Experimental study of the momentum correlation of a pseudothermal field in the photon-counting regime

Thermal (or pseudothermal) radiation has been recently proposed for imaging and interference types of experiments to simulate entangled states. We report an experimental study on the momentum correlation properties of a pseudothermal field in the photon counting regime. The characterization and understanding of such a light source in the context of two-photon physics, especially its similarities and differences compared to entangled two-photon states, is useful in gaining knowledge of entanglement and may help us to assess the real potential of applications of chaotic light in this context.

Figure 1

Sketch of the experimental setup.

Figure 2

Histogram of number of joint detection counts vs time difference of the two photoelectron events. The size of each channel is $0.3\mathrm{ns}$.

Figure 3

Normalized second-order correlation function vs position of detector $D_2$. The various sets of data (points) are for different sizes of the pseudothermal source (circles $\sim 150\mu \mathrm{m}$; squares $\sim 350\mu \mathrm{m}$; triangles $\sim 550\mu \mathrm{m}$; diamonds $\sim 1100\mu \mathrm{m}$) and agree with the theoretical expectation (solid lines).

Figure 4

Normalized second-order correlation function vs position of detector $D_2$ for three fixed positions of detector $D_1$: (a) $x_1\simeq -1.75\mathrm{mm}$; (b) $x_1\simeq 0\mathrm{mm}$; (c) $x_1\simeq 1.75\mathrm{mm}$ (source size $\sim 550\mu \mathrm{m}$). In part (b) is shown also a plot of single counts vs position of the detector for both $D_1$ (filled squares) and $D_2$ (hollow squares). The level of the counts is around $60000∕\mathrm{s}$.