Mode-locked femtosecond vortex laser oscillator with tunable phase singularities

Area of Science:

• Optics and Photonics
• Laser Physics
• Ultrafast Science

Background:

• Femtosecond vortex beams are crucial for applications like advanced manufacturing, laser-matter interaction, and optical communication.
• Existing methods for generating these beams often require additional optical phase elements, adding complexity.

Purpose of the Study:

• To report the direct generation of femtosecond optical vortex beams with tunable phase singularities.
• To achieve this generation using a passive mode-locked Ytterbium-doped Potassium Gadolinium Tungstate (Yb:KGW) laser oscillator without external optical components.

Main Methods:

• Utilized a passive mode-locked Yb:KGW laser oscillator.
• Achieved direct generation of femtosecond vortex beams by manipulating laser parameters, specifically the angle between the laser and pumping beam.
• No additional optical phase elements were employed.

Main Results:

• Successfully generated stable, pure Laguerre-Gaussian (LG₀₁) vortex pulses with an average power of 485 mW and a pulse duration of 247 fs.
• Demonstrated the generation of complex vortex pulses with two phase singularities of opposite chirality by tuning the pump-laser angle, yielding 244 mW average power and 408 fs pulse duration.
• Achieved high-quality ultrafast optical vortex beams.

Conclusions:

• This work presents a simple and effective method for generating high-quality femtosecond optical vortex beams.
• The technique allows for tunable phase singularities and can be extended to other laser oscillators and spectral regions.
• The direct generation approach simplifies the setup and enhances the applicability of ultrafast vortex beams.