Electron Beam Excitation of Metal Vapor Excimers

由于碱二聚体的准分子性质，对其扩散带的研究较多。本文报道了利用电子束抽运的方法研究了Na_2紫、K_2黄、Rb_2红带的发射和增益测量，目的是了解这种扩散带的电激发特性，从而获得新型的可调谐高功率准分子激光器。实验中使用的电子束设备峰值电流为15kA，脉冲宽度为50 ns，电子粒子能量为300 keV。在K/K_2蒸汽与氩气或氦气混合的电子束激发下，K_2黄色扩散带的净增益系数为4.5%。以574 nm为中心的连续光谱归属于三重态-三重态K_2 2^3II_g*1^3SIGMA^+_u无束缚跃迁。当激发能密度超过5 mJ/cm^3时，发现了Na_2紫、K_2黄、Rb_2红波段的ASE。用从头算势计算的Na_2和K_2 2^3II_g*1^3SIGMA^+_u光谱与观测值吻合较好。2^3II_g态的高居布密度是由电子束激发有效产生的碱三聚体离子（Na_3^+， K_3^+或Rb_3^+）的解离重组引起的。K_3^++e^-*K_3^*（不稳定）*K+K_2 (2^3II_g)，由于Na的反应能差e为0.03 eV， K的反应能差e为0.28 eV，预测该反应具有较大的截面。因此，这种特定的准分子跃迁的上层状态可以通过这种反应动力学在非常非选择性电离之后选择性地产生。因此，势碱二聚体2^3II_g*1^3SIGMA^+_u激光器可能非常适合电抽运。可以想象，这种基于解离重组的准分子激光器也可能出现在其他金属蒸汽介质中。

There have been many studies of alkali dimer diffuse bands because of the excimer-type nature.In this work, aimed at understanding the characteristics of the electrical excitation of such diffuse bands and achieving new tunable and high power excimer lasers, we report on the investigation of the Na_2 violet, K_2 yellow and Rb_2 red band emissions and gain measurements by electron beam pumping. The e-beam facility used in the experiment had a peak current of 15kA,a pulse width of 50 ns, and an electron particle energy of 300 keV.A net gain coefficient of 4.5% of the K_2 yellow diffuse band was observed from e-beam-excited mixtures of K/K_2 vapor with argon or helium buffer gas. The continuum spectra centered at 574 nm were attributed to triplet-triplet K_2 2^3II_g*1^3SIGMA^+_u bound-free transitions. Also, an ASE of the Na_2 violet, K_2 yellow and Rb_2 red bands were observed when the excitation energy density exceeded 5 mJ/cm^3. Calculated spectra of the Na_2 and K_2 2^3II_g*1^3SIGMA^+_u by using ab initio potentials are in good agreement with the observed one. The high population density of the 2^3II_g state was proposed to be due to the dissociative recombination of alkali trimer ions (Na_3^+, K_3^+ or Rb_3^+) which are efficiently yielded by electron beam excitation.K_3^++e^-*K_3^* (unstable) *K+K_2 (2^3II_g),Because the reaction energy difference delta E is 0.03 eV for Na and 0.28 eV for K.The process is predicted to have large cross sections. Thus, the upper state of such specific excimer transition may be produced selectively by this reaction kinetics following a very nonselective ionization. For this reason, the potential alkali dimer 2^3II_g*1^3SIGMA^+_u laser might be very suitable for electrically pumping. It is quite conceivable that such dissociative recombination-based excimer lasers might also be presented in the other metal vapor mediums.