Suzuki Takayuki
JEOL RESONANCE Inc., Akishima, Tokyo 196-8558, Japan.
J Magn Reson. 2015 Oct;259:95-101. doi: 10.1016/j.jmr.2015.08.006. Epub 2015 Aug 14.
Longitudinally detected T1 measurement scheme (LOD-T1) is studied in detail. In contrast to the original work on LOD-T1, using high power microwave pulses, this work deals with general and practically frequent cases in which perfect inversion of the electron-spin magnetization is not feasible due to the effect of relaxation during microwave pulses. Theoretical studies, numerical simulations, and experiments reveal a pair of separate contributions of the dynamics of the longitudinal magnetization to the LOD signal, namely, the periodic modulation and the relaxation contributions. The latter alone which is of interest can be extracted to give relaxation curves. In addition, it is shown that T1 information can be obtained even when the available microwave power is so low that the electron magnetization can only be perturbatively modulated, at the cost of reduced sensitivity. To overcome this, a modified pulse sequence is proposed. In this new method, the pulse excitations are repeated during half a period of the resonance of the longitudinal detection circuit. The method is called the perturbative harmonic modulation method for longitudinally detected T1 measurement (HM-LOD-T1). HM-LOD-T1 experiments are demonstrated in 2,2-diphenyl-1-picrylhydrazyl (DPPH).
详细研究了纵向检测T1测量方案（LOD-T1）。与最初关于LOD-T1的工作不同，最初的工作使用高功率微波脉冲，而本工作处理的是一般且实际中常见的情况，即由于微波脉冲期间的弛豫效应，电子自旋磁化强度的完美反转是不可行的。理论研究、数值模拟和实验揭示了纵向磁化强度动力学对LOD信号的一对独立贡献，即周期性调制贡献和弛豫贡献。仅后者这种令人感兴趣的贡献可以被提取出来以给出弛豫曲线。此外，结果表明即使可用微波功率很低以至于电子磁化强度只能被微扰调制，也能获得T1信息，代价是灵敏度降低。为克服这一点，提出了一种改进的脉冲序列。在这种新方法中，脉冲激发在纵向检测电路共振的半个周期内重复。该方法被称为用于纵向检测T1测量的微扰谐波调制方法（HM-LOD-T1）。在2,2-二苯基-1-苦基肼（DPPH）中进行了HM-LOD-T1实验。
