Femtosecond Time-resolved Optical Kerr Effect Research Articles

Search for the origin of synergistic solvation in methanol/chloroform mixture using optical Kerr effect spectroscopy

The synergistic effect of methanol/chloroform mixture on solute solvation was earlier attributed to the formation of an extended hydrogen-bonding network in the mixture. Such a network was proposed to be weak through the solute dipole-moment dependent experiment. In this study, we search for signatures of such interactions using the femtosecond time-resolved optical Kerr effect spectroscopy, which is sensitive to the ultrafast intermolecular dynamics. We observed a 2-3-fold retardation of the orientational diffusion time of chloroform molecules that is attributed to the formation of hydrogen-bonds with methanol. Our frequency domain analysis in terms of the excess reduced spectral density and partial reduced spectral density allowed us to detect a hydrogen-bond stretching band around 90 cm−1 (with 107 cm−1 natural frequency) associated with methanol molecules simultaneously accepting a hydrogen-bond from chloroform and donating a hydrogen-bond to another methanol molecule. Additionally, in an auxiliary mixture used in this study, where chloroform is replaced with carbon tetrachloride, we found evidence of carbon tetrachloride-methanol halogen-bond formation; however, its signature in the spectra is much weaker than in the case of chloroform-methanol hydrogen-bonding.

Femtosecond-pulsed Z-scan study on third- and fifth-order refractive nonlinearities in a side-chain azobenzene copolymer film

By performing the femtosecond-pulsed [Formula: see text]-scan experiments at a wavelength of 780[Formula: see text]nm, we report the observation of simultaneous third- and fifth-order refractive nonlinearities in the film of a side-chain azobenzene copolymer synthesized by free-radical polymerization method. Theoretically, we extend two continuous wave [Formula: see text]-scan theories suitable for the excitation of ultrafast laser pulses. First one is valid only for the situation of the sample with the pure third-order refractive nonlinearity. Second one is applicable when the sample exhibits the simultaneous third- and fifth-order refractive nonlinearities. Both [Formula: see text]-scan theories allow the precise analysis of femtosecond-pulsed [Formula: see text]-scan experimental data. Using the femtosecond time-resolved optical Kerr effect measurements, we estimate the nonlinear response time of the sample to be in the sub-picosecond regime. The physical mechanisms of the observed nonlinearity are also discussed. The high nonlinear figure of merit with ultrafast response in this polymer is desirable in nonlinear photonic devices.

Ultrafast imaging of photoinduced nonlinear response in transparent materials using femtosecond optical polarigraphy technique

Using a femtosecond time-resolved optical polarigraphy (FTOP) imaging technique, we measured the ultrafast propagation dynamics of femtosecond laser pulses in transparent materials, CS2 and fused silica, respectively. The FTOP images showed different profiles in these two media due to their different nonlinear response time. Based on the FTOP technique, a femtosecond time-resolved single-shot optical Kerr effect measurement was demonstrated, which can be accomplished using a single-laser shot and has a time resolution of about 100 fs. The polarization dependence of the image intensity indicated that the FTOP images were mainly induced by the transient birefringence effect induced by the pump pulse.

Study of structural and dynamic properties of liquid phenyltrimethoxysilane

Herein, we present a combined experimental and computational study of liquid phenyltrimethoxysilane. A femtosecond time-resolved optical Kerr effect experiment has been performed to study the rotational diffusion of the molecule. A new all-atoms molecular model of the compound, based on the OPLS force field, has been developed to reproduce the rotational diffusion time constant and other physical and dynamic properties available in the literature. The density obtained from the simulations is 1074 ± 4 kg m(-3), which is within 1% of the experimental value of 1062 kg m(-3). The viscosity from the simulations is 1.6 ± 0.1 mPa s while the experimental value is 2.1 mPa s. The average bulk dipole moment of 1.8 ± 0.5 Debye obtained from the simulation matches the experimental value of 1.77 Debye. The average relative dielectric constant from the simulations is 3.86 ± 0.04, which is within 13% of the experimental value (4.4). The rotational diffusion time of the dipole moment obtained from the simulations is 20.39 ± 0.06 ps, which is in excellent agreement with the experimental value of 20 ± 1 ps obtained from our measurements. The new model has also been used to calculate structural and dynamic properties of the molecule not yet determined experimentally.

Third-order nonlinear optical properties of GeS_2-Sb_2S_3-CdS chalcogenide glasses

The third-order nonlinear optical properties of GeS(2)-Sb(2)S(3)-CdS chalcogenide glasses were investigated utilizing the Z-scan and femtosecond time-resolved optical Kerr effect (OKE) methods at the wavelength of 800 nm, respectively. The compositional dependences were analyzed and the influencing factors including the linear refractive index, the concentration of lone electron pairs, the optical bandgap and the amount of weak covalent/ homopolar bonds were discussed. A glass, i.e. 76GeS(2)·19Sb(2)S()·5CdS, with large nonlinear refrative index (n(2) = 5.63 × 10(-14) cm(2)/W), low nonlinear absorption coefficient (β = 0.88 cm/GW) and minimum figure of merit (FOM = 2βλ/n(2) = 2.51) was finally prepared. The electronic contribution in weak heterpolar covalent and homopolar bonds are responsible for large n(2) in chalcogenide glass, and the Sheik-Bahae rule combining the Moss rule are proved to be an effective guidance for estimating the third-order nonlinearities and further optimizing the compositions in chalcogenide glasses.

Ultrafast non-resonant third-order optical nonlinearity of [formula omitted]– [formula omitted]–CdS chalcogenide glass

Ultrafast third-order nonlinear optical responses of 4(1− x)/5GeS 2-(1− x)/5Ga 2S 3- xCdS ( x=0.05, 0.10 and 0.15 in mol%) chalcogenide glasses was investigated by using the femtosecond time-resolved optical Kerr effect technique at a wavelength of 800 nm. The largest third-order nonlinear susceptibility of all samples was estimated to be 1.65×10 −13 esu. An ultrafast nonlinear response time of about 250 fs was observed, which was dominantly assigned to the ultrafast distortion of the electron cloud under femtosecond laser excitation. A nonlinear relationship between the third-order nonlinear susceptibility and the introduced amount of CdS was discussed, suggesting a possible disturbance between different polarizable bonds in the glass system.

Ultrafast third-order optical non-linearity of 0.56GeS 2–0.24Ga 2S 3–0.2KX(X = Cl, Br, I) chalcohalide glasses by femtosecond Optical Kerr Effect

0.56GeS 2–0.24Ga 2S 3–0.2KX(X = Cl, Br, I) chalcohalide glasses were prepared and their third-order optical non-linearities χ (3) have been studied systematically using the femtosecond time-resolved Optical Kerr Effect technique at wavelength of 800 nm. In this system, 0.56GeS 2–0.24Ga 2S 3–0.2KCl glass shows the largest χ (3) (1.82 × 10 −13 esu), but 0.56GeS 2–0.24Ga 2S 3–0.2KBr glass has the fastest optical non-linear response time in subpicosecond domain (about 340 fs), which is due to the ultrafast distortion of the electron clouds surrounding the balanced position of Ge, Ga, S, K and Br atoms. The local hyperpolarizability determining non-linear optical response are determined by the partially ionic bonds originating from Ge(Ga)–S bonds and halogen valence bonds. They show great potential applications on the glass-based optoelectronic devices like optical switching.

Optical nonlinearity and ultrafast dynamics of ion exchanged silver nanoparticles embedded in soda-lime silicate glass

Ag nanoparticles embedded in soda-lime silicate glass were fabricated by ion-exchange and subsequently annealing method. Z-scan technique, femtosecond time-resolved optical Kerr effect (OKE) technique and femtosecond pump-probe experiment were used to investigate the effects of laser wavelength and laser pulse duration as well as annealing temperature on the third-order optical nonlinearity and ultrafast dynamics of the composites. It was found that the third-order susceptibility of Ag nanoparticles composite glass measured by 400 nm pulse source is larger than that measured by 800 nm pulse source due to an enhancement effect of local field near surface plasmon resonance of Ag nanoparticles in silicate glass. The third-order optical nonlinearity measured by ns laser source is about two orders of magnitude larger than that measured from fs pulse. The annealing temperature has an important effect on the third-order optical nonlinearity and ultrafast dynamics of the composites. Third-order nonlinear susceptibility up to 10−10 esu and fast relaxation process up to 0.2 ps have been obtained in Ag nanoparticles doped glass.

Structure dependence of ultrafast third-order optical nonlinearity for GeS 2–In 2S 3–CsI chalcohalide glasses

Ultrafast third-order nonlinear optical responses of GeS 2–In 2S 3–CsI chalcohalide glasses have been measured by using the femtosecond time-resolved optical Kerr effect (OKE) technique at a wavelength of 820 nm. The third-order nonlinear susceptibility was estimated to be as large as 5.12×10 −13 esu. The full width at half maximum of the Kerr signal was 120 fs and its response was dominantly assigned to the ultrafast distortion of the electron cloud. The relationship between the structural units and the third-order nonlinear optical responses was analysed by Raman spectra. It is suggested that the covalent bonds of S–Ge or S–In constituting the tetrahedral units [GeS 4/2] or [InS 4− x I x ], respectively, play an important role in the ultrafast third-order nonlinear optical responses of these chalcohalide glasses.

Femtosecond Third-Order Optical Nonlinearity ofAu:Bi2O3 Nanocomposite Films

Ultrafast third-order optical nonlinearities of the as-deposited andannealed Au:Bi2O3 nanocomposite films deposited bymagnetron cosputtering are investigated by using femtosecondtime-resolved optical Kerr effect (OKE) and pump–probe techniques. Thethird-order optical nonlinear susceptibility is estimated to be2.6×10−10 esu and 1.8×10−9 esu at wavelength of800 nm, for the as-deposited and the annealed film, respectively. TheOKE signal of the as-deposited film is nearly temporally symmetricalwith a peak centred at zero delay time, which indicates the dominantcontribution from intraband transition of conduction electrons. For theannealed film, the existence of a decay process in OKE signal impliesthe important contribution of hot electrons. These characteristics arein agreement with the hot electron dynamics observed in pump–probemeasurement.

Ultrafast third-order nonlinear optical response of Cu:Bi 2O 3 nanocomposite films

Ultrafast third-order nonlinear optical responses of the as-deposited and annealed Cu:Bi 2O 3 nanocomposite films were investigated by using femtosecond Z-scan and time-resolved optical Kerr effect (OKE) techniques at the wavelength of 800 nm. The Z-scan measurement showed that both the real and imaginary parts of the third-order nonlinear optical susceptibility were enhanced after thermal annealing treatment. The OKE response of the as-deposited film was instantaneous, and the enhanced OKE signal of the annealed film presented additional slow decay processes which imply the important contribution from photoinduced hot electrons in Cu nanoparticles.

Study on the third and second-order nonlinear optical properties of GeS2-Ga2S<suv>3</suv>-AgCl chalcohalide glasses

Third-order optical nonlinearities, chi((3)) of GeS(2)-Ga(2)S(3)-AgCl chalcohalide glasses have been studied systematically utilizing the femtosecond time-resolved optical Kerr effect (OKE) technique at 820nm, showing that the value of chi((3)) enhances with increasing atomic ratio of (S+Cl/2)/(Ge+Ga). From the compositional dependence of glass structure by Raman spectra, a strong dependence of chi;(3) upon glass structure has been found, i.e. compared with [Cl(x)S(3-x)Ge(Ga)-Ge(Ga)S(3-x)Cl(x)] ethane-like s.u. as the structural defectiveness, [Ge(Ga)S(4-x)Cl(x)] mixed tetrahedra make greater contribution to the enhancement of chi((3)). The maximum chi<sp>(3)</sp> among the present glasses is as large as 5.26x10(-13)esu (A1 (80GeS(2)-10Ga(2)S(3-) 10AgCl)), and the nonlinear refractive index (n2) of A1 glass is also up to 4.60x10(-15) cm(2)/W. In addition, using Maker fringe technique, SHG was observed in the representative A1 glass poled by electron beam (25 kV, 25 nA, 15 min), and the second-order optical nonlinear susceptibility is estimated to be greater than 6.1 pm/V. There was no evident structural change detected in the as-prepared and after irradiated A1 glass by the Raman spectra, and maybe only electronic transition and distortion of electron cloud occurred in the glasses. The large third/second-order optical nonlinearities have made these GeS(2)-Ga(2)S(3)-AgCl chalcohalide glasses as promising materials applied in photoelectric fields.

Synthesis, characterization and nonlinear optical properties of plasma-prepared poly(4-biphenylcarbonitrile) thin films

A novel conjugated polymer, poly(4-biphenylcarbonitrile) (PBPCN), was prepared using a plasma polymerization technique. The effect of the discharge power on the chemical structure and surface compositions of PBPCN thin films was investigated using Fourier transform infrared, UV-visible absorption and X-ray photoelectron spectroscopies. A femtosecond time-resolved optical Kerr effect technique was applied to investigate the third-order nonlinearity of the obtained plasma PBPCN thin films. For the first time, a non-resonant optical Kerr effect and ultrafast response for the PBPCN thin films were observed. Copyright © 2006 Society of Chemical Industry

Third- and second-order optical nonlinearity of Ge–Ga–S–PbI 2 chalcohalide glasses

Two series of metal iodide doped chalcohalide glasses (100−2 x)GeS 2· xGa 2S 3· xPbI 2 (0⩽ x⩽20) and (100− x)(0.8GeS 2·0.2Ga 2S 3)· xPbI 2 (0⩽ x⩽15) were prepared and characterized. The microstructure of these glasses has been studied by Raman scattering spectra. Utilizing femtosecond time-resolved optical Kerr effect (OKE) technique at the wavelength of 820 nm, a largest third-order nonlinearity χ (3) of 2.07×10 −13 esu was obtained for the 90GeS 2·5Ga 2S 3·5PbI 2 glass, and it decreases with the addition of PbI 2 in both two series. After thermally poled, second-harmonic generation (SHG) has been observed in these glasses according to Maker fringe method and a large second-order nonlinearity χ (2) as well as 4 pm/V was obtained for the 70GeS 2·15Ga 2S 3·15PbI 2 glass. The variations of χ (2) and χ (3) on glass composition are ascribed to the evolution of micro-structural units in glass. These novel chalcohalide glasses would be expected to be the promising candidate materials for nonlinear optical devices.

Preparation of plasma poly(1-isoquinolinecarbonitrile) thin film and its ultrafast nonlinear optical property

How to get a uniform, defect-free, and reproducible conjugated polymer thin films is now becoming the main fabrication problem for the practical application of these materials as the fast switches and modulators in opto-electronic devices. In this research, a novel plasma-polymerized 1-isoquinolinecarbonitrile (PPIQCN) thin film was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure and surface compositions of the deposited PPIQCN films was investigated by Fourier transform infrared (FTIR), UV-Visible absorption spectra and X-ray photoelectron spectroscopy (XPS). The results show that a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 10 W was used during film formation. In the case of higher discharge power of 30 W, more severe monomer molecular fragmentation can be observed, which results in a decrease in the effective conjugation length of PPIQCN film. The morphology characterized by atomic force microscopy (AFM) indicates that a fine, homogenous PPIQCN film could be obtained under a relatively low discharge power. A femtosecond time-resolved optical Kerr effect technique at a wavelength of 820 nm has been applied to investigate the third-order nonlinearity of the plasma PPIQCN film. For the first time, a non-resonant optical Kerr effect and ultrafast response of the PPIQCN film was observed.

Carrier concentration dependence of optical Kerr nonlinearity in indium tin oxide films

Optical Kerr nonlinearity (n2) in n-type indium tin oxide (ITO) films coated on glass substrates has been measured using Z-scans with 200-fs laser pulses at wavelengths ranging from 720 to 780 nm. The magnitudes of the measured nonlinearity in the ITO films were found to be dependent on the carrier concentration with a maximum n2-value of 4.1 x 10-5 cm2/GW at 720-nm wavelength and an electron density of Nd = 5.8 x 1020 cm-3. The Kerr nonlinearity was also observed to be varied with the laser wavelength. By employing a femtosecond time-resolved optical Kerr effect (OKE) technique, the relaxation time of OKE in the ITO films is determined to be ~1 ps. These findings suggest that the Kerr nonlinearity in ITO can be tailored by controlling the carrier concentration, which should be highly desirable in optoelectronic devices for ultrafast all-optical switching.

Structure dependence of ultrafast third-order optical nonlinearity for Ge–Ga–Cd sulfide glasses

Ultrafast third-order nonlinear optical responses of GeS2?Ga2S3?CdS glasses have been measured by using femtosecond time-resolved optical Kerr effect (OKE) technique at the wavelengths of 820nm and 640nm respectively. The experimental results show that GeS2?Ga2S3?CdS glasses have large femtosecond third-order optical nonlinear responses and their OKE signals vary considerably with the composition. The relationship of structure-property is discussed by means of Raman spectroscopy analysis, suggesting that the tetrahedron unit [GeS4] or [GaS4] plays an important role in the ultrafast third-order nonlinear optical response. In addition, the experimental results also reveal that the ultrafast third-order optical nonlinearity of these glasses does not obey the Miller rule.

Off-Resonant Third-Order Optical Nonlinearity of an Ag:TiO2Composite Film

Using the femtosecond time-resolved optical Kerr effect technique, weinvestigate the off-resonant nonlinear optical response of anAg:TiO2 composite film prepared by a vacuum magnetron sputteringmethod. The third-order nonlinear optical susceptibility of thecomposite film with silver nanoparticle size of about 30 nm isestimated to be 1.9×10−10 esu at the incident laser wavelength of800 nm. When the photon energy of the incident beam is lower than thatfor surface plasmon or the interband transition of silvernanoparticles, the observed third-order optical nonlinearity isattributed to the intraband transition of the free electrons. Based onthe linear limit of the electric field within micro-spherical model, weassign this large optical nonlinearity to the local field enhancementof the third-order nonlinearity.

Annealing effect of linear and nonlinear optical properties of Ag:Bi2O3 nanocomposite films

Silver nanoparticle/bismuth oxide composite films were deposited by cosputtering and annealed at different temperatures. The X-ray diffraction results demonstrate that the silver and bismuth oxide were well crystallized after 600 degrees C thermal annealing. The linear absorption peaks show a red-shift behavior while increasing annealing temperature. The annealing effect of the third-order nonlinear optical susceptibilities and ultrafast nonlinear optical response of the silver nanoparticles/bismuth oxide composite thin films are investigated using the femtosecond time-resolved optical Kerr effect technique under 800 nm wavelength. The maximum value of chi(3) of Ag:Bi2O3 thin films is 2.1X10 esu, which occurs at an annealing temperature of 600 degrees C. The ultrafast optical response spectra demonstrate the temperature dependence of decay process time.

Ultrafast third-order optical nonlinearity of polycyanopyridine

A novel plasma-polymerized 4-cyanopyridine (PP4CPD) thin film of desired thickness was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure and surface compositions of the PP4CPD films was investigated by FT-IR, UV–Vis and X-ray photoelectron spectroscopy (XPS). A high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained at a low discharge power. A red shift in the maximum absorption wavelength ( λ max) for PP4CPD films was observed as compared with the monomer absorption spectrum. The atomic force microscopy (AFM) measurement shows that the PP4CPD film with quite a smooth surface could be grown under a relatively low discharge power. A femtosecond time-resolved optical Kerr effect (OKE) technique has been applied to investigate the third-order nonlinearity of the plasma PP4CPD film. For the first time, a non-resonant optical Kerr effect and ultrafast response of polycyanopyridine was observed.