Development of a laser for chirp cooling of positronium to near the recoil limit using a chirped pulse-train generator

We present the development and characterization of a pulsed 243-nm laser designed for cooling positronium (Ps) to near the recoil limit. The laser, based on the recent chirped pulse-train generator (CPTG) demonstrated spectral widths of 10 GHz. The center frequency of each pulse is shifted upward (up-chirped) in time by 4.9 x 10(2) GHz mu s(-1). These parameters are determined by the mechanism of chirp cooling, a suitable scheme for cooling numerous Ps atoms to the recoil temperature of laser cooling. To achieve the desired performance, we drove an optical phase modulator in the CPTG with a high modulation depth based on the operating principle of the cooling laser. Time-resolved spectroscopic measurements confirmed that the developed laser satisfies the chirp rate and instantaneous spectral width requirements for efficient chirp cooling. We believe that the experimental demonstration of Ps laser cooling with a pulse energy of hundreds of microjoules has become possible using realistic methods for the generation and velocity measurement of Ps.