Signal generation pulse mode

The basis of the experimental femtosecond CARS apparatus developed by Okamoto and Yoshihara (1990) which is reproduced in Fig. 3.6-10 is essentially the same as that of Leonhardt et al. (1987) and Zinth et al. (1988) with the addition of the possibility to change the polarization of the laser radiation. The main parts of the system are two dye lasers with short pulses and high repetition rates, pumped by a cw mode-locked Nd YAG laser (1064 nm, repetition rate 81 MHz). The beam of the first dye-laser which produces light pulses with 75-100 fsec duration is divided into two parts of equal intensities and used as the pump and the probe beam. After fixed (for the pump beam) and variable (for the probe beam) optical delay lines, the radiation is focused onto the sample together with the Stokes radiation produced by the second laser (DL2), which is a standard synchronously pumped dye laser. The anti-Stokes signal generated in the sample is separated from the three input laser beams by an aperture, an interference filter, and a monochromator, and detected by a photomultiplier. For further details we refer to Okamoto and Yoshihara (1990). 

Very different intensities of the P NMR signals from (CH3)3P-derived chemical species on surfaces can be observed by using different NMR pulse modes for generating transverse P magnetization [90j. Figure 45 shows the CP and single-pulse (FT) MAS spectra for two surface concentrations of (CH3)3P adsorbed on y-alumina. The CP-MAS spectrum reveals the presence of Bronsted (-4 ppm) and Lewis ( — 48 ppm) complexes in addition to physisorbed phosphine (-58 ppm). At small (<1 ms) CP contact time the cross-polarization... 

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