Intensity-Intensity Correlation of Light from an Ultracold Thermal Source

Abstract

Light from a thermal source, i.e., a blackbody radiator, shows bunching. In other words, given a photon is emitted by such a source at a time 't', the likelihood that another photon will be emitted at 't + τ' is higher for small τ than for large τ. This is quantified by the second-order 2intensity-intensity correlation, G (τ), which theoretically, for a thermal source must be 2 for τ = 0. However, due to limitations of the timing resolution of the photon 2counting electronics, thus far the values of G (0) obtained have been in the range 1.3-1.5; only recently has there 2been a report [1] of having measured a value of G (0)=2. We report here measurements of the intensity-intensity correlation in the fluorescence from a collection of laser cooled atoms in a magneto-optic trap. The measurement was performed using a home-built FPGA-based time-tagged single photon counting system, APODAS. Fluorescence from the cold atoms was collected by means of a high numerical aperture lens within the vacuum chamber and conveyed by an optical fiber to a pair of avalanche photodetectors in the Hanbury-Brown Twiss configuration. Arrival times of photons was 2recorded for an 8-hour duration and G (τ) determined by 2post-processing. We obtained a value of G (0) = 1.94 and 2G (τ) = 1.05 for large t.