Line narrowing requirements

Evidently, in order to achieve the necessary rapid incoherent rotational motion to produce line-narrowing, orientational perturbations of a particle are required. A variety of mechanisms whereby these can be achieved are possible. 

Line narrowing by multiple-puhe techniques (cf Section 3,3.4) is a promising approach to solid-state imaging with good spatial re.solution. However, high demands on experimental set-up and equipment hamper the use of the technique. Moreover, for line narrowing by multiple-pulse techniques the data points of the free-induction decay are acquired between pulses (cf. Fig. 3.3.10), and the efficiency depends on the quality of the rf pulses [Hael, Mehl. Radio-frequency pulse.s with short rise and fall times require a low quality factor of the rf coil which, at the same time, reduces the sensitivity and therefore limits the. spatial resolution. 

There are many factors to keep in mind when building a CARS measurement system. The first of these is equipment. The most important component in the CARS experiment is the pump laser. Due to signal generation efficiency considerations a 2X-Nd-YAG laser is recommended. Line narrowing devices are not necessary (and in fact not recommended) for the pump laser. Broad spectral profile pump lasers require complicated cross-coherence effects in the generation of the theoretical profiles however, these are well understood [75] and can be implemented in the calculation of theoretical CARS spectra once the spectral width of the pump is taken into account in the signal analysis. 

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