Mode calculations in unstable resonators with flowing saturable gain. 2: Fast Fourier transform method

Area of Science:

• Physics
• Optics
• Laser Technology

Background:

• High-power gas-dynamic lasers (GDLs) are crucial for various applications.
• Accurate modeling of GDLs is complex due to factors like nonuniform flow and index inhomogeneities.
• Previous simulation methods were computationally intensive.

Purpose of the Study:

• To present refined calculations of 3D mode patterns and power outputs for GDLs.
• To incorporate effects of nonuniform, saturable gain media and index inhomogeneities (shocks).
• To develop a faster and more efficient computational method for GDL simulations.

Main Methods:

• Utilized a plane-wave or k-space expansion combined with the Fast Fourier Transform (FFT).
• Introduced a novel expanding-beam coordinate transform to simplify resonator mode calculations.
• Developed a new FFT propagation code.

Main Results:

• Successfully calculated 3D mode patterns and power outputs for a high-power GDL.
• The new expanding-beam transform efficiently handles diverging and converging beam sections.
• The resulting FFT propagation code demonstrates significant speed improvements over previous methods.

Conclusions:

• The enhanced computational approach provides accurate GDL performance predictions.
• The new method offers a substantial speed advantage for GDL simulations.
• This work facilitates more efficient design and analysis of high-power GDL systems.