Increasing mode instability thresholds of fiber amplifiers by gain saturation

Area of Science:

• Fiber optics
• Laser physics
• Nonlinear optics

Background:

• Large mode area fiber amplifiers are crucial for high-power laser systems.
• Mode instability is a major limitation in fiber amplifier power scaling.
• Population inversion saturation and stimulated thermal Rayleigh scattering affect amplifier performance.

Purpose of the Study:

• To investigate the impact of population inversion saturation on stimulated thermal Rayleigh gain.
• To explore methods for increasing mode instability thresholds in fiber amplifiers.
• To compare the mode instability thresholds of co-pumped and counter-pumped amplifiers.

Main Methods:

• Numerical modeling of large mode area fiber amplifiers.
• Analysis of gain dynamics including population inversion saturation.
• Simulation of stimulated Brillouin scattering and thermal effects.

Main Results:

• Population inversion saturation reduces stimulated thermal Rayleigh gain relative to laser gain.
• Exploiting this saturation effect significantly raises mode instability thresholds.
• Counter-pumped amplifiers exhibit higher mode instability thresholds than co-pumped amplifiers.
• Confined doping further enhances mode instability thresholds.

Conclusions:

• Population inversion saturation is a key factor in managing mode instability in fiber amplifiers.
• Strategic amplifier design, including pumping scheme and doping profile, can optimize performance.
• Numerical modeling provides valuable insights for developing advanced fiber laser systems.