26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Understanding anomalous spectral lines in high power single frequency Raman lasers

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Description

High-power single-frequency continuous-wave lasers are essential for a range of applications in precision spectroscopy, metrology, optical clocks, and quantum technologies. However, achieving stable single-frequency operation at high power is often challenging because nonlinear optical processes can generate unwanted frequency components that degrade spectral purity and stability. In continuous-wave diamond Raman lasers (DRLs), spectral sidebands symmetrically spaced about the Raman Stokes wavelength have been observed by several groups, yet the physical mechanism governing their generation and frequency spacing has remained unclear. Here, we present a theoretical and experimental investigation of these sidebands and show that they arise from cavity-enhanced degenerate four-wave mixing (DFWM).
A theoretical framework is developed that incorporates nonlinear parametric interactions and the resonant structure of the Raman cavity. The model predicts that sideband frequencies are governed by the interplay between DFWM phase matching, cavity resonance conditions, and intracavity dispersion. Two distinct regimes are identified. In the near-DFWM regime, where phase mismatch is small, sidebands are generated within <1 THz of the Raman Stokes and their frequency spacing is primarily determined by cavity resonance. In the far-DFWM regime, significant cavity dispersion causes a sideband frequency spacing of order 10 THz, with spacing strongly influenced by the cavity's integrated dispersion. The model also predicts sidebands generated in the far-DFWM regime in higher-order transverse cavity modes.
Experimental observations from three independent DRL systems show good agreement with the model, including examples of near-DFWM, far-DFWM, and higher-order-mode sidebands. These results provide a unified explanation for previous observations and identify the mechanisms limiting spectral purity in high-power single-frequency DRLs. Finally, we discuss strategies to suppress unwanted sidebands through cavity design, while also highlighting opportunities to exploit cavity-enhanced DFWM for frequency-shifted light generation.