Double Cavity Exceptional Point Enhanced Laser Cooling of Semiconductors

Laser cooling of semiconductors requires a high external quantum efficiency for phonon-assisted upconversion while suppressing heat generated by background absorption and non-radiative relaxation. Nanophotonic resonances can strengthen the upconversion channel, but in a single-mode structure may also enhance parasitic pump heating. We introduce a two-cavity non-Hermitian architecture that separates preparation of a lower reservoir state from extraction of the phonon-promoted radiative state. A passive exceptional point, containing no optical gain, is placed in the output branch, where it reshapes the projected final-state optical response; all anti-Hermitian diagonal terms describe radiative leakage, internal absorption, or material decay. For a CdS parameter set, the four-mode calculation gives a 1.23 × 10³ enhancement of upconverted photoluminescence (UCPL) relative to a single-mode control, while the pump-induced heat load rises by only 2.8×10^-3%. The gain consists of a factor of 3.45×10² from the independent output resonance and a further factor of 3.56 from exceptional-point tuning.