Precise test of electromagnetic interactions in ortho-positronium spectroscopy

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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.