Intensity interferometry second order correlation measured on Sirius with 10" telescopes

We present the design and initial results of a stellar intensity interferometer using small 0.25 m Newtonian-style telescopes in an urban backyard setting. Using Sirius as a target star, which yields 2.0 Mcps per detector with matched 1 nm wide filters at 589.6 nm, we obtained a strong second-order correlation spike with an SNR > 10 (FWHM width of 310 ps) after 13.5 hours of integration over a three-night period. The maximum baseline of the telescopes was 3.3 m. Our optical system allows for on-axis guiding and tracking of the star, keeping it centered on a 100 µm diameter fiber optic cable, which ensures a steady detector count rate throughout the evening. Future work includes collecting data with other baselines and bright stars while using a lower jitter setting on our time-tagger (26 ps vs. 140 ps FWHM).