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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.


  • Wide transmission region from 190 nm to 3500 nm
  • Broad phase-matchable range from 409.6 nm to 3500 nm
  • Large effective second-harmonic-generation (SHG) coefficient
  • High damage threshold
  • High Optical homogeneity
  • Excellent mechanical and physical properties


  • Second, third, fourth and fifth harmonic generation of Nd:YAG and Nd:YLF lasers
  • Frequency-doubling, -tripling and -mixing of Dye lasers
  • Second, third and fourth harmonic generation of Ti:Sapphire and Alexandrite lasers
  • Optical parametric amplifier (OPA) and optical parametric oscillators (OPO)
  • Frequency-doubling of Argon ion, Cu-vapor and Ruby lasers.

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.



Figure 1: BBO type I and 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 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.



Figure 2: BBO type I and type II phase-matching angles of THG with fundamental wavelengths form 0.7um to 2.6um

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.

       Figure 2: BBO type I and type II phase-matching angles of OPO with wavelength range form 0.7um to 2.6um


  Crystal Structure Trigonal, space group R3c
  lattice constant (Å) a = b = 12.532, c = 12.717
  Melting Point (°C) 1095±5
  Transition Temperature (°C) 925±5
  Optical Homogeneity (/cm) ≈10-6
  Mohs Hardness 4.5
  Density (g/cm^3) 3.85
  Absorption Coefficient (/cm) α<0.001  at 1064nm
  α<0.01 at  532nm
  Hygroscopic Susceptibility Low
  Relative Dielectric Constant εT11/ε0=6.7
  Resistivity (ohm/cm) >1011
  Linear Coefficient of Thermal Expansion (25°C~900°C)  ( /K)
||C: 36X10-6
C: 4X10-6
  Thermal Conductivity (W/mK)
||C: 1.6
C: 1.2 
  Transmission Range (nm) 189~3500
  Damage Threshold (GW/cm2)
10  at 1064nm (10ns)
  1at 532nm (10ns)
  Constant of Dispersion (dn/dT)  (/°C) dno/dT=-9.3X10-6
  Refractive Indices ne=1.6146, no=1.7571 at 266nm
  ne=1.5555, no=1.6749 at 532nm
  ne=1.5425, no=1.6551 at 1064nm
  Sellmeier Equations (λ in um)
  Nonlinear Optical Coefficients (pm/V)
  Table 1: ß-BaB2O4 Properties

Application Examples :  

  • Harmonic generations of Nd:YAG lasers:
  •    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

  • OPO and OPA pumped by harmonics of Nd:YAG lasers
  •    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

  • Frequency doubling of dye lasers
  •    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

  • Harmonic generations of Ti:Sapphire lasers
  •    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

  • Frequency doubling and tripling of alexandrite lasers
  •    720~800nm SHG --> 360-400nm:Type I, 4X4X7mm, 31° cut

       720~800nm THG --> 240-265nm:Type I, 4X4X7mm, 48° cut

  • Intracavity SHG of Ar+ laser with brewster angle cut BBO
  •    514nm SHG --> 257nm:Type I, 4X4X7mm, 51° B-cut

       488nm SHG --> 244nm:Type I, 4X4X7mm, 55° B-cut

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