QUASAR: Development of 20 picosecond resolution intensity interferometry

Recent developments in single-photon avalanche diodes (SPADs) have lowered detector time resolution to under tens of picoseconds. In 1956, the pioneer experiment of Hanbury Brown and Twiss (HBT) on measuring the sizes of bright stars was limited by the time resolution of their detectors and their telescope size. The QUASAR project aims at building a SPAD-based multichannel intensity interferometer to be installed on large optical telescopes with kilometers-long baselines, improving the S/N obtained by Hanbury Brown and Twiss by one million and aiming to reach EHT-like resolution in visible light. In this work, we report the results of laboratory tests of SPAD detectors to observe the HBT effect in photon-counting mode. Using a simple laboratory setup and cutting-edge SPAD detectors, we deduce a time accuracy of <50ps FWHM. Additionally, using thermal sources and narrow spectral filters, we analyze the second-order correlation function obtained from different light sources of continuous and line spectra. Results are discussed and compared with quantum optics models. Furthermore, we report on a setup, allowing us to simulate and estimate the size of an artificial star of known size to verify the analysis and data correlation techniques employed in the QUASAR project.