| Abstract: | Differential AC Stark shifts arise when light couples differently to distinct atomic energy levels, leading to intensity-dependent shifts of the transition frequency between them. Such shifts limit the performance of atomic states in cooling, detection, and precision metrology. In this work, I study the D1 transition of fermionic 40K atoms confined in far-detuned optical tweezers. While the magic wavelength for potassium has been theoretically predicted, it has not previously been measured. I present the optical-tweezer apparatus and the cooling and state-preparation techniques that enable high-precision spectroscopy. Using loss spectroscopy on few-atom ensembles, I measure the dependence of the transition frequency on trap power and wavelength, allowing identification of the magic wavelength at which the differential shift vanishes. I extract a value of 1227.54(3) nm, in excellent agreement with the theoretical prediction of 1227.55 nm. This measurement provides an important benchmark for 40K tweezer experiments and enables improved detection, more efficient cooling, enhanced single-atom loading, and precise quantum-state control. |