Cooling of positronium (Ps), an electron-positron bound state, leads to important research such as precision measurements of energy intervals or realizing Bose-Einstein condensation. The current coldest limit of Ps, which was achieved by thermalization with cooled solid, is still over 100 K . Laser cooling and other cooling methods are under intense research to give a breakthrough in this field. On this occasion, evaluating the temperature of cold Ps is an important task to be undertaken. Obtaining the Doppler broadening by laser spectroscopy is one of the preferred methods since it allows high-resolution measurements regarding the laser technology of today.
However, since Ps has a short lifetime of 142 ns due to the electron-positron annihilation, it is principally difficult to prepare a large number of Ps at once for observation. Thus, to conduct a high-resolution Doppler broadening spectroscopy, not only should the resolution be high, but also the excitation efficiency by the laser should be kept high enough to realize an observation with a high signal-to-noise ratio. This gives certain requirements to the frequency structure and the power of the probing laser.
To evaluate the required characteristics of the probing laser, we conducted a numerical simulation based on optical Bloch equations under laser fields whose frequency structure was realistically modeled. Based on this evaluation, we have developed a frequency-tunable UV pulsed laser with the characteristics suited for doppler spectroscopy of cold Ps. We will introduce an overview of this laser along with the experimental results to evaluate whether our pulsed laser satisfies the above requirements.
 S. Mariazzi, P. Bettotti, and R. S. Brusa, Physical Review Letters 104, 243401 (2010).
|Presenter name||Ryosuke UOZUMI|
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