Broadband excitation by method of double sweep

TL;DR

This paper introduces a novel method for designing broadband excitation pulses in high-resolution NMR using double sweep techniques, enabling large bandwidth excitation without increasing RF amplitude.

Contribution

The paper presents a new pulse design method employing nested adiabatic sweeps for broadband excitation in NMR, which can be scaled to larger bandwidths with limited RF power.

Findings

Experimental excitation profiles demonstrate effective broadband excitation.

Application to $^{13}$C in Alanine shows practical utility.

Method achieves large bandwidth excitation with limited RF amplitude.

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.