Precise test of electromagnetic interactions in ortho-positronium spectroscopy

1)正电子的产生系统：我们在TMU建造的慢正电子发生器中安装了一个网格调节器，可以将慢正电子的强度提高一个数量级以上。一种剪切聚束系统产生了时间宽度为1ns的聚束oPs光束。为了实现oPs与激光的有效碰撞，我们开发了一种将正电子在磁场中运动时的纵向动量转化为横向动量的正电子积累新方法。利用加热至1000 K的高温钼靶有效地制备了热oPs，并用飞行时间法测量了生产速率。2)激光系统：为了激发oPs，我们制作了一个Cr: LiSAF激光器，该激光器提供200 ns的长脉冲（比oPs的142 ns寿命长），波长为243 nm，线宽足以覆盖初始多普勒展宽，重复频率为25 Hz。二谐波和四谐波发生器相对于输出功率和线宽进行了优化。我们将激光传送到碰撞点并进行辐照试验。3) 1S→2P激光激发：利用蒙特卡罗模拟，详细研究了激光辐照的几何条件、受激冷却对寿命的影响、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.