (MWBN) has been investigated using 800 nm, 100 fs laser pulses, employing the open aperture Z-scan technique. Two-photon absorption coefficients (β) of CS–MWBN films have been measured at 800 nm by Z-scan. While chitosan with 0.01% MWBN doping gives a β value of 0.28×10−13 m/W, 1% doping results in a higher β value of 1.43×10−13 m/W, showing nonlinearity enhancement by a factor of 5. These nonlinearity coefficients are comparable to those reported for silver nanoclusters in glass matrix and Pt-PVA nanocomposites, indicating potential photonic applications for MWBN doped chitosan films. Characterization of the synthesized films using Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) reveals significant interactions between the NH and CO groups of chitosan with boron nitride.

In this paper, we report nonlinear optical properties of a composite nanostructure with the general formula (1−x) CaFe2O4–(x) BaTiO3 (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) prepared by sol–gel and conventional solid-state reaction methods. Structural properties and chemical compositions of the samples were characterized using XRD and HRTEM. Basic optical constants, band gap energy and linear absorption coefficient were calculated through optical absorbance measurements. The nonlinear optical properties were investigated using the single-beam open aperture Z-scan technique. The obtained nonlinearity fits to Two-photon absorption process and all samples display high nonlinear absorption effect. The incorporation of BaTiO3 into CaFe2O4 systems show a significant improvement in the nonlinear optical properties. These composite that exhibit efficient optical limiting can have potential applications in photonic devices.

We herein report a rapid and effective method for the synthesis of graphene oxide quantum dots (GOQDs) with excellent linear and nonlinear optical properties. The GOQDs were prepared by chemical cutting of graphite oxide and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, UV–Vis absorption spectroscopy, Raman spectroscopy and transmission electron microscopy. The Commission International de l’Eclairage 1931 chromaticity coordinates for GOQDs (x = 0.21, y = 0.23) demonstrated that highly pure blue-light emission was achieved upon 330 nm excitation wavelength. Optical nonlinearity measurements conducted at 532 nm using 5 ns laser pulses indicated saturable absorption behavior, which tends to the onset of reverse saturable absorption as the input light fluence was increased.

We report comparative measurements of size dependent nonlinear transmission and optical power limiting in nanocrystalline magnesium ferrite (MgFe2O4) particles excited by short (nanosecond) and ultrashort (femtosecond) laser pulses. A standard sol–gel technique is employed to synthesize particles in the size range of 10–50 nm, using polyvinyl alcohol as the chelating agent. The structure and morphology of the samples are studied using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Growth of the particles in time is tracked through Fourier transform infrared spectroscopy. Nonlinear transmission measurements have been carried out using the open aperture Z-scan technique employing 532 nm, 5 nanosecond pulses and 800 nm, 100 femtosecond pulses, respectively. The measured optical nonlinearity is primarily of a reverse saturable absorption (RSA) nature, arising mostly from excited state absorption for nanosecond excitation, and two-photon absorption for femtosecond excitation. The optical limiting efficiency is found to increase with particle size for both cases. The calculated nonlinear parameters indicate that these materials are potential candidates for optical limiting applications.

In this work, we report the fabrication and characterization of large area micro-/nano-textured silicon surfaces using laser pulses of nanoseconds duration. An area of 6 × 6 mm 2 has been textured by the parallel line scanning method to create hierarchical structures, consisting of microscale channels and self-organized surface nano-capillaries decorated with randomly distributed silicon nanoparticles. The combination of micro-channels and nano-capillaries results in a superhydrophilic silicon surface, with the contact angle reduced substantially from about 80 ° to nearly 5 °. In contrast to most of the reports given in the literature, the superhydrophilicity of the surface remains stable without a shift to hydrophobicity, even after exposure to the atmosphere for about three months. Thus, long-lasting and durable superhydrophilic silicon has been obtained by using maskless, compact, and cost-effective nanosecond laser writing, without the need to employ any chemical post-processing. Potential applications of these surfaces include heat exchangers, biosensors, cell adhesives, and self-cleaning solar cells.

The effect of variation of band gap and electronic defect energy levels within the band gap on non-linear optical absorption of 532 nm (green) laser light by coral-like yttrium aluminium-iron garnet (YAIG, Y3Al5-xFexO12) ceramics prepared by solution combustion route is investigated using Z-scan technique. Our yttrium aluminium garnet (YAG) sample with band gap of ≥ ~ 6.5 eV, is transparent to visible light. The band gap of YAG was tuned by substituting Fe at the aluminium site and consequently, the surface defects in YAG were also modified. The defects in the YAIG samples introduce electronic defect states within the band gap. We observed that the intensity of the non-linear absorption (NLA) signal increases with increase in the amount of iron content. We assigned this enhancement of NLA signal to: (1) the decrease in the band gap from ≥ ~ 6.5 eV for YAG to ~ 2.6 eV for yttrium iron garnet (YIG) facilitating two photon absorption (2 PA) process rather than three photon absorption (3 PA), and (2) the increase in excited state absorption (ESA) due to the spread of the defect energy states into the band gap region. As the band gap gets closer to the photon energy of the laser, the non-linear optical absorption is enhanced due to ESA, in combination with the occurrence of the relatively stronger 2 PA process rather than the very weak 3 PA process. Our results demonstrate a method to tune the NLA performance of YAG through iron substitution at the Al sites and provide a better understanding of the non-linear absorption behaviour of YAIG ceramics for their application in optical limiting devices such as laser shields.

Lead-free perovskite materials with superior physical properties are currently explored for ferroelectric and optoelectronic applications. Ferroelectric materials that have large spontaneous polarization concomitantly possess large nonlinear optical response which is highly suitable for novel photonic applications. Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) is one such novel lead-free ferroelectric material with large piezoelectric response arising from existence of morphotropic phase boundary. Conventional sol–gel technique was adopted for synthesizing nanostructured BCZT (nano-BCZT) powder using citrate precursor route. X-ray powder diffraction confirmed the phase purity and high-resolution transmission electron microscopy (HRTEM) proved that the as-synthesized BCZT was indeed nanostructured. Supportively, Raman vibrational analysis was employed to validate the site occupancies of dopants and structural correlations when compared to undoped and pristine barium titanate. Nanostructured barium titanate is extensively studied as biomarkers in second harmonic generation (SHG) microscopy for bio-medical applications. In our current work, we have explored both second- and third-order nonlinear optical response of nano-BCZT. These were found to exhibit stronger SHG signal than potassium di-hydrogen phosphate (KDP) which is a well-known SHG standard. Subsequently, we also have investigated their third-order nonlinear optical properties using open aperture Z-scan technique at 532-nm excitation wavelength in the nanosecond regime. Nano-BCZT was found to exhibit strong two-photon absorption behavior. Such materials with multiphoton absorption behavior are favorable for nonlinear photonics devices such as optical limiters and contrast agents in nonlinear optical microscopy.

The hydrodynamic expansion features of a laser-produced plasma is governed by initial plume conditions and hence the spot size of the laser beam.1–3 In this work, we investigated the expansion dynamics of a laser produced-plasma as a function of laser spot diameter in a vacuum environment (10–5 Torr) using multiple diagnostic tools. The diagnostic tools used were space- and time-resolved optical emission spectroscopy, 2-D fast-gated self-emission imaging and ion analysis using Faraday cup. The plume dynamics measured for varying spot sizes involves intriguing physics and hence demands detailed investigations, in view of a multitude of applications of laser ablation (LA) including elemental detection (LIBS, LA-LIF etc.), micromachining, laser-welding, nano-structuring, ion beam generation and pulsed laser deposition.

Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for various applications, although many of them suffer from reduced efficiencies at high‐light fluences due to photoinduced deterioration. The nonlinear optical properties of ferrite core/shell nanoparticles showing their robustness for ultrafast optical limiting applications are reported. At 100 fs ultrashort laser pulses the effective two‐photon absorption (2PA) coefficient shows a nonmonotonic dependence on the shell thickness, with a maximum value obtained for thin shells. In view of the local electric field confinement, this indicates that core/shell is an advantageous morphology to improve the nonlinear optical parameters, exhibiting excellent optical limiting performance with effective 2PA coefficients in the range of 10−12 cm W−1 (100 fs excitation), and optical limiting threshold fluences in the range of 1.7 J cm−2. These values are comparable to or better than most of the recently reported optical limiting materials. The quality of the open aperture Z‐scan data recorded from repeat measurements at intensities as high as 35 TW cm−2, indicates their considerably high optical damage thresholds in a toluene dispersion, ensuring their robustness in practical applications. Thus, the high photostability combined with the remarkable nonlinear optical properties makes these nanoparticles excellent candidates for ultrafast optical limiting applications., The authors acknowledge the support of the 2014‐SGR‐1015 project of the Generalitat de Catalunya. A.L.‐O. acknowledges the Spanish Ministrio de Economía y Competitividad through the Juan de la Cierva Program (Grant No. IJCI‐2014‐21530). ICN2 is founded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, Grant No. SEV‐2013‐0295).

We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm � 2 , and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices.

Absorption saturation due to surface plasmon resonance affects the optical limiting efficiency of metal nanoparticles (NPs) by raising the limiting threshold to higher laser fluences. It has been shown that in gold, compared to the larger NPs, smaller quantum clusters (QCs) exhibit better optical limiting with lower limiting thresholds due to the absence of absorption saturation. Here we report optical limiting properties of two novel materials, namely, nine-atom silver (Ag9) QCs and graphitic carbon nitride (GCN) nanosheets. The relatively large nonlinear absorption of Ag9 QCs compared to Ag NPs is revealed from open-aperture Z-scan measurements carried out using 532 nm, 5 ns laser pulses. Optical nonlinearity in the QCs arises mostly from free carrier absorption and a relatively weak saturable absorption. The superior limiting efficiency of Ag9 QCs is complemented by excellent chemical stability, which makes silver quantum clusters ideal candidates for optical limiting applications. The two-dimensional ...

We report a cubic to amorphous transformation of selenium in silica xerogel prepared through a sol–gel route. The crystalline nature of the nanoparticles examined from the SAED pattern and HRTEM revealed an α-cubic structure. The band gap energies calculated from the UV-vis absorption measurements showed a higher band gap of 3.5 eV for the cubic form compared to 2.4 eV for the amorphous form. The ultrafast optical nonlinearity of the samples was investigated by an open aperture Z-scan at 800 nm using 100 fs laser pulses. Although doping with cubic Se did not improve the optical limiting efficiency of silica xerogels, doping with amorphous Se results in substantial enhancement. Numerical analysis of the Z-scan data attributed the nonlinearity to two-photon and three-photon absorption and two-photon induced free carrier absorption. These intensity-dependent, instantaneous nonlinearities make amorphous Se doped silica xerogels attractive candidates for the design of ultrafast optical limiter devices.

A new series of discotic liquid crystals based on a truxene core has been synthesized to study the structure–property relationship in view of the self-assembling property and their linear and nonlinear optical properties. All these branched alkyl chain truxene derivatives show a mesogenic property in a columnar hexagonal fashion at room temperature which is studied by a combination of different techniques. The newly synthesized truxene discotic 7a possesses a clearing temperature of 117 °C, one of the lowest clearing temperatures known in truxene discotic liquid crystals. We have discovered that the introduction of branching near to the core even in a small alkyl chain drastically reduces the isotropic temperature. Due to their C3 symmetry and their large first hyperpolarizability, these truxene derivatives show long-lived emissions in the solution state at room temperature. We also report large effective three-photon absorption in these materials under nanosecond laser pulse excitation at 532 nm, which makes them suitable candidates for optical limiting applications.

A versatile approach to the fabrication of cadmium oxide (CdO) nanospheres, nanoflakes and nanoparallelepiped shapes through chemical precipitation and hydrothermal methods is studied. The growth mechanism of nanostructures is elucidated on the basis of capping agent and reaction time. The crystalline nature and various geometrical shapes of nanostructures are examined by X-ray diffraction and high resolution transmission electron microscopic analysis. Nonlinear optical absorption and optical power limiting studies of nanostructures are carried out using the open aperture z-scan technique in the nanosecond (ns) and femtosecond (fs) excitation time scales. Optical nonlinearity is found to arise from effective two- photon absorption involving excited state absorption. The magnitude of the effective two-photon absorption coefficient is calculated and found to be in the range of 10−10 m W−1 for ns and 10−15 m W−1 for fs. The nonlinear optical study discloses that the nonlinear optical absorption and optical limiting threshold values are strongly related to nanomaterial morphology. The Brunauer–Emmett–Teller (BET) surface area analysis also confirms our claim that the optical nonlinearity is strongly dependent on the morphology as well as surface area of the nanomaterial. Thus the present nanomorphotypes have potential applications in devices for optical limiting, optical switching, pulse shaping, pulse compression and optical diode action.

We report the synthesis of ZnO:Au hetero structures, their Raman scattering and optical power limiting efficiencies. ZnO:Au nanostructures with flower-like morphology were obtained by the self-assembly of ZnO nano entities using Au nanoparticles as seeds. Compared to ZnO nanostructures, ZnO:Au nanocomposites show enhanced UV emission and decrease in green emission. Increases in the intensities of Raman bands and multiphonon Raman bands of nano ZnO are observed substantially in the nanocomposites. Raman results further indicate that lattice vibrations of semiconductors are sensitive to the presence of metal nanoparticles. Open aperture Z-scan measurements carried out at 532 nm using 5 ns laser pulses reveal metal nanoparticle induced changes in the optical limiting properties of the nanocomposites.

Photorefractive polymer composites have gained considerable attention due to their fascinating applications like 3D displays and 3D Telepresence. In this report, the performance of a novel PR polymer composite doped with graphene is studied. The addition of graphene laminates to a photorefractive composite results in up to threefold enhancement of space charge (SC) field build-up time. From our optical and electrical measurements, the faster build-up time is attributed to larger charge generation resulting from electronic interaction between graphene and the 7-DCST chromophores.

In laser-produced plasma experiments, the diameter of the irradiating laser beam on the target surface is a major parameter that influences the ablation mechanisms, plasma emission intensity, charged particle ejection, and plume morphology. In this work, the expansion dynamics of an ultrashort laser-produced aluminum plasma is investigated as a function of the laser beam size on the target, using a combination of diagnostic tools, viz., optical emission spectroscopy, fast gated time-resolved imaging, and ion current measurements. A Ti:sapphire laser delivering 100 fs, 6 mJ pulses at 800 nm is used for producing plasma from a pure Al target placed in vacuum (10−5 Torr) at different positions with respect to the geometrical focus of the beam. Optical emission spectroscopic analysis of the plasma shows that higher emission intensities and ion populations are obtained for smaller beam sizes. Time-resolved Intensified Charge Coupled Device (ICCD) imaging of the expanding plasma shows a spherical morphology for plumes produced by smaller beam sizes and a cylindrical morphology for those produced by larger beam sizes. Temporal profiles of ion emission measured using a Faraday cup are in agreement with ICCD data, featuring a dual peak structure for larger beam sizes indicating distinct slow and fast ionic species, arising from changes in the ablation mechanism for varying laser fluences. Plume expansion is modelled by free expansion for the fast species and by shock wave propagation for the slow species. Ion flux and velocities are relatively high for smaller beam sizes. These studies can be of potential importance for laser processing applications, including laser welding, drilling, and micromachining.

Nanostructured carbons are posited to offer an alternative to silicon and lead to further miniaturization of photonic and electronic devices. Here, we report the experimental realization of the first all-carbon solid-state optical diode that is based on axially asymmetric nonlinear absorption in a thin saturable absorber (graphene) and a thin reverse saturable absorber (C60) arranged in tandem. This all-optical diode action is polarization independent and has no phase-matching constraints. The nonreciprocity factor of the device can be tuned by varying the number of graphene layers and the concentration or thickness of the C60 coating. This ultracompact graphene/C60 based optical diode is versatile with an inherently large bandwidth, chemical and thermal stability, and is poised for cost-effective large-scale integration with existing fabrication technologies.

In this letter we investigate nonlinear optical properties of amorphous selenium (a-Se) nanoparticles and trigonal selenium (t-Se) nanowires using the open aperture Z-scan, employing 100 fs and 5 ns laser pulses, at 800 nm and 532 nm, respectively. In the former case (ultrafast excitation) optical nonlinearity arises largely from absorption saturation and three-photon absorption, whereas in the latter (short-pulse excitation) it occurs mostly due to excited state absorption. Nonlinearity parameters for both regimes have been numerically evaluated from experimental data. Both allotropes are found to be efficient optical limiters, particularly for short-pulse excitation, with potential applications in laser safety devices.

Fluorination of carbon nanomaterials has many advantages due to the unique nature of the carbon–fluorine (C–F) bond. In this work, we report the optical power limiting properties of fluorinated graphene oxide (F–GO) using the optical z-scan technique. In addition, we used the photoacoustic technique to gain insight into the nonlinear processes involved in the optical limiting of samples. The photoacoustic technique enabled us to confirm that optical limiting observed in F–GO at low fluence arises from nonlinear absorption, while that at higher fluence is due to nonlinear scattering. Moreover, we found that F–GO has high nonlinear absorption and nonlinear scattering and its optical limiting threshold is about an order of magnitude better than that of graphene oxide (GO).

Atomic clusters of metals are an emerging class of extremely interesting materials occupying the intermediate size regime between atoms and nanoparticles. Here we report the nonlinear optical (NLO) characteristics of ultrasmall, atomically precise clusters of gold, which are smaller than the critical size for electronic energy quantization (∼2 nm). Our studies reveal remarkable features of the distinct evolution of the optical nonlinearity as the clusters progress in size from the nonplasmonic regime to the plasmonic regime. We ascertain that the smallest atomic clusters do not show saturable absorption at the surface plasmon wavelength of larger gold nanocrystals (>2 nm). Consequently, the third-order optical nonlinearity in these ultrasmall gold clusters exhibits a significantly lower threshold for optical power limiting. This limiting efficiency, which is superior to that of plasmonic nanocrystals, is highly beneficial for optical limiting applications.

We report a novel functionality for the ferroelectric-antiferromagnet YCrO 3 powder of optical limiting upon illumination by nanosecond laser pulses at 532 nm. The optical limiting properties are investigated using the open aperture z -scan technique. The obtained nonlinearity fits to a three-photon like absorption mechanism. It is proposed that this nonlinearity is caused by two-photon absorption, followed by excited state absorption. Two different sized samples were investigated and the nonlinearity is found to be size dependent.

Nonlinear optical effects are revealed when strong light fields interact with matter. It has been shown that nanomaterials exhibit properties which are very different from the bulk, and in many cases, the nonlinear optical (NLO) efficiency of nanomaterials is found to be higher in comparison. Recently there has been substantial interest in developing novel NLO media for various applications. Even though several organic as well as inorganic materials have been studied in this connection, only a limited number of NLO reports exist for oxide nanomaterials. Therefore, in this paper we present results of NLO measurements recently conducted in our laboratory in three different oxide nanosystems. It is found that oxide nanomaterials are generally robust, and exhibit good NLO efficiencies, which make them potential candidates for photonic and optoelectronic applications.

This research article describes a technique to synthesize new donor−acceptor-type conjugated polymers carrying 1,3,4-oxadiazolyl-naphthalene and 3,4-(ethylenedioxy/diphenyl)-thiophene moieties (P1 and P2) starting from 2,2′-sulfanediyldiacetic acid and diethyl ethanedioate through multistep reactions. The newly synthesized intermediates and the final polymers have been characterized by different spectroscopic techniques followed by elemental analysis. Their optical and electrochemical properties have been investigated by UV–visible, fluorescence spectroscopy, and cyclic voltammetric studies, respectively. Furthermore, the nonlinear optical transmission properties of these polymers have been investigated by the open aperture z-scan technique. The new polymers P1 and P2 have well-defined structures, good thermal stability, and band gaps of 1.98 and 1.88 eV, respectively. They emit bluish-green fluorescence both in solution and in film state. Interestingly, these polymers show saturable absorption behavior. The results of nonlinear optical studies reveal that they are potential candidates for photonic switching device applications. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 312–321, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20227

We report the spectral and optical limiting properties of two kinds of HAP nanoparticles (pure HAP and HAP@SiO2 core–shell nanoparticles) that were wet-chemically prepared and coated with silica by means of Stober method. The size, framework substitution and silica coating formation of the resultant particles were confirmed by Transmission Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetric analysis. The nonlinear optical limiting properties of HAP and HAP@SiO2 nanoparticles suspended in ethylene glycol is studied at 532 nm using 5 ns Nd:YAG laser pulses. Observations indicate that effective three-photon absorption is found to be responsible for strong optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity is enhanced in core–shell structures as compared with single counterparts. The nonlinear optical parameters calculated from the data show that these materials are efficient optical limiters.

Nanocomposite thin films consisting of Cu nanoparticles embedded in silica matrix were synthesized by atom beam co-sputtering technique. Plasmonic, optical, and structural properties of the nanocomposite films were investigated by using ultraviolet (UV)–visible absorption spectroscopy, nonlinear optical transmission, X-ray diffraction (XRD), and low-frequency Raman scattering. UV–visible absorption studies revealed the surface plasmon resonance absorption at 564 nm which showed a red shift with increase in Cu fraction. XRD results together with surface plasmon resonance absorption confirmed the presence of Cu nanoparticles of different size. Low-frequency Raman studies of nanocomposite films revealed breathing modes in Cu nanoparticles. Nanocomposites with lower metal fractions were found to behave like optical limiters. The possibility of controllably tuning the optical nonlinearity of these nanocomposites could enable them to be the potential candidates for applications in nanophotonics.

Nonlinear optical (NLO) materials are useful in many of the industrial applications. New NLO chalcone derivative (2 E )-3-[4-(methylsulfanyl)phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (4N4MSP) crystals have been grown by slow evaporation technique at ambient temperature. The grown crystals were subjected to single crystal X-ray diffraction study. The crystal has noncentrosymmetric structure in the orthorhombic system with space group Aba2 and unit cell parameters a =14.0647(15) A, b =33.738(4) A and c =6.0039(6) A. To confirm the presence of various functional groups in the compound, FT-IR spectrum was recorded. The crystal was subjected to TGA/DTA analysis to find its thermal stability. The grown crystals were characterized for their optical transmission and mechanical hardness. The second harmonic generation (SHG) efficiency of the crystal is obtained by classical powdered technique using Nd:YAG laser and its value is 28.57 times that of urea. The laser damage threshold for 4N4MSP crystal was determined using Q-switched Nd:YAG laser. The refractive index values for green and red wavelengths were measured by Brewster angle technique. The dielectric and electrical measurements were carried out to study the different polarization mechanism and conductivity of the crystal. Good thermal, mechanical, transmission and SHG response make it desirable for the NLO applications.

The novel nonlinear optical chalcone derivative (2E)-3-[4-(methylsulfanyl)phenyl]-1-(3-bromophenyl)prop-2-en-1-one (3Br4MSP) crystals have been grown by slow evaporation technique at ambient temperature. The crystal was subjected to different types of characterization method in order to study its possible application in nonlinear optics. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. The morphology of the crystal is studied. The crystal was subjected to thermal analysis to find its thermal stability. The grown crystals were characterized for their optical transmission and mechanical hardness. The second harmonic generation (SHG) efficiency of the crystal is obtained by classical powdered technique. The laser damage threshold for 3Br4MSP crystal was determined using Q-switched Nd:YAG laser.

A new donor–acceptor-type poly[3-{5-[3,4-didodecyloxy-5-(1,3,4-oxadiazol- 2-yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}-9-dodecyl-9H-carbazole] (P) has been synthesized through multistep reactions. The new polymer P exhibited good thermal stability and film-forming behavior. The electrochemical band gap is estimated to be 2.15 eV. The polymer emits intense green fluorescence in the solid state. Third-order nonlinear optical (NLO) studies showed that the strong absorptive nonlinearity observed for the polymer is of the optical limiting type, which is due to an “effective” three-photon absorption (3PA) process. This 3PA process can have potential applications in photonic devices. The studies revealed that the new polymer P is a promising material for development of efficient optoelectronic devices.

We have synthesized Dy3+-doped ZnO nanoparticles at room temperature through the sol-gel method. X-ray diffraction and Scanning electron microscopic studies confirm the crystalline nature of the particles. Excitonic absorption of ZnO shows three different bands, and we observe that incorporation of Dy3+ results in the shifting and broadening of the n=1 absorption band of ZnO. Photoluminescence studies done at the excitation wavelength of 335 nm show broad emission containing five different bands. Open-aperture z-scan studies done at 532 nm using 5 ns laser pulses show an optical limiting behavior, which numerically fits to a three-photon type absorption process. The nonlinearity is essentially resonant, as it is found to increase consistently with Dy3+ concentration. This feature makes Dy3+-doped ZnO a flexible optical limiter for potential device applications.

Laser-induced periodic surface structuring is a powerful technique for modifying the surface properties of solids. Using ultrashort pulses from a Ti:sapphire laser (800 nm, 100 fs), we have fabricated nanoscale order laser-induced periodic surface structures (LIPSSs) on a silicon (100) surface. The LIPSS patterns are found to be strongly dependent on the laser pulse energy, state of polarization, number of shots delivered on the target, and the ambient pressure. The role of laser wavelength is studied by using the second harmonic output (400 nm) also for fabrication. Large area (5 × 4 mm2) surface structuring has been carried out at atmospheric pressure after optimizing the laser parameters at 800 nm. The patterned silicon surface shows a substantial reduction in the reflection of incident light over a wide range of wavelengths, in comparison to plain silicon. Moreover, when used for laser induced breakdown spectroscopy experiments, enhanced optical emission and ion current have been observed from the patterned surface. This indicates that the coupling of laser energy to the surface is enhanced in the case of patterned silicon. While spectral lines emitted by doubly ionized silicon have been observed from the patterned surface, the plain surface gives lines from singly ionized silicon only. A discernible enhancement has been measured in both optical (50%–90%) and electrical (34%) signals from the plasma generated on the patterned surface. These results confirm that LIPSS is a versatile method for enhancing the coupling of laser energy onto irradiated solid surfaces.Laser-induced periodic surface structuring is a powerful technique for modifying the surface properties of solids. Using ultrashort pulses from a Ti:sapphire laser (800 nm, 100 fs), we have fabricated nanoscale order laser-induced periodic surface structures (LIPSSs) on a silicon (100) surface. The LIPSS patterns are found to be strongly dependent on the laser pulse energy, state of polarization, number of shots delivered on the target, and the ambient pressure. The role of laser wavelength is studied by using the second harmonic output (400 nm) also for fabrication. Large area (5 × 4 mm2) surface structuring has been carried out at atmospheric pressure after optimizing the laser parameters at 800 nm. The patterned silicon surface shows a substantial reduction in the reflection of incident light over a wide range of wavelengths, in comparison to plain silicon. Moreover, when used for laser induced breakdown spectroscopy experiments, enhanced optical emission and ion current have been observed from the pat...

We have analyzed the effects of the laser pulse wavelength (400 nm) on femtosecond laser surface structuring of silicon. The features of the produced surface structures are investigated as a function of the number of pulses, N, and compared with the surface textures produced by more standard near-infrared (800 nm) laser pulses at a similar level of excitation. Our experimental findings highlight the importance of the light wavelength for the formation of the supra-wavelength grooves, and, for a large number of pulses (N ~ 1000), the generation of other periodic structures (stripes) at 400 nm, which are not observed at 800 nm. These results provide interesting information on the generation of various surface textures, addressing the effect of the laser pulse wavelength on the generation of grooves and stripes.

A new donor–acceptor type poly{2-(3,4-didecyloxythiophen-2-yl)-5-[3,4-diphenyl-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazole} (P1) has been designed and synthesized starting from thiodiglycolic acid, 1,2-diphenylethane-1,2-dione, and diethyl oxalate through multi-step reactions using precursor polyhydrazide route. The charge-transporting and linear optical property of the polymer has been investigated by cyclic voltammetric, UV–visible, and fluorescence emission spectroscopic studies. The UV–visible absorption spectrum of polymer in thin film form showed maxima at 420 nm. The polymer displayed bluish-green fluorescence both in solution and thin film form. The optical band gap is determined to be 2.27 eV. Third-order nonlinear optical property of the new polymer has been investigated at 532 nm using single beam Z-scan and degenerate four wave mixing (DFWM) techniques with nanosecond laser pulses. The absorptive nonlinearity observed for the polymer P1 is of optical limiting type, which arises due to an “effective” three-photon absorption (3PA) process. The third-order nonlinear optical susceptibility (χ(3)) of the polymer is found to be 0.831 × 10–12 esu. Both linear and nonlinear optical studies revealed that the new polymer (P1) is a promising material for applications in photonic devices.

We report spectroscopic investigations of an ultrafast laser induced plasma generated in a planar water microjet. Plasma recombination emissions along with the spectral blueshift and broadening of the pump laser pulse contribute to the total emission. The laser pulses are of 100 fs duration, and the incident intensity is around 1015 W/cm2. The dominant mechanisms leading to plasma formation are optical tunnel ionization and collisional ionization. Spectrally resolved polarization measurements show that the high frequency region of the emission is unpolarized whereas the low frequency region is polarized. Results indicate that at lower input intensities the emission arises mainly from plasma recombinations, which is accompanied by a weak blueshift of the incident laser pulse. At higher input intensities strong recombination emissions are seen, along with a broadening and asymmetric spectral blueshift of the pump laser pulse. From the nature of the blueshifted laser pulse it is possible to deduce whether the rate of change of free electron density is a constant or variable within the pulse lifetime. Two input laser intensity regimes, in which collisional and tunnel ionizations are dominant respectively, have been thus identified.

Thin films of (Pb1−xSrx)TiO3, x=0,0.5,1.0 have been prepared on glass substrates by the chemical-solution method using the spin-coating technique. The optical nonlinearity in the visible spectral region is investigated using short (5 ns) laser pulses at the off-resonant wavelength of 532 nm employing the open aperture z-scan technique. It is found that the third order nonlinear absorption is dependent on the lead content of the films, with the compositions x=0, 0.5 exhibiting large values (β∼10−7 m/W), thereby suggesting the possible use of these materials as optical limiters. No optical nonlinearity is observed for the composition with x=1.0.