Dual colour cw mode-locking through soft aperture based on second order cascaded nonlinearity

Area of Science:

• Optics and Photonics
• Laser Physics
• Nonlinear Optics

Background:

• Mode-locking is crucial for generating ultrashort laser pulses.
• Second-order nonlinear processes offer unique mechanisms for laser manipulation.
• Nd:YVO4 lasers are widely used for various applications.

Purpose of the Study:

• To achieve stable dual-wavelength continuous-wave (cw) mode-locking in a Nd:YVO4 laser.
• To investigate the use of intracavity cascaded second-order nonlinear processes for mode-locking.
• To analyze the theoretical basis of the observed mode-locking regime.

Main Methods:

• Exploiting intracavity second-order cascaded nonlinear process in a non-phasematched second harmonic generating crystal.
• Transforming nonlinear phase shift into amplitude modulation via soft aperturing.
• Utilizing the nonlinear cavity mode variation within the laser gain medium.
• Theoretical analysis of self-starting and stable cascaded second-order mode-locking.

Main Results:

• Stable dual-wavelength cw mode-locked pulse train generated at 1064 nm and 532 nm.
• Achieved pulse duration of 10.3 ps.
• Obtained average output power of 1.84 W at 1064 nm and 255 mW at 532 nm for 12 W pump power.
• Experimental results were found to be in conformity with theoretical analysis.

Conclusions:

• The cascaded second-order nonlinear process is an effective method for achieving dual-wavelength mode-locking.
• Soft aperturing and nonlinear cavity mode variation play key roles in the mode-locking mechanism.
• The theoretical framework accurately describes the self-starting and stable operation of this mode-locking technique.