Four-wave mixing geometry

FIGURE 1 (a) Four-wave mixing geometry. Kl, K2, and K3 are input beams K4 is the FWM output beam, (b) Beam positions at aperture. 

The first optically induced orientation of chromophores in a grafted DR 1-doped PMMA polymer has been observed in a four-wave mixing geometry (see Fig. 3.8) with two picosecond pump beams at 1,064 nm and a probe beam at double frequency. The observed signal at 532 nm rose slowly with time up to a saturation value, and was observed also after switching off the probe beam. 

Fig. 3.8 Four wave mixing geometry. Pump beams Ii and I2 are at 00 while probe I3 and signal I4 beams at 2 to...

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.)...

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.

Fig. 15. a Geometry for four-wave mixing experiments, b Geometry for two-beam coupling experiments... 

Early theoretical work on FAD was concerned with the dimer equilibrium geometry and the electronic structure (see for example Refs. [32-36]). Ah initio molecular orbital studies on the structure of formic acid dimer in 1984 agreed very well with the experimental structures as determined by electron diffraction [37]. Due to the importance of the double proton transfer of FAD as a key prototype for multiple proton transfer reactions several theoretical studies have been reviewed in the literature [38]. Rotational constants for formic acid dimer were obtained by high resolution spectroscopy of (DCOOH)2 [39] and by femtosecond degenerate four wave mixing experiments in the gas cell at room temperature and under supersonic jet experiments by Matylisky et al. [40]. 

Figure 2. Geometry for the four-wave mixing and two-beam coupling experiments.

FIGURE 49.7. Schematics of experimental arrangement of the degenerate four-wave mixing (backward geometry) experiment. 

Non-deqenerate four-wave mixing considered in the previous section can be extended to hiqher-order processes. These hiqher-order multiwave mixing processes open the way to novel methods for performing PC with frequency multiplication Cl8]. Consider the geometry of Fiq. 5b. in which the nonlinear... 

The forward folded boxcar four-wave mixing technique is illustrated in Fig. la and lb. Three pulsed laser beams are directed, through variable delay lines, toward the sample. Two time-coincident short excitation pulses and a third delayed probe beam cross in the sample. Figure 1 shows the beam geometries on the surface of the sample and at the aperture plane. The three incident beams are labeled 1, 2, and 3. Beam 4 is the signal beam, generated by the input beams via The... 

A typical time-resolved degenerate four-wave mixing signal consists of at least two components a fast component limited by the laser pulse duration and a longer decay due to the medium response. When all three beams are polarized parallel to each other (xxxx geometry), three gratings are formed one grating is from the two... 

Fig. 2. Oblique geometry typically used for characterizing bulk photorefracti ve polsmaers. The magnified portion illustrates the orientational enhancement effect described in the text due to the modulated poling of the electro-optic chromophore in the combined Eb + Esc fields. The beam and grating geometry applies for both four-wave mixing (beams 1-4) and two-beam coupling (beams 1 and 2).

Fig. 3. Experimental schematic for four-wave mixing. The diffraction grating is written by beams 1 and 2 and read by beam 3, which need not be of the same wavelength as the writing beams. In the absence of a reading beam, the same geometry may be used to measure two-beam coupling between the writing beams.

Fig. 6.13 Setup for the simultaneous observation of SHG (using w-light) and DFWM (using 2w-light from the same laser source) in the PC geometry from thin cluster films on transparent substrates. The sample is situated in an ultrahigh vacuum chamber and alkali films are depcsited frcm an alkali oven while monitoring the frequency-doubling and the four-wave mixing signals induced by the growing adsor-...

Fig. 7. Zeeman splitting, in an external magnetic field of 10 gauss, of the four-wave mixing resonance in the geometry of Fig. 1, caused by collision-induced Zeeman coherences with Am = 1.

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