Density distribution of a Bose-Einstein condensate of photons in a dye-filled microcavity

The achievement of Bose-Einstein condensation of photons (phBEC) in a dye-filled microcavity has led to a renewed interest in the density distribution of the ideal Bose gas in a two-dimensional harmonic oscillator. We present measurements of the radial profile of photons inside the microcavity below and above the critical point for phBEC with a good signal-to-noise ratio. We obtain a good agreement with theoretical profiles obtained using exact summation of eigenstates.

Figure 1

Typical images of the photon distribution inside the cavity below (a) and above (b) the critical point for phBEC. The bright core in the right image is the Bose-Einstein condensate, whereas the surrounding distribution is the thermal cloud.

Figure 2

Typical examples of ${\rho }_n\left(r\right)$ normalized to the maximum value.

Figure 3

Examples of experimental radial profiles measured below [blue (dark gray)] and above [orange (light gray) dashed] the critical point for phBEC. We can detect the decrease of intensity in the thermal tail over more than two orders of magnitude. The insets show the (false color) camera images, from which these radial profiles are computed.

Figure 4

Radial averages for measurements under identical pumping conditions, but with a varying numerical aperture for the collecting lens, i.e., $\oslash =12.7\mathrm{mm}$ (bottom), $\oslash =19.0\mathrm{mm}$ (middle), and $\oslash =25.4\mathrm{mm}$ (top). We see that reducing the numerical aperture clearly cuts the thermal tail. The dashed lines show fits to our theoretical model.