High-power-seed femtosecond long-wave infrared difference-frequency generators

Area of Science:

• Optics and Photonics
• Nonlinear Optics
• Laser Technology

Background:

• Conventional difference-frequency generation (DFG) systems often suffer efficiency drops for long-wave infrared (LWIR) generation at longer wavelengths.
• Optical parametric oscillator (OPO) power can decrease near degeneracy, impacting DFG performance.
• Atmospheric absorption can affect pump and seed waves in some DFG configurations.

Purpose of the Study:

• To present a novel high-power-seed DFG system utilizing two equally powered signal pulse trains from optical parametric oscillators (OPOs).
• To overcome the efficiency limitations of conventional signal-idler DFG systems, particularly for LWIR generation.
• To demonstrate a DFG system with enhanced robustness against atmospheric absorption for both pump and seed waves.

Main Methods:

• Implemented a DFG system seeded by two signal pulse trains from separate OPOs, ensuring equal power levels.
• Configured the OPOs to provide tunable femtosecond pulse trains.
• Experimentally characterized the output power, tunability, quantum conversion efficiency (QCE), and repetition rate of the DFG system.

Main Results:

• Achieved femtosecond pulses tunable from 5-20 µm with up to 62 mW power and 23% QCE at a repetition rate of ~82 MHz.
• Obtained over 20 mW power and nearly 20% QCE at a central wavelength of 13 µm.
• Demonstrated the highest reported power and QCE for a DFG system at this high repetition rate.

Conclusions:

• The proposed high-power-seed DFG scheme effectively avoids efficiency drops associated with OPO near-degeneracy.
• This method provides robust generation of LWIR pulses, unaffected by atmospheric absorption of seed and pump waves.
• Represents the first experimental demonstration of a high-repetition-rate DFG system where seed and pump waves possess equal power levels.