When signal averaging in a single-pulse
nuclear magnetic resonance spectroscopy experiment,
flip angle giving the best
signal-to-noise ratio for a given combination of
spin-lattice relaxation time and repetition rate.
Note: Named after Richard Ernst. It is employed to allow the maximum signal to noise to be generated in a fixed amount of time,
\(\cos (\theta_{\rm{E}}) = e^{-(t_{\rm{d}} + t_{\rm{a}})/T_{1}}\), where
\(t_{\rm{d}}\) is the interpulse delay,
\(t_{\rm{a}}\) is the acquisition time, and
\(T_{1}\) is
longitudinal relaxation time.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 687 (https://doi.org/10.1515/pac-2019-0203)