Secondary Raman and Brillouin mode suppression in two- and three-mirror-cavity diamond Raman lasers

Area of Science:

• Laser Physics
• Nonlinear Optics
• Materials Science

Background:

• Single longitudinal mode (SLM) operation is crucial for many laser applications requiring high spectral purity.
• Diamond Raman lasers offer potential for high-power, wavelength-tunable light generation.
• Secondary mode generation, particularly from stimulated Brillouin scattering (SBS), can degrade SLM performance.

Purpose of the Study:

• To investigate methods for suppressing secondary modes in 1240 nm diamond Raman lasers.
• To achieve stable SLM output in a V-shape cavity configuration.
• To quantify the nonlinear susceptibility (χ(2)) coupling required for mode suppression.

Main Methods:

• Utilized a three-mirror V-shape standing-wave cavity.
• Incorporated an intra-cavity Lithium Triborate (LBO) crystal for nonlinear mode suppression.
• Employed an intracavity aperture to mitigate higher-order spatial modes.
• Performed numerical calculations to analyze mode structures and probabilities.

Main Results:

• Achieved stable SLM output with a maximum power of 11.7 W and a slope efficiency of 34.9%.
• Quantified the χ(2) coupling necessary to suppress secondary modes, including those from SBS.
• Demonstrated that SBS modes often correlate with higher-order spatial modes, controllable via an intracavity aperture.
• Numerical analysis indicated higher probabilities of higher-order spatial modes in apertureless V-cavities compared to two-mirror designs.

Conclusions:

• The V-shape cavity with an intra-cavity LBO crystal effectively suppresses secondary modes in 1240 nm diamond Raman lasers.
• Intracavity apertures are vital for suppressing SBS-generated modes that coincide with higher-order spatial modes.
• Cavity design significantly influences the likelihood of higher-order spatial mode generation, impacting SLM stability.