Interferometric nonlinear mixing in multiple-pass femtosecond optical parametric amplification

Area of Science:

• Nonlinear optics
• Laser physics
• Optical engineering

Background:

• Multi-stage optical parametric amplifiers (OPAs) are crucial for generating tunable laser light.
• Phase-dependent conversion in OPAs can negatively impact output stability and beam quality.
• Understanding and controlling interferometric effects is key to optimizing OPA performance.

Purpose of the Study:

• To investigate the impact of spatial and temporal overlap of signal, idler, and pump beams on multi-stage OPAs.
• To identify the underlying cause of phase-dependent conversion in these systems.
• To propose and verify a method for mitigating unwanted interferometric effects.

Main Methods:

• Experimental setup of a multi-stage optical parametric amplifier.
• Characterization of output beam profiles and spectral properties.
• Implementation and testing of a novel beam overlap control technique.

Main Results:

• Demonstrated strong phase dependence of conversion efficiency due to beam overlap on subsequent passes.
• Observed significant effects on output noise and beam profile characteristics.
• Verified a straightforward method to eliminate the interferometric process and stabilize OPA output.

Conclusions:

• Spatial and temporal overlap of all optical products and the pump beam in multi-stage OPAs leads to detrimental phase-dependent conversion.
• The demonstrated method effectively suppresses interferometric effects, leading to improved output stability and beam quality.
• This work provides a practical solution for enhancing the performance of multi-stage optical parametric amplifiers.