Nuclear Magnetic Resonance in Solids: Thermodynamic Effects of a Pair of rf Pulses

摘要: A discussion is given of the effects a pair pulses rf magnetic field (at NMR frequency) on Zeeman and dipolar energies spin system in solid. order partly transformed into when two have different phases. theoretical calculation provides very simple relation between efficiency this transfer energy (as function characteristics their time separation) magnitude shape component free-precession signal. This prediction has been verified quantitatively case ${\mathrm{F}}^{19}$ spins Ca${\mathrm{F}}_{2}$ crystal with large [100] direction. maximum 56% obtained $\frac{\ensuremath{\pi}}{2}$ phase shift first pulse second $\frac{\ensuremath{\pi}}{4}$ pulse, separated by ${T}_{2}$. (An ideal adiabatic demagnetization rotating frame would an 100%.) The experimental results also indicate that reaches internal quasiequilibrium few ${T}_{2}$ after pair. It shown use (both same time) leads to new method for measuring complete signals, which avoids usual difficulties due finite recovery observation circuit.