Laser Frequency Comb (LFC)

After graduating with my engineering degree, I stayed in the lab for one last summer to help guide / manage / supervise two newly-graduated astronomy students, who had no previous lab experience. Together we designed and built a thermal control system for Dr. Steven Osterman's Laser Frequency Comb (LFC), an instrument calibration source for finding earth-sized planets in the habitable zone around other stars by measuring stellar radial velocities with high precision.

The instrument was found to be sensative to temperature fluctuations in early testing, so the three of us designed, built and are currently testing a thermal control system capable of maintaining the instrument at +/- 0.1 degree C of the set point (20-25 deg C) within its acoustic isolation enclosure.

This is the process flow chart of the thermal control system:

We used a blower with a hepa filter for the fan, an automotive heater core with chilled water as a heat exchanger to cool and dehumidfy air from the fan, two 400W radiative heaters, 2250 Ohm thermistors, and a PID Watlow controller.

Here is the physical layout of the enclosure that houses the LFC. A different group of students built the acoustic isolation chamber last year, my group is responsible for designing and building the attached thermal system consisting of the fan, chiller, automotive heater core, radiant heaters, controller, various ducts, tubing and miscellaneous hardware.

We were getting strange differences in temperature throughout the box. I ran this model to see what was going on, it was my first FEA fluid flow analysis. Happily for me, my model seems to match what we measured.

This illuminated the need to develop a method for dispersing the air in the enclosure.

Here is the team that built the system (from left): Myself, Chelsea Donaldson, Amir Mirfakhrai and Beth Brenkert, who joined us for two weeks to help during testing.

We are still adjusting the parameters of the controller, here is one of our first plots:

The system was able to keep the LFC at the set point well within tolerances as the ambient (CASA high bay) temperatures fluctuated. When the bias between the enclosure and ambient temperatures became smaller, the controller began to oscillate out of control. We're working on this...

Please see the Laser Frequency Comb circuits page for more on the project.