Generation of Blue Electro-Optic Frequency Combs via a Four-Wave-Mixing Process in Rubidium Atomic Vapor

Electro-optic frequency combs (EO combs) enable high spectral and temporal resolution in atomic, molecular, and cavity-based spectroscopy that is at the heart of many quantum sensing applications. However, producing EO combs in the visible range remains challenging due to the limited availability of key components such as narrow-linewidth lasers and electro-optic phase modulators. Rubidium (Rb) is a highly nonlinear material that supports various four-wave mixing (4WM) processes, which are utilized for spectral translation and the generation of squeezed light. Here, we show the spectral translation of a 780 nm EO comb to 420 nm (a spectral separation of 330 THz) via a 4WM process in Rb vapor. We demonstrate the capability to extend the output comb bandwidth and signal-to-noise ratio by varying input power levels. Through this coherent process, we can generate frequency-agile combs in the blue, including a 1 kHz spaced comb with over one million individual comb teeth, of relevance for spectroscopic measurement of narrow-linewidth features such as electromagnetically induced transparency. Leveraging this approach across different 4WM interactions in Rb should allow for further wavelength conversion and the generation of correlated frequency combs, paving the way for sub-shot-noise (squeezed-light) measurements.