Construction of adiabatic rapid-passage ESR spectrometer

研制了一种快速灵敏的ESR光谱仪，可在100微秒内检测到低温固体中10^-15摩尔的顺磁中心。谱仪检测到在顺磁中心非共振条件下绝热快速通过时产生的瞬态ESR信号。磁场快速扫描的绝热通道比频率扫描的绝热通道要好得多，因为用于频率扫描的压控微波振荡器产生相位噪声，引起信号幅度的不规则振荡。通过施加微波脉冲，反复扫磁场，达到绝热通道。对瞬态ESR信号的数值分析表明，绝热快速通道适合探测横向弛豫时间大于100微秒的顺磁中心。该光谱仪对此类样品的灵敏度是常规连续波ESR光谱仪的100倍。结果表明，绝热快速通道ESR谱仪对于检测低温固体中极少量的弛豫时间很长的顺磁中心（如有机自由基）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.