1.2  kW clad pumped Raman all-passive-fiber laser with brightness enhancement

Area of Science:

• Optics and Photonics
• Laser Technology
• Materials Science

Background:

• High-power fiber lasers are crucial for various applications, but achieving high efficiency and beam quality simultaneously remains a challenge.
• Raman fiber lasers offer potential for wavelength flexibility and high power, but often require rare-earth doping or struggle with efficiency.
• Brightness enhancement (BE) is a key metric for laser performance, indicating the concentration of power in a high-quality beam.

Purpose of the Study:

• To demonstrate a kilowatt-class, all-fiber clad-pumped Raman fiber laser (FL) oscillator.
• To achieve record-breaking power and efficiency in a Raman FL configuration with brightness enhancement.
• To develop a passive fiber laser oscillator, avoiding rare-earth doping for simplicity and robustness.

Main Methods:

• Utilized a specially designed triple-clad fiber to manage pump power and signal generation.
• Employed a clad-pumping scheme to confine low beam quality (BQ) pump power into the inner clad.
• Engineered the fiber geometry (inner clad-to-core area ratio) and utilized fiber Bragg gratings to suppress unwanted second Stokes generation and enhance Raman signal.

Main Results:

• Achieved a continuous-wave (CW) output power of 1.2 kW with an impressive efficiency of 85%.
• Demonstrated the highest power and efficiency for a Raman FL with brightness enhancement to date.
• Obtained a beam quality of M²=2.75 at 1 kW output power and a pump-Stokes brightness enhancement factor of approximately 7.

Conclusions:

• The presented all-fiber, clad-pumped Raman fiber laser oscillator represents a significant advancement in high-power laser technology.
• This work establishes a new benchmark for power and efficiency in passive, rare-earth-free fiber lasers.
• The design utilizing a triple-clad fiber and optimized geometry offers a scalable and robust platform for future high-power laser development.