Steven Michael Ebstein

Speckle imaging with the PAPA detector

A new 2-D photon-counting camera, the PAPA (precision analog photon address) detector has been built, tested, and used successfully for the acquisition of speckle imaging data. The camera has 512 × 512 pixels and operates at count rates of at least 200,000/sec. In this paper we present technical details on the camera and include some of the laboratory and astronomical results which demonstrate the detectors capabilities.

Recovery of spatial-coherence modulus and phase from complex field correlations: fourth-order correlation interferometry

A method is presented for recovering the modulus and phase of the spatial coherence of a circular complex Gaussian random field, e.g., laser speckle, from fourth-order field correlations. A one-dimensional experimental verification of the method is described, and its usefulness for coherence function imaging is demonstrated. The variance of the measured quantity is shown to agree with a calculation for the high-light-level regime.

Stellar speckle interferometry energy spectrum recovery by convex projections

A new method is described for recovering the object energy spectrum in stellar speckle interferometry. An initial division estimate is improved with a constrained iterative algorithm that uses projections onto convex sets. The technique is demonstrated to recover the energy spectrum out to frequencies where the signal-to-noise ratio is <1.

High-light-level variance of estimators for intensity interferometry and fourth-order correlation interferomel

The variance of certain estimators relevant to intensity interferometry, laser speckle correlography, and fourth-order correlation interferometry are considered when the field amplitude obeys circular complex Gaussian statistics and the classical or high-light-level regime is obtained. A family of optimal unbiased estimators for |μ(Δ)|2, the squared modulus of the spatial-coherence factor, is found when a single measurement is performed and 〈I〉, the mean intensity, is known a priori. Calculations of the variance of multiple-measurement estimators for |μ(Δ)|2 and μ*(Δ)μ*(Δ + e) are performed. Results of statistical measurements of laser speckle are presented and are shown to agree with the calculations.

Bispectral diffraction imagery. I. The bispectral optical transfer function

An integral representation of the bispectral optical transfer function, 〈T(α1)T(α2)T(−α1 − α2)〉, has been obtained in terms of the spatially random wave-front aberrations induced by the turbulent atmosphere and the deterministic wave-front aberrations of an optical system with an exit pupil in the shape of a slit (narrow rectangular aperture). Representative numerical calculations have been carried out for focused and defocused nonaberrated optical systems as well as for systems suffering from third-order coma. The phase of the bispectral transfer function is identically zero for the former cases but not for the latter case. The resultant contour plots of equal phase are shown and discussed.

Estimating the Cramer-Rao bound for restored astronomical observations

This work addresses the problem of assigning confidence intervals to estimated photometry data obtained from astronomical observations. The proposed solution is to estimate the Cramer-Rao bound, which is an analytical expression that describes the minimum obtainable mean square error associated with a given estimate of a parameter. This Letter presents a compact and simple form for the bound associated with a linear estimator such as a Wiener filter estimator. A prescription for estimating the variance associated with each element in a restored object was developed using an analytical model for observed data corrupted by either Poisson or Gaussian noise. Both one- and two-dimensional examples are presented.

Digital recording on video cassette

A system is described that records digital data onto video cassettes and writes the data to a computer tape for subsequent processing. The system is capable of recording and playing back 172 800 bytes/s. This corresponds to the maximum rate achievable with a nine‐track computer tape drive writing 1600 bits per inch at 125 ips. A standard two‐hour cassette has a capacity of 1.2 Gbytes. Six checkbits are written with each 16‐bit word to facilitate error detection and correction. Upon playback, the data are written via DMA into a computer and then to a nine‐track computer tape. Error rates of less than 1 word in 300 000 have been achieved with an off‐the‐shelf portable video recorder and commercially available tape. The system comprises a low‐cost solution to the problem of high‐volume, fast data recording at remote locations when a small error rate can be tolerated.