Efficient Two-photon Absorption Research Articles

Two-photon-excited luminescence from a Eu3+-doped lithium niobate crystal pumped by a near-infrared femtosecond laser

Red upconversion luminescence (UCL) is observed using an 800 nm femtosecond laser to irradiate a Eu3+-doped LiNbO3 single crystal. Power-dependent and polarization-dependent experiments demonstrate that the red UCL originates from Eu3+ two-photon simultaneous absorption rather than second harmonic generation of nonlinear optical crystal followed by reabsorption of Eu3+. Two different kinds of Eu3+-centers, called Eu3+-pairs, are revealed via emission spectra. Besides using femtosecond laser excitation to simulate diode laser excitation with broad line, the efficient two-photon simultaneous absorption can populate more Eu3+ to upper levels, these are beneficial to the study of cross relaxation with submicrosecond resolution between Eu3+-pairs occurred in practical application. Transient UCL spectra and decay curves suggest that the luminescent state D50 is fed by way of both multiphonon relaxation through state D51 and cross relaxation of D52+F70→D50+F75.

Two-Photon Pumped Amplified Spontaneous Emission from Cyano-Substituted Oligo(p-phenylenevinylene) Crystals with Aggregation-Induced Emission Enhancement

We report the effective two-photon absorption-induced upconversion amplified spontaneous emission (ASE) in the cyano-substituted oligo(p-phenylenevinylene) 1,4-bis[1-cyano-2-(4-(diphenylamino)phenyl)vinyl]benzene (TPCNDSB) organic crystals. The material shows enhanced emission in the solid state (31% quantum yield in crystal) and efficient two-photon absorption. The ASE under the one-photon and two-photon excitation were observed. It is demonstrated that the organic crystals of TPCNDSB might be practically used as fluorescent materials for potential upconversion laser applications.

Efficient Two‐Photon Excited Amplified Spontaneous Emission from Organic Single Crystals

E, E-1, 4-bis[4'-(N,N-dibutylamino)styryl]-2,5-dimethoxy-benzene (DBASDMB) organic crystals with high crystalline quality, large size and excellent optical properties are prepared. The linear and nonlinear properties in the crystal are comparatively studied. The relaxation dynamics pumped by two-photon are very similar with that pumped by one-photon. The crystal exhibits very strong two-photon excited fluorescence and amplified spontaneous emission. Efficient two-photon absorption, reasonably high fluorescent quantum efficiency, and high crystal quality together with stimulated emission make organic crystals ideal for the application in frequency upconversion and other optoelectronic fields.

Simultaneous Control of Emission Localization and Two-Photon Absorption Efficiency in Dissymmetrical Chromophores

The aim of the present work is to demonstrate that combined spatial tuning of fluorescence and two-photon absorption (TPA) properties of multipolar chromophores can be achieved by introduction of slight electronic chemical dissymmetry. In that perspective, two model series of structurally related chromophores have been designed and investigated. One is based on rod-like quadrupolar chromophores bearing either two identical or different electron-donating (D) end groups and the other on three-branched octupolar chromophores built from a trigonal donating moiety bearing identical or different acceptor (A) peripheral groups. The influence of the electronic dissymmetry is investigated by combined experimental and theoretical studies of the linear and nonlinear optical properties of dissymmetrical chromophores compared to their symmetrical counterparts. In both types of systems (i.e., quadrupoles and octupoles), experiments and theory reveal that excitation is essentially delocalized and that excitation involves synchronized charge redistribution (i.e., concerted intramolecular charge transfer) between the different D and A moieties within the multipolar structure. In contrast, the emission stems only from a particular dipolar subunit bearing the strongest D or A moiety due to fast excitation localization after excitation, prior to emission. Hence, control of emission characteristics (polarization and emission spectrum), can be achieved, in addition to localization, by controlled introduction of electronic dissymmetry (i.e., replacement of one of the D or A end-groups by a slightly stronger D' or A' unit). Interestingly, slight dissymmetrical functionalization of both quadrupolar and octupolar compounds does not lead to significant loss in TPA responses and can even be beneficial due to the spectral broadening and peak position tuning that it allows. This study thus reveals an original molecular engineering route allowing TPA enhancement in multipolar structures, due to concerted core-to-periphery or periphery-to-core intramolecular charge redistribution upon excitation, while providing for control of emission localization. Such a route could be extended to more intricate (dendritic) and multipolar (3D) systems.

Excited state intramolecular proton transfer and photophysics of a new fluorenyl two-photon fluorescent probe.

The steady-state photophysical, NMR, and two-photon absorption (2PA) properties of a new fluorene derivative (1) containing the 2-(2'-hydroxyphenyl)benzothiazole (HBT) terminal construct is investigated for use as a fluorescence probe in bioimaging. A comprehensive analysis of the linear spectral properties reveals inter- and intramolecular hydrogen bonding and excited state intramolecular proton transfer (ESIPT) processes in the HBT substituent. A specific electronic model with a double minimum potential energy surface is consistent with the observed spectral properties. The 2PA spectra are obtained using a standard two-photon induced fluorescence method with a femtosecond kHz laser system, affording a maximum 2PA cross section of approximately 600 GM, a sufficiently high value for two-photon fluorescence imaging. No dependence of two-photon absorption efficiency on solvent properties and hydrogen bonding in the HBT substituent is observed. The potential use of this fluorenyl probe in bioimaging is demonstrated via one- and two-photon fluorescence imaging of COS-7 cells.

Efficient two-photon absorption of CdSe-CdS/ZnS core-multishell quantum dots under the excitation of near-infrared femtosecond pulsed laser

We report that two-photon absorption (TPA) properties of semiconductor CdSe-core CdS/ZnS-multishell quantum dots (QDs) in toluene under excitation of femtosecond laser at 800 nm. The results show efficient TPA process and large TPA cross section of three types of size QDs, which is 1900, 5710, and 16060 GM (1 GM = 10−50 cm4 s photon−1), respectively. TPA cross section dramatically increases with increased core size, showing a strong size-dependence effect. Furthermore, two-photon excitation (TPE) fluorescence intensity not only depends on TPA capacity, but also relies on improved quantum yield resulting from passivation of QD surface by different coated monolayers (MLs). These facts in combination with the narrow fluorescence bandwidth make these QDs as promising probes for multicolor two-photon microscopy.

Highly efficient nonresonant two-photon absorption in ZnO pellets

In this article, we report direct evidence for efficient nonresonant two-photon absorption-induced luminescence in ZnO pellets at 2K and room temperature. Stimulated emission near the band edge is observed at room temperature employing this form of excitation under low excitation levels over a broad range of excitation wavelengths. The steady-state population dynamics based on the time-integrated photoluminescence spectra at 2K indicates that this nonresonant two-photon excitation is much more efficient in creating excitonic matter, compared with the traditional one-photon excitation method.

Strong Two Photon Absorption and Photophysical Properties of Symmetrical Chromophores with Electron Accepting Edge Substituents

Two photon absorption (TPA) and photophysical properties of three new symmetrical chromophores with electron accepting phthalimide edge substituents have been studied. The three chromophores contain fluorene, alcoxy-substituted divinyl benzene, and carbazole moieties as central cores, respectively. The femtosecond time-resolved fluorescence upconversion spectroscopy and two photon excited fluorescence technique have been carried out. The effect of solvent polarity on TPA and on photophysics has also been determined. Ultrafast fluorescence dynamics, with decay times ranging from 1 to 13 ps, are revealed in polar solvents. This is attributed to the relaxation of the chromophores to the intramolecular charge transfer state. The chromophore bearing fluorene central core, being of the type A-pi-A, is the most efficient concerning TPA. Strong TPA, with a cross section value as high as 2100 GM at an excitation wavelength of 770 nm is found in acetophenone which is a solvent of intermediate polarity. The TPA spectra were also reproduced using a sum over states three-state model. A study of the TPA induced photobleaching of the fluorene molecule, doped in a solid poly(methyl-methacrylate) film, has shown that this material is very promising for efficient TPA optical data storage.

Multi-photon excitation UV emission by femtosecond pulses and nonlinearity in ZnO singlecrystal

Optical nonlinearities and multi-photon ultraviolet (UV) excitation in ZnO single crystalwere investigated by the z-scan method utilizing an intense femtosecond (fs) laser atdifferent wavelengths. Based on the analysis of the experimental results at differentexcitation wavelengths near 800 nm, nonlinear optical effects that may emerge under anintense field are attributed to be responsible for the efficient two-photon absorption processunder detuned excitation.

3D-soliton waveguides in lithium niobate for femtosecond light pulses

We show that efficient waveguides can be written by bright spatial solitons in the volume of lithium niobate photorefractive crystals by cw and pulsed laser beams. Using high-repetition-rate femtosecond laser pulses, an efficient formation of soliton waveguides (SWGs) is possible, after accumulating a large number of pulses, because the characteristic photorefractive build-up time is much longer than the pulse period and the efficient two-photon absorption may contribute to the solitonic confinement. These results open the possibility of writing reconfigurable single SWGs and SWG arrays (with any spatial orientation and large range of periods) and optimally guiding the femtosecond pulsed laser beams through them, creating a graded refractive-index profile matched to the spatial beam profile. Our experiments also show a small increase in pulse duration (small dispersion) in these waveguides.

Synthesis and characterization of water-soluble two-photon excited blue fluorescent chromophores for bioimaging

We report here the synthesis and characterization of a new type of non-ionic blue fluorescent water-soluble chromophores specifically designed for two-photon absorption microscopy. The water solubility is induced by introduction of short oligo(ethylene glycol) monomethyl ether moieties. This work has led to low molecular weight dyes with efficient two-photon absorption cross sections and high fluorescence quantum yield in organic solvents as well as in aqueous solutions.

Measurement of two-photon absorption cross-section in organic molecular salt with linear and circular polarized radiation

We report on the investigation of two-photon absorption (TPA) in 4′-Diethylamino-N-Methyl-4-Stilbazolium Tosylate (DEST) with 40 picosecond, 1064 nm linear and circular polarization laser radiation. The TPA cross-section σ2 measured is larger for linear polarized radiation (948 GM) than that for the circular polarized radiation (840 GM). The large TPA cross-section of DEST facilitates highly directional and efficient TPA induced upconverted emission in the range of 590–640 nm even though the fluorescence efficiency of DEST is very low (∼0.5%). The net single pass efficiency of upconversion is ∼7%.

Synthesis, Characterization and Two‐Photon Absorption Properties of a Novel Pyridinium Salt

AbstractA novel pyridinium salt, 2,4‐bis[p‐(N,N‐dimethylamino)styryl]‐N‐methyl pyridinium iodide (BMSPI) was synthesized and characterized by TG, 1H NMR spectroscopy and elemental analysis. and the reaction process was studied by Using ES‐MS. When BMSPI was pumped by a pulsed 1064 nm, 50 ps laser him. it manifests highly efficient TPA (Two‐Photon Absorption) and up‐conversion superradiance. The up‐conversion efficiency was 6.0% at the pump energy of 4–6 mJ and the Lifetime of two‐photon fluorescence was measured as 59 ps.

Novel Heteroaromatic‐Based Multi‐Branched Dyes with Enhanced Two‐Photon Absorption Activity

AbstractFor Abstract see ChemInform Abstract in Full Text.

Organometallic Complexes for Nonlinear Optics. 33. Electrochemical Switching of the Third-Order Nonlinearity Observed by Simultaneous Femtosecond Degenerate Four-Wave Mixing and Pump−Probe Measurements

The molecular inorganic compound 1,3,5-{trans-[RuCl(dppe)2]C≡C-4-C 6 H 4 C≡C} 3 C 6 H 3 (1) is reversibly oxidized in solution using an optically transparent thin-layer electrochemical (OTTLE) cell, the oxidation to 1 3 + resulting in the appearance of a strong absorption band at 11 200 cm - 1 in contrast to 1, which is optically transparent at frequencies below 20 000 cm - 1 . This linear electrochromic behavior is accompanied by third-order nonlinear optical electrochromic behavior, which has been probed by a combination of femtosecond degenerate four-wave mixing (DFWM) and pump-probe experiments at 12 500 cm - 1 . DFWM studies of 1 and 1 3 + reveal an order of magnitude increase in the hyperpolarizability, ‖γ‖, upon oxidation with ‖γ‖ values of 2000 × 10 - 3 6 esu and 20 000 x 10 - 3 6 esu, respectively; the DFWM signal of the latter is dominated by a delayed response (relaxation time ca. 1 ps). The transient absorption (TA) data for 1 reveal efficient two-photon absorption (σ 2 10 3 GM), whereas the TA data for 1 3 + reveal saturable absorption (decay time ca. 1 ps). The switching of third-order nonlinearity in the 1/1 3 + pair represents the first demonstration of femtosecond time-scale processes being responsible for nonlinear electrochromism.

Novel heteroaromatic-based multi-branched dyes with enhanced two-photon absorption activityElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/cc/b3/b305995b/

The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 x 10(-50) cm4 s photon(-1) molecule(-1), measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.

Resonance enhancement of two-photon absorption in porphyrins

Two-photon absorption spectra in absolute cross-section values are presented for a number of octaethyl-, tetraphenyl-, and tetrabenzo-substituted porphyrins. In excitation spectral region of 710–810 nm, the two-photon absorption efficiency is resonantly enhanced due to nearby Q(0–0) one-photon transition. The cross-section value calculated directly from the ground- and excited-state absorption parameters in a single intermediate level approximation, agrees well with that measured in experiment.

One- and two-photon spectroscopy on single molecules of diphenyloctatetraene

We report investigations on one- and two-photon excitation of single molecules of diphenyloctatetraene in n-tetradecane at cryogenic temperatures. Saturation intensities, count rates and linewidths of single molecules are compared with corresponding ensemble values obtained from statistical fine structure investigations. The single-molecule linewidths under one-photon excitation are generally two to three times narrower than in two-photon excitation spectra. This effect is discussed with respect to saturated spectral diffusion induced by the high power 1R light necessary for efficient two-photon absorption.

Intensity-dependent hot-phonon relaxation in ZnSe

We performed time-resolved anti-Stokes Raman-scattering experiments on ZnSe crystals using pump and probe techniques. To create non-equilibrium phonons we excited the ZnSe crystals at λ = 632.8 nm with an intense pump pulse with a pulse duration of about 4 ps, which leads to efficient two-photon absorption and therefore to the creation of free carriers. By relaxation to the band edge, the highly excited free carriers emit longitudinal optical (LO) phonons. By varying the time delay between the probe and the pump pulse, the dynamical behavior of the pump pulse-induced anti-Stokes Raman signal was studied. The results are discussed with respect to plasma effects influencing the dynamical behavior of the phonon lifetime in ZnSe.

Femtosecond Studies on Third-Order Optical Nonlinearities of Polyanilines

The ultrafast dynamics of third order nonlinearities of polyaniline (PAn) and polyaniline doped in polymethyl mathacrylate (PAn-PMMA) films are investigated using femtosecond absorption spectroscopy. An ultrafast initial exciton deformation time of about 100 fs is observed in PAn film. In PAn-PMMA film, the third-order nonlinearity results in an efficient two-photon absorption at about 2 eV.