Z-scan Data Research Articles

Role of Zn in tuning the band gap, surface morphology, photoluminescence and optical nonlinearities of CdO nanostructures for photonic device applications

We report the role of Zn doping on third-order nonlinear optical properties (NLO) of CdO thin films. Thin Cd1−xZnxO’films’ was prepared using the spray pyrolysis (SP) technique [with x = 0, 0.01, 0.05 and 0.1 at. %] to study the morphological, surface morphology, linear optical, photoluminescence and NLO properties. The study of x-ray diffraction (XRD) revealed the crystalline nature of the prepared thin films, and the Zn-doping improves the crystallite size. The’ films morphology is mainly influenced by the’doping’shown by the images of FESEM (field emission scanning electron microscopy). As the doping concentration of Zn increases, the direct energy band-gap (Eg) value increased from 2.51 eV to 2.60 eV for undoped CdO to 10% of Zn doped CdO. Room temperature photoluminescence spectra (RTPL) of the prepared samples are investigated for an in-depth understanding of the conduction band behavior of defect states. Z-scan data showed strong’two-photon absorption’(2PA) for the deposited films and with an’increase in doping concentrations’from 0 to 10 (at %), the’nonlinear absorption coefficient (β) increasing from 1.22 × 10–4 to 4.50 × 10–4 (cmW−1), nonlinear refractive index from 7.06 × 10–9 to 1.30 × 10–8 (cm2W−1) and χ(3) i.e. third-order NLO susceptibility’values also increased from 4.03 × 10–7 to 7.31 × 10–7 (esu). Optical Limiting characteristics of the prepared films was studied at the experimental wavelength. The inspiring results of the NLO properties propose that Cd1−xZnxO thin film is an accomplished and promising material for’NLO’device applications.

Light-matter Interaction Under Intense Field Conditions: Nonlinear Optical Properties of Metallic-dielectric Nanostructures

Background: Metallic–dielectric plasmonic nanoparticles have recently aroused great interest in view of many and novel technological applications, based on the interaction between light and matter under intense field conditions, in nonlinear integrated photonics and opto-fluidics, thanks to the possibility of tuning their electronic and optical properties through a fine control of the synthesis parameters and their nanoparticles under a high-power laser, like the one used during z-scan measures. Objective: The goal of this work is the study of nonlinear optical properties (as nonlinear refraction, scattering, two-photon absorption, optical limiting) of colloids synthesized in different liquid media by Pulsed laser ablation in liquids (PLAL), which is a photo-assisted synthesis technique ensuring the formation of stable, contaminant-free colloids directly during the ablation process. Methods: Noble metal nanoparticles, metal oxides hybrid nanostructures and silicon-based nanomaterials, were prepared by nanosecond and picosecond PLAL technique, in different media. The third-order nonlinear optical (NLO) properties have been studied by the use of a single beam z-scan technique with Q-switched frequency doubled Nd:YAG laser (λ=532 nm) at 5 ns pulse. Results: 1) A good stability of the PLAL nanocolloids under a high laser power; 2) the limiting threshold reduction inducted by the Ag-Au nanoparticles, the increase of the NLO absorption coefficient β, the reduction of the transmittance/scattering signal and the presence of a pronounced asymmetry of the peak/valley profile of the metal decorated metal oxide nanomaterials compared to the separately produced components. Conclusion: An intriguing coupling between the nature of the optical limiting response and the nanostructures rearrangement upon intense field conditions, explaining z-scan data by a classical approach able to account for the nanoparticles asymmetry and plasmonic effects, are the main results found.

Electronic polarizability and third-order nonlinearity of Nd3+ doped borotellurite glass for potential optical fiber

The glass series with composition of {[(TeO2)0.70 (B2O3)0.30]0.7 (ZnO)0.3}1-y (Nd2O3)y where, y = 0.005, 0.01, 0.02, 0.03, 0.04 and 0.05; was fabricated via melt-quenched technique. The third-order optical nonlinearity was observed by using Z-scan technique. Polarizability and third-order nonlinearity of borotellurite glass doped with neodymium (Nd3+) will be reported. This work presents the effect of neodymium ions on the linear and nonlinear optical performance of borotellurite glass for potential photonics applications. The structure and optical performance of the resulting transparent neodymium doped borotellurite glass are characterized. The reduction of optical band gap energy, Eg is observed which shows the alteration of tellurite structure by the Nd3+. The values of electronic polarizability are enhanced with an increase of Nd3+ ions. The enhancement of electronic polarizability provides an excellent medium for nonlinear optical applications. The optical basicity of the investigated materials shows non-linear trend along with Nd3+ ions concentration. The Z-scan data for third-order optical nonlinearities suggest that the glass materials are excellent to be used as a medium in nonlinear optical fiber. Therefore, the investigated glass materials may provide a good material for photonic applications.

An Efficient Ultrasonic-Assisted Synthesis and Nonlinear Optical Property of Donor (D) -π-Acceptor (A) Chalcone (DDFP)

Abstract 3-(3,4-dimethoxyphenyl)-1-(2,5-dimethylfuran-3-yl)prop-2-en-1-one (DDFP), is prepared by the equimolar ratio of 1-(2,5-dimethylfuran)ethan-1-one and 3,4, dimethoxy benzaldehyde under ultrasonic irradiation. Structure of DDFP was established by the FT-IR, 1H and 13C-NMR spectroscopic methods and elemental analysis. The nonlinear optical properties of this dye using the z-scan technique with a cw argon ion laser at 514.5 nm are studied. Both the closed and open aperture z-scan data is used to estimate the nonlinear refractive index n2 and the nonlinear absorption coefficient β respectively. The measurements are carried out at five concentrations as well as at five laser powers. The values obtained are relatively very high and vary linearly with concentration. The studies on optical limiting behavior of this dye are also reported here.

The structural and third-order nonlinear optical studies of a novel nitro group-substituted chalcone derivative for nonlinear optical applications

A novel optically high-transparent chalcone derivative (E)-3-(3-nitrophenyl)-1-(thiophene-2-yl)prop-2-en-1-one (2AT3N) has been synthesized and crystallized using slow evaporation solution method. The grown single crystals were characterized by FT-IR and FT-RAMAN vibrational technique. The spectroscopic investigations confirmed the presence of various functional groups in the grown single crystals. The single crystal X-ray diffraction analysis revealed that the harvested single crystals possess triclinic crystal structure under centrosymmetric space group P-1. In addition, the intermolecular interactions in the molecule were figured out by Hirshfeld surface analysis. The 2AT3N crystal possesses high optical transmittance beyond cutoff wavelength (358 nm) in the entire visible region. The thermal stability of the crystals has been examined by TG/DTA/DSC measurements. The 2AT3N crystals are thermally stable up to 148.3 °C. The third-order nonlinear optical properties have been studied using Z-scan experiment (532 nm and 200 mW). The Z-scan Experimental results reveal that the 2AT3N single crystals show high-order nonlinear absorption coefficient (β ~ 10−5cm W−1) and nonlinear refractive index (n2 ~ 10−9 cm2 W−1). The optical limiting study on 2AT3N was carried out using open aperture Z-scan data. The grown single crystals possess reverse saturation absorption (RSA) due to excited state absorption. The structural and nonlinear optical property relationship of the molecule along with the role of nitro group substitution in the enhancement of nonlinear optical property has been discussed in detail. Nonlinear optical studies show that, the synthesized novel chalcone derivative is an advisable material for nonlinear optical applications such as optical limiter and optical switches.

Femtosecond nonlinear absorption and optical limiting action in nanoplatelet CuFe2O4-decorated rGO nanocomposites

Using 800 nm infrared, 150 femtosecond (fs), 80 MHz high repetition rate laser pulse excitation, intensity-dependent (Io = 245–735 MW/cm2) measurements on the nonlinear absorption of copper ferrite hetero-architecture functionalized with three rGO contents (15, 25 and 40 wt%) were performed. Copper ferrite–rGO nanocomposite demonstrated a peculiar W-pattern [a peak (saturable absorption) with two valleys [reverse saturable absorption (RSA)] at extreme] in the open aperture Z-scan data for the decorated (15 wt%) rGO systems recorded at a low peak intensity (Io = 245 MW/cm2). The Z-scan traces were dominated by RSA characteristics due to two-photon absorption process at high peak intensities. The variation in intensity-dependent nonlinear absorption coefficient and ground-state absorption at laser excitation wavelength revealed the presence of excited-state absorption (ESA). The maximum two-photon absorption coefficient was recorded for CuFe2O4–(40 wt%) rGO at 735 MW/cm2 excitation, which is attributed to the combined contribution of rGO and CuFe2O4 that is four times higher than pure rGO and CuFe2O4. The presence of layer like CuFe2O4 nanoplatelets upon the layer-structured rGO offers an added advantage in enhancing the nonlinear absorption coefficient. Near-resonant ESA-based optical limiters comprising CuFe2O4–rGO can possibly be used as a versatile optical limiting material for eye safety against intense, high repetition rate fs laser pulses.

Investigation of third-order nonlinear optical properties of nanostructured Ni-doped CdS thin films under continuous wave laser illumination

We report the third-order nonlinear optical (NLO) properties and optical limiting (OL) thresholds of pure CdS and Ni-doped CdS thin films have been investigated with the Z-scan technique under continuous wave laser excitation. Nanocrystalline CdS thin films with various doping concentrations of Ni (0%, 1%, 3%, 5% and 10 at.%) are prepared by spray-pyrolysis technique. XRD patterns reveal that all the prepared films are polycrystalline and the incorporation of Ni does not lead to major changes in the crystalline phase of Cd1−xNixS thin films. The surface morphology of the prepared films is impacted by the Ni-doping and is indicated by Field Emission Scanning Electron Microscopy (FESEM) images. With an increase in Ni-doping concentration, the energy band-gap value decreased from 2.48 eV to 2.23 eV. From the Z-scan data, it is observed that the material show strong two-photon absorption (2PA) and with an increase in Ni-doping concentrations from 0 to 10 at.%, the nonlinear absorption coefficient (β) are enhanced from 0.92 × 10−5 to 4.46 × 10−5 (cm W−1), nonlinear refractive index (n2) from 0.2967 × 10−9 to 0.1297 × 10−8 (cm2 W−1) and thereby the third-order NLO susceptibility (χ(3)) values also increased from 1.7075 × 10−6 to 7.4743 × 10−6 (esu). OL characteristics of the prepared films are studied at the experimental wavelength. The results propose that the Cd1−xNixS film is a capable material for nonlinear optical devices at 532 nm and optical power limiting applications.

Synthesis, spectroscopic characterization, crystal structure, Hirshfeld surface analysis and third-order nonlinear optical properties of 2-(4-chlorophenoxy)-N'-[(1E)-1-(4-methylphenyl) ethylidene] acetohydrazide

A new organic hydrazide derivative crystal, 2-(4-chlorophenoxy)-N′-[(1E)-1-(4-methylphenyl) ethylidene] acetohydrazide (4CP4MPEA) has been successfully synthesized and grown as single crystal from DMF solution. 4CP4MPEA crystallizes in triclinic crystal system with space group P-1 as revealed by single crystal X-ray diffraction (XRD). The molecule adopts an E configuration with respect to its CN double bond. The dihedral angle between the two phenyl rings is 79.29 (14)°. The synthesized compound has been characterized by UV/Vis and 1H NMR spectrum. Thermal properties and close contacts present in the crystal have also been investigated. The intermolecular interactions in the crystal structure were quantified and analyzed using Hirshfeld surface analysis. Open aperture Z-Scan data demonstrate the presence of two-photon absorption. Calculated values of σex and σg are 4.01 × 10−17cm2 and 1.33 × 10−21 cm2 respectively. The value of σex ≫> σg clearly indicates that the nonlinear absorption (NLA) process is due to the reverse saturable absorption (RSA). Observed optical limiting characteristics in 4CP4MPEA are attributed to the RSA. The Optical limiting threshold is found to be 3.13 × 1012 W/m2.

Laser damage threshold, hardness and third order non-linear optical analysis of potassium dihydrogen phosphate with sodium chloride

Abstract z-scan technique was used to investigate the non-linear optical properties of Potassium dihydrogen phosphate doping sodium chloride (PDPSC) were grown slow evaporation solution growth technique at room temperature. The lattice parameters were calculated from single x-ray diffraction. Laser damage threshold value was found to be 13.48 GW/cm2. The Vickers microhardness test was carried out on the grown crystals and there by Vickers hardness number (Hv), work hardening coefficient (n), yield strength (σy), stiffness constant C11 were calculated. The z-scan technique has been employed to determine the third order nonlinear optical (TONLO) nature of PDPSC crystal at 532 nm. The third order nonlinear optical linear absorption coefficient (α), Nonlinear refractive index (n2), Nonlinear absorption coefficient (β), Real part of the third-order susceptibility [Re (χ|3|)], Imaginary part of the third-order susceptibility [Im (χ|3|)] and Third-order nonlinear optical susceptibility (χ3) has been calculated using the Z-scan data.

Nonlinear optical studies of sodium borate glasses embedded with gold nanoparticles

Optical glasses possessing large third-order optical nonlinear susceptibility and fast response times are promising materials for the development of advanced nonlinear photonic devices. In this context, gold nanoparticle (NP)-doped borate glasses were synthesized via the melt-quench method. The nonlinear optical (NLO) properties of thus prepared glasses were investigated at different wavelengths (i.e., at 532 nm using nanosecond pulses, at 750 nm, 800 nm, and 850 nm wavelengths using femtosecond, MHz pulses). At 532 nm, open aperture (OA) Z-scan signatures of gold NP-doped borate glasses demonstrated reverse saturable absorption (RSA), attributed to mixed intra-band and interband transitions, while in the 750‒850 nm region, the OA Z-scan data revealed the presence of saturable absorption (SA), possibly due to intra-band transitions. The NLO coefficients were evaluated at all the spectral regions and further compared with some of the recently reported glasses. The magnitudes of obtained NLO coefficients clearly demonstrate that the investigated glasses are potential materials for photonic device applications.

Design, growth and characterization of D-π-A-π-D based efficient nonlinear optical single crystal for optical device applications

Third order nonlinear material of 4-[(1 E)-3-(5-chlorothiophen-2-yl)-3-oxoprop-1-en-1-yl]phenyl4-methylbenzene-1-sulfonate (4 TP MS) was synthesized by Claisen Schmidt condensation reaction method and single crystals were grown by slow evaporation technique. The functional groups corresponding to the vibrational frequencies has been confirmed through FT-IR and FT-RAMAN spectroscopic techniques. The single crystal XRD analysis revealed the crystal is belonging to monoclinic crystal structure with P21/n space group. The optical properties were studied by UV-VIS spectroscopy and photoluminescence spectroscopy. The cut-off wavelength of 4 TPMS is found to be 432 nm and the crystal is transparent in entire visible and near IR region. Using absorbance data, the parameters like extinction co-efficient, reflectance, electrical conductivity, optical conductivity, complex dielectric constant, lattice dielectric constant and ratio of carrier concentration to effective mass has been analyzed. The crystal has blue light emission property with less defects were observed from photoluminescence studies. The 4 TPMS is thermally stable up to 254 °C. The dielectric properties like dielectric constant and dielectric loss were studied. The low value dielectric loss at high frequency region enhances the optical quality of the material. The third order nonlinear properties of nonlinear absorption and nonlinear refraction were studied through open/closed aperture Z-Scan technique. The high value nonlinear absorption co-efficient of 4 TPMS makes the material suitable for optical limiting application. These optical limiting properties were extracted from open aperture Z-Scan data and this behavior is due to reverse saturable absorption. The large value of third order nonlinear susceptibility is of the order of 10−11 esu and material has better capability to be used optical device applications.

Controlling the nonlinear absorption characteristics of TiO2/carbon nanocomposites on films

In this study, nonlinear and saturable absorption behaviors of nanocomposite TiO2/carbon based materials in PMMA were investigated. Transparent thin films of TiO2, HC/TiO2, CNT/TiO2, CNT/TiO2-Pt nanocomposites were synthesized by spin coating. Linear absorption measurements indicate blueshift in energy due to a quantum confinement effect. Nonlinear optical absorption characteristics of the composite films were investigated using open aperture Z-scan technique with at the same fluence values for nanosecond and femtosecond pulse durations. To derive the transmission in open aperture Z-scan data, a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations were considered. Nonlinear absorption coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results for both pulse durations used for the experiments. Saturation intensity threshold values in femtosecond regime are significantly bigger than the values in nanosecond regime while nonlinear absorption coefficients values in nanosecond regime are significantly bigger than the values in femtosecond regime. These behaviors are attributed to localized defect states in the energy gap due to the loss of long-range order and defects such as dangling bonds and impurities. With thermal annealing processes at 200 °C and 450 °C nonlinear absorption coefficients and saturation intensity thresholds decrease due to reduction of localized defect states.

Femtosecond, broadband nonlinear optical studies of a zinc porphyrin and zinc phthalocyanine

Broadband (700–950 nm) third order nonlinear optical (NLO) properties of porphyrin (ZnTPP) and phthalocyanine (TPA-ZnPc) molecules in solution form have been studied using the Z-scan technique with femtosecond, MHz pulses. Two-photon, three-photon absorption coefficients along with the third-order NLO susceptibility (χ3) and their optical limiting thresholds are estimated from the theoretical fits to experimental data. Closed aperture Z-scan data provided the information on the sign and magnitude of nonlinear refractive indices (n2) at different wavelengths. Our results clearly suggest that these molecules possess the potential for applications such as optical limiting and biological imaging at high repetition rates.

Optical, structural and Near-IR NLO properties of gold nanoparticles doped sodium zinc borate glasses

Gold (Au) nanoparticles (NP) embedded borate glasses with the molar composition of (x‒0.1)Na2O‒10ZnO‒(90‒x)B2O3‒0.1AuCl3 (x = 10, 20, 30 mol %) have been prepared via melt quench technique. The effect of Na2O content on properties such as optical, structural and nonlinear optical (NLO) properties of gold NPs containing sodium zinc borate glasses were studied using UV‒Visible absorption, Fourier Transform Infrared spectroscopy (FTIR), High Resolution-Transmission Electron Microscope (HR‒TEM) and Z-scan measurements. X‒ray diffraction (XRD) measurements confirmed the glassy nature of the samples. UV‒Visible absorption spectra of glasses comprising Au NPs demonstrated a broad surface plasmon resonance (SPR) absorption peak near 577 nm due to the transition from d‒band to the Fermi level and this SPR peak demonstrated a red‒shift with increase in Na2O concentration. HR‒TEM micrographs revealed the presence of uniformly distributed and spherical shaped Au nanoparticles with an estimated average particle size of ∼6 nm (±1.5 nm). Nonlinear Optical (NLO) measurements were performed at three different off‒resonant wavelengths (750 nm, 800 nm, 850 nm) using femtosecond (fs) pulses (150 fs, 80 MHz) delivered by aTi:sapphire oscillator. Saturable Absorption (SA) kind of nonlinearity has been observed in the open aperture (OA) Z-scan data and is attributed to intraband transition within the Au NPs, while the closed aperture (CA) Z-scan data illustrated a negative type of nonlinear refraction attributed to effect of self-defocusing. NLO studies and the obtained nonlinear coefficients suggest that, the NZB glasses are potential candidates for mode-locking and switching applications in near-infrared spectral region.

Surface plasmon resonance and nonlinear optical behavior of pulsed laser-deposited semitransparent nanostructured copper thin films

In this paper, surface plasmon resonance (SPR) and nonlinear optical properties of semitransparent nanostructured copper thin films fabricated on the glass substrate at 400 °C by pulsed laser deposition technique are reported. The thickness, linear absorption coefficient and linear refractive index of the films were measured by spectroscopic ellipsometer. The average particle size as measured via atomic force microscope was in the range of 12.84–26.02 nm for the deposition time ranging from 5 to 10 min, respectively. X-ray diffraction spectra revealed the formation of Cu (111) and Cu (200) planes. All these thin films exhibited broad SPR peak. The third-order optical nonlinearity of all the samples was investigated via modified z-scan technique using cw laser at a wavelength of 632.8 nm. The open aperture z-scan spectra of Cu thin film deposited for 5 min duration exhibited reverse saturation absorption whereas all the other samples displayed saturation absorption behavior. The nonlinear refractive index coefficient of these films showed a positive sign having the magnitude of the order of 10− 4 cm/W. The real and imaginary parts of susceptibilities were also calculated from the z-scan data and found to be of the order of 10− 6 esu.

Mach–Zehnder interferometer implementation for thermo-optical and Kerr effect study

In this paper, we propose the Mach–Zehnder interferometric method for third-order nonlinear optical and thermo-optical studies. Both effects manifest themselves as refractive index dependence on the incident light intensity and are widely employed for multiple opto-optical and thermo-optical applications. With the implemented method, we have measured the Kerr and thermo-optical coefficients of chloroform under CW, ns and ps laser irradiance. The application of lasers with different light wavelengths, pulse duration and energy allowed us to distinguish the processes responsible for refractive index changes in the investigated solution. Presented setup was also used for demonstration of opto-optical switching. Results from Mach–Zehnder experiment were compared to Z-scan data obtained in our previous studies. Based on this, a quality comparison of both methods was assessed and advantages and disadvantages of each method were analyzed.

Linear and nonlinear optical analysis on semiorganic L -proline cadmium chloride single crystal

In the current investigation, L -proline cadmium chloride monohydrate (LPCC) single crystal is grown by a slow solvent evaporation technique to identify its credibility for nonlinear optical device applications. The constituent elements of LPCC crystal are determined by the energy dispersive spectroscopic (EDS) technique. The single crystal x-ray diffraction technique is used to determine the structural dimensions of LPCC crystal. The UV-visible studies are carried out within a wavelength range of 200 nm–1100 nm to determine the optical transmittance of LPCC crystal. The linear optical parameters of LPCC crystal are evaluated using the transmittance data to discuss its importance for distinct optical devices. The Nd:YAG laser assisted Kurtz–Perry test is carried out to determine the enhancement in second harmonic generation efficiency of LPCC crystal with reference to KDP crystal. The Z-scan technique is employed to assess the third order nonlinear optical (TONLO) properties of LPCC crystal at 632.8 nm. The Z-scan data are utilized to evaluate the TONLO refraction, absorption and susceptibility of LPCC crystal. The color oriented luminescence behavior of LPCC crystal is investigated within a spectral range of 350 nm–700 nm. The dependence of dielectric constant and dielectric loss on temperature and frequency is evaluated through the dielectric measurement studies.

Growth and characterization of L-phenylalanine nitric acid (LPN) and tris L-(phenylalanine)-phenylalanininum nitrate (TPLPN) as second and third order nonlinear optical materials

We synthesized noncentrosymmetric single crystals of L-phenylalanine nitrate (LPN) and tris L-(phenylalanine) L-phenylalaninium nitrate (TPLPN) by slow solvent evaporation technique. Both crystallized in monoclinic system with different acentric space groups namely P21 (LPN) and C2 (TPLPN) respectively. The IR and Raman spectral investigation was done for LPN and TPLPN and discussed. The UV-vis-studies accomplished the excitation wavelength of the grown crystals suitable to exhibit second harmonic generation signal. From the absorption data, remarkable optical properties such as direct band gap energy, Urbach energy, extinction coefficient were evaluated. The mechanical strength of the grown crystal was examined by Vickers micro hardness test. The temperature of decomposition was confirmed by TG/DSC analysis. Fluorescence emission spectrum of LPN and TPLPN were recorded and lifetime was also studied. The dielectric constant and dielectric loss of LPN and TPLPN has been determined as a function of frequency and temperature. Also the surface topologies of the crystallized salts were assessed by SEM studies. The third-order nonlinearities of LPN and TPLPN were determined by Z-scan technique with Nd: YAG at 532 nm and thereby from closed and open Z-scan data, third-order susceptibilities were calculated to be χ(3) = 8.826 × 10−6 esu for LPN and χ(3) = 2.552 × 10−7 esu for TPLPN.

Broadband femtosecond nonlinear optical properties of CsPbBr3 perovskite nanocrystals.

We report the broadband nonlinear optical (NLO) properties of CsPbBr3 perovskite films achieved from colloidal nanocrystals prepared following a room temperature and open atmosphere anti-solvent precipitation method. The NLO studies were performed on the films of nanocubes (NCs) and nanorods (NRs) using the Z-scan technique with 1kHz femtosecond pulses at 600, 700, and 800nm. Large two-photon absorption cross sections (∼105 GM) were retrieved by fitting the open-aperture Z-scan data. Strong third-order NLO susceptibility (∼10-10 esu) was observed in these films. At higher peak intensities a switching of sign (in both NCs and NRs) in the real and imaginary parts of the NLO susceptibility was observed from the studies on these CsPbBr3 nanocrystals. The obtained NLO coefficients clearly suggest that these materials are promising for ultrafast photonic applications.

Enhanced Ultrafast Nonlinear Optical Response in Ferrite Core/Shell Nanostructures with Excellent Optical Limiting Performance.

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.