NASA — Rotary Shearing Interferometer

Designing a compact, time-saving device for a space telescope testing lab


At the NASA Goddard Space Flight Center, I designed a rotary shearing interferometer to speed up space telescope alignment and collimation in the ICESat-2 Optical Design System lab, the mission's optics sandbox for running experiments on the ground to validate designs and components before launch.

The ICESat-2 mission aims to quantify climate change by measuring ice sheet thickness, sea level changes, and forest canopy height with a laser altimeter system in space. The satellite beams a laser at Earth and captures reflected photons using a high-power telescope.


Optomechanical Engineering Intern


Jan 2013 — Feb 2013 (2 mos)


Fully-assembled device

NASA Goddard space flight center — icesat-2 mission / winter 2013

The Tilt'N'Whirl

Mechanical design and engineering

Every optics experiment begins with calibrating laser-telescope for proper instrument alignment and laser collimation as vibrations and minor changes in temperature and humidity can offset these conditions. Massive 3' and 1'-diameter mirrors are moved into the lab reflect laser light the into a camera for inspection. Because the mirrors are so large and heavy, alignment is incredibly cumbersome. The whole process can take up to four hours.

My solution in place of these cumbersome mirrors was a rotary shearing interferometer, internally nicknamed the Tilt'N'Whirl. It consists of two 6" glass wedges that offset incident laser light and display the interference pattern onto a textured glass sheet. If the interference patterns, or fringes, are parallel to the shear axis of the glass wedge, then the laser light is collimated.

The Tilt'N'Whirl, a lightweight and collapsable rotary shearing interferometer for quick laser collimation inspection.

Each glass wedge is angled to inspect the interference patterns on two orthogonal shearing axes to determine proper collimation. The glass wedges sit on a linear track that rotates 360 degrees at its center. With radial travel on a rotating linear track, the glass wedges can be used to quickly inspect the quality of the 3-ft diameter incident laser light.

Custom shearing interferometer module. A machined aluminum cradle houses the glass wedge which displays interference patterns from incident light on a textured glass plate.

The two shearing interferometers sit on a linear track that rotates 360 degrees at its center.

The Tilt'N'Whirl is designed in 80/20, an easy-to-use aluminum extrusion rail system. It's lightweight and collapsable when not in use, making the laser-telescope setup much easier. The Tilt'N'Whirl reduced the setup time from up to four hours to just 30 minutes.

The Tilt'N'Whirl in its collapsed configuration used for storage.

The interferometers sit on a quick-lock/release slide. The ends of the linear track are capped in red for visibility and safety.