A method for exciting transverse magnetization in nmr pulse experiments

In NMR pulse experiments transverse magnetization is excited by irradiating the nuclear spin system with a two pulse sequence of a first RF chirp pulse and a second RF chirp pulse, generated after a defocusing time interval tau . The pulse duration of the second chirp pulse is half the duration of the first pulse, and the amplitude of the second chirp pulse is approximately three times the amplitude of the first chirp pulse. The first pulse being a 90 DEG -pulse, the second pulse being a 180 DEG -pulse, a refocusing of the magnetization vectors occurs at a time tau min = tau + tau after elapse of the second chirp pulse, and acquisition of the resulting echo signal is started at peak of the echo.