超二代像增强器多碱阴极光电发射特性研究

通过测量超二代像增强器多碱阴极的光谱反射率和透射率,根据能量守恒定律计算得到了多碱阴极的光谱吸收率.结果表明,只有当光子的能量大于1.333 eV以后,多碱阴极的吸收率才开始快速增大.这说明多碱阴极的光谱吸收存在一个1.333 eV的长波吸收限,入射光的光子能量如果小于该吸收限,多碱阴极将不吸收.在多碱阴极的表面电子亲合势进一步降低的情况下,多碱阴极光电发射的长波理论阈值由长波吸收限所决定.多碱阴极在吸收光子之后的电子跃迁过程中,跃迁电子的能量增加小于所吸收入射光子的能量,即存在一个"能量损失".光子的能量越高,所激发的跃迁电子所处的能级越高,能量损失越大.同时光子的能量越高,跃迁电子所处的能级越高,电子跃迁的几率越低.多碱阴极的量子效率由吸收率、跃迁几率和跃迁能级、扩散过程中的能量损失等因素共同决定,因此多碱阴极的量子效率存在长波阈的同时也存在短波阈.多碱阴极的量子效率在2.11 eV达到最大值之后,随着光子能量的增加而单调减小,在3.6 eV时,量子效率减小到零.多碱阴极在3.6 eV时的吸收系数仍然很高,但由于电子跃迁的几率低,同时电子扩散过程中的能量损失大,导致尽管多碱阴极对短波具有较高的吸收系数,但量子效率仍然较低.因此对多碱阴极所吸收的光子能量中,转换成为光电导、晶格热振动等其他非光电发射形式能量的比例而言,短波较长波高,对光电发射的贡献率而言,短波较长波低.

Photoemission Process Study of Multi-alkali Photocathode in the Super Second Generation Image Intensifier

Multi-alkali photocathode in super generation image intensifier is different from previous multi-alkali photocathode between the production processes, so the photoelectric emission characteristics are different from previous multi-alkali photocathode. In this paper, through the measurement of multi-alkali photocathode spectral reflectivity and transmissivity, according to the law of conservation of energy, cathode spectral absorption rate was obtained. Spectral absorption rate indicates that, only when the photon energy greater than 1.333 eV, cathode absorption rates began to increase quickly. The cathode spectral absorption shows that cathode will not absorb any photons if light incident photon energy is less than the absorption limit, i.e. 933 nm wave absorption limit. In the cathode surface electron affinity further reduced circumstances, cathode photoemission long wave theory threshold is determined by long-wave absorption limit. In the electronic transition process after absorption of a photon, transition energies increase less than the absorption of the incident photon energy, i.e. the presence of an "energy loss". The higher energy of a photon is, the higher electronic transition energy level is, the more energy loss is. At the same time, the higher energy of a photon is; the higher-energy level transition electron, the lower electronic transition probability is. Photocathode quantum efficiency is determined by the absorption rate, the transition probability and transition level, energy loss of diffusion process and other factors, thus photocathode quantum efficiency is in the presence of long wave threshold and shortwave threshold also. Photocathode quantum efficiency in 587 nm reaches the maximum value, after that decreases with the photon energy increases, when 3.6 eV, the quantum efficiency is reduced to zero. Cathode in photon energy of 3.6 eV the absorption coefficient is still high, but due to the electronic transition probability is low, while the electron diffusion process of energy loss is big, thus in spite of cathode on lower wavelength has high absorption coefficient, but the quantum efficiency is still low. Therefore on shortwave, cathode absorbed shortwave photon energy is converted into a photoconductive, lattice vibration and other forms of energy; the photoelectric emission utilization rate is very low.