Sum-frequency generation with femtosecond conical refraction pulses

Area of Science:

• Nonlinear optics
• Laser physics
• Crystallography

Background:

• Conical refraction (CR) is a unique optical phenomenon occurring in biaxial crystals.
• Sum-frequency generation (SFG) is a nonlinear optical process that combines two photons into one higher-energy photon.
• Previous studies have not explored short-wavelength CR via femtosecond SFG.

Purpose of the Study:

• To investigate the generation of short-wavelength conical refraction (CR) beams using sum-frequency generation (SFG).
• To explore the application of femtosecond lasers in CR and SFG processes.
• To analyze the characteristics of CR beams generated through SFG in a biaxial crystal.

Main Methods:

• Utilized a biaxial crystal of KGd(WO4)2 with negligible optical-axis orientation dispersion in the near-infrared (near-IR).
• Employed conventional femtosecond lasers at 800 nm and 1054 nm to generate near-IR CR beams.
• Generated femtosecond CR beams at 454 nm via SFG using the near-IR CR beams.

Main Results:

• Successfully generated femtosecond CR beams at 454 nm through SFG.
• Observed that while the sum-frequency ring is often incomplete, a full-ring distribution can be achieved.
• Demonstrated that the femtosecond sum-frequency ring evolves similarly to typical CR beams under various phase-matching conditions, especially with Type-II SFG and large phase mismatch.

Conclusions:

• Short-wavelength conical refraction can be effectively generated using femtosecond sum-frequency generation.
• Type-II SFG with a large phase mismatch is crucial for achieving a complete sum-frequency ring.
• The generated femtosecond CR beams exhibit behavior consistent with established CR characteristics.