Nonlinear beam self-cleaning in a coupled cavity composite laser based on multimode fiber

Area of Science:

• Laser Physics
• Nonlinear Optics
• Fiber Optics

Background:

• Passively Q-switched lasers are crucial for pulsed operation.
• Multimode fibers typically support multiple spatial modes, complicating beam quality.
• Coupled cavity configurations can modify laser dynamics and output characteristics.

Purpose of the Study:

• To investigate beam self-cleaning in a coupled cavity laser system.
• To explore the impact of nonlinear modal coupling on laser output.
• To achieve quasi-single mode operation and shorter pulse durations.

Main Methods:

• Utilized a passively Q-switched Nd:YAG microchip laser.
• Integrated an extended cavity with a doped multimode fiber.
• Varied coupling levels between the laser and the extended cavity.

Main Results:

• Observed beam self-cleaning in the multimode fiber at specific coupling levels.
• Achieved quasi-single mode laser output.
• Reduced laser pulse duration from 525 ps to 225 ps.
• Demonstrated Q-switched mode-locked operation with nonlinear frequency conversion.

Conclusions:

• Beam self-cleaning in multimode fibers can be induced in coupled cavity lasers.
• This phenomenon leads to improved beam quality and shorter pulses.
• The system exhibits potential for nonlinear frequency conversion applications.