Two-colour double resonance

In sections 4.2 and 4.4 emission spectroscopy provided more information than could be obtained from an excitation spectrum. Even so, the weakness of such emission makes it difficult to obtain high resolution in its dispersed spectrum, and data are only obtained about levels lying below that excited. Two-colour double resonance can remove both these limitations in favourable cases. We may envisage three basic schemes for optical-optical double resonance using two lasers. 

This is just one of many instances where two-colour, double-resonance multiphoton spectroscopy can of great help in providing additional spectroscopic, structural and dynamical information about the... 

The epoxide formation has been shown to occur in canned fruit juice and can give rise to considerable loss of colour. This loss of colour can be accounted for by the reduced resonance stabilisation of the product, there is basically a loss of two conjugated double bonds, one in the 6 membered ring and alternate to this (Wong, 1989). 

Fig. 13 Level schemes for two-colour optical-optical double resonance Either the pump laser or the probe laser may be scanned with the frequency of the other laser held fixed, (a) Sequential OODR. (b) Competitive excitation. (c) Stimulated emission pumping.

Colour in organic compounds is also due to resonance. This also explains why a system of open conjugate double bonds containing two or more double bonds imparts colour to it. 

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