Raman fiber laser harmonically mode-locked by exploiting the intermodal beating of CW multimode pump source

Area of Science:

• Photonics
• Laser Physics
• Fiber Optics

Background:

• Mode-locking is crucial for generating ultrashort laser pulses.
• Raman fiber lasers offer unique wavelength generation capabilities.
• Harmonic mode-locking can increase pulse repetition rates.

Purpose of the Study:

• To demonstrate a new method for harmonic mode-locking in Raman fiber lasers.
• To utilize intermodal beating of a continuous-wave pump laser for mode-locking.
• To characterize the generated nanosecond pulses and tuning capabilities.

Main Methods:

• Employing a continuous-wave multiple-longitudinal-mode pump laser.
• Matching Raman cavity round-trip frequency with pump intermodal-beating frequency.
• Utilizing a phosphosilicate Raman fiber for laser operation.

Main Results:

• Stable harmonic mode-locking achieved at the first-order Stokes (1239.5 nm).
• Generated rectangular-shape nanosecond pulses with up to 4.25 nJ pulse energy.
• Harmonic order tunable from 78th to 693rd order.
• Supermode suppression up to 51.1 dB and signal-to-noise ratio > 65 dB.

Conclusions:

• The intermodal beating method offers a novel approach for harmonic mode-locking in Raman fiber lasers.
• This technique enables stable generation of tunable nanosecond pulses with high energy.
• Demonstrated significant supermode suppression and high signal-to-noise ratio.