Time-resolved Degenerate Four-wave Mixing Research Articles

Structural and ultrafast third-order nonlinearities of methyl and methoxy substituted anthracene chalcones: Z-scan, four-wave mixing, and DFT approaches

We report on the structural, thermal, linear, and ultrafast third-order nonlinear optical (NLO) properties of two novel anthracene chalcones: (2E)-1-(anthracen-9-yl)-3-(5-methylthiophen-2-yl)prop-2-en-1-one (5ML2SANC) and (2E)-1-(9-anthryl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-one (245TMANC). The chalcones were synthesized by Claisen-Schmidt condensation reaction, and the single crystals were grown by the solvent evaporation method. The molecular structure was confirmed by FTIR and NMR spectroscopy, while the crystal structure was determined using the single crystal XRD. Both crystals belong to centrosymmetric monoclinic crystal system with space group P21/n. The Hirshfeld surface was analyzed to understand intermolecular interactions, and the band structures - including HOMO-LUMO levels, excited state energies, GCRDs and MEPs-were studied using DFT. The ultrafast third-order NLO properties were investigated by Z-scan and degenerate four-wave mixing (DFWM) techniques using Ti: Sapphire amplifier laser delivering ∼50 fs pulses at 800 nm (1 kHz, ∼4 mJ, 2 W). Two-photon absorption, positive nonlinear refraction, optical limiting and optical switching behaviors were observed by Z-scan measurements. The time-resolved DFWM show that the decay time of 5ML2SANC is ∼127 fs, while for 245TMANC it is ∼142 fs. The second hyperpolarizability (γ) measured by Z-scan, DFWM and the estimations from the DFT theory are found to be in good agreement (∼10−34 esu). The ultrafast optical response, significant NLO properties and thermal stability of the synthesized chalcones demonstrate their potential suitability in optical limiting and switching applications.

Ultrafast Nonlinear Optical and Structure-Property Relationship Studies of Pyridine-Based Anthracene Chalcones Using Z-Scan, Degenerate Four-Wave Mixing, and Computational Approaches.

The structural, thermal, linear, and femtosecond third-order nonlinear optical (NLO) properties of two pyridine-based anthracene chalcones, (2E)-1-(anthracen-9-yl)-3-(pyridin-2-yl)prop-2-en-1-one (2PANC) and (2E)-1-(anthracen-9-yl)-3-(pyridin-3-yl)prop-2-en-1-one (3PANC), were investigated. These two chalcones were synthesized following the Claisen-Schmidt condensation method. Optically transparent single crystals were achieved using a slow evaporation solution growth technique. The presence of functional groups in these molecules was established by Fourier transform infrared and NMR spectroscopic data. The detailed solid-state structure of both chalcones was determined from the single-crystal X-ray diffraction data. Both crystals crystallized in the centrosymmetric triclinic space group P1̅ with the nuance of unit cell parameters. The crystals (labeled as 2PANC and 3PANC) have been found to be transparent optically [in the entire visible spectral region] and were found to be thermally stable up to 169 and 194 °C, respectively. The intermolecular interactions were investigated using the Hirshfeld surface analysis, and the band structures (highest occupied molecular orbital-lowest unoccupied molecular orbital, excited-state energies, global chemical reactivity descriptors, and molecular electrostatic potentials) were studied using density functional theory (DFT) techniques. The ultrafast third-order NLO properties were investigated using (a) Z-scan and (b) degenerate four-wave mixing (DFWM) techniques using ∼50 fs pulses at 800 nm (1 kHz, ∼4 mJ) from a Ti:sapphire laser amplifier. Two-photon-assisted reverse saturable absorption, self-focusing nonlinear refraction, optical limiting, and optical switching behaviors were witnessed from the Z-scan data. 3PANC demonstrated a stronger two-photon absorption coefficient, while 2PANC depicted a stronger nonlinear refractive index among the two. The time-resolved DFWM data demonstrated that the decay times of 2PANC and 3PANC were ∼162 and ∼180 fs, respectively. The second hyperpolarizability (γ) values determined by DFT, Z-scan, and DFWM were found to be in good correlation (with a magnitude of ∼10-34 esu). The ultrafast third-order NLO response, significant NLO properties, and thermal stability of these chalcones brands them as potential candidates for optical power limiting and switching applications.

Ultrafast nonlinear optical properties and excited-state dynamics of Soret-band excited D-π-D porphyrins

Herein, we report results from our studies on the ultrafast nonlinear optical (NLO) properties and excited-state dynamics in three different porphyrin molecules designed in D-π-D fashion (phenothiazine-porphyrin-phenothiazine) and with two different central metal ions [Zn(II) and Cu(II)]. We have performed extensive target analysis of the femtosecond transient absorption data obtained conveying the true exited state/species spectra of each process with respective lifetimes along with microscopic rate constants of each excited state. The obtained life time values were in the range of 250–500 fs, 20–142 ps, 1.5–6.2 ns and 0.1–1.23 μs and have been associated from relaxation with the Sn, Hot S1 (to S1), S1, and T1 states. Furthermore, the third-order nonlinear (NLO) coefficients [two-photon absorption (TPA) and nonlinear refractive index (n2)] of CPPHT and ZPPHT exhibited superior values compared to HPPHT recorded with ~50 fs, 1 kHz repetition rate pulses at a wavelength of 800 nm. The magnitude of the TPA coefficients of these molecules was compared with some of the recently reported porphyrin moieties and were found to be superior. The time-resolved degenerate four-wave mixing (DFWM) measurements confirmed a large magnitude and an ultrafast response of the χ(3) in these molecules suggesting potential photonic and all-optical switching applications.

Dynamic Nonlinear Optical Characterization of Expanded Porphyrin Complexes by Using Time-resolved Degenerate Four-Wave Mixing

Dynamic Nonlinear Optical Characterization of Expanded Porphyrin Complexes by Using Time-resolved Degenerate Four-Wave Mixing

Diameter dependence of phase relaxation time and third-order nonlinear susceptibilities in semiconducting single-walled carbon nanotubes

Diameter dependence of the phase relaxation time T2 in semiconducting single-walled carbon nanotubes was measured using a two-beam time-resolved degenerate four-wave mixing method. The T2 value increases with increasing tube diameter. This experimental trend can be understood by the diameter dependence of exciton-phonon interaction. We also discuss the origin of diameter dependence of third-order nonlinearity connected with relaxation times.

Large Amplitude Motions in Cyclopentene and 1-Butene: Quantum Chemical Insights into the Ground- and Excited State Potential Energy Surfaces

Abstract The ring-puckering motion in cyclopentene as well as the hindered internal rotation around the central C–C bond in 1-butene have been studied by high-level quantum chemical calculations. Relevant potential energy surfaces of these molecules along these large-amplitude motions are provided as well as rotational constants are given allowing for thorough comparison with recent results from time-resolved femtosecond degenerate four-wave mixing (fs DFWM) spectroscopy. Emphasis is put on the performance of various post-Hartree Fock methods, the required level of electron correlation as well as the basis set quality.

Nonlinear optical properties and phase-relaxation processes in single-walled carbon nanotubes

We have investigated third-order nonlinear optical properties of bundled and isolated semiconducting single-walled carbon nanotubes (SWNTs) by means of Z-scan method, pump–probe method, and two-beam time-resolved degenerate four-wave mixing (DFWM) method. The figures of merit Im χ (3)/ α in both bundled and isolated SWNTs samples were found to be enhanced with increasing tube diameter. The measured Im χ (3)/ α value in the bundled SWNTs was an order of magnitude smaller than that in the isolated SWNTs. Both population relaxation time T 1 and phase-relaxation time T 2 for bundled samples were smaller than those in the isolated samples. These experimental results can be explained by an increase in nonradiative recombination rate and phase-relaxation rate in the bundled sample. The phase-relaxation time T 2 is considered to have a significant role in the enhancement of Im χ (3)/ α.

Preparation of polysiloxane with pendant Cr-bound carbazole chromophore for nonlinear optics

A novel η6-complex of N-allylcarbazole containing chromium tricarbonyl was synthesized. This complex was hydrosilylated with polymethylhydrosiloxane to afford a substituted polymer. Both the complex and the polymer were characterized by classical spectroscopy techniques (FTIR, NMR, and UV–vis), gel permeation chromatography, elemental analysis, and thermal analysis (TGA and DSC). The glass transition temperature of the polymer was found to be above 100°C and its thermal decomposition temperature was above 280°C. The polymer was amorphous in nature and formed excellent homogeneous films of good optical transparency. The third nonlinear optical properties of this polymer film coated on quartz substrate were studied by time-resolved forward degenerate four-wave mixing (DFWM). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of aggregation on nonlinear optical properties of a naphthalocyanine

The magnitude and dynamic response of the third-order optical nonlinearity of silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (SiNc) were measured by femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least two components, i.e., the coherent instantaneous nonlinear response (electronic response) and the slow response due to the excited state population grating. The present SiNc in neat film shows small red-shift compared to monomer absorption because of the large distance between adjacent naphthalocyanine rings, which results in weak delocalization of Frenkel exciton in the aggregated state. However, time-resolved DFWM measurements indicate that the SiNc films show fast nonlinear optical response and large third-order nonlinear susceptibility. The effective χ e ( 3 ) value of the neat SiNc film was evaluated to be as high as 4 × 10 −7 esu, and the figure of merit of third-order nonlinearity F ( F = χ (3)/ α), was calculated to be about 4.1 × 10 −13 esu cm.

Synthesis and characterization of symmetrical benzodifuranone compounds with femtosecond time-resolved degenerate four-wave mixing technique

We synthesized four symmetrical benzodifuranone compounds. Their structures were confirmed by UV, IR, 1H NMR and elemental analysis. The off-resonant third-order nonlinear optical properties of the compounds were investigated via femtosecond time-resolved degenerate four-wave mixing technique with 80fs pulse width at 800nm. The third-order nonlinear optical susceptibilities X(3) were 2.86–3.21×10−13esu. The nonlinear refractive index n2 were 5.26–5.91×10−12esu. The second-order hyperpolarizabilities γ of the molecules were 2.92–3.42×10−31esu. The response times were 88–91fs. These results show that symmetrical benzodifuranone compounds have potential nonlinear optical applications.

Electrochemical, Spectroelectrochemical, and Molecular Quadratic and Cubic Nonlinear Optical Properties of Alkynylruthenium Dendrimers1

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.

Prospect of temperature determination using degenerate four‐wave mixing with sub‐20 fs pulses

AbstractFemtosecond time‐resolved degenerate four‐wave mixing (DFWM) spectroscopy with ultrashort laser pulses was applied to probe pure rotational Raman transitions of the H2 molecule. Owing to the broad bandwidth of the sub‐20 fs pulse, several pure rotational Stokes and anti‐Stokes transitions are simultaneously excited with the same pulse, making the experiment relevant for thermometry in combustion processes. Simulations of the DFWM signal accurately predict how the change in population distribution due to changes in temperature influences the shape of the transients and the corresponding Fourier transform. The influence of the pulse duration was also investigated. The relative peak intensities in fast Fourier transform spectra were employed for temperature determination. First measurements at room temperature show good agreement with theory. Copyright © 2004 John Wiley & Sons, Ltd.

Nonlinear optical properties of 75TeO 2 –20Nb 2 O 5 –5ZnO glasses doped with CeO 2

Nonlinear optical properties of 75TeO2–20Nb2O5–5ZnO glasses doped with CeO2 have been investigated with a self-diffracted time-resolved degenerate four-wave mixing (DFWM) technique at different excitation intensities and lattice temperatures. The DFWM signal exhibits three peaks at higher excitation intensities, where a main peak appears at zero delay time and two rather weak side peaks are located symmetrically at the negative and positive time delay. Due to destructive interferences between the fifth- and third-order polarizations, the line-shape of the main peak around the zero time delay evolves from single peak into a double-peak structure with increasing excitation intensity. Two side peaks emerge at the positive and negative time delay and gradually intensify with increasing excitation intensity or lattice temperature and their positions are independent of the pulse duration, temperature and excitation intensity, which are attributed to the many-body Coulomb interaction.

Third-order nonlinear optical behaviour of hybrid phenylene–ethynylene/phenylene–vinylene polymers

The |n2|-values of novel hybrid phenylene?ethynylene/phenylene?vinylene polymers 1, 2, 3, 4, together with those of corresponding phenyleneethynylene 5 and phenylenevinylene 6 and 7 'homopolymers', have been studied by time-resolved degenerate four-wave mixing (DFWM). The measurements were performed on thin films at 800?nm with femtosecond time resolution using a folded boxcars setup. No clear relationship between |n2|-values and the backbone conjugation pattern of the compounds could be established. In contrast, a quasi-exponential relationship between film thickness and the |n2|-value was observed, irrespective of the chemical structure of the samples.

Third-order nonlinear optical responses of nanoparticulate Co 3O 4 films

Third-order nonlinear optical responses of nanoparticulate Co 3O 4 films, prepared by sputtering and pyrolysis, were investigated. The sputtered Co 3O 4 film showed a large third-order nonlinear susceptibility (| χ (3)|) of 3.2×10 −8 esu, determined by degenerate four-wave mixing (DFWM). This | χ (3)| is 7.1 times greater than that of the pyrolyzed Co 3O 4 film, attributable to the greater density and refractive index of the sputtered film. Time-resolved DFWM experiments show a slowly decaying component with a lifetime of approximately 100 ps existing for both films in addition to a fast decaying component. Nonlinear transmission experiments revealed both films exhibiting significant nonlinear absorption. The imaginary part of the susceptibility (Im[ χ (3)]) found for each film was of the same order of magnitude as the | χ (3)| found by the DFWM method, showing that the major part of the fast decaying component of | χ (3)| comes from the nonlinear absorption.

Insights into the structure of cyclohexane from femtosecond degenerate four-wave mixing spectroscopy and ab initio calculations.

In this paper, we report the use of femtosecond time-resolved degenerate four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane. Apart from highlighting the versatility of this method in determining accurate structures of large and complex molecules without dipole moment, the present study also details the comparison of the experimentally determined rotational constant B(0) with that obtained from high-level ab initio calculations. The theoretical calculations, which were carried out at both the second-order Møller-Plesset (MP2) and coupled-cluster with single, double, and perturbative triple substitutions [CCSD(T)] levels of theory, also take into account vibrational averaging effects. A detailed investigation of the vibrational averaging effects reveals that the corrections emerge from only the six highly symmetric A(1g) modes, a justification of which is provided by an analysis of these modes.

Degenerate four-wave mixing measurements of the third-order nonlinearity of poly(aryleneethynylenes) and their model substances

The |n2| of poly(aryleneethynylenes), a novel class of conjugated polymers, their derivatives, and model substances was studied by time-resolved degenerate four-wave mixing. The measurements were performed in solutions at 1047 nm with picosecond time resolution and on thin films at 800 nm with femtosecond time resolution. A time response of the nonlinearities faster than the pulse durations used was found. |n2| values of as much as 4.9×10-13 cm2/W were measured on thin films of the polymers.

Dephasing time characterization of InAs quantum dots by four-wave mixing measurement

We performed dephasing time characterization of InAs quantum dots waveguide and observed photon echo signal by time-resolved degenerate four-wave mixing. For large dots with a diameter of 40 nm , a relatively long T 2 of 330 fs was obtained. For small dots with a diameter of 30 nm , a short T 2 of 230 fs was obtained. Based on a comparison of the samples, it was suggested that this increase in T 2 in large dots was due to the size dependence of carrier–LO phonon coupling.

Femtosecond Time-Resolved Third-Order Nonlinear Response of 4-(N, N-Diethylamino)-β-Nitrostyrene Solutions in the Nonresonant Region—Experimental Evidence of Group-Velocity Dispersion Effec—

We measure the femtosecond time-dependent, third-order nonlinear optical response for 4-(N, N-diethylamino)-β-nitrostyrene (DEANST) dissolved in N, N-dimethylformamide (DMF) from 0.1 to 1.4 M concentrations in the nonresonant region using time-resolved degenerate four-wave mixing (DFWM) spectroscopy. It is found that the DFWM signal profile with delayed responses depends on the concentration. This concentration dependence is determined to be mainly due to the group-velocity dispersion effect of the DEANST solution at the high concentration and the nonlinear response of the DMF solvent at the low concentration, but not due to the change in third-order nonlinear response of DEANST itself.

Numerical Analysis of Femtosecond Time-Resolved Degenerate Four-Wave Mixing Signal including Group-Velocity Dispersion Effect

We numerically analyze the group-velocity dispersion (GVD) effect of the nonlinear medium on the femtosecond time-resolved degenerate four-wave mixing (DFWM) signal with the third-order nonlinear delayed response. As a result, we find that material GVD greatly influences not only the magnitude but also the temporal profile of the DFWM signal.