Publications

The orthogonal transfer array (OTA) is a novel charge-coupled device (CCD) imager based on the orthogonal-transfer CCD (OTCCD). The OTCCD, in turn, is a device capable of charge transfer in all directions and has been developed for adaptive imaging in ground-based astronomy. By using a bright guide star as a beacon, the OTCCD can correct for wavefront tilt due to atmospheric effects as well as compensation for telescope shake, which in turn enhances the resolution and SNR. However, for wide field-of-view imaging the atmospheric wavefront distortions decorrelate over distances more than a few 10's of arcmin and hence an array of independently driven OTCCDs is required. To resolve this issue we developed the OTA, which consists of a two-dimensional array of OTCCDs combined with addressing and control logic to enable independent clocking of each OTCCD. This device enables spatially varying electronic tip-tilt correction and was developed for the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) program at the University of Hawaii Institute for Astronomy (UH/IfA)

The orthogonal-transfer array (OTA) is a new CCD architecture designed to provide wide-field tip-tilt correction of astronomical images. The device consists of an 8..8 array of small (~500x500 pixels) orthogonal-transfer CCDs (OTCCD) with independent addressing and readout of each OTCCD. This approach enables an optimum tip-tilt correction to be applied independently to each OTCCD across the focal plane. The first design of this device has been carried out at MIT Lincoln Laboratory in support of the Pan-STARRS program with a collaborative parallel effort at Semiconductor Technology Associates (STA) for the WIYN Observatory. The two versions of this device are functionally compatible and share a common pinout and package. The first wafer lots are complete at Lincoln and at Dalsa and are undergoing wafer probing.

Improved and stable blue/UV quantum efficiency has been demonstrated on 2Kx4K imagers using molecular-beam epitaxy to create a thin doped layer on the back surface. Quantum efficiency data on thick (40-50 pm) imagers with single and dual-layer anti-reflection coatings is presented that demonstrates high and broadband response. Measurements of the optical point-spread response show the devices to be fully depleted with good response across a broad spectrum, but interesting features appear in the near-IR as a result of deeply penetrating light being scattered off the surface structure of the CCD.