Third harmonic generation films

Third-order susceptibilities of the PAV cast films were evaluated with the third-harmonic generation (THG) measurement [31,32]. The THG measurement was carried out at fundamental wavelength of 1064 nm and between 1500 nm and 2100 nm using difference-frequency generation combined with a Q-switched Nd YAG laser and a tunable dye laser. From the ratio of third-harmonic intensities I3m from the PAV films and a fused quartz plate ( 1 thick) as a standard, the value of x(3) was estimated according to the following equation derived by Kajzar et al. [33] ... 

In addition to the blueshifling of the optical absorbance of Q-state semiconductor particles, a linear optical effect, there are nonlinear optical effects demonstrated by Q-state semiconductors. Two types have been observed by MCs prepared in organized films. One is the third harmonic generation or frequency tripling (44). A... 

To date, results have only been acquired for the ethoxy-substituted poly(ester) with a pentamethylene spacer. A 2.5 pm film produced a third-harmonic signal at 632.8 nm 29 times the intensity of a quartz signal, corresponding to a of approximately 8 x 10 13 esu. Degenerate four-wave mixing experiments are underway on this and other materials, and preliminary results are comparable to the values from third harmonic generation. 

Churikov, V. M., and Hsu, C. C. (2000). Optical control of third harmonic generation in azo-doped polymethylmethacrylate thin films. Appl. Phys. Lett. 77, 2095-2097. 

Nonlinear optical properties have recently been observed for the polysilane (PhMeSi) 132, suggesting that polysilanes may eventually find use in optical technology. Irradiation of a thin film of the polysilane at 1064 nm gave rise to efficient third-harmonic generation, while irradiation at 1907 cm-1 produced no nonlinear signal. The third-harmonic resonance is believed to be due to a three-photon process, but its origin is uncertain. Farther research will undoubtedly be carried out on this new phenomenon. 

The experiments on second- and third-harmonic generation in the reflection geometry demonstrate a giant enhancement of nonlinearities of the bireffingent PS films. The effect cannot be explained in terms of effective medium approximation and is apparently related to strong local fields in nanostructured solids (Fig. 3). 

R.D. Schaffer, P.T. Snee, J.C. Johnson, L.F. Lee, K.R. Wilson, L.H. Haber, R.J. SaykaUy, T.Q. Nguyen, and B.J. Schwartz, Nanoscopic interchain aggregate domain formation in conjugated polymer films studied by third harmonic generation near-field scanning optical microscopy. J. Chem. Phys., 117, 6688 (2002). 

The optical absorption maxima are revealed to be at 520, 500 and 420 nm for PTV, MOPPV and PPV films, respectively. X-ray diffraction patterns indicate that the PAV films have low crystallinity. The values of these PAV films evaluated by third-harmonic generation (THG) measurement at 1.85 pm are found to be 5.85 x 10 " esu, 3.2 X 10 esu, and 7.8 x 10 esu for PTV, MOPPV and PPV films, respectively. These values are non resonant values and are almost the same as that reported for a processible polydiacetylene (n-butoxycarbonylmethyl urethane) (n-BCMU-PDA, n = 4,3) thin film [18]. 

The existence of the 2 Ag state below the PBu state in polyacetylene thin films was suggested by a number of experiments. Third harmonic generation (THG) and two-photon absorption by Halvorson and Heeger (1993) indicates that a Ag state lies below 1.1 eV in energy, while hnear absorption, which locates the state, typically rises at 1.8 eV and peaks at 2.0 eV (Vardeny 1993), as illustrated in Fig. 10.1. Peaks at 0.6 and 0.89 eV were observed in the THG spectrum by Farm et al. (1989). From the discussion of THG in Chapter 8, we know that this data implies some combination of Ag states at twice the photon energy (namely 1.2 and 1.8 eV), and states at three times the photon energy (namely 1.8 and 2.7 eV). Fann et al. interpreted the experiments as indicating the Ag and states virtually coincident at 1.8 eV. 

The NLO properties in the above-mentioned Pis are attributed to the NLO chromophores which are molecularly dispersed in or covalently bonded to thermally stable PI chains. Aromatic polyisoimides (Pil), isomers of PI, have conjugated structure along their main chains, and hence are supposed to show intrinsic third-order NLO properties. The third-order non-linear susceptibility, of several Pil films was estimated to be in the order of esu by third harmonic generation measurements (Table 13) with... 

Polydiacetylenes are known to possess large nonlinear susceptibilities which were measured in cristals (1), in solutions (2) and in thin films by third harmonic generation (3) No second harmonic generation is observed owing to the centrosyrametric character of the polymeric chain When an external DC-field E is applied the symmetry is broken and this allows the second harmonic generation to be observed Its intensity is proportional to... 

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