Tesora

Tesora, a hooded cold-watcher, senses a single photon by its tiny warmth.

The Physics

A transition-edge sensor is a thin superconducting film held right at the edge of its superconducting transition, where its resistance rises from zero to normal within a tiny temperature range. Absorb a photon or particle and the film warms very slightly, its resistance jumps, and the current through it changes measurably. K. D. Irwin showed how to hold it stable on the edge with voltage bias and electrothermal feedback (Appl. Phys. Lett. 66, 1998, 1995). The steepness is measured by a logarithmic sensitivity.

α = d ln R / d ln T

• α: logarithmic temperature sensitivity, dimensionless
• R: film resistance (Ω)
• T: film temperature (K)

The larger α is, the steeper the edge and the smaller the energy that can be detected. TES arrays measure single optical photons, X-rays and the cosmic microwave background.

Honest caveat: The film must be cooled to its transition temperature, typically well below 1 K. Out of the transition, α is small and the sensor is not sensitive.

On the sticker

Tesora, a hooded figure in cold blue light; the steep transition curve is not drawn. Printed text: TESORA with the line α = dlnR/dlnT. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.