Lasers nonlinear optical properties

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Keywords. Core-shell structure. Cone structure. Laser emission. Nonlinear optical property... 

Third-order nonlinear optical properties of CdTe QDs were examined by Z-scan and FWM experiments in the nonresonant wavelength region. We found that the two-photon absorption cross section, a, is as high as 10 GM, although this value decreases with decreasing size. In addition, the nonlinear response is comparable to the pulse width of a fs laser and the figures of merit (FOM = Re Xqd/ Xqd)... 

The nonlinear optical properties of the films were subsequently investigated using second-harmonic generation. A Q-switched Nd YAG laser (A = 1064 nm) with a pulse width of 8 ns and a pulse... 

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. 

Nonlinear optical properties arise when materials are subjected to electromagnetic radiation of very high intensity (usually from lasers). Low-intensity electromagnetic fields give a linear response for the induced dipole moment vector in a molecule ... 

Spiropyrans show promise for optical recording, three-dimensional optical memories,214 and holography.215 The dyes currently under study for these applications very probably will not be used merely dissolved in a bulk polymer matrix, but will be oriented in films and membranes, or adsorbed or vapor deposited on solid substrates to take advantage of the nonlinear optical properties of the colored forms. For example, thick (0.5 mm) PMMA films of 6-nitro-thiaBIPS can be used to record wavelength-multiplexed volume holograms with an infrared diode laser. This system is impractical at present because of fatigue and poor diffraction efficiencies.216... 

Several papers and patents deal with the preparation of pyrrole-, indole-, and carbazole-derived dyes for application in organic laser device production, coloring of textiles and other materials, photography, analytical chemistry and physiological and organ function monitoring. Sulfonyl-substituted 2-[4-(dialkylamino)phenyliminomethyl]pyrrole dyes have been prepared, for example, 50-53, and their ultraviolet-visible (UV-Vis) absorptions, second-order nonlinear optical properties, and thermal stabilities have been described <1999TL2157>. 

Main group oxides with three-dimensional stmctures or transition metal oxides with d° or d ° configurations are wideband gap materials and are colorless when pure. As such they may serve as transparent optical materials or hosts for such applications as lasers or luminescent materials when properly doped. Others that lack a center of symmetry may have ferroelectric or ferroic properties that make them useful for a variety of device applications. Some of these may have nonlinear optical properties so important to modem communication networks (see Sections 6.3 and 6.5 and see Luminescence and see Ferroelectricity). 

The extensive jt-delocalized system of metal-dithiolene complexes is also responsible for the nonlinear optical properties (NLO) which have been recently reviewed . The interaction of radiation with the matter induces an instantaneous displacement (polarization Pq = /X = aE, where a is the linear polarizability) of the electronic density away from the nucleus at small field (linear optics). At high fields (laser light) the polarizability of the molecule can be driven beyond the linear regime and a nonlinear polarization is induced (NLO) = aE + fiE" + y E + and for the bulk material... 

Both TCSPC and frequency-domain fluorimetry are limited in time resolution by the response of available detectors, typically >25 ps. For cases in which higher time resolution is needed, fluorescence up-conversion can be used (22). This technique uses short laser pulses (usually sub-picosecond) both to excite the sample and to resolve the fluorescence decay. Fluorescence collected from the sample is directed through a material with nonlinear optical properties. A portion of the laser pulse is used to gate the fluorescence by sum frequency generation. The fluorescence is up-converted to the sum frequency only when the gate pulse is present in the nonlinear material. The up-converted signal is detected. The resolution of the experiment therefore depends only on the laser pulse widths and not on the response time of the detectors. As a result, fluorescence can be resolved on the 100-fs time scale. For a recent application of fluorescence up-conversion to proteins, see Reference 23. 

Garito, A.F. Singer, K.D. Laser Foe Nonlinear Optical Properties olymeric Materials" Williams, D., E(f. Plenum... 

As the local electric field in the particles is enhanced at the SPR, the metal nonlinear optical response can be amplified as compared to the bulk solid one. Moreover, the intrinsic nonlinear properties of metals may themselves be modified by effects linked with electronic confinement. These interesting features have led an increasing number of people to devote their research to the study of nonlinear optical properties of nanocomposite media for about two decades. Tire third-order nonlinear response known as optical Kerr effect have been particularly investigated, both theoretically and experimentally. It results in the linear variation of both the refraction index and the absorption coefficient as a function of light intensity. These effects are usually measured by techniques employing pulsed lasers. 

Yang, G., Wang, W.-T., Yang. G.-Z., Chen, Z.-H. Enhanced nonlinear optical properties of laser deposited Ag/BaTiO3 nanocomposite films. Chin. Phys. Lett. 20, 924-927 (2003)... 

The problem of designing new polymer-based composite materials containing metal nanoparticles (MNPs) is of current interest, particularly in the fabrication of magnetooptic data storages, picosecond optical switches, directional connectors, and so on. The nonlinear optical properties of these composites stem from the dependence of their refractive index on incident light intensity. This effect is associated with MNPs, which exhibit a high nonlinear susceptibility of the third order when exposed to ultrashort (picosecond or femtosecond) laser pulses [1]. 

When a high-intensity laser beam impinges on material, its electromagnetic field induces electrical polarization that gives rise to a variety of nonlinear optical properties, because in this case the higher terms in Eq. (3-4) are not negligible. The determination of the coefficients and that serve to characterize the nonlinear properties is complicated by the fact that they are composed of many elements. With a being equal to two and three, and are composed of 3 = 27 and 81 elements, respectively. Fortunately, these tensors possess symmetry properties that can be invoked to reduce the number of independent elements, for instance, when the optical frequencies involved in the nonhnear interaction are far away from resonance (absorption) [15]. 

Azobenzene-containing polymers are reported in the literature at a rate of about 150 papers/year for the last five years. There are two main directions of interest the first relates to the donor-acceptor substituted azobenzenes as the structure generating second-order polarizability and - by noncentrosymmetrical alignment - second order nonlinear optical properties in poled films. The second direction of interest is related to the photoinduced isomerization between the trans (more stable) and cis configurations of the azobenzene. This photoisomerization has a wealth of unexpected and useful consequences which were noted only in the last decade. Both these directions appeared because of the availability of lasers, which on the one hand allowed the observation of the nonlinear optical properties and on the other hand... 

Doping PZT with lanthanum ions (La replaces Pb ) shifts the morphotropic boundary to higher x-values and lowers the Curie temperature of the oxidic alloy. At 5% La, the Curie temperature can even drop below room temperature if X is high enough. The solid has become cubic and paraelectric and no longer has a permanent electric dipole moment at room temperature but is very polarizable. This material is called PLZT (short for lead lanthanum zirconate titanate) and is used for its nonlinear optical properties, e.g., in doubling the frequency of laser radiation. 

Due to their miscellaneous photophysical and photochemical properties, stilbene compounds can be used for many applications in materials science. Data on the photochemistry of stilbenoid compounds and their role in materials science were reviewed [1-3]. In this chapter, we briefly discuss materials for lasers, nonlinear optical systems, photoconductive materials, and imaging and switching techniques. 

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