Pulses adiabaticity factor

Adiabatic pulses are described by their frequency sweep and amplitude profile, which, when combined with the peak rf amplitude cc max), defines the total power of the pulse. The total frequency range, AF, over which the pulse sweeps is commonly many tens of kilohertz and pulse durations, T, are typically of the order of 1 ms, corresponding to frequency sweep rates of 10-100 MHz/s. The degree to which the adiabatic condition is satisfied for the pulse is quantified by the adiabaticity factor Q... 

The sinc fiinction describes the best possible case, with often a much stronger frequency dependence of power output delivered at the probe-head. (It should be noted here that other excitation schemes are possible such as adiabatic passage [9] and stochastic excitation [fO] but these are only infrequently applied.) The excitation/recording of the NMR signal is further complicated as the pulse is then fed into the probe circuit which itself has a frequency response. As a result, a broad line will not only experience non-unifonn irradiation but also the intensity detected per spin at different frequency offsets will depend on this probe response, which depends on the quality factor (0. The quality factor is a measure of the sharpness of the resonance of the probe circuit and one definition is the resonance frequency/haltwidth of the resonance response of the circuit (also = a L/R where L is the inductance and R is the probe resistance). Flence, the width of the frequency response decreases as Q increases so that, typically, for a 2 of 100, the haltwidth of the frequency response at 100 MFIz is about 1 MFIz. Flence, direct FT-piilse observation of broad spectral lines becomes impractical with pulse teclmiques for linewidths greater than 200 kFIz. For a great majority of... 

We study two adiabatic schemes that, use a sequence of time-delayed transform limited pulses. The first one, known as STIRAP (Stimulated Raman adiabatic passage) controls the population transfer between three vibrational states. The frequency of the first pulse (t)[ is tuned in resonance with the transition from 4> (x) to the intermediate state (f>i0 x), and the frequency of the second pulse [ 2(t)] is resonant with the transition from i0 x) to 4>q x) i0 x) is the intermediate state that maximizes the Franck-Condon factors for both transitions at the same time, working as an efficient wave function bridge between the initial and target wave functions [5]. Using counterintuitive pulses, such that (t) precedes x (t), the wave function of the system has the interesting form [3]... 

Adiabatic pulses may be studied using the Waveform analysis. These pulses can either be frequency or phase swept pulses but during the frequency sweep the adiabatic condition must always be met. For an estimation of this condition an effective B field is represented by the angles 0m and 0eff(B]), the calculation then displays the angles 0m and 0eff(Bj), a further quality factor and the frequency sweep as function of time in as a series of graphs. Adiabatic pulses are discussed in more detail in section 5.3.1. 

An adiabatic pulse is a special type of shaped pulse where either a frequency or a phase sweep occurs during the pulse duration. Adiabatic pulses are discussed in detail in section 5.3.1. So far the simulations involving the Bloch module have not considered the exact time related frequency sweep of a shaped pulse yet it is this factor that determines if each point in the pulse shape obeys the adiabatic condition. Using an adiabatic chirp pulse Check its 4.3.33 and 4.3.3.6 will examine various aspects of adiabatic pulses starting with the time evolution and the graphical representation of the amplitude and phase modulation. 

The time evolution representation shows how well the magnetization vectors with different rf offsets are tilted to the same degree by the adiabatic pulse. Check it 4.3.3.6 examines a number of different quality factors of the pulse to determine how well the pulse fulfills the adiabatic condition. 

---