Wavelength-Resolved Timing of Near-Infrared Scintillation in Gaseous Xenon

The near-infrared (NIR) scintillation signal of xenon has the potential to enhance the performance of xenon-based detectors, but a robust understanding of its properties is a prerequisite for its application. In this work, we measure the NIR time response for $\alpha$-particle interactions in gaseous xenon in 12 wavelength bands spanning approximately $(950-1620)$nm. The time response is decomposed into a fast (ns-scale) component and a dominant slow ($\mu$s-scale) component. The fast-component spectrum coincides with strong atomic emission lines, predominantly 6p$\to$6s, whereas the slow-component spectrum follows the broad continuum centred around $1.3\mu$m. The pressure dependence of the continuum can be described by a two-step kinetic model in which the emitting state is formed by a three-body process and depopulated by a two-body collisional process, with density-independent terms in both rates. Interpreting the slower of these as radiative decay yields an intrinsic lifetime of $\sim 3\mu$s. Theoretical calculations identify a neutral-excimer transition $0_u^{-}\to 0_g^{-}$ and an ionic-dimer transition $1\mathrm{/}{2}_u\to 1\mathrm{/}{2}_g$ as plausible candidates for the continuum emission, with the ionic-dimer transition showing better overall agreement with the measurements.