Approximate theory of Stokes amplification and conversion valid at large gain

Area of Science:

• Nonlinear optics
• Laser physics
• Quantum optics

Background:

• Raman amplifiers are crucial for generating specific laser wavelengths.
• Understanding beam divergence and gain is essential for optimizing amplifier performance.
• Previous models often lacked simple analytical solutions for large-gain regimes.

Purpose of the Study:

• To derive simple analytical expressions for Stokes-beam divergence, origin, and gain in large-gain Raman amplifiers.
• To investigate the dependence of amplifier performance on pump-beam divergence and pump power.
• To provide a theoretical framework that explains experimental findings.

Main Methods:

• Derivation of analytical expressions based on physical principles.
• Analysis of Stokes divergence as a function of pump power, particularly around the threshold.
• Comparison of analytical predictions with exact numerical simulations.

Main Results:

• Stokes-beam divergence peaks at a pump power twice above the amplification threshold.
• Analytical expressions accurately predict Stokes-beam characteristics.
• The derived formulas show excellent agreement with computer solutions.

Conclusions:

• The developed analytical expressions offer a simplified yet accurate method for predicting Raman amplifier behavior.
• These findings reconcile theoretical predictions with experimental observations in high-gain Raman amplifiers.
• The study provides valuable insights for the design and optimization of laser systems utilizing Raman amplification.