This arXiv preprint (v1, June 2026) details an experimental frequency upconversion scheme that translates 3-micron mid-infrared photons into the visible band at 80% internal efficiency before detection with a silicon avalanche photodiode, yielding 37% overall efficiency and noise-equivalent power of 1.8e-17 W/sqrt(Hz). The setup further demonstrates photon-number resolution up to 9 photons using a multi-pixel counter at 0.14% noise probability. Unlike prior upconversion work focused on continuous-wave or low-efficiency regimes, the spectro-temporal engineering here enables pulsed single-photon operation. The paper is a preprint without peer review and reports a controlled lab demonstration rather than field trials or statistical sample sizes across multiple devices. Earlier demonstrations, such as those in Optica 2022 on MIR upconversion for spectroscopy, achieved lower efficiencies around 20-30% and lacked number resolution; this work surpasses them but inherits common limitations like cryogenic or stabilized pump requirements not fully quantified here. Applications in trace-gas sensing and free-space links could accelerate once integrated with on-chip waveguides, yet the approach risks overlooking thermal noise floors in uncooled environments that competing superconducting detectors already mitigate in niche quantum LIDAR tests.