Optical phase locking among femtosecond subharmonic pulses

Area of Science:

• Nonlinear optics
• Femtosecond laser technology
• Quantum optics

Background:

• Femtosecond optical parametric oscillators (OPOs) are crucial for generating ultrashort laser pulses.
• Maintaining phase coherence among pump, signal, and idler pulses in OPOs is challenging.
• Carrier-envelope phase (CEP) slip affects the stability and coherence of generated optical pulses.

Purpose of the Study:

• To stabilize the relative carrier-envelope phase slip between pump and subharmonic pulses in a femtosecond OPO.
• To achieve long-term phase coherence among all generated pulses.
• To demonstrate the effectiveness of the stabilization technique through precise beat signal measurements.

Main Methods:

• Stabilization of the relative carrier-envelope phase slip using a feedback loop.
• Measurement of the beat signal corresponding to the phase slip between subharmonic pulses.
• Utilizing a femtosecond optical parametric oscillator (OPO) setup.
• Employing a 1-s-averaged counter for beat frequency fluctuation analysis.

Main Results:

• Achieved long-term phase coherence among pump, signal, and idler pulses.
• The stabilized beat signal exhibited an accumulated phase error of only 0.24 rad over the 1 mHz–1 MHz region.
• Beat frequency fluctuation was measured to be less than 1 mHz over a 1480-second interval.

Conclusions:

• The developed stabilization method effectively controls carrier-envelope phase slip in femtosecond OPOs.
• Long-term phase coherence is demonstrated, paving the way for more stable ultrashort pulse generation.
• The results indicate high precision and stability for femtosecond OPO systems.