What is an excitation profile?
Hard pulses
During a regular (non-selective) pulse-acquire experiment (e.g. a 1D 1H experiment), the NMR sample is irradiated with an RF pulse. This pulse should excite all the frequencies within the entire spectral width. Such pulses should be short in length (e.g. around 10 µs for 1H) and high in power and are referred to as hard pulses. This is the case when the offset of the peaks with respect to the carrier frequency (Ω in rad/s) is much smaller than the RF field strength (ω1 in rad/s). For a simple rectangular pulse, the excitation profile varies accoring to the sinc(x) function, symmetrically decaying around the transmitter frequency (i.e. the middle of the spectrum, O1P). The excitation profile of a rectangular pulse follows the equation