Fundamental mechanisms of single-pulse NMR echo formation

Single-pulse and secondary echoes in systems with a large inhomogeneous broadening of NMR lines

“…Recently in [5,4] the formation of secondary nuclear spin echo signals in systems with large Larmor and Rabi inhomogeneous broadenings of a NMR line at periodical…”

“…It is also known that information on spin-system usually obtained with the help of two pulse Hahn echo (TPE) could be obtained by the singlepulse echo (SPE) [2,3]. But in a number of cases the most convenient proves to be the spin echo excitation by multipulse series of RF pulses which, in particular, provide an operative measurement of relaxation times T 1 and T 2 of the investigated systems [4].Recently in [5,4] the formation of secondary nuclear spin echo signals in systems with large Larmor and Rabi inhomogeneous broadenings of a NMR line at periodical …”

“…It is on this basis that the evolution away from OFID (LIB only) or echolike step anomaly (LIB plus RIB) for a single-pulse excitation, toward the formation of a well-defined echo at τ (τ is a RF pulse duration), together with the emergence of secondary echoes for a multipulse train was established [5] analytically and numerically.…”

“…By the way a conclusion was made that properties of main and secondary echoes, In work [5], using the statistical tensor formalism, a theoretical investigation was made on formation of SPE and its secondary signals at the presence of both Larmor and Rabi inhomogeneous broadenings of NMR lines, at conditions when the period T of RF pulse repetition obeys inequality T 3 <<T 2 < T< T 1 , and only the longitudinal component of the nuclear magnetization is important before RF pulse, and an unequilibrium of spinsystem precedes RF pulses .It was shown in [5] that a dephasing of nuclear spin-system was accumulated during n pulse excitations and restored within a time interval elapsing from the trailing edge of the last "counting" [(n+1)th] pulse of a multipulse train. It is on this basis that the evolution away from OFID (LIB only) or echolike step anomaly (LIB plus RIB) for a single-pulse excitation, toward the formation of a well-defined echo at τ (τ is a RF pulse duration), together with the emergence of secondary echoes for a multipulse train was established [5] analytically and numerically.…”

“…Recently in [5,4] the formation of secondary nuclear spin echo signals in systems with large Larmor and Rabi inhomogeneous broadenings of a NMR line at periodical 2 excitation of a sample by series of single or two RF pulses was considered in conditions when the spin-system unequilibrium preceded RF pulses .…”