A-star bbo crystal type 1
bbo crystal Type 1 and bbo crystal Type 2 phase matching are used in OPO devices based on BBO crystals and designed for pump at different harmonics (up to fifth) of Nd:YAG lasers. bbo crystal Type 1 of interaction gives a larger tuning range and higher parametric amplification rate comparing to bbo crystal type 2 of interaction, while using bbo crystal type 2 interaction you are obtaining narrower bandwidth of output as shown in Fig.2. Parametric gain in BBO Crystal is about 10 times higher then in KDP in case of 355 nm pump for bbo crystal type 1 interaction. Up to 30% energy conversion efficiency has been obtained using BBO crystal of 12 mm length in OPO device synchronously pumped at 532 nm, which outputs at 640-3170 nm. Because of small acceptance angle and? large walk off, the use of input laser radiation with good beam quality and low divergence is required for efficient conversion.
bbo crystal type 1
For both bbo crystal Type I and bbo crystal 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:
bbo crystal Type I: deff=d31sin(θ)+(d11cos(3φ)-d22sin(3φ))cos(θ)
bbo crystal Type II: deff=(d11sin(3φ)+d22cos(3φ))cos2(θ)
where θ and φ are polar coordinates referring to z=c and x=a, respectively.
Figure 1: BBO type I and BBo type II phase-matching angles of SHG with fundamental wavelengths form 0.5um to 2.8um
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 bbo crystal type I (ooo->e) and bbo crystal 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.
Figure 2: BBO type I and type II phase-matching angles of THG with fundamental wavelengths form 0.7um to 2.6um