PHASERS

Time period

June 1998 to November 1998

Project description

PHASERS stands for Prototype Holographic Atmospheric Scanner for Environmental Remote Sensing. The main element of the instrument is a Holographic Optical Element, or HOE, that acts both as a focusing telescope and a scanning mirror. The HOE is shown as the gray/green colored flat disk below the tripod in the picture to the right. The laser beam shoots parallel to the table top, reflects off a turn mirror above the HOE, strikes the HOE surface and is reflected off into the atmosphere at approximately 45 degrees from the horizon. This laser beam excites the atmosphere and the HOE collects the photons returned by the atmosphere and focuses them upward into the orange cylindrical light baffle. At the top of the baffle is a fiber optic coupler where the focused light is fed into a fiber optic and routed to a photo-multiplier tube in a convenient location in the test setup.

In this system, the HOE is on a motorized stage so that it can rotate about its center. This allows the instrument to view a cone, approximately 90 degrees full width. An example of the data taken with the early version of this system can be seen here.

The system shown in these pictures is a redesign of an original instrument. The original instrument had poor stray light baffling, was structurally unstable, and had a PMT located at the HOE focus. The new design relocates the PMT via a fiber optic coupling to a more convenient location. Structural rigidity was improved by replacing the three thin legs supporting the heavy PMT with a stiffer, buttressed set of short legs attached to a very rigid aluminum tube. Stray light layouts were created to design the best possible baffle for this system. The conical scanning path made it even more difficult to design effective stray light baffles.

We installed the mechanics of the system in November of 1998 at Saint Anselm College for Dr. David Guerra.

Challenges and lessons learned

This was the first system we designed that incorporated a HOE and fiber optic coupling. The knowledge gained on this project proved to be quite useful in projects we worked on later.