Efficient first-order quasi-phase-matched backward second-harmonic generation.

Area of Science:

• Nonlinear optics
• Solid-state laser technology

Background:

• Backward second-harmonic generation (BSHG) has historically suffered from low efficiencies.
• Previous BSHG experiments utilized higher-order quasi-phase-matching, limiting performance.

Purpose of the Study:

• To demonstrate highly efficient first-order quasi-phase-matched BSHG.
• To investigate the properties of efficient BSHG in Rb:KTiOPO4.
• To compare BSHG characteristics with co-propagating second harmonic generation.

Main Methods:

• Utilizing bulk periodically poled Rb:KTiOPO4 with a 317 nm poling period.
• Achieving frequency doubling in the backward direction for a 2309 nm fundamental wavelength.
• Employing broadband and narrowband fundamental sources to study spectral bandwidth, temperature tuning, and temperature bandwidth.

Main Results:

• Demonstrated a first-order quasi-phase-matched BSHG efficiency of 18.7%.
• Achieved a two-orders-of-magnitude increase in efficiency compared to previous higher-order quasi-phase-matching methods.
• Characterized spectral and thermal properties of BSHG.

Conclusions:

• First-order quasi-phase-matched BSHG in Rb:KTiOPO4 is highly efficient.
• The demonstrated efficiency opens doors for previously theoretical BSHG applications.
• Comparative analysis with co-propagating SHG highlights unique BSHG potential.