Intermode beating mode-locking technique for a rare-earth-doped fiber pulsed laser

Area of Science:

• Photonics
• Laser Physics
• Materials Science

Background:

• Fiber lasers are crucial for various applications, but achieving stable pulsed operation often requires complex components.
• Thulium-doped fiber lasers (TDFLs) operating in the 2-micrometer range are valuable for spectroscopy and medical applications.
• Mode-locking is essential for generating ultrashort or nanosecond pulses from lasers.

Purpose of the Study:

• To demonstrate a novel approach for achieving mode-locking in a TDFL.
• To investigate the use of pump source intermode beating for laser mode-locking.
• To characterize the performance of the mode-locked TDFL.

Main Methods:

• Utilized a 1565 nm continuous-wave multi-longitudinal-mode laser as the pump source for a 2 µm TDFL.
• Exploited the intermode beating phenomenon of the pump laser to induce periodic modulation of the intracavity power.
• Achieved stable mode-locking by synchronizing the TDFL's cavity frequency with the pump's intermode-beating frequency.

Main Results:

• Successfully achieved stable intermode beating mode-locking in the TDFL without external mode-locking elements.
• Generated rectangular nanosecond pulses with a center wavelength of 1980.35 nm.
• Observed a signal-to-noise ratio greater than 61 dB and a repetition rate of 34.496 MHz.

Conclusions:

• Intermode beating mode-locking is a viable and simple method for pulsed TDFL operation.
• This technique offers a promising alternative for developing compact, cost-effective, and high-performance pulsed laser sources.
• Further research can optimize this method for enhanced laser performance.