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) symmetrically with respect to the carrier frequency. Simulations and experiments 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 density operator components is proposed.
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Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA.
Ermakov
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Bodenhausen
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D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008432:Mathematical Computing