Third harmonic generation
Thin single crystal
Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Nonlinear optical susceptibility χ(3) of polydiacetylenes has been evaluated by third harmonic generation. First, in order to obtain the χ(3) tensor component along the polymer main chain, thin single crystals of two representative polydiacetylenes, poly-PTS and poly-DCHD were made by utilization of sampling technique in microscopy, i.e., the microtome cutting of single crystal embedded in plastic resin. The THG intensity observed was proportional to cos8θ, where θ was the angle between the polymer main chain and the polarization of laser light. The χ(3) value of poly-DCHD was found to be rather higher than that of poly-PTS. At resonant wavelength of 1.97 μm, the χ(3) of poly-DCHD attained 8 x 10-10 esu. Furthermore, it was confirmed that when geometrical correction were properly made, the χ(3) obtained from polycrystalline thin film of poly-PTS agreed well with that from thin single crystals. Secondary, regarding poly-diphenyldiacetylene derivatives, it was found that the π-conjugation between the polymer main chain and aromatic substituents was effective on the improvement of χ(3) values. The χ(3) magnitudes of poly-BTFP and poly-DFMP reflect well the dihedral angles between polymer main chain and the phenyl substituents (58° for poly-BTFP and 67° for poly-DFMP) as a measure of π-conjugation. Especially, at nonresonant region of 2.1 μm the χ(3) of poly-BTFP is about 5 times greater than that of poly-PTS.
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