Nonlinear organic materials

Table I lists a variety of organic nonlinear materials which have appeared in the literature their relative powder efficiencies, absorption cutoffs and /3 values (if available) are also provided. These materials are "typical" only in that they represent results from the few classes of organic compounds investigated to date, yet they are instructive in that one learns which molecular properties may be important. A few caveats are in order to avoid misinterpretation of the data in Table I. Except for compound 10 (19) all the powder efficiency and cutoff data are from our own measurements. Powder measurements were performed on ungraded samples using the Nd YAG output at 1.06/t as fundamental since powder efficiency is a function of particle size distribution and a variety of other factors (3) these values are only semiquantitative. The cutoff values are the wavelengths for which 10-4M solutions in ethanol (unless otherwise indicated) have no absorbance. The cutoff values will be similar to those found in crystal state except where intermolecular charge transfer is important in the crystal or the molecule is solvatochromic, this latter effect being quite common for cyanine dyes such as...

Nonlinear optical organic materials such as porphyrins, dyes, and phthalocyanines provide optical limiting properties for photonic devices to control light frequency and intensity in a predictable manner. The optical limit of CNTs composites is saturated at CNTs exceeding 3.8wt% relative to the polymer mass (Chen et al., 2002). Polymer/ CNT composites could also be used to protect human eyes, for example, optical elements, optical sensors, and optical switching (Cao et al., 2002). 

We have recently conducted a set of intracavity second harmonic generation experiments using the organic nonlinear material DAN (4-(N,N-dimethylamino)-3-acetamidonitrobenzcne) and an optically pumped cw Nd YAG laser (2). Figure 3 shows the experimental setup. Quasi-cw operation was achieved with crystal samples immersed in index matching fluid in an antireflection coated cuvette that was placed internal to the Nd YAG laser cavity. 

The organic NLO materials reported here have good processabilities, so they have an advantage for developing new nonlinear optical organic devices. 

LeBozec and co-workers have reported nonlinear behavior in a series ofterpyri-dyl and dipicolinic acid complexes, with further studies on these complexes by Maury and co-workers [83, 84]. Their research was on new molecular materials for optoelectronics, with studies based on octupolar nonlinear optical molecules showing that molecular quadratic hyperpolarizability values were strongly influenced by the symmetry of the complexes [85]. Other studies on organic-lanthanide complexes with nonlinear optics have also reported second- and third-harmonic generation behavior with simultaneous multiphoton absorption properties [50]. Such studies have shown the importance of coordination chemistry as a versatile tool in the design of nonlinear materials. 

The device performance of any application in the real world has to be guaranteed for a certain time without or only minor degradation. Some 10,000 hours of operation at temperatures up to 80 °C under illumination are required. Research about the lifetime of organic nonlinear optical material has only started in the past years as the chances for applications based on the second-order susceptibilities x have improved. Nevertheless, only little is known about the longtime effects in nonlinear materials under real world conditions. 

Bosshard C, Bosch M, Liakatas I, Jager M, Gunter P (2000) Second-order nonlinear optical organic materials recent developments. In Gunter P (ed) Nonlinear Optical Effects and Materials. Springer Verlag, p. 163... 

Introduction of the diazoarylamino groups into position 2 of 6-nitrobenzothiazoles leads to the thermal stability of nonlinear optical organic materials on the base nitrobenzazoles [577],... 

Recently, the investigations of nitrobenzisoxazoles mainly 6-nitrobenzisoxazole-3-carboxilate ions have received considerable interest due to their participation in reverse micellar systems [679-682], Reverse micelles are of considerable interest as reaction media because they are powerful models for biological compartmental-ization, enzymatic catalysis, and separation of biomolecules. Solutions of ionic surfactants in apolar media may contain reverse micelles, but they may also contain ion pairs or small clusters with water of hydration [679], Molecular design of nonlinear optical organic materials based on 6-nitrobenzoxazole chromophores has been developed [451],... 

Tabei, H. Kurihara, T. and Kaino, T. (1987). Recrystallization solvent effects on second-order nonlinear optical organic materials. Appl Phys. Lett., 50, 1855-7. [213]... 

The increasing interest in obtaining efficient organic optically nonlinear materials resulted in a combinational chemistry approach to their synthesis. The structures of several nitroaniline derivatives (including five Schiff bases), the compounds which belong to a chemical class having potential application as nonlinear optical materials, have been reported4,5. 

In the early days, optical nonlinearity of organic materials was measured usually with powder samples, mainly because it is very difficult to isolate organic compounds in the form of molecular crystals. In the case of centrosymmetric crystal lattices, macroscopic second-order nonlinear optical characteristics are not detected. Molecular crystals are organized assemblies of individual molecules held together by intermolecular forces. Their macroscopic nonlinear optical constants are estimated as the sum of the molecular polarizability of individual molecules. Thus, neglecting intermolecular interactions in the crystal, the nonlinear optical constant, dtlK, is expressed by... 

For devices the important classes of nonlinear materials are (i) molecular and polymeric materials, (ii) multiple quantum well semi-conductors, (hi) bulk semiconductors and (iv) semiconductor doped glasses. Of these classes, organic polymeric structures have shown the largest non-resonant x - Important nonlinearities observed in inorganic semiconductor materials are in a narrow wavelength region determined by excitonic resonances. Therefore, these nonlinearities are resonant, slower in response and produce thermal effects. 

The nonlinear material is critical to the operation of a limiter. Several different nonlinear effects can be used in the nonlinear element to provide a limiting function. Nonlinear absorption, where the material absorbance increases with the intensity of the incident light, is the most useful mechanism to remove light from the transmitted beam. A large number of organic and organometallic materials have been reported to exhibit an intensity dependent increase in absorption, sometimes called a reverse saturable absorption. The most effective are phthalocyanines (2, 3,4, 5) and porphyrins. (6,7)... 

Because of their large optical nonlinearities and good mechanical, chemical, thermal, and optical stability, organic nonlinear materials are among the leading practical materials for device applications [2]. A number of experimental techniques have been proposed to obtain information about the dispersion, the sign, and the contributions of both the real and imaginary parts of the nonlinear optical response. In this chapter, we will explore the methods most widely used to characterize the third-order nonlinear coefficient and introduce some of the more recent results. 

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