Broadband excitation by method of double sweep

Abstract

The paper describes the design of broadband excitation pulses in high resolution NMR by method of double sweep. We first show the design of a pulse sequence that produces broadband excitation to the equator of Bloch sphere with phase linearly dispersed as frequency. We show how this linear dispersion can then be refocused by nesting free evolution between two adiabatic inversions (sweeps). We then show how this construction can be generalized to exciting arbitrary large bandwidths without increasing the peak rf-amplitude and by incorporating more adiabatic sweeps. Finally, we show how the basic design can then be modified to give a broadband $x$ rotation over arbitrary large bandwidth and with limited rf-amplitude. Experimental excitation profiles for the residual HDO signal in a sample of $99.5\%$ D$_2$0 are displayed as a function of resonance offset. Application of the excitation is shown for $^{13}$C excitation in a labelled sample of Alanine.