Spin echo
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Spin echo refers to an increase in the NMR signal after a certain time interval, following the application of an intense radiofrequency pulse to an ensemble of spins in a constant magnetic field.
Echo phenomena belong to the most prominent features of coherent spectroscopy. They have been observed and utilized in various fields reaching from magnetic resonance to laser spectroscopy. Echoes have for the first time been detected in nuclear magnetic resonance by Erwin Hahn in 1950.
The creation of an echo usually requires the application of two exciting pulses. The first pulse at t = 0 generates coherence which defocuses under the influence of an inhomogeneous interaction, e.g. caused by an inhomogeneous magnetic field. A second pulse, applied at t = T, inverts the accumulated effects of the inhomogeneous interaction and initiates the refocusing which leads then to an echo at t = 2T.
[edit] References
- Erwin L. Hahn, Physical Review 80, 580–594 (1950)
