Figure 1

${\mathrm{Ps}}_2$ resonance measured inside a porous silica film. All data recorded in four separate runs as a function of the laser (vacuum) wavelength (a) and rebinned data (b) The vertical scale is the change in the delayed fraction in percent. The measurement for the single square point in (b) was obtained as described in the text. The solid lines are simple Gaussian fits to the data from which we determine a line center of ${\lambda }_0=(250.979\pm 0.006)\mathrm{nm}$, amplitude $(0.027\pm 0.008)\%$, and a full width at half maximum (FWHM) of $(0.069\pm 0.026)\mathrm{nm}$. The dashed vertical line indicates the theoretical resonant wavelength for the ${\mathrm{Ps}}_2$ excitation in vacuum.Reuse & Permissions

Figure 2

${\mathrm{Ps}}_2$ resonance measured in vacuum with an Al(111) crystal at room temperature: (a) data with uv laser-on and off showing variations in $f_d$ during the measurement and the quadratic fit to the laser-off data. Measurements are labeled sequentially using upper (lower) case letters for green photoionizing laser on (off). (b) lineshape measured with the uv and green lasers on. The dashed line in (b) is a single Gaussian fit to the data and the solid line is a Double Gaussian fit (with a single width), as explained in the text. The dashed vertical line indicates the theoretical resonant wavelength for the ${\mathrm{Ps}}_2$ excitation in vacuum. (c) Measurement with uv laser on and green laser off, showing the best fitting horizontal line, $\Delta f_d=(0.016\pm 0.087)\%$, consistent with no effect.Reuse & Permissions