Two-photon Absorption Behavior Research Articles

Investigation of Nonlinear Optical Properties of NiO Nanoparticles using the Z-Scan Technique

In this research, linear and nonlinear optical properties of NiO nanoparticles (NPs) dissolved in ethanol were investigated. Linear optical characteristics of NiO NPs were studied using a UV-Vis spectrophotometer. The linear absorption coefficient (α0) was 0.88 and 0.57 cm-1 at 405 and 532 nm wavelengths, respectively. The band gap energy rose from 3.56 eV for a sample with a 10-7 g/ml concentration to 3.92 eV for the 10-3 g/ml concentration sample. Using the Z-scan technique, the nonlinear optical characteristics of the NPs were investigated. Two continuous wave laser diodes with 405 and 532 nm wavelengths and different powers were used. The Z-scan system with a closed aperture revealed that NiO NPs have a negative n2 (self-defocusing effect) at various laser powers. n2 increases as the power of the laser increases. The value of n2 was found to be 0.51×10-4 cm2/mW at a wavelength of 405 nm and a power of 0.33 mW. It improved as the laser power increased, reaching a maximum of 0.64×10-4 cm2/mW at a laser power of 1.51 mW. For the laser with a wavelength of 532 nm, the n2 value was 0.27×10-4 cm2/mW for a laser power of 1.01 mW. This value increased to 0.76×10-4 cm2/mW when the laser power increased to 6.2 mW. As measured by the Z-scan system with an open aperture, NiO NPs have a nonlinear absorption coefficient and display a two-photon absorption behavior.

Structural characteristics and enhanced two-photon absorption behavior of Pb-doped ZnMoO4 nanostructures for optoelectronic device applications

Structural characteristics and enhanced two-photon absorption behavior of Pb-doped ZnMoO4 nanostructures for optoelectronic device applications

2D Ti3AlC2 and Ti3C2 nanosheets: Excellent optical limiting materials for laser protection

MXenes have important research value in the field of photonics. In this work, Ti3C2 MXene was obtained by etching the Ti3AlC2 MAX phase with hydrofluoric acid, Ti3AlC2 and Ti3C2 nanosheets with a thickness of several nanometers were prepared by ultrasound-assisted liquid-phase exfoliation using anhydrous ethanol as the exfoliation solvent. The nonlinear absorption properties of the two nanosheets at 1064, 532 and 355 nm excitation wavelengths (infrared to ultraviolet band), especially the optical limiting behavior, were systematically investigated with the help of open aperture Z-scan technique. Interestingly, Ti3C2 MXene, obtained from Ti3AlC2 MAX by a simple hydrofluoric acid etching operation only, exhibits different nonlinear optical properties from Ti3AlC2 MAX under the same experimental conditions. Ti3AlC2 nanosheets exhibited excellent two-photon absorption behavior in the visible light band, while the two-photon absorption behavior of Ti3C2 nanosheets is better in the ultraviolet band. The excellent nonlinear absorption properties exhibited by Ti3AlC2 and Ti3C2 nanosheets demonstrate their advantages as OL materials with great potential for applications in laser protection.

Two-photon absorption behavior of conjugated oligomers suitable for low colour temperature LEDs.

Light emitting diodes (LEDs) with low colour temperatures (CTs) have been proved to be physiologically-friendly light sources. However, there are few reports on the photophysical properties of luminescent materials with CTs lower than candlelight. Herein, one- and two-photon optical properties of four fluorenone-based conjugated oligomers have been systemically investigated. By using a sum-over-essential states (SOS) approach, we obtained the transition dipole moments and two-photon absorption (TPA) cross sections. The triphenylamine end-capped oligomer exhibits reddish orange luminescence with extremely low colour temperature of 1686 K, which is much lower than that of candlelight. Fluorene-ethylene units serving as π-spacers could weaken the role of electron-donating units and effectively enhance the TPA performance of oligomers. Our results provide an effective way for the design and optimization of universal light-emitting material candidates in optoelectronic devices.

Ultrasonication assisted exfoliation of MoSe2 nanosheets for optical and optical power limiting applications

We report direct, economic, and facile preparation of two-dimensional transition metal dichalcogenide material molybdenum diselenide nanosheets through the ultrasonication assisted liquid exfoliation method. The optical absorption spectra confirm the formation of MoSe2 nanosheets. The Kramers–Kronig expression was used to estimate the refractive index and extinction coefficient values of the prepared nanosheets. The emission properties of the prepared samples were done using photoluminescence spectroscopy. The nonlinear optical studies were performed using an open aperture Z-scan method under nanosecond pulsed laser excitation of a second harmonic generation wavelength of 532 nm. The obtained results demonstrate the strong optical power limiting (OPL) properties of the MoSe2 nanosheets. This OPL is due to two-photon absorption behavior of MoSe2 nanosheets.

The enhanced two-photon absorption behavior of twistfuranacenes to phenylacetylene-functionalized twistacenes

Three novel furanacenes (5/D5c) have been synthesized and characterized.

Two-photon absorption spectrum of solid solution nanocrystals of ZnS-AgInS2

Two-photon absorption behavior of dispersion of solid solution nanocrystals of ZnS-AgInS2 was investigated, the measured maximum two-photon absorption cross-section of this nanoparticle being 3900 ...

Nonlinear optical properties of lead-free ferroelectric nanostructured perovskite

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.

Synthesis, photoluminescence and ultrafast nonlinear optical properties of copper nanolayers/particles uniformly decorated ZnO nanowires

Copper (Cu) nanolayers/particles decorated zinc oxide (Cu-ZnO) nanowires have been successfully synthesized by two-step chemical vapour deposition to prepare ZnO nanowires and magnetron sputtering method to deposit Cu nanolayers/particles. The field emission scanning electron microscopy images indicated the Cu nanolayers/particles are clearly visualized on surface of ZnO nanowires. The impact of sputtering time and sputtering power was analyzed. The results show that the atomic percent of Cu was gradually increased with the sputtering time and sputtering power was increased. The photoluminescence results demonstrated two major emission peaks for the Cu-ZnO nanowires, and the visible emission peaks of Cu-ZnO nanowires stronger than that of unmodified ZnO nanowires. Moreover, the results of open-aperture Z-scan measurements that all samples show the two-photon absorption behavior, and the two-photon absorption coefficients of Cu-ZnO is higher than that of unmodified ZnO nanowires. The results of closed-aperture Z-scan results demonstrated that all samples show self-focusing optical nonlinearity. These studies promise their potential applications in multifunctional optical devices.

Selective and Real-Time Detection of Nitric Oxide by a Two-Photon Fluorescent Probe in Live Cells and Tissue Slices.

Nitric oxide (NO) is an important signaling molecule involved in many physiological and pathological processes. To understand these NO-mediated processes, it is a key to develop rapid and specific detection methods for NO. In the past 2 decades, numerous excellent fluorescent probes for NO have been designed; however, it still remains limitations such as slow response, low selectivity, and short excitation wavelength (<600 nm). In this Article, a two-photon fluorescent probe, NO-QA5, has been developed with 3-dimethylaminophenyl linking at the 6-position of 5-aminoquinoline as both the active site and prefluorophore for detection of NO. The nonfluorescent NO-QA5 can fast react with NO via a diazonium intermediate to generate two azoic regioisomers, one of which exhibits intramolecular charge transfer (ICT) emission, and two-photon absorption behavior (δΦ = 57 GM), giving a turn-on fluorescence rapid response. The sensing reaction is pH-insensitive in the range of 6-11 and highly selective and well sensitive (LOD = 15 nM), possible undergoing the same intermediate diazonium with the reaction under diazotization condition (NaNO2/HCl). Also, as a nitrite fluorescent probe NO-QA5 exhibits highly sensitive (LOD = 7 nM). Therefore, NO-QA5 can serve as a dual functional fluorescent probe for NO and NO2-. Furthermore, NO-QA5 as a specific imaging agent has been demonstrated by achieving both exogenous and endogenous detections of NO in living cells under both one- and two-photon excitation and high resolution in tissue slices under two-photon excitation.

Ultrafast third-order nonlinear optical response of pyrene derivatives

Two mono-substituted pyrene derivatives with delocalized electron system 1-(pyren-1-yl)−3-(4-Methyl thiophene-2-yl) acrylic ketone (13#) and 1-(pyren-1-yl)−3-(4-bromo thiophene-2-yl) acrylic ketone (15#) were successfully synthesized. The resultant compounds were characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (IR), high resolution mass spectrum (HR-MS), and UV–vis spectra. The third-order nonlinear optical properties of the compounds were investigated using Z-scan technique with femtosecond laser pulses at 500nm and 700nm, respectively. Both of the compounds showed a decrease in transmittance about the focus, which are typical of two-photon absorption. It was found that the two-photon absorption behavior of the pyrene derivatives were modified by substituents on thiophene ring. These results indicate that both compounds can be promising candidates for future optoelectronic and bio-imaging applications.

Study of Third-Order Optical Nonlinearities of Se-Sn (Bi,Te) Quaternary Chalcogenide Thin Films Using Ti: Sapphire Laser in Femtosecond Regime

The objective of the present research work is to study the nonlinear optical properties of quaternary Se-Sn (Bi,Te) chalcogenide thin films. A Z-scan technique utilizing 800 nm femtosecond laser source has been used for the determination of the nonlinear refractive index (n 2), two-photon absorption coefficient (β 2) and third-order susceptibility (χ (3)). In the measurement of n 2, an aperture is placed in the far field before the detector (closed aperture), while for the measurement of β 2, entire transmitted light is collected by the detector without an aperture (open aperture). Self-focusing has been observed in closed aperture transmission spectra. The appearance of the peak after the valley in this spectrum reflects the positive nonlinear refractive index. The calculated value of n 2 of the studied thin films varies from 1.06 × 10−12 cm2/W to 0.88 × 10−12 cm2/W. The compound-dependent behavior of n 2 is explained in this paper. We have also compared the experimental values of n 2 with the theoretically determined values, other compounds of chalcogenide glass and pure silica. The n 2 of the investigated thin films is found to be 3200 times higher than pure silica. The results of the open aperture Z-scan revealed that the value of β 2 of the studied compound is in the order of 10−8 cm/W. The behavior of two-photon absorption is described by means of the optical band gap (E g) of the studied compound. The variation in the figure-of-merit from 0.32 to 1.4 with varying Sn content is also reported in this paper. The higher value of nonlinearity makes this material advantageous for optical fibers, waveguides and optical limiting devices.

Two-photon polymerization of a branched hollow fiber structure with predefined circular pores

Porous fiber structures are of great concern to many fields of life-science engineering, but require a complex assembly processes that have geometric constraints. For this reason, tremendous efforts were expended in recent years to develop micro-/nano fabrication techniques. We report on the 3D structuring of a 3.5 mm long branched hollow fiber with 150 μm outer diameter and predefined circular pores (diameter: 30 μm). The investigated process is based on two-photon polymerization (2PP) of the UV curing resin OrmoComp®. The incident light of a femtosecond pulsed laser at 790 nm wavelength is used to generate the structure. Utilizing the non-linear behavior of two-photon absorption due to a tightly focused, high-intensity laser beam allows the local fabrication of three-dimensional structures in the photoresist. Voxels fabricated by 2PP are studied by controlling average laser power and exposure time. The appropriate average pulse energy and writing speed are determined to apply the optimal exposure parameters concerning the geometric accuracy and overall quality of the structure. The 2PP direct laser writing process is employed to generate the hollow fiber at an average laser power of 105 mW, and a writing speed of 5.0 mm/s. Water flowing through the fiber provides evidence that the core is hollow.

Theoretical investigation of two-photon absorption properties and optical limiting behavior of two symmetrical fluorene derivatives

Two-photon absorption and optical limiting of two fluorenyl-based derivatives, 9,9-dimethyl-2,7-bis((E)-4-nitrostyryl)-9H-fluorene and 9,9-dimethyl-2,7-bis((E)-4-((E)-4-nitrostyryl)styryl)-9H-fluorene, in gas phase and solvent with nanosecond laser pulse have been theoretically investigated by solving the coupled rate equations and the field intensity equation employing an iterative predictor–corrector finite-difference time-domain (FDTD) method. The results show that both optical limiting properties and two-photon absorption cross-section strongly depend on the length of these molecules and the solvent. Moreover, the dynamical two-photon absorption behavior is affected by the thickness of samples and the pulse duration. These discoveries demonstrate that these fluorenyl-based derivatives possess highly promising characteristics and have potential applications for optical limiting devices.

A series of homoleptic bis(phthalocyaninato) rare earth sandwich complexes with large two-photon absorption cross-section

The third-order nonlinear optical properties of a series of homoleptic substituted phthalocyaninato rare earth double-decker complexes were experimentally investigated by the Z-scan technique at the wavelength of 800 nm. All complexes were revealed to exhibit large two-photon absorption cross-sections. The measured two-photon absorption values of these complexes remain constant at different laser intensities, indicating nonlinearity is originated from pure two-photon absorption behavior. In addition, the two-photon absorption cross-section of these complexes increases along with the decrease of the rare earth atomic radius, suggesting that intense intramolecular π–π interaction between the phthalocyaninato macrocycles improves the third-order nonlinear optical properties. The optical limiting behavior of these complexes in chloroform was also investigated by using femtosecond laser pulses. The excellent two-photon absorption properties and optical limiting performance indicate their good application potential in photonic and optoelectronic devices.

Modulation on Optical Limiting and Two-Photon Absorption Behavior of a Molecular Medium by Two-Color Ultrashort Laser Pulses

The dynamical behavior of two-color ultrashort laser pulse propagating in a molecular medium 4,4'-bis(di-n -butylamino)stilbene (BDBAS) has been studied by employing an iterative predictor-corrector finite-difference time domain (FDTD) tech- nique to solve the Maxwell-Bloch equations. The results indicate that the spectrum of electric field shows oscillation feature around the two-photon resonant frequency when the delay time exists due to the interaction between two sub-pulses. The opti- cal limiting window turns narrower and the saturation value of output intensity gets larger with the presence of delay time compared with no delay time case. The dynam- ical TPA cross section is smaller with the increase of delay time. The studies suggest a method to modulate the nonlinear optical properties of the medium by controlling the delay time of the two-color pulse. PACS: 33.80.-b, 82.50.Pt, 31.15.A-

Hydrosoluble two-photon absorbing materials: A series of sulfonated organic inner salts in biological imaging application

Designed to achieve high two-photon absorptivity dyes, a novel series of D-π-A type hydrosoluble inner salts (SL1, SL2, SL3 and SL4) based on pyridinium have been synthesized and fully characterized. Photophysical properties including linear absorption, one-photon excited fluorescence and two-photon absorption properties were systematically investigated. These results show that there is a shift in the absorption and emission maxima with variation of solvent polarity. Furthermore, the chromophore SL4 shows the strongest intensity of two-photon excited fluorescence among the four chromophores and the largest two-photon absorption cross-section in the near infrared region (∼960 nm), indicating the steric bulk of the electron-donating terminal group plays an important role in two-photon absorption behavior. In addition, SL4 displays two-photon absorption activity when dissolved in water, which can be effectively used in two-photon bioimaging for its reasonable two-photon absorption cross-section. SL4-labeled cells revealed a distinct vesicular localization, most likely representing lysosomal compartments.

Effect of intramolecular charge transfer on the two-photon absorption behavior of multibranched triphenylamine derivations

Solvent polarity effect on the absorption spectra and fluorescence spectra of a series of multibranched structure triphenylamine derivations (Ph-G0, Ph-G1, and Ph-G2) were analyzed to reveal the factors that determine the two-photon absorption (TPA) ability in these molecules. It was found that the dominate factor is the extent of intramolecular charge transfer upon photoexcitation, rather than coherent coupling between branches. This result suggests that it is more effective to change the electron withdrawing ability or electron giving ability of branches and core than simply increase the number of branches for enhancing the TPA ability in multibranched structure molecules.

Engineering conjugation in para-phenylene-bridged porphyrin tapes

We report the synthesis of 7 new para-phenylene-bridged zinc porphyrin dimers, five of which were characterized by single-crystal X-ray analysis. A variety of links were tested for holding the para-phenylene bridges in π-conjugation with the porphyrins, and the natures of these restraining links strongly influence the properties of the porphyrin dimers. The keto-linked dimer exhibits a long-lived singlet excited state and strong fluorescence at 960 nm (1.7% quantum yield) in contrast to most previously reported conjugated porphyrin tapes, which are essentially non-emissive. Replacement of the cross-conjugated keto links by directly conjugated C–C bonds eradicates the fluorescence and shifts the absorption maximum to 1077 nm. On the other hand, replacement of the keto links with non-conjugated CPh2 links confers fluorescence at 736 nm (10% quantum yield) and results in remarkably similar one- and two-photon absorption behavior to that of meso–meso ethynylene-bridged porphyrin dimers (peak two-photon cross section: 7,300 GM at 878 nm). Cross-conjugated keto links do more than just hold the para-phenylene bridge coplanar with the porphyrins; they reduce the HOMO–LUMO gap, although to a lesser extent than direct π-conjugated links. Planarized para-phenylene-bridged porphyrin dimers provide insights into the relationship between previously investigated classes of conjugated porphyrin oligomers, and they open up possibilities for the synthesis of new types of near-IR two-photon absorbing dyes.

Synthesis and Photophysical Properties of Stilbeneoctasilsesquioxanes. Emission Behavior Coupled with Theoretical Modeling Studies Suggest a 3-D Excited State Involving the Silica Core

A set of stilbene-substituted octasilicates [p-RStil(x)Ph(8-x)SiO(1.5)](8) (R = H, Me, MeO, Cl, NMe(2) and x = 5.3-8) and [o-MeStilSiO(1.5)](8) were prepared. Model compounds were also prepared including the corner and half cages: [p-MeStilSi(OEt)(3)], [p-Me(2)NStilSi(OSiMe(3))(3)], and [p-Me(2)NStilSi(O)(OSiMe)](4). These compounds were characterized by MALDI-TOF, TGA, FTIR, and (1)H NMR techniques. Their photophysical properties were characterized by UV-vis, two-photon absorption, and cathodoluminescence spectroscopy (on solid powders), including studies on the effects of solvent polarity and changes in concentration. These molecules are typically soluble, easily purified, and robust, showing T(d(5%)) > 400 degrees C in air. The full and partial cages all show UV-vis absorption spectra (in THF) identical to the spectrum of trans-stilbene, except for [o-MeStilSiO(1.5)](8), which exhibits an absorption spectrum blue-shifted from trans-stilbene. However, the partial cages show emissions that are red-shifted by approximately 20 nm, as found for stilbene-siloxane macrocycles, suggesting some interaction of the silicon center(s) with the stilbene pi* orbital in both the corner and half cages. In contrast, the emission spectra of the full cages show red-shifts of 60-100 nm. These large red-shifts are supported by density functional theoretical calculations and proposed to result from interactions of the stilbene pi* orbitals with a LUMO centered within the cage that has 4A(1) symmetry and involves contributions from all Si and oxygen atoms and the organic substituents. Given that this LUMO has 3-D symmetry, it appears that all of the stilbene units interact in the excited state, consistent with theoretical results, which show an increased red-shift with an increase in the functionalization of a single corner to functionalization of all eight corners with stilbene. In the case of the Me(2)N- derivatives, this interaction is primarily a charge-transfer interaction, as witnessed by the influence of solvent polarity on the emission behavior. More importantly, the two-photon absorption behavior is 2-3 times greater on a per p-Me(2)Nstilbene basis for the full cage than for the corner or half cages. Similar observations were made for p-NH(2)stilbenevinyl(8)OS cages, where the greater conjugation lengths led to even greater red-shifts (120 nm) and two-photon absorption cross sections. Cathodoluminescence studies done on [p-MeStilSiO(1.5)](8) or [p-MeStilOS](8) powders exhibit essentially the same emissions as seen in solution at high dilution. Given that only the emissions are greatly red-shifted in these molecules, whereas the ground-state UV-vis absorptions are not changed from trans-stilbene, except for the ortho derivative, which is blue-shifted 10 nm. It appears that the interactions are only in the excited state. Theoretical results show that the HOMO and LUMO states are always the pi and pi* states on the stilbene, which show very weak shifts with increasing degrees of functionalization, consistent with the small changes in the UV-vis spectra. The band gap between the lowest unoccupied 4a1 symmetry core state localized inside the silsesquioxane cage and the highest occupied state (pi state on stilbene), however, is markedly decreased as the number of stilbene functional groups is increased. This is consistent with the significant red-shifts in the emission spectra. The results suggest that the emission occurs from the 4a1 state localized on the cage. Moreover, for the compounds [p-RStil(6-7)Ph(2-1)OS](8), the emissions are blue-shifted compared to those of the fully substituted compounds, suggesting the molecular symmetry is reduced (from cubic), thereby reducing the potential for 3-D delocalization and raising the energy of the LUMO. The implications are that these octafunctional molecules exhibit some form of 3-D interaction in the excited state that might permit their use as molecular transistors as well as for energy collection and dispersion as molecular antennas, for example, and for nonlinear optical applications.