Strong Nonlinear Optical Absorption Research Articles

Phase Transitions, Dielectric Response, and Nonlinear Optical Properties of Aziridinium Lead Halide Perovskites.

Hybrid organic-inorganic lead halide perovskites are promising candidates for next-generation solar cells, light-emitting diodes, photodetectors, and lasers. The structural, dynamic, and phase-transition properties play a key role in the performance of these materials. In this work, we use a multitechnique experimental (thermal, X-ray diffraction, Raman scattering, dielectric, nonlinear optical) and theoretical (machine-learning force field) approach to map the phase diagrams and obtain information on molecular dynamics and mechanism of the structural phase transitions in novel 3D AZRPbX3 perovskites (AZR = aziridinium; X = Cl, Br, I). Our work reveals that all perovskites undergo order-disorder phase transitions at low temperatures, which significantly affect the structural, dielectric, phonon, and nonlinear optical properties of these compounds. The desirable cubic phases of AZRPbX3 remain stable at lower temperatures (132, 145, and 162 K for I, Br, and Cl) compared to the methylammonium and formamidinium analogues. Similar to other 3D-connected hybrid perovskites, the dielectric response reveals a rather high dielectric permittivity, an important feature for defect tolerance. We further show that AZRPbBr3 and AZRPbI3 exhibit strong nonlinear optical absorption. The high two-photon brightness of AZRPbI3 emission stands out among lead perovskites emitting in the near-infrared region.

Nonlinear optical properties and applications of 2D metal oxides

Two-dimensional (2D) materials have stimulated continued interest due to their potential applications in fields from electronic, optical to catalysis and energy. Compared with the widely studied 2D metal chalcogenides, 2D oxides could be of particular interest for a ranges of applications where oxidative and high temperature conditions are involved. This feature of 2D oxides, combined with the inherent benefits of 2D systems could also be important for nonlinear optical (NLO) studies that involves strong light-matter interactions. Here we focus on the recent advances in the exploration of 2D metal oxides for nonlinear optics and ultrafast photonic applications. Along with a brief description of the crystal structures, fabrication methods and general properties of 2D oxides, we concentrate our discussion on the recent progresses in the nonlinear optical studies on 2D systems of both metallic and nonmetallic nature. The strong NLO absorption of these 2D oxides has been utilized for the development of optical switches for driving pulse generation in a number of fiber and solid-state lasers operating in the near infrared range. This review finally presents a brief analysis of main challenges of 2D metal oxides in the field nonlinear photonics and a short discussion on potential future directions.

Improved Haacke's quality factor, third order nonlinear susceptibility and specific capacitance realized for PbS thin films through La3+ doping

The present study examines the third order NLO and electrochemical properties of spray deposited lanthanum doped PbS (PbS:La) thin films. FCC crystallization was confirmed by XRD patterns along the plane (2 0 0). PbS crystallites vary in size between 27 and 36 nm with La doping concentration. Surface morphology improved with La doping. La doping increases the band gap from 1.97 to 2.18 eV. Near band edge (NBE) emissions in PL spectra originates from electron-hole recombination. A low resistivity of 0.23 x10−3 Ω-m was realized for PbS film doped with 4 wt% La concentration. Figure of merit of pure PbS improves from 1.32 x 10−3 Ω−1 to 1.607 x 10−2 Ω−1 with La doping. La doping modifies the energy states and band gap of PbS favouring strong nonlinear optical absorption. PbS:La thin films demonstrate self-defocusing due to temperature effects caused by absorption of single photons or free carriers. As a result of the low cationic field strength and high polarizability of La3+ ions, PbS exhibits a higher nonlinear refractive index. The nonlinear susceptibility and refractive index were found to be in the range 3.23–5.33 x 10−6 esu and 2.74 to 3.64 x 10−9 cm2/W, respectively. From the electrochemical studies, increased specific capacitance (256.46 F/g) and decreased charge transfer resistance (12 x 103 Ω) was observed for the 4 wt% La doped film.

Heptazine‐Based TADF Materials for Nanoparticle‐Based Nonlinear Optical Bioimaging

Abstracts‐Heptazines are emerging as strong electron acceptors for efficient thermally activated delayed fluorescent (TADF) materials, yet the difficulties in synthesizing them have limited their practical use. Here, three novel s‐heptazine TADF materials with green to deep‐red emission (λmax = 525–664 nm) and high photoluminescence quantum yields, synthesized by either pseudoelectrophilic substitution or Negishi coupling routes, are described. These materials also demonstrate strong nonlinear optical absorption, with two‐photon cross sections up to 1260 GM. With deep‐red fluorescence, strong two‐photon absorption, high quantum yield, and delayed fluorescence, the emitter HAP‐3MeOTPA is ideally suited for use in nanoparticle‐based bioimaging experiments. The two kinds of luminescent nanoparticle are prepared, namely hostless, aggregate‐based organic dots (a‐Odots) and rigid, glassy Odots (g‐Odots) as biocompatible and water‐dispersible TADF probes. The g‐Odots are shown to retain the nonlinear optical properties, high photoluminescence quantum yield, and TADF observed in the constituent heptazine dye. These g‐Odots are then used as biological imaging probes with immortalized human kidney cancer (HEK293) cells, and single and multi‐photon‐excited microscopy coupled with time‐gated luminescence measurements are demonstrated. This work not only describes new routes to efficient heptazine‐based TADF materials, but also demonstrates their potential as nanoparticle‐based bioimaging probes combining several advanced optical functions.

Facile Synthesis of Monodispersed Titanium Nitride Quantum Dots for Harmonic Mode-Locking Generation in an Ultrafast Fiber Laser.

As a member of the transition metal nitride material family, titanium nitride (TiN) quantum dots (QDs) have attracted great attention in optical and electronic fields because of their excellent optoelectronic properties and favorable stability. Herein, TiN QDs were synthesized and served as a saturable absorber (SA) for an ultrafast fiber laser. Due to the strong nonlinear optical absorption characteristics with a modulation depth of ~33%, the typical fundamental mode-locked pulses and harmonics mode-locked pulses can be easily obtained in an ultrafast erbium-doped fiber laser with a TiN-QD SA. In addition, at the maximum pump power, harmonic mode-locked pulses with a repetition rate of ~1 GHz (164th order) and a pulse duration of ~1.45 ps are achieved. As far as we know, the repetition rate is the highest in the ultrafast fiber laser using TiN QDs as an SA. Thus, these experimental results indicate that TiN QDs can be considered a promising material, showing more potential in the category of ultrafast laser and nonlinear optics.

Third-order nonlinear optical responses of CuO nanosheets for ultrafast pulse generation

As a representative transition metal oxide, cupric oxide (CuO) has attracted a lot of interest in miscellaneous fields. In the present work, the prominent third-order nonlinear optical (NLO) features of CuO nanosheets were demonstrated via the typical Z-scan technique at 1 μm. The open-aperture (OA) Z-scan measurements at different intensities clearly showed that CuO nanosheets possessed the saturable absorption (SA), reverse saturable absorption (RSA) and optical limiting behaviors. The closed-aperture (CA) Z-scan technology was implanted to investigate the nonlinear refractive index and the third-order nonlinear susceptibility. In virtue of the strong nonlinear optical absorption properties of CuO nanosheets, a stable all-solid-state mode-locked laser with the as-prepared CuO nanosheets as saturable absorber at 1.06 μm was realized for the first time. Our work confirmed that CuO nanosheets exhibited outstanding NLO properties, which might stimulate the development in ultrafast photonics and nonlinear optics.

Passively Q-switched Ytterbium-doped fiber laser based on broadband multilayer Platinum Ditelluride (PtTe2) saturable absorber

Two-dimensional (2D) layered Platinum Ditelluride (PtTe2), a novel candidate of group 10 transition-metal dichalcogenides (TMDs), which provides enormous potential for pulsed laser applications due to its highly stable and strong nonlinear optical absorption (NOA) properties. PtTe2 saturable absorber (SA) is successfully fabricated with firstly demonstrated the passively Q-switched laser operation within a Yb-doped fiber laser cavity at 1066 nm. Few layered PtTe2 is produced by uncomplicated and cost-efficient ultrasonic liquid exfoliation and follow by incorporating into polyvinyl alcohol (PVA) polymer to form a PtTe2-PVA composite thin film saturable absorber. The highest achieved single pulse energy is 74.0 nJ corresponding to pulse duration, repetition rate and average output power of 5.2 μs, 33.5 kHz and 2.48 mW, respectively. This work has further exploited the immeasurable utilization potential of the air stable and broadband group 10 TMDs for ultrafast photonic applications.

Z-scan studies of Sn doped CuO nano-colloidal suspension

We report synthesis and characterization of l-valine capped Sn doped CuO nanoparticles (NPs). Pure and Sn doped CuO NPs were obtained by chemical co-precipitation method and were calcined at 500 °C for 2 h. X-ray diffraction (XRD) shows formation of crystalline CuO having monoclinic phase with average particle size of 8 nm. Utraviolet-visible (UV-vis) spectroscopy attests the formation of NPs and strong blue shift in the excitonic absorption has been observed for both uncalcined and calcined NPs. All samples show broad excitonic absorption in the wavelength range 351–654 nm due to inter band surface states transitions in CuO NPs. Fourier transform infra-red (FT-IR) spectroscopy confirms the role of l-valine as capping agent. Energy dispersive X-ray (EDX) spectroscopy confirms Sn doping into CuO. Transmission electron microscopy (TEM) attest the formation of CuO NPs having uniform near spherical shape. Third order NLO properties of undoped and Sn doped CuO NPs in the form of colloidal suspension have been investigated using Z-scan technique employing the fundamental wave at 1064 nm of a 7ns mode-locked Nd-YAG laser operating at 10 Hz. Sample with 5% Sn doping is found to possess strong nonlinear optical absorption and refraction due strong quantum confinement effect, TPA, ESA, etc. processess.

Impact of electronegative character on ultrafast nonlinear optical absorption of azine derivatives

Two azine derivatives (NO(Cl) and NS(Cl)) with different electronegative central core were prepared and spectroscopically characterized. Their ultrafast third-order nonlinear optical (NLO) responses were investigated using open aperture Z-scan and optical limiting method with 190 fs laser pulses at 515 nm. The frontier molecular orbitals and energy gaps of samples were obtained through quantum chemical calculation. Transient absorption spectra demonstrated that the origin of strong NLO absorption of two molecules was attributed to excited-state absorption. A simplified three-energy-level model was used to determine their photo-physical parameters. Our results show that the stronger the electronegative cationic groups is, the stronger the NLO absorption performs. The azine compounds have large excited-state lifetime and large ratio of singlet excited-state absorption cross-section to that of ground state cross-section (∼20.2), indicating it is a candidate material for future ultrafast optical limiters.

Q-switched Yb3+:YAG laser using plasmonic Cu2-xSe quantum dots as saturable absorbers

Cu2-xSe quantum dots (QDs) were synthesized by organometallic synthesis methods. Due to heavy self-doping, the Cu2-xSe QDs exhibit particle plasmon resonance in the near-infrared. Transient absorption spectroscopic investigation revealed strong nonlinear optical absorption and bleaching performance of the QDs under femtosecond pulse excitation, which enabled the Cu2-xSe QDs to be excellent saturable absorbers and applied in Q-switched or mode-locked lasers. A passively Q-switched Yb3+:YAG solid-state laser at 1.03 μm was achieved by coating Cu2-xSe QDs as saturable absorbers onto one of the output coupler of the V-shaped linear cavity.

Composition-structure–physical property relationship and nonlinear optical properties of multiferroic hexagonal ErMn1−xCrxO3 nanoparticles

Nanocrystalline multiferroic ErMn1−xCrxO3 exhibits canted antiferromagnetism with a spin-glass transition and strong nonlinear optical absorption.

Synthesis, structures, and third-order nonlinear optical properties of three new copper complexes based on salicylaldehyde phenoxyacetohydrazide ligand

Three copper complexes, [Cu2(Hsa)2(pipe)]·2DMF (1), [Cu(Hsa)(MEA)]n (2), and {[Cu4(Hsa)4(DMF)](DMF)}n (3) (pipe = piperazine; MEA = methenamine, Hsa = (2-hydroxybenzylidene)-2-phenoxyacetohydrazide), have been synthesized in methanol/DMF solution at room temperature and structurally characterized by single-crystal X-ray diffraction. In 1, the copper(II) complexes are bridged by pipe ligands to form binuclear clusters. In 2, the MEA ligands link copper(II) complexes to result in an infinite chain structure. Compound 3 contains tetranuclear clusters, which are bridged by Hsa to give an infinite chain structure. Third-order nonlinear optical (NLO) properties of the compounds were determined by Z-scan technique in DMF solution. All three compounds show very strong NLO absorption properties with absorptive coefficients β(MKS), 1.71 × 10−10 m W−1 for 1, 1.39 × 10−10 m W−1 for 2, and 9.30 × 10−11 m W−1 for 3, respectively. The NLO refractive index value γ(MKS) of 3 is 5.97 × 10−18 m2 W−1. Compound 3 shows strong self-focusing behavior.

Syntheses, Structures and Third-Order Nonlinear Optical Properties of Two-Dimensional Rhombohedral Grid Coordination Polymers: [Cd(imz)3]2(BTC)·0.5H2O and [Cu4(H2O)2(imz)8](BTC)2·7H2O(BTC = 1, 2, 4, 5-benzenetetracarboxylate anion, imz = imidazole)

Hydrothermal reactions of 1, 2, 4, 5-benzenetetracarboxylic acid (H4BTC) with cadmium acetate and copper acetate in the presence of imidazole (imz) resulted in two new coordination polymers, namely, [Cd(imz)3]2(BTC)·0.5H2O 1, [Cu4(H2O)2(imz)8](BTC)2·7H2O 2. Two compounds have been characterized structurally using single-crystal diffraction, elemental analysis, and FT-IR spectrum. In compound 1, the hexa-coordinated Cd(II) ions are bridged by BTC to form two-dimensional rhombohedral grid sheets. In compound 2, the coordination polyhedrons [CuO4N2] and [CuO3N2] are bridged by BTC to lead to a 2D framework with rectangular-shaped cavities. Two compounds of third-order nonlinear optical (NLO) properties were determined by Z-scan technique in DMSO solution. The results showed that two compounds exhibited strong NLO absorption and strong self-focusing effects. The third-order NLO absorptive coefficients β(MKS) are 5.45 × 10−11 m W−1 for 1 and 9.81 × 10−11 m W−1 for 2. The refractive indexes γ(MKS) are 3.96 × 10−18 m2 W−1 for 1 and 7.60 × 10−18 m2 W−1 for 2. The third-order NLO susceptibility χ(3) are calculated to be 1.25 × 10−11 for 1, 2.32 × 10−11 esu for 2, respectively. These values are larger than those of metal coordination polymers reported. Two novel two-dimensional transition metal coordination polymers have been reported. Two compounds exhibit strong NLO absorption and strong self-focusing effects. The third-order NLO susceptibility χ(3) are calculated to be 1.25 × 10−11 for 1, 2.32 × 10−11 esu for 2, respectively

Multiphoton absorption in amyloid protein fibres

Fibrillization of peptides leads to the formation of amyloid fibres, which, when in large aggregates, are responsible for diseases such as Alzheimer's and Parkinson's. Here, we show that amyloids have strong nonlinear optical absorption, which is not present in native non-fibrillized protein. Z-scan and pump-probe experiments indicate that insulin and lysozyme β-amyloids, as well as α-synuclein fibres, exhibit either two-photon, three-photon or higher multiphoton absorption processes, depending on the wavelength of light. We propose that the enhanced multiphoton absorption is due to a cooperative mechanism involving through-space dipolar coupling between excited states of aromatic amino acids densely packed in the fibrous structures. This finding will provide the opportunity to develop nonlinear optical techniques to detect and study amyloid structures and also suggests that new protein-based materials with sizable multiphoton absorption could be designed for specific applications in nanotechnology, photonics and optoelectronics.

Synthesis, Crystal Structure and NLO of a Pb(II) Coordination Compound Based on HO-H<sub>2</sub>BDC

A new three-dimensional Pb(II) coordination polymer, [Pb3(O-BDC)2]n (1) (HO-H2BDC = 5-Hydroxy-1,3-benzenedicarboxylate), has been solvothermally synthesized from the reaction of HO-H2BDC, Pb(NO3)2•6H2O and NaAc. Single-crystal X-ray diffraction analysis reveal that polymer 1 exhibit a unprecedented 3D structure and ligand HO-H2BDC has been observed to exhibit a new coordination mode. The third-order nonlinear optical (NLO) properties in DMF solution have been studied by Z-scan technique using 8 ns laser at 532 nm. The results reveal that the new compound exhibits strong NLO absorption effect and self-focusing refractive performance (α2 = 1.2 × 10-10 mW-1; n2 = -2.4×10-17 m2•W-1).

Synthesis and Third-Order Nonlinear Optical Properties of Copper and Nickel Coordination Complexes of Azo Dyes

An azo dye, 2-(4,5-dicyano-1-H-imidazolyazo)-5-N, N-diethylaminophenol, and the corresponding divalent copper and nickel mononuclear coordination complexes were synthesized. The molecular third-order nonlinear optical characteristics of these azo transition metallic chelates were investigated in N,N′-dimethylformamide solution using a standard Z-scan technique with a 7-ns laser pulses at 1,064 nm. The results of n 2 (the nonlinear refraction index) and γ (the hyperpolarizability) values of the two complexes indicated that metal chelating lead to considerable enhancement in third-order optical nonlinearities, which revealed that such coordination complexes exhibit strong nonlinear optical absorption effects and self-defocusing performance. These materials are promising candidates as large third-order nonlinear optical materials.

60]Fullerene metal complexes with large effective two-photon absorption cross-section

Fourteen novel complexes of fullerene C(60) with metal dialkyldithiophosphate, {[(RO)(2)PS(2)](2)M}·2C(60) (R = Me and Et; M = Mn, Fe, Co, Ni, Cu, Zn and Pd), can be obtained in high yield by the reaction of metal(II) dialkyldithiophosphate complexes with C(60) fullerene. Their structures are determined by (1)H, (13)C, and (31)P NMR spectroscopy, elemental analysis, FT-IR and UV-vis, and are supplied by single crystal X-ray data. The compound {[(EtO)(2)PS(2)](2)Pd}·2C(60) was also studied by the HRTEM image and SAED patterns. Studies of the optical properties of the complexes of fullerene C(60) with metal dialkyldithiophosphate show that these compounds all have very strong nonlinear optical absorption effects. The nonlinear absorption of fourteen complexes of fullerene C(60) with metal dialkyldithiophosphate (in o-dichlorobenzene and in the solid state) was measured by the open-aperture Z-scan technique at a wavelength of 532 nm. DFT calculations are also used to discuss the stability of these complexes and to confirm the structural assignments.

Carbon Nanotube Polycarbonate Composites for Ultrafast Lasers

Carbon nanotube polycarbonate composites with controlled nanotube-bundle size are prepared by dispersion with conjugated polymers followed by blending with polycarbonate. The composite has uniform sub-micrometer nanotube bundles in high concentration, shows strong nonlinear optical absorption, and generates 193 fs pulses when used as passive mode-locker in a fiber laser.

Very strong nonlinear optical absorption in green GaInN/GaN multiple quantum well structures

AbstractThe efficiency of green GaInN/GaN light emitting diodes (LEDs) is known to drop under high current densities. To explore the reason, 535 nm emitting GaInN/GaN multiple quantum well (MQW) and GaN epilayers were characterized using Z‐scan techniques under comparable excitation conditions with a continuous wave laser. Two wavelengths, 514 nm and 488 nm, were selected right below and above the apparent optical absorption edge. At 514 nm, a very large nonlinear absorption coefficient β = 2.6 cm/W was obtained. This leads to a 20% absorption enhancement at a photon flux of 21 kW/cm2. We attribute this to nonlinear free‐carrier absorption. On the other hand, at 488 nm, a nonlinear saturable absorption with β = –1.7 cm/W was observed. This induced transparency indicates photon bleaching in the MQW. Apparently, free carrier dynamics strongly affects optical nonlinearity, while nonlinear absorption provides a small contribution to the limitations of current green LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydrothermal synthesis, crystal structure and third-order nonlinear optical properties of a 3D coordination polymer containing 3,3′,4,4′-benzophenone-tetracarboxylate (BPTC) and pyrazine ligands

A mixed-ligand compound, [Ni2(BPTC)(pyz) · 2H2O] n (0.5H2O) n (BPTC = 3,3′,4, 4′-benzophenone-tetracarboxylate, pyz = pyrazine), has been prepared hydrothermally by assembly of BPTC, NiCl2·6H2O and pyz. X-ray diffraction analysis of a single crystal reveals the three-dimensional framework assembled from pyz-pillared two-dimensional sheets. Three types of channels in one direction are established inside the structure. The third-order nonlinear optical (NLO) properties in DMF have been studied by Z-scan technique using an 8 ns laser at 532 nm. The results reveal that the new compound exhibits strong NLO absorption and self-focusing refractive performance (n 2 = 2.7 × 10−17 m2 W−1).