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Simplified experimental scheme of the vacuum chamber where Ps is emitted from the \pos{}/Ps converter upon \pos{} implantation. The cooling laser ($\lambda_{243}$) and the two probing lasers pulses ($\lambda_{205}$ and $\lambda_{1064}$) enter and exit the chamber through view-ports. The $\mathrm{PbWO_4}$ crystal is represented in cyan, with the white rectangle above depicting the photo-multiplier tube. The photoionization laser ($\lambda_{1064}$) is injected under a slight angle, to avoid laser-induced damage to the dichroic mirror.

SSPALS spectra of Ps in vacuum without lasers (black dotted curve), \SI{205}{\nano\meter}+\SI{1064}{\nano\meter} lasers (red dashed curve), \SI{243}{\nano\meter} laser only (green dash-dotted curve), and all three lasers \SI{243}{\nano\meter}+\SI{205}{\nano\meter}+\SI{1064}{\nano\meter} (blue solid curve). The \SI{243}{\nano\meter} laser is firing during the time window from \SIrange{-20}{50}{ns} (green band), while the \SI{205}{\nano\meter}+\SI{1064}{\nano\meter} (red vertical line) are injected \SI{75}{\nano\second} after \pos{} implantation time ($t= \text{\SI{0}{\nano\second}}$). Each curve is an average of 90 individual spectra. For analysis, the window between \SI{150}{ns} and \SI{400}{ns} (light grey area) was used.

Ps velocity distribution measured by SSPALS. \\ a) Transverse Doppler profile measured by two-photon resonant ionization (205 and \SI{1064}{\nano\meter} lasers) by means of the $S_{\text{205+1064}}$ parameter. A Gaussian fit yields a rms-width of \SI{44\pm1}{pm}, which translates to a Ps rms-velocity of \SI{5.3\pm0.2e4}{\meter\per\second} after de-convolution of the laser bandwidth.\\ b) Velocity-resolved increase in the number of ground state Ps atoms, induced by the \SI{243}{\nano\meter} transitory excitation to the \tP{} level, represented by the $S_{\text{243}}$ parameter. At resonance, the Lamb dip is clearly visible. A 2-Gaussian fit yields a rms-width of the engulfing Gaussian of \SI{44\pm3}{pm}, which corresponds to a Ps rms-velocity of \SI{4.9\pm0.4e4}{\meter\per\second}.

Ps velocity distribution measured by SSPALS. \\ a) Transverse Doppler profile measured by two-photon resonant ionization (205 and \SI{1064}{\nano\meter} lasers) by means of the $S_{\text{205+1064}}$ parameter. A Gaussian fit yields a rms-width of \SI{44\pm1}{pm}, which translates to a Ps rms-velocity of \SI{5.3\pm0.2e4}{\meter\per\second} after de-convolution of the laser bandwidth.\\ b) Velocity-resolved increase in the number of ground state Ps atoms, induced by the \SI{243}{\nano\meter} transitory excitation to the \tP{} level, represented by the $S_{\text{243}}$ parameter. At resonance, the Lamb dip is clearly visible. A 2-Gaussian fit yields a rms-width of the engulfing Gaussian of \SI{44\pm3}{pm}, which corresponds to a Ps rms-velocity of \SI{4.9\pm0.4e4}{\meter\per\second}.

One-dimensional transverse Doppler profiles of the Ps cloud with (solid curve), and without (dotted curve) interaction with the \SI{243}{\nano\meter} cooling laser beam at a fixed frequency detuning of \SI{-200}{GHz}. The semi-transparent bands represent the statistical measurement error (one standard deviation of the average).

Number of Ps atoms with a velocity within the bandwidth of the \SI{205}{\nano\meter} probing laser, which is kept at resonance, as a function of the cooling laser frequency detuning, normalized to the number of Ps atoms in the absence of all lasers. The dashed horizontal line represents the reference population of Ps atoms in this velocity range with the cooling laser off. The amount of Ps atoms in the center increases by up to \SI{58\pm9}{\percent} at a cooling laser frequency detuning of \SI{-350}{\giga\hertz}. The semi-transparent bands represent the statistical uncertainties (one standard deviation of the average).