Degenerated four-wave mixing

Joo T and Albrecht A C 1993 Electronic dephasing studies of molecules in solution at room temperature by femtosecond degenerate four wave mixing Chem. Phys. 176 233—47... 

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.)...

In a separate study, the cross section of diphenylbutadiene in chloroform has been measured at 532 nm by two different methods and reported to be 40 8GM by degenerate four-wave mixing, and 34 12GM by nonlinear transmission [66]. It should be pointed out that both results were obtained using ns excitation pulses, but that the cross sections obtained by the two methods are comparable one to the other and on the same order of the cross sections listed earher (although those were obtained in a different wavelength range). 

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... 

The structure of carboxylic acid dimers results by time-resolved femtosecond degenerate four-wave mixing spectroscopy... 

Fig. 2. RCS of cyclohexylbenzene. Experimental data a) from pump-probe photoionization in a molecular beam (T 10 K) [2], b) from time-resolved degenerate four-wave mixing in a gas cell (T 305 K).

RCS OF THE GROUND STATE TIME-RESOLVED DEGENERATE FOUR-WAVE MIXING... 

Femtosecond degenerate four-wave mixing of cycloalkanes... 

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... 

Fig. 1. Degenerate four-wave mixing transient of cyclopropane (left) and cyclobutane (right). The upper traces in the insets are simulations. The recurrences in cyclobutane are very weak compared to the coherence peak at time zero.

Fig. 2. Geometry of degenerate four-wave mixing (BOXCARS geometry) for short-pulse, time-resolved measurements of the nonlinear response. Beams 1, 2, and 3 are derived from a single laser beam by the use of beam splitters and the beam paths are adjusted for the pulses to arrive simultaneously at the sample. By delaying one of the beams with respect to the others, the time-resolved measurements can be performed.

Degenerate four-wave mixing has been widely used for the study of organometallics. At present, it forms a complementary technique to the technically less difficult Z-scan, in that is can be used to verify that the origin of the observed nonlinearity is electronic in nature. 

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... 

---