Achieving high angular resolution has always been a key goal in astronomy. While radio interferometry, such as the Event Horizon Telescope, has reached micro-arcsecond scales, achieving similar resolution in optical wavelengths is much harder because phase coherence cannot be maintained over kilometer-scale baselines. HBT Interferometry, first demonstrated by Hanbury Brown and Twiss (HBT), offers a powerful alternative by correlating intensity fluctuations instead of phases, making it far more robust for long-baseline optical observations.
In this talk, I will explain advanced HBT-based Intensity Interferometry for both single and binary stars. It includes reconstructing images of fast-rotating stars using machine learning and detecting radial pulsations in Polaris-type stars through simulated intensity correlations. I will also show some initiated efforts to develop collaborations aimed at bringing high-time-resolution photon detectors to Devasthal Observatory. In parallel, this talk will explain the other aspect of DFOT and DOT as Speckle Interferometry, which applies similar principles (HBT effect) using fast CMOS/CCD detectors. Together, these efforts form the initial steps toward establishing optical interferometry capabilities at Devasthal Observatory and strengthening India’s high-resolution optical astronomy program.