Cheng Ho

The XMM-Newton optical/UV monitor telescope

The XMM-OM instrument extends the spec- tral coverage of the XMM-Newton observatory into the ul- traviolet and optical range. It provides imaging and time- resolved data on targets simultaneously with observations in the EPIC and RGS. It also has the ability to track stars in its field of view, thus providing an improved post- facto aspect solution for the spacecraft. An overview of the XMM-OM and its operation is given, together with cur- rent information on the performance of the instrument.

Laser ranging and mapping with a photon-counting detector.

We propose a new technique for remote sensing: photon-counting laser mapping. MicroChannel plate detectors with a crossed delay-line (MCP/CDL) readout combine high position accuracy and subnanosecond photon timing, at event rates of 10(6) detected photons per second and more. A mapping system would combine an MCP/CDL detector with a fast-pulse, high-repetition-rate laser illuminator. The system would map solid targets with exceptional in-range and cross-range resolution. The resulting images would be intrinsically three dimensional, without resorting to multiple viewing angles, so that objects of identical albedo could be discriminated. For a detector time resolution and pulse width of the order of 10(-10) s, the in-range resolution would be a few centimeters, permitting the discrimination of surfaces by their textures. Images could be taken at night, at illumination levels up to full moonlight, from ground, airborne, or space platforms. We discuss signal to noise as a function of laser flux and background level and present simulated images.

Demonstration of literal three-dimensional imaging

In a recent paper a new technique was proposed for remote ranging and topographical mapping by using a system with a single-photon-counting detector and a low-power pulsed laser [Appl. Opt. 35, 441 (1996)]. We report on the results from the laboratory and the field demonstration of this literal three-dimensional imaging technique. Using a detector system developed at Los Alamos with a commercial pulsed laser and observing from a single remote vantage point, we demonstrate use of this technique in the literal mapping of three-dimensional topography and the probing of a complex scene. With a reasonably short exposure this system can resolve features with height variations as small as 5 cm.

XMM Optical/UV Monitor Telescope

The optical/UV monitor (OM) on the ESA x-ray cornerstone mission XMM is designed to provide simultaneous optical and UV coverage of x-ray targets viewed by the observatory. The instrument consists of a 30 cm modified Ritchey-Chretien telescope. This feeds a compact photon counting detector operating in the blue part of the optical spectrum and the UV (1600 - 6000 angstrom). The OM has a square field of view of approximately 24 arcmin along the diagonal, and will cover the central region of the field of view of the EPIC x- ray cameras where the x-ray image quality is best. Because of the low sky background in space, the sensitivity of the OM for detecting stars will be comparable to that of a 4-m telescope at the Earths surface; it should detect a B equals 24th magnitude star in a 1000 s observation using unfiltered light. The pixel size of the detector corresponds to 0.5 arc seconds on the sky in normal operation. In front of each of two redundant detectors are filter wheels containing broad band filters. The filter wheels also contain Grisms for low resolution spectroscopy of brighter sources (lambda/Delta lambda 200) and a 4x field expander which will allow high spatial resolution images of the field center to be taken in optical light.

Probing galaxy evolution with the optical/UV monitor on XMM

The Optical Monitor is one of the three instruments on XMM, the X-ray Multi-Mirror Mission, scheduled to launch in August of 1999. The Optical Monitor is a 30 cm telescope system that will image in 7 bands from 1500 A to 6000 A, with a resolution of 1 arcsecond. Two grisms are available for low-dispersion spectral discrimination. The Optical Monitor will be coaligned with the X-ray instruments and the expected long integrations will allow detection of point sources as faint as 24th magnitude. Over the course of the XMM mission, a large database of galaxy observations, both targeted and serendiptous, will be assembled, covering far-ultraviolet through optical wavelengths. We indicate here ways in which these observations will be used to study galaxy evolution.

Preliminary analysis of lidar techniques for regional meteorological studies

Preliminary scoping exercises indicate that remote-sensing lidar can play a useful role in missions that involve determining regional weather patterns and atmospheric transport conditions. Both meteorological modeling and local atmospheric sensing should be employed. Satellite-based remote sensing systems, using an incoherent Doppler wind-sensor, seem feasible.

Laser ranging and mapping with a photon-counting detector

We propose a new technique for remote sensing: photon-counting laser mapping. Micro- channel plate detectors with crossed delay-line (MCP/CDL) readout combine high position accuracy and sub-nanosecond photon timing, at event rates of 106 detected photons per second and more. A mapping system would combine an MCP/CDL detector with a fast pulse, high repetition rate laser illuminator. The system would map solid targets with exceptional range and cross-range resolution. The resulting images would be intrinsically three- dimensional, without resorting to multiple viewing angles, so that objects of identical albedo could be discriminated. For a detector time resolution and pulse width of order 1010 seconds, the in-range resolution would be a few centimeters, allowing the discrimination of surfaces by their textures. Images could be taken at night, at illumination levels up to full moonlight, from ground, airborne, or space platforms. We discuss signal-to-noise as a function of laser flux and background level.

Flare star observations with a single-photon counting imaging detector

At Los Alamos National Laboratory we are developing a new imaging sensor which combines high spatial and high temporal resolution over a large area format, while maintaining single-photon counting sensitivity and sustaining a high count rate. The detector is called a microchannel plate with crossed delay line readout, or MCP/CDL. This detector is ideally suited to the observation of weak transient events, such as stellar flares from red dwarf flare stars in our Galaxy. At present we are initiating an experiment with the MCP/CDL detector which will utilize a 30-cm aperture f/7 telescope to characterize U-band, B-band, and V-band emission from such low-luminosity flare stars, and to search for weak optical transients associated with other astrophysical sources.

Breadboard phase of the XMM optical monitor

A multi-national consortium of research groups are developing the XMM (x-ray multi-mirror mission) optical monitor to provide a capability for optical identification and photometry of x-ray sources observed by the XMM observatory. This will be the first multi-wavelength facility dedicated to monitoring the variability of diverse sources from the optical through to x-ray wavelengths. Here we describe the system design and discuss progress in the breadboard phase of the development program.