Variable-amplitude phase generator

In complete analogy to NMR, FT EPR has been extended into two dimensions. Two-dimensional correlation spectroscopy (COSY) is essentially subject to the same restrictions regarding excitation bandwidth and detection deadtime as was described for one-dimensional FT EPR. In 2D-COSY EPR a second time dimension is added to the FID collection time by a preparatory pulse in front of the FID detection pulse and by variation of the evolution time between them (see figure B1.15.10(B)). The FID is recorded during the detection period of duration t, which begins with the second 7r/2-pulse. For each the FID is collected, then the phase of the first pulse is advanced by 90°, and a second set of FIDs is collected. The two sets of FIDs, whose amplitudes oscillate as functions of t, then undergo a two-dimensional complex Fourier transformation, generating a spectrum over the two frequency variables co and co,. 

Instead of a gated switch in the fluorescence detector for pulsed excitation, one may also use excitation by a cw laser that is phase-modulated with a modulation amplitude of tt (Fig. 9.81). The fluorescence generated under sub-Doppler excitation in a collimated atomic beam is observed during a short time interval A, which is shifted by the variable delay T against the time to of the phase jump. If the fluorescence intensity T) is monitored as a function of the laser frequency cu,... 

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