Positronium (Ps), a bound state of an electron and a positron, is a purely leptonic and anti-particle system. Preparing a cold gas of Ps leads to precision spectroscopy and a realization of Bose-Einstein condensation of exotic atoms. Owing to the nature of the particle-antiparticle pair, Ps has a finite lifetime of 142 ns. Therefore, developing a rapid cooling method is the key to cool Ps effectively.
Laser cooling using the 1S-2P transition is one of the most promising methods for Ps cooling. With laser cooling, Ps atoms at room temperature could ideally be cooled to the photon recoil limit of 0.6 K within one microsecond. The temperature is well below 150 K, achieved by a conventional cooling method via momentum exchange processes with a cold Ps converter.
It is well known that laser cooling using continuous-wave lasers can reduce the temperature of a gas of atoms to submillikelvin temperatures. However, because of the finite lifetime and the small mass of Ps, a cooling laser for Ps should be a unique pulsed laser that has a broadband spectrum, a frequency chirp, and a long pulse duration of several hundred nanoseconds. We designed and developed a prototypical cooling laser (Figure 1) that satisfies these requirements. We also numerically simulated its oscillation dynamics and successfully reproduced the measured temporal and spectral structures of the laser.
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|Presenter name||Tajima Yohei|
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