MANUFACTURERS OF CUSTOM, HIGH PRECISION INSTRUMENTATION AND SUPPORT EQUIPMENT

Projects

AROTEL Detector Package for the SOLVE Mission

Computer rendition of AROTEL
receiver on 2'x2' breadboard

Time Period

May 1999 to July 1999

Project Description

Airborne Raman Ozone, Temperature, and Aerosol Lidar (AROTEL) is a Lidar instrument for making measurements of ozone, temperature, and aerosols in the atmosphere. AROTEL consists of a transmitter (laser), receiver, and data acquisition electronics. AROTEL's users wanted to upgrade the system before taking the instrument into the SOLVE (SAGE III Ozone Loss Validation Experiment) deployment on-board the DC-8 aircraft.

Photograph of assembled AROTEL receiver prior to adding optics and electronics

The receiver package for the instrument needed to be redesigned. The new design used 10 Photomultiplier Tubes (PMT) each looking at a specific wavelength returned by the atmosphere. The wavelengths are separated by optical beam splitters and filters in front of each PMT further block unwanted wavelengths.

A modular design was desired so that additional channels could be added in the future. This gives the system the ability to quickly be modified to detect a different wavelength or to add more wavelengths. The package I designed uses 10 lens barrel - PMT mounts. Two barrels attach to each beam splitter mount (shown in light bluish-purple in the top image).

Five of these subassemblies make up the ten channels of the system. A chopper wheel and deformable mirror are contained inside of the boxes holding the ten channels together. These two components help to attenuate the strong reflections from the laser beam as it passes through the aircraft window and the atmosphere close to the aircraft. These steps prevent the most sensitive detectors from saturating. The boxes, barrels, and beam splitter mounts are all mounted to an intermediate base-plate shown in gray in the top image. This keeps all of the elements in this receiver package rigidly aligned. Finally, the package is mounted to a 2-foot (61-centimeter) x 2-foot x 2-inch (5.1-centimeter) optical breadboard along side a receiver package designed and built by Langley Research Center.

Challenges and Lessons Learned

Photo of AROTEL Receiver

The biggest challenge on this project was schedule. The entire package was designed in less than one month while Welch Mechanical Designs, LLC (WMD, LLC) was working full time on another project. The hardware was machined in approximately one month, and the final product delivered about 2.5 months after we were brought onto the project.

This is the first project in which we implemented a new design philosophy. Typically, the instrument users want as many alignment adjustments as possible for each optic. The optical engineer wanted to remove all but the most essential optical adjustments for alignment. Recent improvements in machining technology that allow tighter tolerances in complex parts and our attention to detail on the component drawings helped make implementation of this new philosophy possible. The system has one axis of rotation at each beam splitter and focus adjustment at the photomultiplier tubes. Implementing this new philosophy resulted in a final design that simply bolts together, is easy to align, and remains stable during operation.

Photo of Langley receiver module to the left, my receiver design in
the middle and the 16" telescope to the right