Nonlinear optical susceptibilities crystals

Let us consider the crystal growth of the three previous compounds which have retained our attention by their high nonlinear optical susceptibilities (POM, MAP, NPP) plus an additional one R(+)N-methylidene (gem-carbethoxiphenyl) amide of 4-N-dime-thylamino- benzylidene cyanacetlc acid -AMA, of potential interest but not yet investigated from the optical point of view. We look successively into their synthesis, purification, crystal growth and characterization. 

The basic structural units responsible for the second order nonlinear optical susceptibility in most oxide crystals are the acentric anionic groups. (4,6) The... 

Selected References Employing Crystal Orbital Methods to Evaluate the Nonlinear Optical Susceptibilities of Infinite Periodic Polymers... 

The temporal response of the third-order nonlinear optical susceptibility in poly(PTS) crystal was determined by time-resolved degenerate four-wave mixing (DFWM) by Carter and coworkers. The excited lifetime T ws measured to be 1.8 0.5 ps at 652 nm in the resonant region. The values of phase relxation time T2 measures by Hattori and Kobayashi for a cast film of poly(3BCMU) were 30 and 90 fs for the respective incident... 

Organic compounds with delocalized jr-electron systems, e,g., jr-conjugated polymers, are considered to be candidates for third-order nonlinear optical materials. Among them, polydiacetylenes (PDAs) are an important class of conjugated polymers that has attracted investigators from many different fields (7,2). PDAs, which can be obtained as single crystals by topochemical solid-state polymerization (5), have been extensively studied since 1976 (4). PDAs show large third-order nonlinear optical susceptibilities (5) and ultrafast optical... 

Chiral smectic ferroelectric liquid crystals are liquids that possess spontaneous polar order. Combined with their excellent processibility on silicon integrated circuits, these liquid crystals provide an attractive potential approach to synthesis of materials for second order nonlinear optics, provided adequate second order susceptibility can be obtained. Unfortunately, the second-order nonlinear optical susceptibility of the ferroelectric liquid crystals are usually low and their thermal stability is limited. Several, very interesting approaches to utilization of liquid crystals, however, were carried out. 

Theoretical studies on the nonlinear optical susceptibilities of 3-methoxy-4-hydroxy-benzaldehyde crystal ... 

Optical field-induced director reorientation is responsible for the largest nonlinear optical susceptibility observed in liquid crystals, the largest in any known material. Although the process is slow, the nonlinearity is about 10 times greater than that of CS2. Because of its magnitude, the orientational nonlinearity of liquid crystals has been termed giant optical nonlinearity (GON). 

D. M. Walha. M. a Roe, N. A. dark. R. Shao. K. M. Johnson. M. O. Robinson. J. Y. Un. and D. Doroski. An approach to the design of ferroelectric liquid crystals with large second order electronic nonlinear optical susceptibility. MoL Cryst Liq. CrysL J98 51 (1991). 

Table 7 Experimental second-order nonlinear optical susceptibilities dn of organic crystals...

The nonlinear optical susceptibilities can be calculated, in principle, on the basis of the density matrix formalism. However, one can often draw some conclusions about the nonlinear optical output from symmetry considerations. The nonlinear susceptibility tensors reflect the structural symmetry of the crystal since they are determined by its electronic or vibrational states. 

Levine, B.F. (1973) Bond-charge calculation of nonlinear optical susceptibilities for various crystal structures. Physical Review B Condensed Matter, 7, 2600. 

These examples involve pendant groups that interact with each other. There are, of course, several examples of polymers containing pendant chromophores, particularly as liquid crystal mesogens, that have been investigated as nonlinear optical matoials. In these materials, the electronic interaction between chromophores does not generally contribute to the material s nonlinear optical susceptibility. ... 

Seidler, T., Stadnicka, K., and Champagne, B. (2014) Second-order nonlinear optical susceptibilities and refractive indices of organic crystals from a multiscale numerical simulation approach. Adv. Opt Mater.,... 

The first and third order terms in odd powers of the applied electric field are present for all materials. In the second order term, a polarization is induced proportional to the square of the applied electric field, and the. nonlinear second order optical susceptibility must, therefore, vanish in crystals that possess a center of symmetry. In addition to the noncentrosymmetric structure, efficient second harmonic generation requires crystals to possess propagation directions where the crystal birefringence cancels the natural dispersion leading to phase matching. 

One result of studying nonlinear optical phenomena is, for instance, the determination of this susceptibility tensor, which supplies information about the anharmonicity of the potential between atoms in a crystal lattice. A simple electrodynamic model which relates the anharmonic motion of the bond charge to the higher-order nonlinear susceptibilities has been proposed by Levine The application of his theory to calculations of the nonlinearities in a-quarz yields excellent agreement with experimental data. 

The use of femtosecond pulses in nonlinear optics has one obvious advantage high peak power, necessary to observe the nonlinear effect, can be obtained from low total power in the pulse. This made samples with a low damage threshold amenable for HRS measurements. One example of such sample is amorphous polymer films. These films do not have the optical quality of single crystals. They are more susceptible to optical damage. With the femtosecond pulses, we have been able to perform HRS measurements on solid thin films, to study the orientational correlation between nonlinear optical chromophores in the film.10 13... 

The model embodied in Equations (6) and (7) can be used to evaluate the potential of doped poled polymer films in nonlinear optics. Using reasonable values for the parameters of the model and molecules with large values of / 333M3 susceptibilities comparable to those measured in crystals can be realized (See Table 2). 

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