Direct phase-matching measurements

The success of spectral identification depends on the appropriate reference spectra for comparison. IR measurement of eluates that are at slightly subambient temperature is advantageous considering that the large databases of condensed-state spectra may be searched. Spectra measured by matrix-isolation GC-FTIR have characteristically narrow bandwidths compared with the spectra of samples in the condensed phase near ambient temperature or in the gas phase. In addition, the relative intensities of bands in the spectra of matrix-isolated samples often change compared with either gas- or condensed-phase spectra [195]. GC-FTIR spectra obtained by direct deposition match well with the corresponding reference spectra in standard phase... 

The femtosecond (fs) laser system consists of a TiiSapphire laser and a regenerative amplifier pumping two independent optical parametric amplifiers that provide laser pulses of around 100 fs duration over a very broad range of wavelengths (250-2000 nm). The signal is detected in the transmitted phase-matching direction lc = k3 + k2 — ki and recorded by a spectrometer with spectral resolution = 2 nm. The spectra are measured by scanning over the... 

Figure 3 (a) Time sequence of the (stimulated) three-pulse photon echo experiment. The times ti, t2, and t3 represent the time coordinates used in the response functions [Equations (7)—(12)] while r, T, and t measure the delay times with respect to the peak positions of the light pulses. For 5-shaped light pulses, both sets of times would be equivalent, (b) The so-called box configuration, (101) which allows the spatial separation of the third-order polarization generated in the —ki + k2 + kj and the +ki — k2 + k3 phase matched directions. 

With numerical values derived from previous experiments [Ikeda 1999] and from the crystal structure [Fillaux 2003 (a)] we estimate Nx = 33 3 and Ny = 4.5 0.5. These values are quite compatible with the phase matching conditions but, regarding error bars, it is not possible to conclude whether the grating-like structures can be observed. We need direct measurement of the diffraction pattern (see next subsection) to confirm long-range quantum entanglement of protons. 

Fig. 6.13. The polariton wavepacket, created by coherent scattering of picosecond laser and Stokes pulses, propagates in the crystal at the angle 0 with respect to the excitation direction. This angle is determined by the excitation wavevector geometry (see above). The coherent amplitude of the propagating wavepacket may be measured by phase-matched coherent anti-Stokes scattering of a probe pulse suitably delayed in time (fn) and displaced in space (by Xn)- Reprinted with permission from Gale et al. (68). Copyright (1986), American Physical Society.

Optical attenuation measurements with a TEo-mode were carried out at a wavelength of A = 926.5 nm (we could not measure the attenuation exactly at the phase-matching wavelength because the generated second-harmonic light would have disturbed our results). The mode was scanned by a fiber probe which measured the scattered light in the direction... 

The influence of viscosity on Et was studied by Hikita and Kikukawa (73). Only a small effect was found, i.e. ELa/i"0 2. Liquid phase dispersion coefficients in aerated non-Newtonian media were not yet measured directly. When matching experimental profiles of liquid phase oxygen concentrations with the predictions of the dispersion model, Schumpe et al. (18) obtained higher Ejj values than for low viscous media. However, these preliminary results need further clarification by direct measurements. 

The zero-field and field-induced optical second harmonic generation (SHG) was investigated for the nematic and smectic A phases of various liquid crystals. The components of the cubic non-linear susceptibility tensor were measured for substances with different molecular structure. The phase-matched SHG was observed for all the compounds investigated. The directions of the phase synchronisms as well as the corresponding non-linear susceptibilities were determined for the ee-o and oe-o interactions. The zero-field phase-matched SHG was observed for the oe-o interaction. It was accounted for by a multipolar mechanism. 

In experiments with the field-induced SHG we always tried to obtain the phase-matched generation, having in mind to study the zero-field SHG in the same synchronism directions when the external field is switched off. The search for zero-field SHG in the phase-matched conditions increases markedly the sensitivity of an experimental set-up and allows the pump beam intensity to be lowered. The study of the field-induced SHG was also used for the calculation of the number of parameters of the liquid crystalline medium (a cubic non-linear susceptibility a quadratic hyperpolarizability " and the discussion of their connection with molecular structure. In contrast to isotropic liquids, the value of Fy / depends not only on molecular parameters but on the orientational order parameters P- and (P4) of liquid crystal as well. The latter opens the possibility to measure (P2) and (P4). 

FIGURE 2 Cells for measuring coherence lengths / and non-linear susceptibilities (a) cells for observation of phase-matching (b) 1. glass plates 2. electrodes 3. liquid crystal 4. glass rectangular prisms y-axis coincides with beam direction. 

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