BBO (Beta-Barium Borate) is a negative uniaxial crystal (no > ne) and is widely used in frequency doubling, sum-frequency generation, and optical parametric amplification for high-power ultrafast lasers. Third-harmonic generation (THG) can usually be regarded as a sum-frequency process between the fundamental wave and its second harmonic inside the same crystal, producing the third-harmonic output.
For Type I phase matching, if both the fundamental and second-harmonic waves are ordinary polarized (o), and the third-harmonic wave is extraordinarily polarized (e), the phase-matching condition is:
3 neeff(λ/3) = no(λ) + 2 no(λ/2)
By adjusting the crystal cut angle (the angle between the optical axis and the crystal surface normal), this condition can be satisfied, enabling high conversion efficiency.
1. This calculator is for theoretical reference only. In practice, the optimal angle should be fine-tuned experimentally.
2. BBO refractive index data are based on commonly used Sellmeier equations; variations may occur due to crystal batch and temperature.
3. For higher accuracy or more comprehensive simulations, professional software such as SNLO is recommended.