多碱光电阴极光电发射过程研究

论述了多碱阴极及光致荧光的特点,测量了多碱阴极在514.5 nm和785 nm波长激光激发条件下的荧光谱。结果表明,多碱阴极在514.5 nm波长激光激发条件下,荧光峰值强度比785 nm波长激光激发条件下荧光峰值强度强40倍,说明514.5nm波长的电子跃迁几率低于785nm波长的电子跃迁几率,同时514.5 nm波长激光激发的荧光峰值波长为860 nm,而785 nm波长激光激发的荧光峰值波长为870 nm,514.5 nm波长激光激发的荧光峰值波长与激发光波长的偏移为345 nm,而785 nm波长激光激发的荧光峰值波长与激发光波长的偏移仅为85 nm,说明514.5 nm波长激发的跃迁电子的能量损失远大于785nm波长激发的跃迁电子的能量损失。原因是短波光子的能量较高,所激发的跃迁电子来源于较深能级,因此能量损失较大。多碱阴极的量子效率在2.11 eV达到最大,当光子的能量大于2.11 eV以后,由于跃迁电子的能量损失随光子能量的增加而增加,因此多碱阴极的量子效率随光子能量的增加而减小。多碱阴极的量子效率与电子跃迁几率成正比,但实测的量子效率曲线与电子跃迁几率曲线的峰值波长不一致,原因是随着光子能量的增加,跃迁电子的能级也增加,当电子跃迁的几率达到最大并下降时,尽管跃迁电子的几率减小,但因电子跃迁的能级还在提高,因此量子效率仍在增加。只有当跃迁几率的因素超过能级的因素以后,量子效率才随光子能量的增加而减小,因此造成量子效率曲线的峰值波长与跃迁几率的峰值波长不一致。通过多碱阴极光致荧光谱的分析,揭示了多碱阴极电子跃迁过程中的客观规律,解释了多碱阴极量子效率在达到最大值之后,量子效率随光子能量增加而减小以及多碱阴极量子效率存在短波限的原因。

Study on Photoemission Process of Multi-alkali Cathode

This paper discusses the characteristics of multi-alkali cathode and photoluminescence. The fluorescence spectrum of the multi-alkali cathode excitated with laser of 514.5 nm and 785 nm wavelength is measured. The result shows that the peak strength of fluorescence excitated at 514.5 nm wavelength is 40 times higher than that at 785 nm wavelength. This is a testimony that electronic transition probability of 514.5 nm wavelength is lower than that of 785 nm wavelength. The peak wavelength of fluorescence excitated at 514.5 nm wavelength is 860 nm, while that at 785 nm wavelength is 870 nm, where the deviation of the former from excitation wavelength is 345 nm, while that of the latter is 85 nm, indicating that the energy loss in transition electron of the former is far greater than that of the latter. The reason is that the energy of short wave photon is relatively high, where the transition electron excitated comes from deep energy level, leading to great energy loss. The quantum efficiency of multi-alkali cathode reaches the maximum at 2.11 eV, and when the energy of photon is greater than 2.11 eV, it decreases as the energy of photon increases due to the increase of the energy loss in transition electron. The quantum efficiency of multi-alkali cathode is in direct proportion to electronic transition probability. However, the peak wavelengths measured in quantum efficiency curve and electronic transition probability curve are inconsistent, and the reason for which is that, the energy in transition electron increases with that in photon, and when electron transition probability reaches the maximum and then fall, energy level of electronic transition improves despite the decreasing transition electron probability, leading to increasing quantum efficiency. Only when the factor of transition probability exceeds that of energy level, quantum efficiency decreases with the increase of photon energy, which leads to the inconsistent peak wavelengths. The analysis on multi-alkali cathode and photoluminescence reveals the objective law in the course of electronic transition of multi-alkali cathode, and explains why quantum efficiency decreases with the increase of photon energy and the quantum efficiency of multi-alkali cathode has short wave limit when the quantum efficiency of multi-alkali reaches the maximum.