THG measurements

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] ... 

Third-order optical nonlinearity of the oriented MOPPV LB film was evaluated by the THG measurement [30]. The detailed procedure is described in the section 2.1. 

Some simple organometallics have been studied. Poly(silanes) and germanes exhibit very interesting behavior, since they are photochromic and appear to possess excitonic, charge delocalized excited states involving the sigma electrons of the organometallic backbone. 112) THG measured susceptibilities of up to 1 x... 

THG measurements on poly- -butylCOT films, referenced to a bare fused silica plate, were made using 1064 nm pulses. These measurements showed that the l/(3)l values of films of poly-rt-butylCOT, lxl0 10 esu, were comparable to that for unoriented polyacetylene at the same wavelength (39). However, comparison of the linear transmission spectra of these materials in the near infrared shows that the partially substituted polyacetylene has greatly improved optical quality. (See Figure 7.)... 

A powder THG measurement revealed that the DEANST crystal has a third-order... 

THG measurements can be either performed in solution or thin films. For thin films larger sample quantities are necessary (>50 mg) than for measurements in solution (1 mg), which can be of central importance for novel materials. With thin films, the THG experiments can be performed with the harmonic frequency in the absorption band and the phase of the second-order hyperpolarizability can be retrieved (see e.g. Refs.[28-30]). 

Fig. 4. Measurement sequence of third-harmonic generation in solution. A THG experiment of fused silica in vacuum yields the calibration of the whole setup. The same fused silica plate measured in air leads to the air contribution, which is afterwards taken into account in the THG measurements of the various sample concentrations...

THG measurements are performed for different concentrations. From the third-order susceptibilities y of the solution series the second-order hyperpolarizabilities y of the molecules are determined by analyzing the data points with... 

The procedure for the THG measurements of thin films needs less steps. As the thin films can be directly measured in vacuum, the calibration of the air contribution is not required. Furthermore, the film substrate is usually fused silica that makes also the initial calibration of the THG setup with a fused silica plate superfluous. However, the film thickness and its refractive index have to be determined prior to the THG analysis. 

Table 2. THG measurements of the second-order hyperpolarizabilities y(-3co, co, co, co) for substituted monomers and dimers of PTA at a fundamental wavelength of A =1907 nm. e is the extinction coefficient at the harmonic wavelength of the THG experiment (reference X = 1.6xl0 22 m2/V2,10% experimental error)...

More difficult is the THG measurement (Fig. 11.34), which usually requires a way to generate an infrared primary beam from the Nd YAG source, since a near-IR Nd YAG source (A = 1064 nm), if frequency-tripled, yields A/3 354.7... 

THG measurements on cis- and rrani-polyacetylene were carried out over the pump frequency range from 0.55 eV though 1.25 eV [224,225]. The results show that x X3w (o,(o,a)) for rra i-polyacetylene is an order of magnitude larger than that for the cw-isomer over the entire spectral range, even comparing the respective 3o) resonance maxima. The results are summarized in Fig. VE-2 the solid points represent trans- CH and the open circles represent c/s -(CH),. The... 

Figure VE-2 x (3i<>) results obtained from THG measurements on cis - (open circles) and trans-(CH), (solid points) the solid curve represents the fit to Eq. (1) with Eg (cis) = 2.09 eV and Eg(trans) = 1.72 eV. The dashed and dot-dashed curves represent pure cis-(CH), and trans-(CH), respectively. (Taken from ref. 224)...

In practice, THG measurements are complicated by the fact that all materials show third-order nonlinear effects (unlike second-order nonlinear effects which require non-centrosymmetry). This means that the surroundings of the sample (including air) will contribute to Different ways of minimizing the contributions of the air and film support materials have been proposed [59-62],... 

Figure 1 shows a compendium of THg measurements for both constructed and real crude oils on a (natural) log scale for clarity of trend in time dependence. Real, as opposed to elemental mercury spiked crude oils, decay to a seemingly constant value that is thought to represent the non-volatile fraction. The elemental mercury-spiked dodecane decreased in mercury concentration from approximately 170 ppb originally to approximately 7 ppb after numerous bottle openings for various purposes. 

For THG measurements, pulsed laser systems operating at infrared wavelengths (typically 1064, 1850, 1907 or 2100 nm) are used. Most commonly, is ob-... 

Table 3.5 presents a selection of values of various conjugated polymers, determined by THG measurements, while Table 3.6 shows values of some full-ladder and semi-ladder polymers, determined by means of the DFWM technique. 

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]. 

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