18 W single-stage single-frequency acoustically tailored Raman fiber amplifier

Area of Science:

• Fiber optics
• Laser physics
• Nonlinear optics

Background:

• Raman fiber amplifiers are crucial for generating high-power laser output.
• Stimulated Brillouin scattering (SBS) is a major limitation in high-power fiber amplifiers, reducing efficiency and potentially damaging components.
• Developing effective SBS suppression techniques is essential for advancing fiber amplifier performance.

Purpose of the Study:

• To design and characterize a single-stage, counter-pumped Raman fiber amplifier with enhanced SBS suppression.
• To investigate the impact of acoustic tailoring and thermal gradients on amplifier performance.
• To achieve high continuous wave (cw) output power with a narrow linewidth.

Main Methods:

• Utilized a single-mode, polarization-maintaining fiber doped for increased Raman gain and SBS suppression.
• Employed acoustic tailoring of the fiber core to mitigate SBS.
• Conducted pump-probe experiments to characterize Brillouin gain and identify multiple Brillouin peaks.
• Applied a thermal gradient to further suppress SBS and enhance output power.

Main Results:

• Achieved 11.5 W of cw output power from a 15 mW seed at 1178 nm with a linewidth ≤2 MHz.
• Demonstrated increased output power to 18 W by applying a thermal gradient.
• Obtained a net amplifier gain exceeding 30 dB.
• Characterized multiple Brillouin peaks, confirming the effectiveness of SBS mitigation strategies.

Conclusions:

• Acoustic tailoring and thermal gradients are effective methods for suppressing SBS in Raman fiber amplifiers.
• The developed amplifier design enables high-power, narrow-linewidth operation.
• This work contributes to the advancement of high-power fiber laser technology.