Two-dimensional binary arrays with good autocorrelation

Calabro and Wolf (1968)Inform. Contr. 11) investigate the autocorrelation properties of certain periodic two-dimensional arrays. This note points out a relationship between periodic p × q-arrays with two-level autocorrelation and difference sets in the group C(p) × C(q), where C(n) denote the cyclic group of order n. This observation enables us to construct several families of such arrays, some of which are perfect

Binary matrices of optimal autocorrelations as alignment marks

We define a new class of binary matrices by maximizing the peak-sidelobe distances in the aperiodic autocorrelations. These matrices can be used as robust position marks for in-plane spatial alignment. The optimal square matrices of dimensions up to 7 by 7 and optimal diagonally-symmetric matrices of 8 by 8 and 9 by 9 were found by exhaustive searches.Comment: 8 pages, 6 figures and 1 tabl

Stellar intensity interferometry over kilometer baselines: Laboratory simulation of observations with the Cherenkov Telescope Array

A long-held astronomical vision is to realize diffraction-limited optical aperture synthesis over kilometer baselines. This will enable imaging of stellar surfaces and their environments, show their evolution over time, and reveal interactions of stellar winds and gas flows in binary star systems. An opportunity is now opening up with the large telescope arrays primarily erected for measuring Cherenkov light in air induced by gamma rays. With suitable software, such telescopes could be electronically connected and used also for intensity interferometry. With no optical connection between the telescopes, the error budget is set by the electronic time resolution of a few nanoseconds. Corresponding light-travel distances are on the order of one meter, making the method practically insensitive to atmospheric turbulence or optical imperfections, permitting both very long baselines and observing at short optical wavelengths. Theoretical modeling has shown how stellar surface images can be retrieved from such observations and here we report on experimental simulations. In an optical laboratory, artificial stars (single and double, round and elliptic) are observed by an array of telescopes. Using high-speed photon-counting solid-state detectors and real-time electronics, intensity fluctuations are cross correlated between up to a hundred baselines between pairs of telescopes, producing maps of the second-order spatial coherence across the interferometric Fourier-transform plane. These experiments serve to verify the concepts and to optimize the instrumentation and observing procedures for future observations with (in particular) CTA, the Cherenkov Telescope Array, aiming at order-of-magnitude improvements of the angular resolution in optical astronomy.Comment: 18 pages, 11 figures; Presented at SPIE conference on Astronomical Telescopes + Instrumentation in Montreal, Quebec, Canada, June 2014. To appear in SPIE Proc.9146, Optical and Infrared Interferometry IV (J.K.Rajagopal, M.J.Creech-Eakman, F.Malbet, eds.), 201