Forward Degenerate Four-wave Mixing Research Articles

Third order optical nonlinear studies and its use to estimate thickness of sandwiched films of tetra-phenyl porphyrin derivatives

Third-order nonlinear optical properties of tetra-phenyl porphyrin (H[Formula: see text]TPP) derivatives viz., H[Formula: see text]TPP(OH)[Formula: see text] and Zn(II)TPP doped in boric acid glass thin films were measured using single beam Z-scan and forward degenerate four-wave mixing (DFWM) techniques. Excited state lifetimes and absorption cross-sections were estimated from these experiments. Thickness of the porphyrin doped sandwich glass films were determined using DFWM technique for the first time. The values of nonlinear refractive index ([Formula: see text]) obtained for these systems are are found to be sensitive to the nature of substituents in porphyrin molecule. These results are interpreted in terms of delocalized [Formula: see text] electrons contributing to the third-order optical nonlinearity.

Fast Optical Switching Using Cyanine Dye-Doped Nematic Liquid Crystal

Two kinds of cyanine dye were doped respectively in 4-cyano-4'-pentylbiphenyl (5CB) at a concentration ca. 1.0 wt%, and the mixture was sandwiched between two pieces of rubbed glass plates. The third-order nonlinear optical responses of cyanine dye-doped 5CB layers were measured for light polarized parallel to the oriented direction by the resonant femtosecond forward degenerate four-wave mixing technique at 820 nm. The time resolution of the system was ca. 0.3 ps. The amplified spontaneous emission spectra of cyanine dye-doped 5CB layers indicate that the decay of the slow response was accelerated with increasing laser power. The population grating disappears within ca. 5 ps.

Self-Aggregation Enhanced Third-Order Optical Nonlinearities of Aryloxy Substituted Zinc Phthalocyanines

Third-order optical nonlinearities of three aryloxy substituted phthalocyanines are measured by femtosecond forward degenerate four-wave mixing technique at 800 nm. Ultrafast optical responses are observed and the magnitude of the second-order hyperpolarizabilities γ of the phthalocyanines is measured to be as large as 10−31 esu. Due to the enhancement of J-aggregates, the γ value of an aryloxy substituted zinc phthalocyanine in chloroform is approximately 2.2 times larger than that of the dye in methanol. Moreover, the morphologies of aryloxy substituted zinc phthalocyanine in chloroform exhibit that the nanowires with a diameter of 50–100 nm are connected to each other to form an indefinite network structure, while no aggregates are detected when the samples are prepared from a solution in the methanol.

Electromagnetic interference shielding of single-wall carbon nanotube buckypaper/epoxy composites

In the present study, forward degenerate four-wave mixing (FDFWM) is employed to measure rubidium (Rb) isotope ratio quantitatively with excellent reproducibility regardless of laser intensity turbulence. The effects of power saturation, atomic absorption and Doppler broadening on measurements are investigated. The results indicate that optimized pump power for isotope ratio measurement is 5-37.3 mW and the optimized atomic number density is around 10(14) m(-3) for the sample cell with a length of 50 mm. In addition, the signal of FDFWM is almost independent on Doppler effect in isotope ratio determination. The measured Rb-85 and Rb-87 ratios in Rb vapor cell and RbCl are 2.590 +/- 0.001 and 2.649 +/- 0.002 respectively, which are in good agreement with the values obtained by absorption spectroscopy and mass spectrometry. A low detection limit as 18.41 fg/mL is achieved. The information obtained from this work suggests that FDFWM is a reliable laser spectroscopic technique in quantitative isotope trace analysis for various applications such as geological and archeological dating. (C) 2012 Elsevier B.V. All rights reserved.

Quantitative measurement of rubidium isotope ratio using forward degenerate four-wave mixing

In the present study, forward degenerate four-wave mixing (FDFWM) is employed to measure rubidium (Rb) isotope ratio quantitatively with excellent reproducibility regardless of laser intensity turbulence. The effects of power saturation, atomic absorption and Doppler broadening on measurements are investigated. The results indicate that optimized pump power for isotope ratio measurement is 5–37.3mW and the optimized atomic number density is around 1014m−3 for the sample cell with a length of 50mm. In addition, the signal of FDFWM is almost independent on Doppler effect in isotope ratio determination. The measured 85Rb and 87Rb ratios in Rb vapor cell and RbCl are 2.590±0.001 and 2.649±0.002 respectively, which are in good agreement with the values obtained by absorption spectroscopy and mass spectrometry. A low detection limit as 18.41fg/mL is achieved. The information obtained from this work suggests that FDFWM is a reliable laser spectroscopic technique in quantitative isotope trace analysis for various applications such as geological and archeological dating.

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.

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.

The second hyperpolarizability of CdTe nanocrystals using polarization-resolved degenerate four-wave mixing

Polarization-resolved forward degenerate four-wave mixing (DFWM) in a nonresonant region revealed the effective third-order nonlinear susceptibility of colloidal CdTe nanocrystals (NCs) with the size near the Bohr radius and various concentrations. The second hyperpolarizabilities, 〈 γ x x x x h 〉 and 〈 γ x y y x h 〉 , of the CdTe NCs were ∼1.15 × 10 −41 m 5/V 2 and ∼3.01 × 10 −42 m 5/V 2 from the measurement of the concentration-dependent third-order nonlinear susceptibility of CdTe NCs, respectively. The ratio ( 〈 γ x y y x h 〉 / 〈 γ x x x x h 〉 ) of the hyperpolarizabilities was ∼0.26, which indicated a large contribution of an electronic polarization process to the third-order nonlinearity of CdTe NCs.

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

Optical holographic recording properties of l-(2-Pyridylazo)-2-Naphthol thin film

The optical holographic recording properties of the azo dye l-(2-Pyridylazo)-2-Naphthol in PMMA thin film were studied by using the three-dimensional forward degenerate four-wave mixing technique with a ps pulse laser at 532nm. It demonstrated that the transient grating turned into a permanent grating with the increase of the pulse energy and the grating can be erased through a thermal treatment of the film. The mechanism of the fixed grating was attributed to the trans–cis isomerization of the azo molecules induced by singlet excited-state absorption and the subsequent orientation of the molecules.

Resonant Third-Order Optical Nonlinearities of Chloroform Solution and Neat Film of Poly(9,9-dioctylfluorenyl-2,7-yleneethynylene)

The third-order nonlinear optical properties of a chloroform solution and a neat film of poly(9,9-dioctylfluorenyl-2,7-yleneethynylene) (PDOFE) were investigated by forward degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of PDOFE were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least three components, i.e., a coherent instantaneous nonlinear response (electronic response) and two slow responses due to the formation of excited molecules for both the chloroform solution and the neat film of PDOFE. The electronic component of molecular hyperpolarizability per repeat unit of PDOFE in the chloroform solution was determined to be ca. (6.2±0.3)×10-31 esu at 388 nm. The third-order nonlinear optical susceptibility of the neat film of PDOFE was estimated to be ca. (1.2±0.1)×10-8 esu at 387 nm.

Syntheses and third-order NLO properties of η6complexes of N-ethylcarbazole with Cr(CO)3and Cr(CO)2PPh3moieties

Carbazole mono- and bimetallic complexes [(N-ethylcarbazole){Cr(CO)3}2] (3) and [(N-ethylcarbazole)Cr(CO)2L] (L = CO (2) and PPh3 (4)) have been synthesized, and X-ray crystal structure analyses performed for 2 and 4. Each complex possesses spectroscopically intense intraligand (IL) and metal-to-ligand charge-transfer (MLCT) excitations that are well separated in energy. The MLCT bands display a small to moderate negative solvatochromism. The third-order non-linear optical (NLO) properties, measured by the time-resolved forward degenerate four-wave mixing (DFWM) technique in solution at 532 nm, have been studied for these complexes, together with N-ethylcarbazole for comparison. It is found that the third-order NLO response can be tuned by chromium complexation. The molecular second-order hyperpolarizabilities, γ, of the synthesized complexes are determined to be in the order of 10−30 esu and clearly depend on both the nature of the ligand and the extent of chromium tricarbonyl coordination by the carbazole ring. The carbazole-mediated metal–metal electronic interaction existing in 3 is believed to be a possible factor responsible for a large improvement in the non-linearity.

Time-Resolved Femtosecond Degenerate Four-Wave Mixing inLiNbO3:Fe,Mg Crystal

Forward degenerate four-wave mixing (DFWM) processes are investigatedwith a femtosecond pulsed laser in lithium niobate crystal doubly-dopedwith magnesium and iron (LiNbO3:Fe,Mg). The pulse energydependence reveals a pure third-order nonlinear response, and thethird-order nonlinear susceptibility χ(3) in the materialis evaluated to be 4.96×10−13 esu. The time-resolved DFWMprocess shows a response time of χ(3) shorter than 100 fs,which is due to the nonresonant electronic nonlinearities. Our resultsindicate that LiNbO3 crystals have potentials for ultrafastreal-time optical processing systems, which require a large and fastχ(3) optical nonlinearity.

Effects of laser-beam temporal pulse shape on signal strength and spectral line shape of forward degenerate four-wave mixing

We investigate the effects of the input laser beam’s temporal pulse shape on a forward degenerate four-wave mixing (FDFWM) signal, assuming two-level saturable absorbers. Under conditions in which the coherence time is far shorter than the pulse-duration, we can calculate the signal easily in the time and frequency domains. From this result it is shown that, when the pulse duration is longer than ten times the population relaxation time, the calculated signal intensity is almost the same as that obtained by assuming a steady state throughout duration of the laser pulse. With this assumption, we obtain the signal by summing all the steady-state signals at each time-domain grid point during the pulse. The calculation is performed with three input beam temporal pulse shapes: square, Gaussian, and typical Q-switched pulses. After reaching a maximum, the signal intensity decreases. The rates of the signal increase and decrease depend strongly on the temporal shape of the input beam. For the same average power, the square-pulse input saturates the absorber faster than the other pulses. These results indicate that the weak part of the pulse input plays an important role in generating the signal, yielding differences in saturation behavior of the signal intensity and the spectral line shape. We compare the calculations with experiments by fitting the saturation curve of the FDFWM signal of argon atoms in a radio frequency inductively coupled plasma. Also, the spectral line shape of the DFWM signal is fitted with the calculation by use of published experimental data.

Forward degenerate four-wave-mixing spectra of NO in the strong-field regime including polarization, line coupling, and multipole effects. I. Theory

In the present paper, we investigate the saturation mechanism of FDFWM (forward degenerate four-wave-mixing) spectra, observed with different polarizations of the input beams, line coupling, and Doppler effect. Our theoretical approach uses a nonperturbative resolution of the density matrix equations, decomposed on the irreducible tensor basis. This formalism greatly simplifies analytical expressions and allows for a correct treatment of magnetic sublevels structure in a three-J level system. Systematic calculations of the FDFWM signal for specific NO lines are performed to characterize intensities and line shapes as a function of saturation. Relative intensities exhibit strong changes in the intermediate regime of saturation further supporting the necessity for using such a complete model. Under saturating conditions, line coupling is shown to distort the spectra, according to the type of transition and the polarization configuration. This effect is observed in the following paper [V. Kr\uger et al., paper II, Phys. Rev. A 2001 (to be published)], where saturated experimental spectra of NO are presented and interpreted for two polarization configurations of interest for diagnostic purposes.

On the potential of forward-scattering degenerate four-wave mixing detection in capillary electrophoresis

The question is addressed, whether in capillary electrophoresis (CE) the laser-based forward degenerate four-wave mixing (F-D4WM) detection method can become a realistic alternative to conventional ultraviolet (UV) absorption detection. In order to answer this question F-D4WM experiments at 351 nm have been performed. As test analytes the herbicides dinitro- ortho-cresol and dinitro-( tert-butyl)- ortho-phenol (trivial names DNOC and dinoterb, respectively) were used without derivatisation. These compounds show moderate absorption (molar absorptivity 4000 M −1 cm −1) at 351 nm under the conditions (buffer pH 8.2) used for CE separation. The detection limits obtained (1 μM) were 25-fold better than with on-column absorption detection at 351 nm. This result is shown to be typical for CE, where commonly buffer solutions with a high water content are used. For micro-separation systems that are compatible with liquid solutions with a low water content F-D4WM detection has a much wider potential.

Interference effects in time-delayed degenerate four-wave mixing with broadband noisy light

Femtosecond beats in time-delayed forward degenerate four-wave mixing (DFWM) with incoherent light in liquid and solid materials have been observed, and their origin is discussed. It is shown that the oscillations are due to the interference between pure DFWM signal and Rayleigh scattering from the excitation beams. It is also shown that, if this effect is not taken into account, incorrect conclusions can be reached.

Theory of forward degenerate four-wave mixing in two-level saturable absorbers

A theoretical description for a forward degenerate four-wave mixing process in homogeneously broadened two-level absorbers with arbitrary intensities of all four beams is presented. Assuming no pump absorption and depletion, we obtain an analytical solution of forward degenerate four-wave mixing signal intensity in the limit of the strong pumps and weak probe and signal. In the case of low absorption or large detuning, this solution is shown to become equivalent to that of the phase-conjugate degenerate four-wave mixing derived by Abrams and Lind [Opt. Lett.2, 94 (1978)]. For arbitrary beam intensities and absorption parameters, the signal intensity is numerically calculated by solution of the coupled equations of complex wave amplitudes. Comparing the results of the numerical calculation with those of the analytical solution, we discuss the validity of using the analytical solution in practical experiments and show the saturation behavior that is due to the strong probe beam. The line shapes under the various ratios among the input beams and absorption parameters are also obtained and discussed.

π-electron density dependence of third-order optical nonlinearities in poly(1,4-phenylene vinylene) derivatives

The third-order nonlinear optical properties of poly(1,4-phenylene vinylene) (PPV), poly(2-bromo-1,4-phenylene vinylene) (BrPPV) and poly(2-chloro-1,4-phenylene vinylene) (ClPPV) were studied by forward degenerate four-wave mixing (DFWM). 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 backbone. It was found that there was a significant contribution to π-electron density and thus χ (3) values from the substituents at the phenylene ring.

Forward Degenerate Four-Wave Mixing as a Detection Method in Liquid Separation Systems: Improving Detection Limits by Means of a Fabry—Perot Interferometer

A simple, small, and low-resolution confocal Fabry–Perot interferometer (CFP) has been developed to improve the signal-to-noise ratio (S/N) in forward degenerate four-wave mixing (F-D4WM) detection, coupled to high-performance liquid chromatography (HPLC). Its appropriateness is based on the difference in coherence between the F-D4WM signal and the background stray light. A detailed description of the specially designed CFP and its performance is presented. The improvement in S/N was calculated from the chromatographic peaks recorded after an HPLC separation of 1- and 2-aminoanthraquinone. The concentration limit of detection (LOD) was improved by a factor of 30; for 1-aminoanthraquinone it was 2 × 10−8 M injected (corresponding to about 3 × 10−9 M in the detector cell), which is quite favorable in view of its low molar extinction coefficient being 2000 M−1 cm−1 at the utilized laser wavelength (514.5 nm).