Optical-Mechanical Design for the Remote Infrared Detection Trailer

The FM Dial system is shown on the optical table
The FM Dial system is shown on the optical table and
consists of a quantum cascade laser transmitter,
turning mirror, and receiver telescope. The turning mirror
steers both the transmitted beam and the telescope
field of view, and allows selection of the direction for the
remote sensing experiment.
Photo of remote infrared detection trailer
Field experiments are being conducted by the Remote
Sensing and Electro-optics Group at PNNL to explore the
instrument response for different configurations.

Scientists in the Remote Sensing and Electro-optics Group of Pacific Northwest National Laboratory's National Security Directorate are developing advanced infrared sensors for detecting and identifying chemicals of interest to national security concerns, science research, environmental monitoring, and industrial activities. Spectroscopic techniques are of interest because they can be used to detect and identify chemicals at a distance, or to provide ultra-sensitive, real-time identification of chemicals in collected air samples. National security priorities dictate a rapid-transference of laboratory-based results to fieldable systems. Towards this end, staff from the Mechanical and Robotics Systems Group have supported the Remote Sensing and Electro-optics Group by designing several rugged optical-mechanical systems capable of being transported to remote locations.

To perform LIDAR experiments, it is desirable to manipulate the telescope beam in the vertical and horizontal trajectories while keeping the telescope stationary. One way to accomplish this is to point the telescope at the center of a gimbal-mounted mirror, and use the gimbal to modify the optical field of view. For this application, a 21.875-inch diameter, 3.5-inch thick, borosilicate glass mirror was required. An economical approach consisting of mounting the mirror to a commercially available telescope gimbal was pursued. A mirror mounting ring was designed and fabricated to attach the mirror to the telescope gimbal. The mount consists of a large aluminum flange, a three-point back support, spring-loaded mirror clips, and bearing posts. Spring-loaded mirror clips were added to maintain contact between the ring and the mirror during downward viewing and to accommodate the mismatch in thermal expansion between the glass and the aluminum. Prior to fabrication, gimbal tests were undertaken to verify that the worm-gear drives had sufficient capacity to handle the substantial inertia of the large 22-inch diameter mirror. The gimbal has been in service for several months and is working well.

Engineers from the Mechanical Solutions Group were also involved in the development of a Remote Infrared Detection Trailer to allow chemical emissions and background variability experiments to be performed at a number of remote locations. A custom jacking system was designed for the optical table to affix the optical table directly to the ground through holes in the trailer floor. The jacking system allows infrared detection systems to be used at longer ranges (up to 5 km) by eliminating jitter caused by wind or personnel movement within the trailer. The jack itself was fabricated at a reasonable cost by attaching telescoping column actuators to the legs of the optical table.

Project Contact: B. Hatchell