Third-order Optical Response Research Articles

Large resonant third-order optical nonlinearity of thin film containing J-like aggregates of a bis[4-(N-dibutylamino)phenyl]squarylium dye

The third-order optical nonlinearity and response of thin film containing J-like aggregates of a bis[4-(N-dibutylamino)phenyl]squarylium dye were measured by degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profile of DFWM signal was obtained with a time resolution of 0·3 ps (FWHM), and was 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 effective χ (3) value of thin squarylium dye film was evaluated to be as high as 1·1 × 10 − 7 esu, and the figure of merit of third-order nonlinearity F (F = χ (3)/α), was calculated to be about 2·1 × 10 − 13 esu cm.

Alkali-Responsive Absorption Spectra and Third-Order Optical Nonlinearities of Imino Squaramides

Third-order optical nonlinearities and dynamic responses of two imino squaramides under neutral and base conditions were studied using the femtosecond degenerate four-wave mixing technique at 800 nm. Ultrafast optical responses have been observed and the magnitude of the second-order hyperpolarizabilities of the squaramides has been measured to be as large as 10−31 esu. The absorption spectra, color of solution, and third-order optical nonlinearities of two imino squaramides change with the addition of sodium hydroxide. The γ value under the base condition for each dye is approximately 1.25 times larger than that under neutral conditions.

Novel coherent two-dimensional optical spectroscopy probes of chirality exchange and fluctuations in molecules

We demonstrate how stochastic transitions between molecular configurations with opposite senses of chirality may be probed by 2D optical signals with specific pulse polarization configurations. The third-order optical response of molecular dimers (such as biphenyls) with dynamical axial chirality is calculated to order of k(2) in the wavevector of light. Spectroscopic signatures of equilibrium chirality fluctuations are predicted for three dynamical models (Ornstein-Uhlenbeck, two-state jump, and diffusion in double well) of the dihedral angle that controls the chirality.

Optimized hierarchical equations of motion theory for Drude dissipation and efficient implementation to nonlinear spectroscopies

Hierarchical equations of motion theory for Drude dissipation is optimized, with a convenient convergence criterion proposed in advance of numerical propagations. The theoretical construction is on the basis of a Padé spectrum decomposition that has been qualified to be the best sum-over-poles scheme for quantum distribution function. The resulting hierarchical dynamics under the a priori convergence criterion are exemplified with a benchmark spin-boson system, and also the transient absorption and related coherent two-dimensional spectroscopy of a model exciton dimer system. We combine the present theory with several advanced techniques such as the block hierarchical dynamics in mixed Heisenberg-Schrödinger picture and the on-the-fly filtering algorithm for the efficient evaluation of third-order optical response functions.

Symmetry breaking in plasmonic waveguides with metal nonlinearities

We studied nonlinear effects in plasmonic metal film waveguides and couplers stimulated by third-order optical response due to ponderomotive metal nonlinearities. We analyzed the structure and dispersion of nonlinear plasmonic guided modes and predicted the bifurcations and symmetry breaking of nonlinear modes for the critical powers, depending on the structure dimensions.

Plasmonic couplers with metal nonlinearities

Usually nonlinear response of metals is neglected in the study of plasmonic waveguiding structures. Recent prediction of strong third-order optical response of metals due to ponderomotive forces opens up novel possibilities for utilizing this effect in the design of active plasmonic devices. We discuss the possibility of implementation of nonlinear response of metals in the design of plasmonic coupler. We analyze the structure and dispersions of linear and nonlinear guided plasmonic modes of two coupled thin metallic films and predict bifurcations of symmetry breaking.

Implementation of room temperature femtosecond echo-processing

Conditions for implementing room temperature femtosecond echo-processing in a phtalocyanine-doped polyvinylbutyral film were studied. A logical operation of bit-by-bit multiplication on the basis of the nonlinear third-order optical response (primary photon echo) of the medium was performed in a time of less than 1 ps.

Comparison of transient grating signals from spheroidene in an organic solvent and in pigment-protein complexes fromRhodobacter sphaeroides2.4.1

The concurrent dynamics of the electronic excitation and vibronic oscillations of spheroidene have been investigated by means of the transient grating (TG) spectroscopy. The third-order optical responses of spheroidene in an organic solvent, in the LH2 light-harvesting antenna complexes, and in chromatophores have been compared in order to investigate the influence of the environment surrounding this photosynthetic pigment. Vibronic coherent oscillations with a period of several tens of femtosecond have been clearly observed superimposed on a slowly varying background, which reflects the electronic dynamics. The dynamics of the coherent oscillations have been analyzed by means of the wavelet analysis. Within our experimental accuracy, the decay times of the $\text{C}\text{C}$ and $\text{C}\text{C}$ stretching modes and ${\text{C}\text{CH}}_{3}$ rocking mode of each specimen are very close. The experimental results have also been analyzed using a Brownian oscillator model. For these numerical calculations, the spectral density for the underdamped modes has been determined from the Raman spectrum of spheroidene. It was found that the low-frequency modes that reflect the influence of the protein environment can be approximated by the overdamped Brownian oscillator. The experimentally observed linear absorption spectra as well as the third-order optical responses, i.e., TG curves, are reproduced very well by these calculations. The close agreement between the experiments and calculations indicates that the Feynman-diagrammatic approach can be applied to express not only the internal conversion but also the intermolecular excitation energy-transfer processes. The vibronic decay rates of spheroidene in LH2 complexes and chromatophores are evaluated to be about 20% larger than in the organic solvent.

Optically excited near-surface phonons of TiO2 (110) observed by fourth-order coherent Raman spectroscopy

We observed the fourth-order and third-order optical responses in the time domain on a TiO(2) (110) surface covered with trimethyl acetates. Coherent vibrations assignable to near-surface phonon modes were present at 179, 191, 359, 440, 507, 609, and 823 cm(-1) in the fourth-order responses. The amplitude and phase of each mode were determined with different azimuths and polarizations of pump and probe light pulses. Vibrational assignments and possible mechanisms to excite the vibrations were discussed.

Nonlinear optical imaging of individual carbon nanotubes with four-wave-mixing microscopy.

Dual color four-wave-mixing (FWM) microscopy is used to spatially resolve the third-order optical response from individual carbon nanotubes. Good signal-to-noise is obtained from single-walled carbon nanotubes (SWNT) sitting on substrates, when the excitation beams are resonant with electronic transitions of the nanotube, by detecting the FWM response at the anti-Stokes frequency. Whereas the coherent anti-Stokes (CAS) signal is sensitive to both electronic and vibrational resonances of the material, it is shown that the signal from individual SWNTs is dominated by the electronic response. The CAS signal is strongly polarization dependent, with the highest signals found parallel with the enhanced electronic polarizibility along the long axis of the SWNT.

Photon echo spectroscopy reveals structure-dynamics relationships in carotenoids

Based on simultaneous analysis of the frequency-resolved transient grating, peak shift, and echo width signals, we present a model for the third-order optical response of carotenoids including population dynamics and system-bath interactions. Our frequency-resolved photon echo experiments show that the model needs to incorporate the excited-state absorption from both the S-2 and the S-1 states. We apply our model to analyze the experimental results on astaxanthin and lycopene, aiming to elucidate the relation between structure and system-bath interactions. Our analysis allows us to relate structural motifs to changes in the energy-gap correlation functions. We find that the terminal rings of astaxanthin lead to increased coupling between slow molecular motions and the electronic transition. We also find evidence for stronger coupling to higher frequency overdamped modes in astaxanthin, pointing to the importance of the functional groups in providing coupling to fluctuations influencing the dynamics in the passage through the conical intersection governing the S-2-S-1 relaxation.

Optical nonlinear characteristics of MgF2 films containing Cu nanoparticles

An investigation is made on the optical nonlinear characteristics of MgF2 films containing Cu nanoparticles. When the Cu volume fraction is 0.1, at approximately \varem+ 2ed= 0, the film exhibits a strong third-order optical nonlinear refractive coefficient of 1.010-9 cm2/W, a nonlinear refractive index of about -4.0×10-7 esu, a third-order optical nonlinear response of about 6.810-8 esu, and a figure of merit of about 1.010-11. The result shows that the film may have potential applications in optoelectronic technology.

Large Third-Order Optical Nonlinearity of a Novel Copper Phthalocyanine–Ferrocene Dyad

Third-order optical nonlinearity of a novel copper phthalocyanine-ferrocene dyad is measured by femtosecond forward degenerate four-wave mixing (DFWM) technique at 800 nm. The second-order hyperpolarizability of the novel copper phthalocyanine–ferrocene dyad is measured to be 1.74 × 10-30 esu. This large and ultrafast third-order optical nonlinear response is mainly enhanced by the formation of intramolecular charge-transfer which can enhance the delocalized movements of the large π-electrons in the molecules.

Selection of dominant multi-exciton transitions in disordered linear J-aggregates

We show that the third-order optical response of disordered linear J-aggregates can be calculated by considering only a limited number of transitions between (multi-) exciton states. We calculate the pump-probe absorption spectrum resulting from the truncated set of transitions and show that, apart from the blue wing of the induced absorption peak, it agrees well with the exact spectrum.

Third-order optical nonlinearities of lead-free (Na1−xKx)0.5Bi0.5TiO3 thin films

(Na1−xKx)0.5Bi0.5TiO3 (NKBT) (x=0.1, 0.2, and 0.3) thin films with good surface morphology and rhombohedral perovskite structure were fabricated on quartz substrates by a sol–gel process. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties were investigated by Z-scan technique performed at 532nm with a picosecond laser. A two-photon absorption effect closely related with potassium-doping content was found in thin films, and the nonlinear refractive index n2 increases evidently with potassium-doping. The real part of the third-order nonlinear susceptibility χ(3) is much larger than its imaginary part, indicating that the third-order optical nonlinear response of the NKBT films is dominated by the optical nonlinear refractive behavior. These results show that NKBT thin films have potential applications in nonlinear optics.

Off-resonant third-order optical nonlinearities of novel diarylethene–phthalocyanine dyads

Third-order optical nonlinearities of the novel diarylethene–phthalocyanine dyads were measured by femtosecond forward degenerate four-wave mixing (DFWM) technique at 800 nm. They have large and ultrafast third-order optical nonlinear responses, which mainly arise from the distortion of the large π-conjugated electronic charge distribution in the molecules. The second-order hyperpolarizabilities of the diarylethene–phthalocyanine dyads was measured to be (0.76–1.12) × 10 −30 esu.

Resonant third-order optical nonlinearities of 1,3-bis[(3,3-dimethylindolin-2-ylidene)methyl]croconine

The third-order optical nonlinearities and responses of a croconium dye (1,3-bis[(3,3-dimethylindolin-2-ylidene)methyl]croconine) in tetrahydrofuran (THF) solution and in poly(methyl methacrylate) (PMMA) coating films were measured using a femtosecond degenerate four-wave mixing (DFWM) technique with a time resolution of 0.3 ps (FWHM) system under resonant conditions. The electronic component of molecular hyperpolarizability, γ e of the croconium dye in THF solution was determined to be about 5.3×10 −29 esu at 773 nm. The electronic component of third-order nonlinear optical susceptibilities, χ e ( 3 ) of the present PMMA coating films containing the croconium dye was measured to be of the order of 10 −8 esu, and the figure of merit of third-order nonlinearity F ( F = χ ( 3 ) / α ) , was evaluated to be about 8.3×10 −14 esu cm. The χ e ( 3 ) for a neat film was about 4.9×10 −8 esu at 820 nm.

Crystal structure, magnetic and optical properties of (2-picoloylcarbonyl) thiosemicarbazonatocopper(II) ([Cu 3L 2(H 2O) 2] · 2ClO 4 · 3H 2O, and L = [C 7H 8N 4OS] 2−)

Trinuclear copper(II) complex of [Cu 3L 2(H 2O) 2] · 2ClO 4 · 3H 2O was prepared by the reaction of (2-picoloylcarbonyl)thiosemicarbazone(H 2L) and copper perchlorate hydrate, and the magnetic properties and absorption spectra were measured for the title compound, and the origin of third-order optical response was identified in terms of calculated results using density functional theory combined with sum-over-states methods.

Anomalous continuous-time random-walk spectral diffusion in coherent third-order optical response

Recursive relations are derived for nonlinear optical response functions of a two-level chromophore with stochastic frequency fluctuations described by a continuous-time random walk. Stationary ensembles are constructed and signatures of anomalous relaxation in the photon echo signal are discussed for a two state jump modulation with a power law waiting time density function psi(t) approximately t(-alpha-1). Stretched exponential decay of the photon echo signal is predicted for 0<alpha<1 and power law asymptotics for 1<alpha<2.

Time-domain chirally-sensitive three-pulse coherent probes of vibrational excitons in proteins

The third-order optical response of Bosonic excitons is calculated using the Green’s function solution of the nonlinear exciton equations (NEE), which establish a quasi particle-scattering mechanism for optical nonlinearities. Both time-ordered and non-ordered forms of the response function which represent time and frequency domain techniques, respectively, are derived. New components of the response tensor are predicted for isotropic ensembles of periodic chiral structures to first order in the optical wavevector. The nonlocal nonlinear response function is calculated in momentum space. The finite exciton–exciton interaction length is used to greatly reduce the computational effort. Applications arc made to coupled anharmonic vibrations in the amide I infrared band of peptides. Chirally sensitive and non-sensitive signals for α helices and antiparallel β sheets are compared.