Brookhaven National Laboratory

My project is the thermal characterization of an ellipsoidal reflector furnace. An ellipsoid has a useful geometric property: every ray leaving one focus reflects off the surface and lands on the other focus. Put a high-power lamp at the first focus of a mirrored ellipsoidal shell, and all of its light converges on the second focus, heating whatever sits there to temperatures up to about 1200 °C, with no heating element and no contact.

The setup includes an xyz positioning stage that moves samples with 0.1 mm precision and a camera with a microscope objective for watching the sample as it heats. Furnaces like this are used for crystal growth, materials synthesis, and rapid thermal processing in semiconductor manufacturing. Before anyone can run careful experiments with one, someone has to answer a basic question: what temperature is it actually producing, and where? That is this project.

Measuring temperature inside a furnace built from focused light is harder than it sounds. A thermocouple sitting in the beam blocks the light path and heats up on its own, so it reads wrong. A non-contact pyrometer depends on knowing the sample's emissivity, which varies from material to material.

Melting points sidestep both problems. They are fixed physical constants, and a solid-to-liquid transition is unmistakable on camera. The calibration ladder runs from zinc to iron: