A robust phase-locking strategy for optimal applications of various optical feedback cavity-enhanced spectroscopies in harsh environments

Abstract

In various optical feedback cavity-enhanced spectroscopies (OF-CESs) based on absorption or scattering, conventional phase-locking methods are constrained by their ability to handle only minor phase deviations. This limitation is due to the source of an error signal for phase adjustment. This paper introduces a robust approach for phase-locking, which combines the shape and intensity of cavity transmission profiles to identify phase deviations. The advantage of this combination is that it can always generate a suitable error signal, irrespective of the phase's position in the entire 2π period. The outstanding performance of the corresponding servo loop under severe airflow shocks demonstrates that our approach significantly increases the feasibility of applying various OF-CES setups for real-time, in situ gas detection in harsh environments.