Suppressing transverse mode instability through multimode excitation in a fiber amplifier

Area of Science:

• Optics and Photonics
• Laser Physics

Background:

• High-power fiber laser amplifiers are crucial for industrial, scientific, and defense applications.
• Transverse Mode Instability (TMI) currently limits power scaling in fiber amplifiers.
• Existing TMI suppression methods often rely on single- or few-mode fibers, limiting beam quality.

Purpose of the Study:

• To theoretically investigate the use of highly multimode fiber amplifiers with many-mode excitation.
• To explore efficient suppression of thermo-optical nonlinearity and TMI.
• To achieve high average power, narrow spectral width, and good beam quality simultaneously.

Main Methods:

• Theoretical study of a highly multimode fiber amplifier.
• Analysis of many-mode excitation for suppressing thermo-optical effects.
• Investigating the impact of seed laser bandwidth on spatial coherence.

Main Results:

• Thermo-optical coupling between fiber modes is weakened due to mismatched length scales.
• The TMI threshold power scales linearly with the number of equally excited modes.
• High spatial coherence is maintained when seed laser bandwidth is narrower than the fiber's spectral correlation width.

Conclusions:

• Multimode fiber amplifiers offer an effective strategy for overcoming TMI and nonlinearities.
• This method allows for simultaneous achievement of high power, narrow spectral width, and excellent beam quality.
• The amplified light can be manipulated for various applications requiring specific spatial patterns or focused spots.