Construction of adiabatic rapid-passage ESR spectrometer

研制了一种快速灵敏的ESR谱仪，可在100微秒内检测低温固体中10^-15摩尔的顺磁中心。该光谱仪检测瞬态ESR信号产生的绝热快速通过顺磁中心的共振条件。由于用于频率扫描的压控微波振荡器产生相位噪声，该相位噪声引起信号幅度的不规则振荡，所以通过磁场的快速扫描的绝热通过比频率扫描好得多。通过施加微波脉冲同时反复扫过磁场来实现绝热通道。对瞬态ESR信号的数值分析表明，绝热快速通道适用于横向弛豫时间大于100微秒的顺磁中心的探测。该谱仪对样品的灵敏度是常规CW ESR谱仪的100倍以上。结果表明，绝热快速通道ESR谱仪对于低温固体中的有机自由基等弛豫时间很长的极少量顺磁中心的检测是非常有效的。

A fast and sensitive ESR spectrometer was developed for detecting 10^-15 mole of paramagnetic centers in cryogenic solids within 100 microseconds. The spectrometer detected transient ESR signals generated during adiabatic rapid-passage through the on-resonant condition of paramagnetic centers. The adiabatic passage by the rapid sweep of the magnetic field was much better than the frequency sweep, since a voltage-controlled microwave oscillator for the frequency sweep generated phase noises which induced irregular oscillation of the signal amplitude. The adiabatic passage was attained by applying microwave pulses while sweeping the magnetic field repeatedly. The numerical analysis of the transient ESR signals revealed that the adiabatic rapid passage was suitable for detecting paramagnetic centers with the transverse relaxation time longer than 100 microseconds. The sensitivity of the spectrometer for such a sample was 100 times more than a conventional CW ESR spectrometer. It was concluded that the adiabatic rapid-passage ESR spectrometer was quite powerful for detecting a very small amount of paramagnetic centers with very long relaxation times such as organic free radicals in cryogenic solids.