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Low-phase-noise, single-frequency, single-mode 608 W thulium fiber amplifier
Gregory D Goodno1, Lewis D Book, Joshua E Rothenberg
1Northrop Grumman Aerospace Systems, One Space Park, R1-1184D, Redondo Beach, California 90278, USA. gregory.goodno@ngc.com
Optics Letters
|April 17, 2009
Summary
Researchers achieved 608 W from a single-frequency, thulium-doped fiber laser, the highest power reported for such a laser. This high power suggests potential for further scaling through coherent beam combining.
Area of Science:
- Laser physics
- Optical engineering
- Materials science
Background:
- Thulium-doped fiber lasers (TDFLs) are crucial for generating light in the 2-micron wavelength range.
- Scaling TDFL power is essential for applications in remote sensing, spectroscopy, and medical treatments.
- Previous TDFL power records were limited by nonlinear effects and thermal management.
Purpose of the Study:
- To investigate the power scaling capabilities of a single-frequency, single-mode TDFL system.
- To identify and mitigate power-limiting factors such as stimulated Brillouin scattering (SBS).
- To assess the beam quality and phase noise for future applications like coherent beam combining.
Main Methods:
- A master oscillator power amplifier (MOPA) configuration utilizing four cascaded thulium-doped fiber amplifier stages.
- A 2040 nm diode laser served as the seed source.
- Varying lengths of passive fiber were spliced to the output to study SBS thresholds.
- Beam quality was quantified using the M-squared parameter.
- Phase noise was measured using integrated root-mean-square (rms) phase noise above 1 kHz.
Main Results:
- Achieved a maximum output power of 608 W from the TDFL system.
- The amplified laser maintained excellent beam quality with an M-squared value of 1.05+/-0.03.
- Stimulated Brillouin scattering (SBS) was identified as a potential limiting factor, investigated through fiber length variations.
- Integrated rms phase noise above 1 kHz was measured to be less than lambda/30.
- This represents the highest power reported for a single-frequency, single-mode fiber laser to date.
Conclusions:
- The developed TDFL system demonstrates unprecedented power scaling for single-frequency, single-mode fiber lasers.
- The low phase noise indicates suitability for coherent beam combining, enabling even higher power levels.
- Further power scaling is primarily limited by the available pump power, not fundamental laser limitations.
