th  - 1988 - 51st ENC Conference

TUE 10"40 I
COMPOSITE PULSES: NEW APPLICATIONS AND METHODS
Tony Bielecki and Malcolm H. Levitt ,
Massachusetts Institute of Technology, Cambridge, MA 02139;
James L. Sudmeier and William H. Bachovchin,
Tufts University School of Medicine, Boston, MA 02111
The application of composite pulses as solvent peak suppression
sequences will be discussed. A combination of coherent averaging
theory with numerical optimization allows one to find simple
six-pulse sequences which hold the phase of excited signals almost
constant, while cutting out a narrow, flat notch at the solvent
resonance. This helps greatly to reduce distortions of the baseline
and of broad or overlapping signals. Suppression ratios are not
dramatic, but seem to be sufficient, especially in conjunction with
an improved receiver design.
It is also hoped to show results for composite pulses where the
component pulses have different frequencies. New advances in direct
digital frequency synthesis have made it feasible to achieve very
fast jumps in carrier frequency, while maintaining phase coherence.
This is expected to allow short but very broadband composite pulses,
which will have implications in low-power population inversion and
decouplinq experiment~.
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