Mid-infrared spontaneous and stimulated emission dynamics in black phosphorus
Abstract
Black phosphorus (BP) has attracted attention as a light-emitting layered semiconductor for mid-infrared (MIR) photonics owing to its direct and thickness-tunable bandgap energy, highly anisotropic optical transitions, and potentially suppressed Auger recombination. However, spontaneous and stimulated emission dynamics governed by carrier recombination in BP have remained unexplored because time-resolved emission spectroscopy is challenging in the MIR region. Here we develop a time-resolved MIR emission microscope combining wavelength upconversion with superconducting single photon detection. This approach enables observation of emission dynamics in photoexcited BP at a wavelength around 4.6 {\mu}m with sub-100-ps temporal resolution. Temperature-dependent measurements reveal a crossover from excitonic to electron-hole plasma emission at around 70 K, supported by independent results in the characteristic transition temperature, pump-fluence dependence, and rise and decay dynamics of MIR emission. In a suspended BP structure, we further observe a nonlinear increase in the emission intensity above a well-defined pump threshold. Spectral narrowing and intense picosecond emission pulses appear above the threshold, providing solid evidence of stimulated emission assisted by optical feedback from a Fabry-P\'erot cavity. These results elucidate ultrafast carrier dynamics and optical gain formation in BP and establish time-resolved upconversion spectroscopy as a powerful approach for investigating MIR photonic materials and devices.
Keywords
Cite
@article{arxiv.2608.03346,
title = {Mid-infrared spontaneous and stimulated emission dynamics in black phosphorus},
author = {Hisashi Sumikura and Akihiko Shinya and Masaya Notomi},
journal= {arXiv preprint arXiv:2608.03346},
year = {2026}
}