Beta Barium Borate (β-BaB2O4)
Barium borate (BBO) is a nonhydroscopic and chemically stable material. Crystallization takes place in two phases, alpha and beta, and the phase transition temperature equals to 925±5°C. The higher temperature phase-alpha is centric symmetrical within its crystal structure, whose square nonlinearity tensor components are identically equal to zero. In contrast to the alpha-phase, the Beta-phase of BBO is non-centric symmetrical and the crystals grown in this phase possess nonlinear optical properties.
Beta-BBO was discovered and developed in 1984 by a group of Chinese investigators at Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science. It is a crystal frequently used for frequency mixing and other nonlinear optics applications.
Phase Matching Angles:
For both Type I and Type II processes, phase matching condition is critical to improve the conversion efficiency and it can be achieved by angle tuning. Figure 1 shows the phase matching angles of SHG. The effective SHG coefficients are given by:
Type I: deff=d31sin(θ)+(d11cos(3φ)-d22sin(3φ))cos(θ)
Type II: deff=(d11sin(3φ)+d22cos(3φ))cos2(θ)
where θ and φ are polar coordinates referring to z=c and x=a, respectively.
For both type I and Type II THG processes, phase matching condition to improve the conversion efficiency is different from the SHG. Taking the wavelength 1064nm as an example, the phase matching angles of both type I (ooo->e) and type II (ooe->e) confirmations are 37.33° and 46.93° respectively. However, the conversion efficiency is much higher when the phase matching angles of both type I and type II are 31.3° and 38.6° respectively. It is evident that the cascaded, second-order interactions (SHG and sum of frequencies) can contribute strongly to THG, so does 4HG. Figure 2 shows the phase matching angles of THG.
Optical parametric oscillator (OPO)is a powerful tool to generate widely tunable coherent radiation. By combining OPO and harmonics (532nm, 355nm and 266nm) of Nd:YAG lasers, the new tunable wavelength range can be extended from 200nm to 3000nm. Figure 3 shows the phase matching angles of OPO.
Application Examples :
1064nm SHG --> 532nm:Type I, 4X4X7mm, 22.8° cut
1064nm THG --> 355nm:Type I, 4X4X7mm, 31.3° cut
1064nm THG --> 355nm:Type II, 4X4X7mm, 38.6° cut
1064nm 4HG --> 266nm:Type I, 4X4X7mm, 47.6° cut
1064nm 5HG --> 532nm:Type I, 4X4X7mm, 51.1° cut
532nm Pump --> 680-2600nm:Type I , 4X4X12mm, 21° cut
355nm Pump --> 410-2600nm:Type I, 6X4X12mm, 30° cut
355nm Pump --> 410-2600nm:Type II, 6X4X12mm, 37° cut
266nm Pump --> 295-2600nm:Type II, 6X4X12mm, 39° cut
670~530nm SHG --> 335-265nm:Type I, 8X4X7mm, 36.3° cut
600~440nm SHG --> 300-220nm:Type I, 8X4X7mm, 55° cut
444~410nm SHG --> 222-205nm:Type I, 8X4X7mm, 80° cut
700~1000nm SHG --> 350-500nm:Type I, 7X4X7mm, 28° cut
700~1000nm THG --> 240-333nm:Type I, 8X4X7mm, 42° cut
700~1000nm 4HG --> 210-240nm:Type I, 8X4X7mm, 66° cut
720~800nm SHG --> 360-400nm:Type I, 4X4X7mm, 31° cut
720~800nm THG --> 240-265nm:Type I, 4X4X7mm, 48° cut
514nm SHG --> 257nm:Type I, 4X4X7mm, 51° B-cut
488nm SHG --> 244nm:Type I, 4X4X7mm, 55° B-cut
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