Nonlinear-optical measurement

For the measurements of the NLO properties of organoftillerenes 1,2 and 3, the Z-scan technique has been employed [151]. Z-scan is arelatively simple experimental technique allowing for the simultaneous determination of the real and imaginary parts of the third-order susceptibility Then, the second-order hyperpolarisability 

In the present study, the second harmonic at 532 nm of a 35 ps mode-locked Nd YAG laser operating at a repetition rate of 10 Hz has been employed. The spatial and the temporal profile of the laser beam were characterized and found to have a Gaussian distribution. For the needs of the measurements several solutions in toluene have been prepared having different concentrations for each fullerene system. The UV-Vis-NIR absorption spectra of the prepared solutions were recorded before and after the measurements to ensure that no photodegradation due to laser irradiation has occurred. 

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For 2PA or ESA spectral measurements, it is necessary to use tunable laser sources where optical parametric oscillators/amplifiers (OPOs/OPAs) are extensively used for nonlinear optical measurements. An alternative approach, which overcomes the need of expensive and misalignment prone OPO/OPA sources, is the use of an intense femtosecond white-light continuum (WLC) for Z-scan measurements [71,72]. Balu et al. have developed the WLC Z-scan technique by generating a strong WLC in krypton gas, allowing for a rapid characterization of the nonlinear absorption and refraction spectra in the range of 400-800 nm [72]. 

However, its was found possible to infer all four microscopic tensor coefficients from macroscopic crystalline values and this impossibility could be related to the molecular unit anisotropy. It can be shown that the molecular unit anisotropy imposes structural relations between coefficients of macroscopic nonlinearities, in addition to the usual relations resulting from crystal symmetry. Such additional relations appear for crystal point group 2,ra and 3. For the monoclinic point group 2, this relation has been tested in the case of MAP crystals, and excellent agreement has been found, triten taking into account crystal structure data (24), and nonlinear optical measurements on single crystal (19). This approach has been extended to the electrooptic tensor (4) and should lead to similar relations, trtten the electrooptic effect is primarily of electronic origin. 

Ben-Oren, L, Peleg, G., Lewis, A., Minke, B., and Loew, L. M. 1999. Infrared nonlinear optical measurements of membrane potential in photoreceptor cells. Biophys. J. 71 1616-20. 

Phase-space wavepackets for nuclear motions have been applied to the interpretation of nonlinear optical measurements using the Liouville space... 

S. Mukamel I would like to make a comment regarding interference effects in quantum and classical nonlinear response functions [1, 2]. Nonlinear optical measurements may be interpreted by expanding the polarization P in powers of the incoming electric field E. To nth order we have... 

The work described in this paper represents the contributions of several people. Laura Davis is responsible for the linear optical property measurements and the development of the microreffactometer. Most of the nonlinear optical measurements on small single crystals have been made by Mark Webb, who is also responsible for several improvements in the apparatus and technique. Francis Wang synthesized the chiral organic salts and did the powder SHG measurements. David Eimerl was the source of much encouragement, advice, and support during the course of this work. 

In order to understand the origin of the high values of the third-order nonlinearity observed, we picked polybenzidine for more detailed study. The real and imaginary components of the third-order susceptibility x are measured separately. The real part Rex leads to nonlinear refraction, and the imaginary part Imx ) is responsible for nonlinear absorption. The nonlinear-optical measurements were made using dilute solutions of the polymer in DimethyLsulfoxide/Methanol in the ratio 4 1 (DMSO MeOH). 

More reeently, higher-order nonlinear optical measurements such as three-pulse photon eeho peak shift measurements have been carried out to study the SD. Fleming and co-workers studied such three-pulse photon echo from the dye molecule eosin in water. They found that a substantial amplitude (about 60%) of aqueous solvation oecurs within 30 fs. A three-exponential fit (up to 100 ps) to the data of eosin in water yields time eonstants of 17 fs (73%), 330 fs (15%), and 3 ps (12%). Analysis... 

From the results presented, it has been shown that the sealed capillary DSC technique for estimating thermal stability can be used to determine the comparative stabilities of a variety of NLO chromophores. Furthermore, the data compare favorably with actual nonlinear optical measurements, namely the decrease in EFISH values with time at temperature. 

Nonlinear optical measurements provide the most direct probe of the electronic states. Conversely, the nonlinear susceptibilities can be calculated if there exists a theoretical imderstanding of the excited states. We describe the theory of linear and nonlinear optical processes, and recast the so-called essential states model in terms of the primary excitons. 

The nonlinear optical (NLO) susceptibilities of bioengineered aromatic polymers synthesized by enzyme-catalyzed reactions are given in Tables 2, 3, and 4. Homopolymers and copolymers are synthesized by enzyme-catalyzed reactions from aromatic monomers such as phenols and aromatic amines and their alkyl-substituted derivatives. The third-order nonlinear optical measurements are carried out in solutions at a concentration of 1 mg/mL of the solvent. Unless otherwise indicated, most of the polymers are solubilized in a solvent mixture of dimethyl formamide and methanol (DMF-MeOH) or dimethyl sulfoxide and methanol (DMSO-MeOH), both in a 4 1 ratio. These solvent mixtures are selected on the basis of their optical properties at 532 nm (where all the NLO measurements reported here are carried out), such as low noise and optical absorption, and solubility of the bioengineered polymers in the solvent system selected. To reduce light scattering, the polymer solutions are filtered to remove undissolved materials, the polymer concentrations are corrected for the final x calculations, and x values are extrapolated to the pure sample based on the concentrations of NLO materials in the solvent used. Other details of the experimental setup and calculations used to determine third-order nonlinear susceptibilities were given earlier and described in earlier publications [5,6,9,17-19]. 

Nonlinear optical measurements on elastomers were performed by J. Benne et al. with mechanically aligned samples. Due to the alignment procedure, the helicoidal superstructure is untwisted and the two-step cross-linking process locks in the ferroelectric structure. Without applying external fields, these networks spontaneously produce frequency doubling and, from the SHG signal in a Marker-fringe experiment, the C2 symmetry of the elastomer is confirmed [35], [36]. 

Four calculations have been reported in related areas of molecule-field interactions. Evans (1982) has simulated the bulk anisotropy for a collection of molecules, which while dipolar were not polarizable nor based on the properties of a real molecule. The field-induced force was not explicitly defined in terms of a dipole-field interaction, rather a full Lennard-Jones potential was used. Coffey has examined the inertial relaxation of dipolar molecules in intense fields (Coffey et al., 1983). Madden has focused on interaction-induced effects in dielectric absorption (Tildesley and Madden, 1983) and transient nonlinear optical measurements in CS2 (Madden, 1987). Samios and Dorfmuller used a similar local field formalism to ours when they examined far IR absorption and utilized equilibrium fluctations to obtain correlation functions for liquid CS2 (Gburski et al., 1987). More details on these calculations... 

Hayden, L.M., Sauter, G.F., Ore, F.R., and Pasillas, P.L. (1990) Second-order nonlinear optical measurements in guest-host and side-chain polymers. 

G. Pel% A. Lewis, M. Linial, and L. M. Loew, Nonlinear optical measurement of membrane potential around single molecules at selected cellular sites, Proc. Nall. Acad. ScL USA 96,6700-6704 (1999). 

Chen, F. Gindre, D. Nunzi, J. M. First order distributed feedback dye laser effect in reflection pumping geometry for nonlinear optical measurements. Proc. SPIE-Int. Soc. Opt. Eng. 2007, 6653, 665304/1-665304/5. 

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