Third harmonic generation applications

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. 

Optical processing systems are proposed based on relative intensity changes of second harmonic generation in sorbate complexes of p-nitroaniline and 2-methyl-p-nitroaniline in molecular sieve hosts [98]. Optical data storage would be one of a variety of potential electro-optical applications. In addition, molecular optical effects by third harmonic generation are suggested for optical data storage based on the possible formation of bistabilities for the local fields [65,99]. 

These acceptor substitution effects on the nonlinear response of carotenoid have been studied extensively. Experimental investigations reveal that the substitution resulted in third-harmonic generation values up to 35 times higher than in /1-carotene which corresponds to N(ll) molecule. Subsequent CI/SOS quantum-chemical calculations rationalized the origin of this enhancement and assessed the applicability of simple models to describe the evolution of the molecular polarizabilities. In particular, this study shows a steplike increase of the longitudinal component of the dipole moment with the applied external field, caused by charge-transfer toward the acceptor end leading to an enhanced nonlinear response. 

Finally, fhe application of higher order nonlinear optical processes such as third-harmonic generation (Berkovic 1995 Tsang 1995) or fourth-harmonic generation (Lee et al. 1997) could provide even more detailed interface information. For example, in the case of fourth-harmonic generation the induced polarization is given by Pj 4u>) = j k,l,m,nx]tL Ek u>)Ei co)Em u>)E io), i.e., the hyperpolarizability is a tensor of rank 5. Hence if is possible fo resolve up to five-fold surface symmetries. However, the absolute values are... 

The solution of PDD/dichloroethane was spread over the quartz substrate and then a high quality film could be obtained. Though the as prepared film was opaque, it turned to be colored but transparent by annealing at 150 C for 48 hrs, which indicates the formation of 1-D tt-conjugated system. From the IR spectra of this film the formation of C=C bonds can be confirmed. The film was applicable for the third harmonic generation (THG) measurement. Under the UV irradiation, however, the PDD film becomes dark purple in color and less applicable for THG measurement. The film of PDEDBB was eilso obtained by a spin coating technique. X-ray diffraction pattern indicates that PDEDBB film is completely amorphous, though PDEDBB powders show some indication of crystalline diffraction. 

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