Highly efficient stimulated Raman scattering at the air–heavy water interface

Abstract

In this study, we conducted a detailed exploration of stimulated Raman scattering (SRS) in heavy water (D2O), focusing specifically on its behavior at the air–D2O interface. The analysis revealed discernible SRS characteristic peaks corresponding to different vibrational modes, showing a 3.31-fold reduction in the SRS threshold at the air–D2O interface. Notably, we achieved a remarkable 6.83% energy conversion efficiency, approximately 3.36 times higher than the 2.03% efficiency observed in bulk D2O. Through cascaded Raman scattering and Raman-enhanced four-wave mixing (FWM) processes, up to third-order Stokes and corresponding anti-Stokes SRS were obtained in an unprecedented manner at a low pump energy of 8.26 mJ. Additionally, distinctive conical spatial structures of Stokes and anti-Stokes generated at air–D2O interface were attributed to Raman-enhanced FWM processes. Our investigation into the temporal behavior of SRS pulses revealed a unique mechanism: the initial decline of pump pulse was due to SRS-induced pump energy loss and heat dissipation, while the behavior of latter half resulted from non-uniform refractive index, causing self-defocusing and inhibiting the sustained generation of SRS. Our study sheds light on the development of multi-wavelength and significant frequency shift Raman lasers, offering valuable perspectives for future research endeavors.