A convenient method for calibration of the pulse-length in high field-gradients using Hahn echo-trains.

A new method is presented for calibration of the pulse-length in the case that the sample, which can be either a liquid or a solid, is placed in a high field-gradient such as it experiences in the stray-, fringe-field of a solenoid. The method employs a pulse-train, with a constant phase, of the form alpha X-tau-(alpha X-tau-echo-tau-)n. This produces Hahn echoes which have variable phase in the form of phase-alternations along the echo-train. For alpha = 90 degrees the relative phase-sequence in degrees is (0, 0, 180, 180), and we may characterise this by m = 2, since there are two signals of one phase in each group. For other cases with these phase angles (0 and 180) but different numbers, m, of signals with opposite phase, we have alpha = 180/m, where m is an integer.