Precise test of electromagnetic interactions in ortho-positronium spectroscopy

1)正电子(Ps)产生系统：我们在TMU建造的慢正电子(OPS)发生器上安装了网目慢慢化器，能够将慢正电子(OPS)的强度提高一个数量级以上。一个斩波聚束器系统产生了时间宽度为1 ns的聚束OPS光束。为了实现OPS与激光的有效碰撞，我们发展了一种新的正电子积累方法，将正电子在磁场中运动时的纵向动量转换为横向动量。利用加热到1000K的高温钼靶有效地产生了热OPS，并用飞行时间法测量了其产生率。2)激光系统：对于OPS的激发，我们制作了一台长脉冲为200 ns(长于OPS寿命142 ns)的Cr：LiSAF激光器。具有243 nm的波长，足够宽的线宽来覆盖初始的多普勒展宽和25赫兹的重复频率。根据输出功率和线宽对二次谐波和四次谐波发生器进行了优化。3)1S→2P激光激发：利用蒙特卡罗模拟方法，详细研究了激光照射的几何条件、受激冷却对寿命的影响以及激光与正电子束之间的相互关系。

1) Production system of positronium (Ps) : We installed a mesh-moderator in the slow ortho-positron (oPs) generator constructed at TMU and were able to increase the intensity of slow oPs by more than one order. A chopper-buncher system created the bunched oPs beam with the time width of 1ns. For achieving efficient collisions of oPs with laser, we have developed a new method of positron accumulation by converting the longitudinal momentum to the transverse one while positron is traveling in magnetic fields. Thermal oPs was efficently produced using a high temperature Mo target heated up to 1000 K and the production rate was measured by means of time-of-flight method.2) Laser system : For the excitation of oPs, we fabricated a Cr : LiSAF laser which provides a long pulse of 200 ns (longer than the oPs lifetime of 142 ns.) having a wave length of 243 nm, sufficiently wide line width to cover the initial Doppler broadening and the repetitio of 25 Hz. The second harmonic and forth harmonic genrators are optimized with respect to the oputput power and the line woidth. We transported the laser to the collision point and made an irradiation test.3) 1S→2P laser excitation : Using Monte Carlo simulation, we examined in detail geometrical condition of laser irradiation, variation of the lifetime owing to the stimulated cooling, mutual relation between laser and positron beams.