Nonlinear Absorption Cross Section Research Articles

In-Brain Multiphoton Imaging of Vaterite Cargoes Loaded with Carbon Dots.

Biocompatible fluorescent agents are key contributors to the theranostic paradigm by enabling real-time in vivo imaging. This study explores the optical properties of phenylenediamine carbon dots (CDs) and demonstrates their potential for fluorescence imaging in cells and brain blood vessels. The nonlinear absorption cross-section of the CDs was measured and achieved values near 50 Goeppert-Mayer (GM) units with efficient excitation in the 775-895 nm spectral range. Mesoporous vaterite nanoparticles were loaded with CDs to examine the possibility of a biocompatible imaging platform. Efficient one- and two-photon imaging of the CD-vaterite composites uptaken by diverse cells was demonstrated. For an in vivo scenario, CD-vaterite composites were injected into the bloodstream of a mouse, and their flow was monitored within the blood vessels of the brain through a cranial window. These results show the potential of the platform for high-brightness biocompatible imaging with the potential for both sensing and simultaneous drug delivery.

Large third-order optical nonlinearities of two-dimensional CsPbBr3 nanoplatelets

Metal halide perovskites show considerable optical nonlinearity and could be used for cost-effective nonlinear optical devices if their nonlinear susceptibilities can be improved. Here, we report large optical nonlinearity, including third-order nonlinear absorption, refraction, and two-photon absorption excited luminescence, of CsPbBr3 nanoplatelets with a thickness of two or three atomic layers and a plane size of about 60 nm. Specifically, the nonlinear absorption was mainly induced by two-photon absorption at low incident powers, and the nonlinear absorption cross section reached 2.15 × 107 GM. It is two orders of magnitude larger than that of CsPbBr3 nanocrystals, which makes them an ideal optical limiting material. Furthermore, the nanoplatelets exhibited large self-phase modulation-induced nonlinear refraction, and the figures of merit W and T satisfied W >1 and T <1, which allow for optical switching. The large optical nonlinearity of CsPbBr3 nanoplatelets provides a basis for multifunctional applications in nonlinear optical devices.

Scanning the optical characteristics of lead-free cesium titanium bromide double perovskite nanocrystals

Cs2TiBr6 nanocrystals (NCs) are a type of promising optoelectronic materials, owing to their high photoelectric properties and non-toxicity. Here, we synthesize the colloidal Cs2TiBr6 NCs using a hot-injection approach. The temperature-dependent absorption data shows that its energy band changes about 30 meV with temperature, reflecting that its energy band structure is much stable. The excitation intensity-dependent transient absorption data confirms its linear absorption cross-sections and carrier recombination rate constants, involving monomolecular and bimolecular recombination, which are all superior to those of conventional perovskite bromide counterparts. In addition, its nonlinear absorption cross-sections are also measured based on femtosecond Z-scan. Our results suggest that Cs2TiBr6 NCs can be extensively applied in the field of optoelectronics, owing to its excellent carrier dynamics and nonlinear optical properties.

Photophysical and nonlinear optical properties of the positional isomers of 4-(4-tertbutylphenoxy) substituted cobalt, nickel and copper phthalocyanines

This paper reports on the third order nonlinear optical properties of cobalt, nickel and tetrakis(4-terbutylphenoxy)phthalocyaninatocopper(II) isomers, using the Z-scan technique. Metal-free isomers were found to have high nonlinear absorption coefficient (β) values compared to the metalated isomers. Metal-free C2v isomer was found to have the highest β value of 1.52 × 10−10 mMW−1 in THF. All the metal-free and metal phthalocyanine isomers nonlinear properties were found to be dependent on the singlet state absorption. Imaginary second order nonlinear hyperpolarizability (Im[γ]), ground state cross section (σg), excited states cross sections (σs and σt) and two photon absorption (TPA) cross section (σTPA) values are reported in this work. The five-energy level model rate equations were used to model the nonlinear response and absorption cross sections.

Penta(zinc porphyrin)[60]fullerenes: Strong reverse saturable absorption for optical limiting applications

Penta(zinc porphyrin)[60]fullerene, in which a fullerene (C60) with attached five electron donating zinc porphyrin moieties was synthesized. The nonlinear optical response was studied together with reference penta(trimethylsilyl)C60 and triazole-zinc porphyrin compounds. The second and third harmonic generation in both guest-host polymeric films deposited by means of spin coating technique and films obtained by physical vapor deposition technique was investigated via Maker fringe technique employing 30 ps laser pulses at 1064 nm. The second and third order susceptibilities as well as second hyperpolarizabilities were determined. Penta(zinc porphyrin)[60]fullerene in solutions and PMMA films demonstrated strong reverse saturable absorption in Z-scan measurements employing the laser double frequency. The nonlinear absorption coefficient and imaginary part of cubic susceptibility were obtained for solutions and films. The second hyperpolarizability and nonlinear absorption cross section were extracted as well. Penta(zinc porphyrin)[60]fullerene shows attractive optical limiting response property suitable for photonic applications.

CdSe/CdS/CdTe Core/Barrier/Crown Nanoplatelets: Synthesis, Optoelectronic Properties, and Multiphoton Fluorescence Upconversion.

Colloidal two-dimensional (2D) nanoplatelet heterostructures are particularly interesting as they combine strong confinement of excitons in 2D materials with a wide range of possible semiconductor junctions due to a template-free, solution-based growth. Here, we present the synthesis of a ternary 2D architecture consisting of a core of CdSe, laterally encapsulated by a type-I barrier of CdS, and finally a type-II outer layer of CdTe as so-called crown. The CdS acts as a tunneling barrier between CdSe- and CdTe-localized hole states, and through strain at the CdS/CdTe interface, it can induce a shallow electron barrier for CdTe-localized electrons as well. Consequently, next to an extended fluorescence lifetime, the barrier also yields emission from CdSe and CdTe direct transitions. The core/barrier/crown configuration further enables two-photon fluorescence upconversion and, due to a high nonlinear absorption cross section, even allows to upconvert three near-infrared photons into a single green photon. These results demonstrate the capability of 2D heterostructured nanoplatelets to combine weak and strong confinement regimes to engineer their optoelectronic properties.

Wavelength-Dependent Nonlinear Optical Properties of Ag Nanoparticles Dispersed in a Glass Host

The linear and nonlinear optical properties of metal nanoparticles are highly tunable by variation of parameters such as particle size, shape, composition, and environment. To fully exploit this tunability, however, quantitative information on nonlinear absorption cross sections is required, as well as a sufficient understanding of the physical mechanism underlying these nonlinearities. In this work, we present a detailed and systematic investigation of the wavelength-dependent nonlinear optical properties of Ag nanoparticles embedded in a glass host, in which the most important parameters determining the nonlinear behavior of the system are characterized. This allows a proper quantification of absorption cross sections and elucidation of the excitation mechanism. Based on small-angle X-ray scattering measurements average particle diameters of 3 and 17 nm are estimated for the studied samples. The nonlinear optical properties of the nanoparticle–glass composite are studied in an extended wavelength range ...

Solvent Effect on the Third-Order Nonlinear Optical Properties of α- and β-Tertbutyl Phenoxy-Substituted Tin(IV) Chloride Phthalocyanines.

This paper investigates the third-order nonlinear optical properties of 4α-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc) in different organic solvents. The third-order susceptibilities of α-SnOtBpPc and β-SnOtBpPc are reported in different solvents, using Z-scan techniques with 10 ns laser pulses at 532 nm. Their nonlinear absorption coefficient and absorption cross sections were also determined. The molecular imaginary components of the second-order hyperpolarizability Im[γ] of α-SnOtBpPc and β-SnOtBpPc were found to be 2.60 × 10-31 and 2.94 × 10-31 esu (tetrahydrofuran), 2.12 × 10-31 and 2.54 × 10-31 esu (chloroform), 3.06 × 10-31 and 2.54 × 10-31 esu (dichloromethane), and 1.27 × 10-31 and 1.50 × 10-31 esu (toluene), respectively. This study found that substitution at the α position has an effect of lowering the two-photon (2PA) cross section value for α-SnOtBpPc compared to that for β-SnOtBpPc, with values of 64.30 and 456.65 GM, respectively. The large 2PA cross section observed in β-SnOtBpPc is attributed to the decreased energy difference between the virtual state and the LUMO.

4-N, N-bis(4-methoxylphenyl) aniline substituted anthraquinone: X-ray crystal structures, theoretical calculations and third-order nonlinear optical properties

In this paper, mono- and di-4-N,N-bis(4-methoxylphenyl)aniline-substituted anthraquinone have been designed and synthesized through Suzuki reaction. For mono-4-N,N-bis(4-methoxylphenyl)aniline-substituted anthraquinone, polymorphous crystal structures have been obtained in different crystallization conditions. Electrochemical characterization combined with theoretical calculation suggests that the addition of a second triphenylamine unit causes a larger band gap with higher lying LUMO (Lowest Unoccupied Molecular Orbital) and HOMO (Highest Occupied Molecular Orbital). The linear optical property shows that the introduction of a second triphenylamine unit bring about a significant hyperchromic effect with the extinction coefficients increasing from 11199 M−1 cm−1 to 22136 M−1 cm−1. The third-order nonlinear optical properties indicate that the introduction of a second triphenylamine unit lead to a much larger nonlinear absorption coefficient and two-photon absorption cross section, with the relevant value increasing from 2.04 × 10−12 cm W−1 to 3.91 × 10−12 cm W−1, and from 148 GM to 286 GM, respectively.

Dynamics, Efficiency, and Energy Distribution of Nonlinear Plasmon-Assisted Generation of Hot Carriers

We employ nonlinear autocorrelation measurements to investigate plasmon-assisted hot carrier dynamics occurring in optical gold antennas. A nonlinear formation of hot carriers is produced by the excitation of surface plasmons, providing thus a unique lever to optimize the energy distribution and generation efficiency of the photoexcited charges. The temporal response of the carriers’ relaxation is controlled within a range extending from 500 fs to 2.5 ps. By conducting a quantitative analysis of the dynamics, we determine the nonlinear absorption cross-section of individual optical antennas. This work sheds new insights on the understanding of plasmon-induced hot carrier generation, especially in view of applications where the time response plays a preponderant role.

Measurement of Two-Photon Absorption Cross Section of Metal Ions by a Mass Sedimentation Approach.

The photo-reduction of metal ions in solution induced by femtosecond laser is an important and novel method for fabricating three-dimensional metal microstructures. However, the nonlinear absorption cross section of metal ions remains unknown because its measurement is difficult. In the present study, a method based on Two-Photon Excited Sedimentation (TPES) is proposed to measure the two-photon absorption cross section (TPACS) of metal ions in solution. The power-squared dependence of the amount of sediment on the excitation intensity was confirmed, revealing that 800 nm femtosecond laser induced reduction of metal ions was a two photon absorption process. We believe that the proposed method may be applied to measure the TPACS of several metal ions, thereby opening a new avenue towards future analysis of two-photon absorption materials.

Excited State Absorption from Real-Time Time-Dependent Density Functional Theory

The optical response of excited states is a key property used to probe photophysical and photochemical dynamics. Additionally, materials with a large nonlinear absorption cross-section caused by two-photon (TPA) and excited state absorption (ESA) are desirable for optical limiting applications. The ability to predict the optical response of excited states would help in the interpretation of transient absorption experiments and aid in the search for and design of optical limiting materials. We have developed an approach to obtain excited state absorption spectra by combining real-time (RT) and linear-response (LR) time-dependent density functional theory (TDDFT). Being based on RT-TDDFT, our method is aimed at tackling larger molecular complexes and materials systems where excited state absorption is predominantly seen and many time-resolved experimental efforts are focused. To demonstrate our method, we have calculated the ground and excited state spectra of H₂⁺ and H₂ due to the simplicity in the interpretation of the spectra. We have validated our new approach by comparing our results for butadiene with previously published results based on quadratic response (QR). We also present results for oligofluorenes, where we compare our results with both QR-TDDFT and experimental measurements. Because our method directly measures the response of an excited state, stimulated emission features are also captured; although, these features are underestimated in energy which could be attributed to a change of the reference from the ground to the excited state.

Synthesis and optical characterization of lanthanide-doped colloidal Ga2O3 nanoparticles

We demonstrate the use of thermal decomposition reaction to obtain Ga2O3 nanoparticles with average size around 5nm. The obtained nanoparticles presented a good colloidal stability and high optical transparency. We were also able to incorporate Eu3+ and Tb3+ ions inside the crystal host. The synthesized nanomaterials exhibited dual mode emission upon UV excitation, consisting of a broad band in the blue region and a characteristic series of sharp lines. The former resulted from donor–acceptor pairs recombination in Ga2O3 host, while the latter from 4f–4f electronic transitions in lanthanide ions. For fuller optical characterization of the obtained nanoparticles, we have performed wide wavelength range Z-scan studies, and calculated the values of nonlinear absorption cross-sections. Gallium (III) oxide nanoparticles showed two-photon absorption in the range between 500nm and 700nm, with molecular weight scaled nonlinear optical parameters exceeding the values for other lanthanide-doped nanoparticles of similar size.

Chromophore design for large two-photon absorption

Conjugated oligothiophene chromophores are compared and studied for designing large linear and nonlinear absorption cross-sections. Optical properties of chromophores synthesized by the Naval Research Laboratory are modeled to construct a design factor of merit to predict and understand two-photon absorption (TPA) designs. Computer modeling to optimize parameters to produce photo active chromophores is conducted. Geometry, π-center (electron relay) and the electron donor or acceptor groups attached to the π-centers are considered for importance in TPA. This work could serve equally well as guide for quick back of the envelop research or industrial design verifications as well as an outline for introducing computation methods to students.

Femtosecond pulse train shaping improves two-photon excited fluorescence measurements.

Measurements of two-photon absorption (TPA) cross sections are greatly confounded by even very weak linear absorption, for example from hot bands. In this case, the experimental power dependence of fluorescence from amplified and mode-locked laser systems can differ drastically, even if the peak intensity is adjusted to be the same in both cases. A simple pulse train shaping method suppresses linear contributions and extracts the nonlinear absorption cross section, demonstrated here for a meso-to-meso ethyne-bridged bis[(porphinato)zinc(II)] fluorophore (DD) at 800 nm. This approach permits reliable TPA cross-section measurement, even with standard modelocked lasers under conditions identical to that used for multiphoton microscopy.

Design, synthesis, linear and nonlinear photophysical properties and biological imaging application of a novel Λ-type pyrimidine-based thiophene derivative

A novel D–π–A–π–D type thiophene pyrimidine derivative, 2,2′-thiophene-4, 6-bis (4-N,N-diethylbenzene ethenyl) pyrimidine (L), was designed, synthesized via Knoevenagel and Suzuki coupling reactions, and fully characterized. The results of X-ray diffraction analysis revealed that single crystal of L belongs to P212121 non-centrosymmetric space group, and the whole molecular skeleton exhibits a good coplanarity. Systematic photophysical properties were investigated for L. The connections between the properties and structure were explained relying on theoretical calculation. The thiophene pyrimidine derivative shows strong third-order nonlinear optical response and large two-photon absorption (2PA) cross section in high polar solvents. Finally, preliminary exploration in biological imaging also has been carried out, it shows a good biological application prospect.

Nonlinear Optical Properties of Conjugated Platinum(II) Acetylides with Multibranched Donor–Acceptor Structures

AbstractSix conjugated platinum(II) acetylides with multibranched donor‐acceptor structures (1–6) were synthesized. The absorption maxima of triazine‐centered complexes 1–3 are red‐shifted by 36–43 nm compared with those of triphenylamine‐centered complexes 4–6. The luminescence spectra of 4–6 in air‐saturated chloroform showed one fluorescence peak and one phosphorescence peak. However, only one fluorescence peak was detected for 1–3 in air‐saturated chloroform. The transient absorption spectra of the compounds indicate the effective intersystem crossing from S1 to T1. The nonlinear optical properties of 1–6 in N,N‐dimethylformamide were studied using open Z‐scan method. The results indicate that complexes 1 and 6 exhibit good nonlinear optical performance. The ratios of the effective nonlinear absorption cross section to ground‐state absorption cross section σeff/σ0 of complexes 1–6 are in the range of 4–22.

Synthesis, crystal structures and third-order nonlinear optical properties of 4-formylpyridine Schiff base of thiosemicarbazide, and its dinuclear copper(I) and silver(I) complexes

A novel thiosemicarbazide ligand L and its dinuclear complexes M2(dppm)2L(NO3)2 [where dppm=bis(diphenylphosphino)methane, M=Cu(I) (1), Ag(I) (2)] were designed, synthesized and characterized by 1H NMR spectroscopy, elemental analysis, IR, MALDI-TOF mass spectroscopy, and single crystal X-ray diffraction analysis. The third-order nonlinear optical (NLO) properties of the metal complexes were determined by the open/close aperture Z-scan technique. The results reveal that the complexes possess much larger third-order nonlinear susceptibility and two-photon absorption cross sections than that of its free ligand L in the near IR region, especially for complex 2. The photophysical properties of them were investigated and interpreted on the basis of theoretical calculations (TD-DFT).

Efficient generation of blue light in oligothiophene chromophores doped in polymer films and fiber

A conjugated oligothiophene chromophore with large linear and nonlinear absorption cross-sections that emits light in the blue region is studied. Here measurements of the one- and two-photon absorption and fluorescence of an oligothiophene chromophore doped in polymethyl-methacrylate (PMMA) polymer is presented. It was observed that oligothiophene/PMMA fluoresces strongly and through amplified spontaneous emission (ASE), is an efficient source of blue light around 460nm. Using these materials, a polymer fiber-based blue ASE light source is demonstrated. Blue emitting molecules (mainly in PMMA) are tabulated for comparison.

Plasmon Blockade in Nanostructured Graphene

Among the many extraordinary properties of graphene, its optical response allows one to easily tune its interaction with nearby molecules via electrostatic doping. The large confinement displayed by plasmons in graphene nanodisks makes it possible to reach the strong-coupling regime with a nearby quantum emitter, such as a quantum dot or a molecule. In this limit, the quantum emitter can introduce a significant plasmon-plasmon interaction, which gives rise to a plasmon blockade effect. This produces, in turn, strongly nonlinear absorption cross sections and modified statistics of the bosonic plasmon mode. We characterize these phenomena by studying the equal-time second-order correlation function g((2))(0), which plunges below a value of 1, thus revealing the existence of nonclassical plasmon states. The plasmon-emitter coupling, and therefore the plasmon blockade, can be efficiently controlled by tuning the doping level of the graphene nanodisks. The proposed system emerges as a new promising platform to realize quantum plasmonic devices capable of commuting optical signals at the single-photon/plasmon level.