• Charged Particle Calibration Facility
• Vacuum Ultraviolet Calibration Facility

Vacuum Ultraviolet Calibration Facility

The rotation stage whose axis is vertical (aligned to the cylindrical axis of the vacuum tank ) can turn through 360 degrees while carrying a full sized load. For small packages the horizontal stage also turns through 360 degrees , but its motion is increasingly restricted as the size of the load increases. For a payload on the order of 25cm to a side, this axis is constrained to rotations of 45 degrees about its center position. The configuration described above is ideal for studying cameras that will be mounted aboard a spinning spacecraft where the vertical axis can be used to simulate the effects of spacecraft rotation. Both rotation axes are equipped with shaft encoders having a resolution of 0.001 degrees.

The three translation stages have ranges on the order of 30cm and shaft encoders with resolutions of 1 micron. Having three degrees of translation and two of rotation means that a payload can be oriented equally well with respect to any of the ports and can be exposed to a variety of experiments without breaking the vacuum in order to reconfigure the system.

A monochromatic collimated beam can be generated anywhere in the passband from 150 nm through to the NIR. In order to do this efficiently we have divided the passband into long and short wavelength regions with a separate set of optics and sources for each. The basic arrangement of the VUV optics is described below. The VIS/NIR channel is identical to this except for the passband.

A VUV source and the associated optics required to generate a collimated beam approximately 30mm in diameter have been mounted on one of the vacuum tank ports. This subassembly consists of a focussed Deuterium source whose passband spans the range 115 nm-370 nm, a crossed Czerny monochromator with a 2400 groves/mm UV grating blazed for 150nm, pinholes and slits to vary the throughput and spectral resolution, a diamond machined off-axis parabolic mirror to generate the collimated beam from the f/5.6 monochromator output, a f2 beam splitter to direct approximately 10 percent of the beam to a reference photomultiplier tube (PMT), and the reference PMT with its associated amplifiers, line drivers, and photon counting electronics. The crossed Czerny design significantly reduces those optical aberrations characteristic of one mirror monochromator configurations that would seriously degrade the beam collimation.

There is a flat field source available to users of the system in the form of an integrating sphere with a 100 mm diameter exit port that has been absolutely calibrated spectrally to an accuracy of 3 inch steps of 10nm from 280nm out to 2000nm. This is being used to calibrate an imaging spectrometer that was flown aboard the Odin spacecraft in 1997.

The system has the capability to cool a payload mounted on the manipulator using liquid N₂, although the degree of cooling and the complexity of the mechanical and thermal fixturing can vary substantially from payload to payload.

Much of the equipment described above has either RS232 or IEEE interfaces connected to a Pentium PC for the purpose of data acquisition and control. In particular, the manipulator, monochromator, temperature controller, vacuum gauges, and photon counters are computer controlled. The PC is connected by ethernet to a Silicon Graphics workstation where computationally intensive analysis can be undertaken and where very large numbers of images can be stored and quickly retrieved from hard disk.

A few of the smaller ports on the vacuum tank have been outfitted with electrical feedthroughs. These include BNC connections for low level signals, MHV and SHV connectors for voltages up to several kiloVolts, and general purpose feedthroughs for digital signals. In addition there are feedthroughs dedicated to the manipulator, encoders, temperature sensors, and other housekeeping functions.