Axicons for mode conversion in high peak power, higher-order mode, fiber amplifiers

Area of Science:

• Fiber optics
• Laser technology
• Nonlinear optics

Background:

• Higher-order mode (HOM) fiber amplifiers offer large effective areas for high pulse energy.
• Traditional mode conversion using long-period gratings is limited by nonlinearity at high peak powers.

Purpose of the Study:

• To propose and demonstrate axicons as a nonlinearity-free bulk-optic solution for output mode conversion in HOM fiber amplifiers.
• To investigate the energy scalability of HOM amplifiers with axicon mode converters for femtosecond pulse amplification.

Main Methods:

• Utilized axicons for linear bulk-optic mode conversion at the output of HOM amplifiers.
• Experimentally verified mode conversion efficiency and beam quality (M2).
• Conducted experiments with pulsed and chirped pulse amplifiers to assess nonlinearity and energy scalability.

Main Results:

• Achieved M2 < 1.25 with 80% mode conversion efficiency using axicons.
• Demonstrated that axicon-based mode conversion is free from nonlinearity.
• Confirmed energy scalability in femtosecond pulses for HOM amplifiers with axicons compared to fundamental mode amplifiers.

Conclusions:

• Axicons provide an effective and robust method for output mode conversion in HOM fiber amplifiers.
• This technology overcomes nonlinearity limitations, enabling higher energy amplification for femtosecond lasers.
• Proposed and demonstrated fiber integration of axicon mode converters for practical applications.