Toward the In Situ Detection of Individual He2* Excimers Using a Ti TES in Superfluid Helium

We characterize a single titanium (Ti) transition edge sensor (TES) designed for in situ detection of individual He₂ excimers. We find a critical temperature of 420 mK, an electrothermal time constant of ~3 μs, and a total energy resolution of 1.5 eV. We observe the detector response to short laser pulses and present a successful analysis strategy for extracting direct-TES-hit pulses from a much larger background (due to substrate hits). We also present the response of a similar Ti TES with a built-in aperture designed to eliminate substrate background; this device has an energy resolution of better than 1.5 eV and a much reduced substrate signal. We discuss near-term plans for coupling multiple such TESs together with a shared aluminum (Al) absorber, increasing the He₂ collection area to millimeter scales.