Speaker
Description
The Quantum Astrometry project at Brookhaven National Laboratory (USA) is working towards a demonstration of the SNSV scheme of intensity interferometry, as first proposed in Stankus et al. (2022, DOI: astro:2010.09100). By measuring the oscillation of HBT visibility between two optically-disconnected telescope stations as the Earth rotates, the SNSV scheme determines the opening angle between two widely separated sources, an astrometric measurement. While this scheme recovers phase information, technically making it amplitude interferometry, it can be thought of as a generalization of the HBT measurement of a binary system to wide angles. The scheme is similar to intensity interferometry in both the challenges it faces — coupling to single-mode fibers, high time and spectral resolution, sensitivity with dim sources — and in the advantages it provides over traditional Michelson interferometry — optically-disconnected telescopes, scalability to many baselines, spectroscopic multiplexing.
After giving an overview of the SNSV scheme, I will discuss an on-the-ground simulation of a single and binary star HBT measurement with small telescopes (⌀102 mm), using multimode fibers (⌀50 μm) as simulated stars. Our source of light was a red LED filtered by an ultranarrow bandpass filter (0.1 nm FWHM). Starting with one bare fiber end emitting light 70 m from the telescopes, we determined the diameter of the fiber core by tracking the HBT visibility as the telescope baseline was varied from 20 to 80 cm. We then measured the HBT visibility of two fibers separated by 125 μm as their angular orientation relative to the baseline was varied. The visibility vs angle curve was observed to have a local minimum between two local maxima, a feature characteristic of observing an unresolved target comprised of multiple sources.
