Divergent double chirp pulses for refocusing quadrupolar interactions

To excite and refocus single quantum coherences in a three-level system with a quadrupolar interaction, it is possible to use frequency-modulated pulses with two diverging frequency components that are swept simultaneously through the two single-quantum transitions. This is achieved by time-dependent amplitude-modulation of the carrier frequency, so as to generate two sidebands with frequencies that are diverging (or converging) sym. with respect to the carrier frequency. Simulations and expts. show that such modulated pulses can be used to refocus single quantum coherences to form quadrupole echoes, using much weaker RF amplitudes than in conventional echo sequences. To visualize the evolution of the coherences in a three-level system, a graphical representation of the d. operator components is proposed. [on SciFinder (R)]