Non Linear Optical Properties Third Order

Bis-Cp acetylide titanium complexes have drawn considerable attention in regard to their third-order non-linear optical properties.2002... 

The third order non-linear optical properties of pseudoisocyanine J-aggregates in thin soiid films... 

The third order non-linear optical properties of pseudoisocyanine J-aggregates in thin solid films were studied using the Z-scan method as well for PIC iodide anion as for PIC with closo-hexahydrodecaborate anion (BioHio -) (Markov et al., 1998a, 1998b Plekhanov et al., 1998a, 1998b). The dispersions values of imaginary and real parts of cubic... 

Third-order non-linearity optical properties of the film of the cyanine dye with borate anion. Proc. SPIE. Vol. 3473. pp. 100-107. (a)... 

Solution properties indicate that the metal-poly(yne)s exist in a rod-like structure. They display lyotropic nematic mesophases [30] and form crystallites with a diameter of up to 50 nm [31]. Absorption and luminescence spectra of the polymers show that 7t-electron conjugation is expanded over the whole polymer chain, and third-order non-linear optical properties are exhibited. For polymer 7 good photocurrents were found in sandwich-diodes. 

Polythiophene is a material which is the center of interest of many groups for its possible applications. It shows high conductivity when doped [110], large third order non linear optical properties [111] and it has been used as a semiconducting active material in the first attempts to build MISFET devices [112]. Of more relevant practical importance is the fact that its alkyl-derivatives are soluble thus opening new horizons for workable polyconjugated polymers. 

Measurement of non-linear optical properties [580] also provides a means for characterizing size-quantized semiconductor particles. Third-order optical non-linearity of size-quantized semiconductor particles has been discussed in terms of resonant and non-resonant contributions [11]. Resonant non-linearity is expected to increase with decreasing particle size and increasing absorption coefficients. 

In addition to photoconductivity, polysilanes have been found to exhibit marked nonlinear optical properties,95-97 suggesting that they may eventually be useful in laser and other optical technology. The third-order non-linear susceptibility, X3, is a measure of the strength of this effect. The non-linear properties of polysilanes, like the absorption spectra, seem to be dependent on chain conformation and are enhanced for polymers having an extended, near anti conformation (Table 5.5). The value of 11 x 10 12 esu observed for (n-Hex2Si) below its transition temperature is the largest ever observed for a polymer which is transparent in the visible region. 

Another potential application of fully converted polydiacetylenes is based upon their unusual non-linear optical properties. Sauteret et al. found that the third order susceptibilities of TCDU and TS increases by about a factor of 600 upon polymerization and become comparable to those of inorganic semiconductors like GaAs or germanium. This is a consequence of the increase of n-electron delocalization upon polymerization. Polymeric diacetylenes can therefore be used as efficient elements for third harmonic generation. In Ref. this effect has been employed for tripling the frequencies of 1.89 pm and 2.62 pm radiation. 

Nonlinear optical properties of conjugated polymers have been extensively studied in the last decade [165-167]. Experimentally it has been shown that third-order non-linearities of conjugated polymers are very fast and reach very high magnitudes opening the perspective of the possible development of organic based all-optical switches and modulators. 

The fundamental component (aE) is linear in E and represents the linear optical properties discussed above. The second (jfiE-E) third ( yE-E-E) and subsequent harmonic terms are nonlinear in E and give rise to NTO effects. The / and values are referred to, respectively, as the first and second hyperpolarisabilities. The second harmonic term gives rise to second harmonic generation (SHG), the third results in frequency tripling effects, and so on. Importantly, since only the time-averaged asymmetrically induced polarisation leads to second-order NLO effects, the molecule and crystal must be non-centrosymmetric, otherwise the effects will cancel one another. Third-order effects, however, may be observed in both centrosymmetric and non-centrosymmetric materials. 

It is not surprising therefore that the optical properties of small metal particles have received a considerable interest worldwide. Their large range of applications goes from surface sensitive spectroscopic analysis to catalysis and even photonics with microwave polarizers [9-15]. These developments have sparked a renewed interest in the optical characterization of metallic particle suspensions, often routinely carried out by transmission electron microscopy (TEM) and UV-visible photo-absorption spectroscopy. The recent observation of large SP enhancements of the non linear optical response from these particles, initially for third order processes and more recently for second order processes has also initiated a particular attention for non linear optical phenomena [16-18]. Furthermore, the paradox that second order processes should vanish at first order for perfectly spherical particles whereas experimentally large intensities were collected for supposedly near-spherical particle suspensions had to be resolved. It is the purpose of tire present review to describe the current picture on the problem. 

Furthermore, buckminsterfullerene shows quite interesting non-linear optical (NLO) properties which are important from the point of view of photonics applications. Third order NLO response and optical limiting have been reported for C o [30-34]. The role of intersystem crossing on the photophysics of C o and C70 has been investigated by photoexcitation spectro-copy [35-40]. 

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