Thermal optimization of second harmonic generation at high pump powers

Area of Science:

• Nonlinear optics
• Solid-state materials science

Background:

• Periodically poled lithium niobate (PPLN) crystals are crucial for nonlinear optical applications like second harmonic generation (SHG).
• Temperature homogeneity is vital for efficient SHG, as thermal gradients can reduce conversion efficiency.

Purpose of the Study:

• To measure and analyze the temperature distribution in a PPLN crystal during SHG.
• To investigate the effect of sectional offset heating on temperature homogenization and SHG efficiency.
• To validate experimental results with a theoretical model.

Main Methods:

• A single-pass SHG setup using a 3 cm PPLN crystal was employed.
• The crystal was divided into three sections, each controlled by resistance heaters and monitored by Pt100 sensors.
• Infrared pump light (9.4 W) and generated SHG light (1.3 W) were used to induce thermal gradients.

Main Results:

• A temperature de-homogenization of 0.2 K was observed between the middle and back sections of the crystal.
• Sectional offset heating successfully homogenized the temperature distribution in these sections.
• A 15% increase in SHG output power was achieved, consistent with theoretical predictions.

Conclusions:

• Temperature gradients significantly impact SHG efficiency in PPLN crystals.
• Sectional offset heating is an effective method for improving temperature homogeneity and enhancing SHG conversion efficiency.
• The experimental findings align well with the developed theoretical model, validating its predictive capabilities.