Highly sensitive beam quality measurements on large-mode-area fiber amplifiers

Area of Science:

• Optics and Photonics
• Laser Physics
• Fiber Optics

Background:

• Large-mode-area fiber amplifiers are crucial for high-power laser systems.
• Maintaining high beam quality in these amplifiers is challenging.
• Existing methods like M2 measurements have limitations in detecting subtle beam quality improvements.

Purpose of the Study:

• To investigate the beam quality of large-mode-area fiber amplifiers at the 10 W power level.
• To evaluate the effectiveness of a tunable ring cavity for mode filtering and beam quality assessment.
• To compare the performance with single-mode fibers.

Main Methods:

• Utilized a tunable ring cavity, also employed in the GEO600 laboratory system, for pre-mode cleaning.
• Investigated beam quality at a 10 W power level.
• Employed high-sensitivity ring cavity analysis and conventional M2 measurements.
• Varied the coiling diameter of the fiber amplifier.

Main Results:

• Achieved over 98% of output power within the polarized TEM00 mode by optimizing coiling diameter.
• Demonstrated beam quality improvement through decreasing coiling diameter using ring cavity analysis.
• Observed that conventional M2 measurements did not reveal the same beam quality enhancements.
• Results were compared to the characteristics of single-mode fibers.

Conclusions:

• A tunable ring cavity is a sensitive tool for assessing beam quality improvements in fiber amplifiers.
• Optimizing fiber coiling diameter significantly enhances TEM00 mode content and beam quality.
• Ring cavity analysis offers advantages over M2 measurements for detecting subtle beam quality changes in high-power fiber lasers.