Rb-He excimer involved in four-wave mixing process to produce redshifted collimated blue light

The four-wave mixing (FWM) process is an important method for generating collimated blue light from alkali vapor. In this paper, we introduced high-pressure He gas to broaden the absorption linewidth of Rb atoms for the pump laser. By using an optical parametric oscillator (OPO) that outputs tunable wavelength pump laser, we performed two-photon excitation of the Rb-He mixture and achieved redshifted and asymmetric broadened collimated light (CL) around 420 nm. We demonstrated the participation of Rb-He excimers in the FWM process for the first time, to the best of our knowledge, from both spectral and temporal dimensions, and revealed the underlying mechanism. Experiments showed that the peak of the ∼420 nm CL intensity appeared at higher heating temperatures, influenced by changes in the optical depth of the Rb-He mixture. This study provides both theoretical and experimental support for the promotion of a collimated blue light scheme in alkali metal -buffer gas systems, balancing the pump laser absorption and FWM efficiency.