Third degenerate four-wave mixing

Table 1 Coefficients for 7[ (a ) for third harmonic generation (THG), degenerate four wave mixing (DFWM), electric field induced second harmonic generation (ESHG), and Kerr effect in methane at the experimental geometry rcH = 2.052 a.u. A CCSD wavefunction and the t-aug-cc-pVDZ basis were used. (Results given in atomic units, the number in parentheses indicate powers of ten.)...

Absorption spectroscopy, quartz crystal microbalance and electrical measurements and femtosecond degenerate four-wave mixing studies of third-order optical non-linearity... 

TEM and absorption spectrophotometry a large third order non-linearity was observed by degenerate four-wave mixing... 

Time resolved femtosecond degenerate four-wave mixing is based on the response of the third order polarisability. With a femtosecond pulse rotational levels are coherently prepared by a... 

The third-harmonic generation method has the advantage that it probes purely electronic nonlinearity. Therefore, orientational and thermal effects as well as other dynamic nonlinearities derived from excitations under resonance condition are eliminated (7). The THG method, however, does not provide any information on the time-response of optical nonlinearity. Another disadvantage of the method is that one has to consider resonances at oj, 2w and 3o> as opposed to degenerate four wave mixing discussed below which utilizes the intensity dependence of refractive index and where only resonances at a) and 2a) manifest. 

Third-Order NLO Techniques. There is a wider range of third-order techniques commonly used to characterize materials, including electric field induced second harmonic generation (EFISH) (15, 16), third harmonic generation (THG) (17) and degenerate four wave mixing (DFWM) (18). EFISH and DFWM will be discussed briefly then... 

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. 

In a recent communication we reported that the third order nonlinear optical susceptibility of Pt, Pb, and H2 tetrakis(cumylphenoxy)phthalocyanines was large and varied substantially with the metal substituent. (1) The structure of these compounds is shown in Fig. 1. The susceptibility was measured by degenerate four-wave mixing at 1.064 pm, a wavelength far from the main absorption bands of phthalocyanines near 650 nm. The nonlinear susceptibility of the Pt phthalocyanine was about a factor of 9 larger than that of the Pb phthalocyanine and a factor of 45 larger than the metal free compound. 

The third order optical susceptibility was measured by degenerate four-wave mixing (DFWM). A single pulse at 1.064 pm with a full width at half maximum of 35 ps was selected from the output of a passively mode locked Nd/YAG laser and split into three... 

Poly(3-alkyl-a-thiophene) systems show significant third-order nonlinear susceptibilities ( ) Though, oligothiophenes have been studied for their third-order susceptibilities, accurate third-order optical nonlinearity data obtained by degenerate four-wave mixing or electric-field-induced second harmonic generation (EFISH) are difficult to attain reliably on samples with poor solubility characteristics (92MM1901). 

In the degenerate four wave mixing (DFWM) experiment the third-order susceptibility 3)(-tt>,tt>,-CL>,CL>) with degenerate frequencies can be determined [22]. This nonlinear susceptibility is directly proportional to the nonlinear refractive index n2, which is used to describe optically induced refractive index changes. An advantage of this technique is the possibility to record the temporal shape of the third-order nonlinear optical signal. 

Most experiments can measure either x(3)( 3co third harmonic generation) or (—to co, -co, co) (degenerate four-wave mixing). 

Table 9.3 Third harmonic generation (THG) and degenerate four wave mixing (DFWM) non-linear optical coefficients of conjugated polymers.

Degenerate four-wave mixing (DFWM) Degenerate four-wave mixing (DFWM) is another well-known nonlinear technique based on third-order nonlinear susceptibility similar to CARS... 

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