Zero-spindle spectral drill: Real-time spectral measurement in a fixed Fabry–Pérot cavity

An optical configuration for Fabry–Pérot cavity scanning using a geometric phase shifter, known as the “spectral drill,” is improved to acquire a spectrum in real-time. Previously, the resonance condition of the spectral drill is swept by the mechanical rotation of a phase plate comprising a geometric phase shifter, and the acquisition time is limited. In this work, using a q-plate and a camera instead of phase plate rotation and a photo detector, we remove all the spinning mechanics and increase the acquisition rate by a factor 720. This technique will be applied to locking laser frequency.