Optical limiters nanocomposites

Understanding the mechanisms of the optical limiting effect in metal dendrimer nanocomposites may also require understanding the timescale of the effect. In general, for optical excitation close to the linear absorption band, such... 

Indeed, the timescale of the optical limiting effect in dendrimer nanocomposites is somewhat different than that found in other materials and this may be crucial to the understanding of the mechanism. Recent reports have investigated... 

Tlie usual experimental techniques developed to study the optical Kerr effect in materials have already been described in a preceding chapter of this book. We only mention here the methods which have especially been used for nanocomposite materials as colloidal solutions or thin films Degenerate four-wave mixing (DFWM) and optical phase conjugation, which provide the modulus of x only and may be completed by Interferometry techniques to get its phase as well, optical limiting, optical Kerr shutter, and z-scan, which is probably the most common technique used in recent years due to its ability to provide simultaneously the nonlinear refraction and absorption coefficients of the same sample point [118],... 

The case (3 > 0, opposite to the previous one, can stem in nanocomposite media from reverse saturation of absorption (RSA), multi-photon absorption, or nonlinear scattering. It is of course of high interest for optical limiting applications. 

Let us now examine the case of a nonlinear scattering process. Ispasoiu et al. deduced from considerations regarding the excited-state lifetime that the optical limiting observed using nanosecond laser pulses at X = 532 nm in their silver-dendrimer nanocomposite aqueous solution was due to absorption-induced nonlinear scattering [142]. They suggested that the scattering centres were micro-bubbles... 

Whatever the nonlinear process involved, the metal/dielectric nanocomposites have been often inquired into for their optical limiting (OL) properties [120, 123, 124, 140-150], owing to the important stake that such a functionality represents for civil and military applications in human eye or detector protection. Indeed, as for telecom applications, metal nanoparticles present the advantages of both intense and fast nonlinear response. 

Ispasoiu, R.G.. Balogh, L., Vamavski, O.P., Tomalia, D.A., Goodson, III, T. Large optical limiting from novel metal-dendrimer nanocomposite materials. J. Am. Chem. Soc. 122, 11005— 11006(2000)... 

Sun, N., Wang, Y., Song, Y., Guo, Z., Dai, L., Zhu, D. Novel [60]fullerene-silver nanocomposite with large optical limiting effect. Chem. Phys. Lett. 344, 277-282 (2001)... 

The OL efficiency of the fullerene-hybrid system can be enhanced, in principle, applying the bottleneck principle (Fig. 23-5) (Miles, 1994) to design a multilayer structure. The device optimizes the attenuation capabihty of a RSA optical limiter (Miles, 1994). To reach an efficient population of the excited state the laser fluence must be kept constant over the beam. The high flexibility of the FULP-hybrid nanocomposites allows to fabricate multilayer systems where the thickness of each layer can be easily adjusted, a multilayer system is formed, in fact, by FULP doped and undoped layers of controlled thickness (limocenzi, 1999). 

Tang and Xu [68] have prepared soluble MWNT-containing photoconductive poly(phenylacetylenes) (NTs/PPAs) by in situ polymerizations of phenylacetylene catalyzed by WClis-Ph4Sn and [Rh(nbd)Cl]2 (nbd = 2,5-norbornardiene) in the presence of the NTs. They demonstrated that the NTs in the composite solutions can be easily aligned by mechanical shear, and an efficient optical limiting property was observed in these nanocomposite materials. 

Polymer-embedded gold nanoparticles have been extensively studied [1]. Because of unique physical characteristics, gold-polymer nanocomposites are potentially useful for a number of advanced functional applications, especially in the optical and photonic fields. In particular, these materials can be used as light-stable color filters [2], polarizers [3, 4], ultra-low refractive index materials [5], nonlinear optical devices [6], optical sensors [7], and so on. However, still limited are the chemical routes that allow us to obtain monodispersed thiol-derivatized gold nanoparticles with controlled size to be embedded into poly-... 

Polymer clay nanocomposites are already used in many applications to enhance existing properties of a particular material, and development should be focused on the true multifunctional materials. Certainly, clay nanocomposites will continue to be used for enhanced mechanical, flammability, and gas barrier properties, but fundamental limits in clay chemistry prevent them from being used easily in applications requiring electrical/ thermal conductivity or optical properties. Similarly, combinations of... 

In this chapter, we present an overview of the development of novel soft, nanohybrid materials (e.g., nanocomposite gels [19, 21, 28-30] and soft polymer nanocomposites [31-33]) with unique organic-inorganic network structures that overcome the previous limitations and exhibit excellent optical and mechanical properties in addition to outstanding new characteristics. 

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