Z-Scan

In this work, the nonlinear optical properties of Zinc Oxide (ZnO) thin films produced on microscope slide glass substrates at room temperature (RT) using Pulsed Laser Deposition (PLD) method has been presented. PLD system consists of a vacuum chamber (pumped by a turbo molecular pump, backed with a rotary pump), rotating sample and substrate holders, optical thickness measurement system, infrared temperature measurement system and a nanosecond laser system. Previously deposition vacuum chamber evacuated down to ∼10-8 mbar and deposition was taken place about 1.3×10-1 mbar oxygen background gas pressure value. Morphological properties of thin films were obtained by Atomic Force Microscopy (AFM) that shows homogenous and smooth film structure. Thin films crystallinity were investigated by using X-Ray Diffraction (XRD) method and showed that polycrystalline ZnO structure with the largest peak corresponding to (002) orientation but some films contain Zn with (101) orientation . The thicknesses of the films were deduced from reflectance measurement using a fitting software and crosschecked with profilometer and AFM measurements. The thickness of the films ranged between 10 nm and 220 nm. Linear optical properties were obtained by using UV-VIS Spectrometer. Furthermore, we presented the nonlinear optical properties of the ZnO thin films that were obtained by the z-scan method.

Good quality bulk size single crystals of inverse soluble lithium sulphate monohydrate (LSMH) have been grown by the modified Sankaranarayanan–Ramasamy (SR) method. A growth rate as high as 3 mm per day has been obtained for LSMH growth without substantially degrading the optical quality. The rocking curve recorded using the high resolution X-ray diffraction (HRXRD) technique reveals that the crystals grown by this method have a high degree of crystalline perfection. The optical quality of the crystals was studied using an UV-vis-NIR spectrum and the optical constants of the LSMH crystals were calculated. The laser damage threshold value of the grown crystals has been determined using a nanosecond Nd:YAG laser operating at 532 nm. Photoconductivity studies of the grown LSMH crystals reveal a positive photoconductiv-ity behaviour of the grown crystals. The photoluminescence spectrum of the LSMH crystals shows a prominent emission peak at 373 nm. The third order non-linear optical properties of the LSMH crystals were investigated in detail by the Z-scan technique using a He–Ne laser operating at 632.8 nm. The non-linear refractive index (n 2), non-linear absorption coefficient (β) and third order non-linear susceptibility (χ (3)) of the LSMH crystals were calculated.

Diverse microstructures of monoclinic copper niobate (m-CuNbO 3) were synthesized by solid-state reaction (900 °C, 3–12 h). FESEM data demonstrated that agglomerated clusters grew as an elongated grains which migrated to form web-shaped equiaxed structure and dissected to form individual equiaxed microstructure. With femtosecond laser excitation (800 nm, 150 fs), open aperture Z-scan data revealed the presence of two-photon absorption. The nonlinear refractive index (n 2) toggled between positive and negative nonlinearity for different microstructures. Web-shaped equiaxed structure kindled both the nonlinear absorption (b eff = 2.0 Â 10 À12 m/W), nonlinear refraction (n 2 = 3.16 Â 10 À17 m 2 /W) and a strong optical limiting action (onset limiting threshold of 22.24 mJ/cm 2).

The nonlinear optical properties of Rh-Pd and Rh-Pt solid-solution alloy nanopar-ticles (NPs) were experimentally investigated by means of the z-scan technique. The open aperture (OA) measurement showed a reverse saturable behavior, whereas the closed aperture (CA) measurement showed a peak-and valley-shape. Both the Rh-Pd and Rh-Pt NPs exhibited a positive nonlinear optical index of refraction at 800 nm relating to the self-focusing phenomenon. In addition, the nonlinear absorption of the Rh-Pt NPs (4.39 × 10 −12 cm/W) was higher than that of the Rh-Pd NPs (1.63 × 10 −12 cm/W) due to the small interval between the occupied and unoccupied density of states (DOS) of Rh-Pt than Rh-Pd. The nonlinear responses of the Rh-Pd and Rh-Pt NPs was attributed to the hot electron contribution and the reverse saturation of intraband and interband transitions.

Two novel sterically demanding zinc phthalocyanines were synthesized and characterized. Their optical and
electrochemical properties were investigated in detail. The emission spectra were recorded in different
solvents and the fluorescence yields obtained were in the range of 0.2–0.3 while time-resolved
fluorescence data revealed radiative lifetimes of typically few ns. Nonlinear optical (NLO) properties were
also evaluated at wavelengths of 600, 640, 680, and 800 nm using picosecond (
1.5 ps) pulses and
further studies with femtosecond (
140 fs) pulses at 800 and 780 nm were also performed. Two-photon
absorption (2PA) and saturable absorption (SA) were the dominant nonlinear absorption mechanisms
observed with ps/fs excitation at different wavelengths in the visible spectral region. NLO coefficients
were extracted from ps/fs closed and open aperture Z-scan measurements. Large two-photon
absorption cross-sections of
14 000 GM and n2 values in the range of 1–7  1016 cm2 W1 were
retrieved for these molecules from the ps Z-scan data. The excited state decay dynamics were
investigated using degenerate pump-probe experiments with
70 fs pulses near 600 nm. Double
exponential fits of the pump-probe data suggested two decay times for both molecules investigated

Carbazole-based π-conjugated 2,2 ′-Bipyridines, a new class of organic chromophores: Photophysical, ultrafast nonlinear optical and computational studies A B S T R A C T The developmen of donor-acceptor (D-A) architecture based organic chromophores with large two-photon absorption (2 PA) cross-sections are essential for myriad of applications, ranging from nonlinear microscopy to biomedical imaging. Here, we present the results from a comprehensive study of 2 PA cross-sections of a new series of carbazole mono substituted-π-conjugated-2,2 ′-bipyridine derivatives with D-π-A architecture, possessing carbazole as the donor moiety and bipyridine core as an acceptor. Further, we have extended the π-conjugation by introducing the phenyl and butoxy substituted phenyl linkers. The fluorescence properties of these D-A chromophores are highly sensitive to solvent polarity and alteration of electron donor functionalities. The relevant computation studies support our experimental results, e.g., a shift in emission maxima and band gaps of the molecules. The third-order nonlinear optical (NLO) properties of the title donor-acceptor (D-A) chromo-phores demonstrated that 2 PA cross-section values are in the range of 6-39 GM, obtained using ~50 fs (fs) laser pulses at a wavelength of 800 nm. Further, the nonlinear refractive indices (n 2) of these chromophores were found to be ~10 − 14 cm 2 /W, rendering them potential optical switching candidates since the coefficients were obtained with kHz, fs pulses extracting pure electronic nonlinearities. Based on our experimental findings and theoretical calculations presented in this study, we believe that carbazole-based π-conjugated 2,2 ′-bipyridines, demonstrated in this work, would be potential ligands to obtain a series of transition metal coordination complexes of interesting physical properties (for example, superior NLO behaviour).

This article demonstrates a series of cyclo-metalated Ir(III) complexes of the type [Ir III (C^N) 2 (N^N)]-(PF 6), where C^N is 2-phenylpyridine, and N^N corresponds to the 4,4′-π-conjugated 2,2′-bipyridine ancillary ligands. All these compounds were synthesized through splitting of the binuclear dichloro-bridged complex precursor, [Ir(C^N) 2 (μ-Cl)] 2 , with the appropriate bipyridine ligands followed by the anion exchange reaction. The linear and nonlinear absorption properties of the synthesized complexes were investigated. The absorption spectra of all the title complexes exhibit a broad structureless feature in the spectral region of 350−700 nm with two bands being well-resolved in most of the cases. The structures of all the compounds were modeled in dichloromethane using the density functional theory (DFT) algorithm. The nature of electronic transitions was further comprehended on the basis of time-dependent DFT analysis, which indicates that the origins of various bands are primarily due to intraligand charge transfer transitions along with mixed-metal and ligand-centered transitions. The synthesized compounds are found to be nonemissive at room temperature because of probable nonradiative deactivation pathways of the T 1 state that compete with the radiative (phosphorescence) decay modes. However, the frozen solutions of compounds Ir(MS 3) and Ir(MS 5) phosphoresce at the near-IR region, the other complexes remaining nonemissive up to 800 nm wavelength window. The two-photon absorption studies on the synthesized complexes reveal that values of the absorption cross-section are quite notable and lie in the range of 300−1000 GM in the picosecond case and 45−186 GM in the femtosecond case.

A novel zinc phthalocyanine derivative [2(3), 9(10), 16(17), 23(24) tetrakis-4-((4-(1,4,5-triphenyl-1Himidazol-2-yl)phenyl)ethynyl)phthalocyanine zinc(II) (PBIPC)] was synthesized by incorporating a triphenyl imidazole moiety at its peripheral positions. The detailed mechanisms of absorption, emission, electrochemical, nonlinear optical (NLO) and photophysical (excited state dynamics) properties of PBIPC were explored. The absorption and emission properties of the compound were studied in different solvents. The incorporation of a triphenyl imidazole moiety at the peripheral position of the zinc phthalocyanine slightly broadened the Soret band. The emission studies revealed fluorescence quantum yields to be in the range of 0.11-0.22. The time-resolved fluorescence data established the radiative lifetimes to be in the nanosecond range. The oxidation and reduction processes were found to be ring centered, which were studied using the cyclic voltammetry (CV) technique. The energy optimized structures and HOMO-LUMO levels were calculated using DFT, TD-DFT analysis and were employed by means of hybrid functional theory (B3LYP) at 6-31G (d,p) basis set in the Gaussian 09 package. Twophoton absorption was observed in the NLO studies performed in the visible wavelength range of 600-800 nm while the nonlinear absorption was dominated by three-and four-photon absorption processes in the NIR wavelength range (1.0-1.5 mm). The molecule exhibited self-focusing behavior for all the wavelengths. Finally, the excited state dynamics of the title molecule PBIPC were investigated using femtosecond transient absorption spectroscopy and the results obtained were understood on the basis of a simple three kinetic model, for excitation wavelengths of 400 nm (Soret band) and 650 nm (Qband). Both the spectra demonstrated a broad positive transient absorption (TA) data which overlapped with the ground state bleach (GSB), which in turn displayed a red shift over a delay of $2 ns. The lifetimes revealed a possibility of intersystem crossing (s > 1 ns) owing to the triplet state transition.

Nonlinear absorption (NLA) properties and excited state dynamics of a porphyrin and phthalocyanine in the presence of explosive molecules were investigated using the nanosecond Z-scan and femtosecond pump-probe techniques, respectively. The NLA coefficients Is and  increased in the presence of explosive molecules. The change in first excited state decay time was evaluated through degenerate pump-probe measurements near 700 nm and it was observed that decay time decreased in the presence of explosive molecules. The reduction in decay time and increase in NLA coefficients varied with different molecules according to their absorption, emission properties and affinity towards the explosive molecule.

Lead halide perovskite nanocrystals (NCs) apart from their overwhelming optoelectronic applications have recently demonstrated promising nonlinear optical (NLO) properties such as strong two-photon absorption cross-sections (∼10 5 GM), two-photon fluorescence, and saturable absorption even at very high peak intensity. Zero-dimensional perovskite-related materials (0-D PRMs) are a new class of materials offering a high exciton binding energy (E g ≥ 180 meV) with a strong photoluminescence (PL) quantum yield in few cases. Herein, we report the broadband third-order NLO properties of phase pure Cs 4 PbBr 6 0-D PRM achieved using the Z-scan and degenerate four-wave mixing techniques in the femtosecond regime. Considering the growing content of the fluorescent and non-fluorescent forms of this material, we have performed our studies on both of them. These perovskite NCs exhibited strong multi-photon absorption properties in the near-infrared region with two-photon absorption (2PA) (cross-section, σ 2 = 10 −43-10 −44 cm 4 s equivalent to ∼10 6 GM) in the 500-800 nm region, three-photon absorption (3PA) (cross-section, σ 3 ∼10 −73 cm 6 s 2) in the 900-1200 nm region and four-photon absorption (4PA) (cross-section, σ 4 ∼10 −100 cm 8 s 3) in the 1300-1500 nm spectral region. These multi-photon absorption processes are explained using a simple band diagram. The measured NLO coefficients and cross-sections are fairly large when compared to some of the earlier reports on perovskite-based NCs. Cs 4 PbBr 6 0-D PRM also demonstrated a large third-order NLO susceptibility χ (3) (∼10 −7 esu), which can be attributed to the strong quantum confinement arising from spatially isolated, exciton containing individual [PbBr 6 ] 4− octahedron. These results clearly suggest the potential of 0D-PRMs in applications such as photonics and ultrafast alloptical switching devices. † Electronic supplementary information (ESI) available: Z-Scan experimental details, DFWM experimental details, NLO coefficients and cross-section calculations, and film thickness data (AFM).

We present our experimental and theoretical results on the dispersion studies of non-linear absorption in C solution. Open-aperture Z-scans are performed over the visible region 440–660 nm using an ns OPO. Our results are interpreted using a 5-level model taking into account both the excited state absorption and two-photon absorption processes. Results indicate that the excited state absorption dominates in the shorter-wavelength region 440–560 nm whereas the two-photon absorption dominates in the longer-wavelength region 580–660 nm

Nonlinear absorption (NLA) properties and excited state dynamics of a porphyrin and phthalocyanine inthe presence of explosive molecules were investigated using the nanosecond Z-scan and femtosecondpump-probe techniques, respectively. The NLA coefficients Isand ˇ increased in the presence of explosivemolecules. The change in first excited state decay time was evaluated through degenerate pump-probemeasurements near 700 nm and it was observed that decay time decreased in the presence of explosivemolecules. The reduction in decay time and increase in NLA coefficients varied with different moleculesaccording to their absorption, emission properties and affinity towards the explosive molecule.