**BBO crystal ** or beta-BaB2O4 is a nonlinear optical crystal which combines a number of unique features. These features include wide transparency and phase matching ranges, large nonlinear coefficient, high damage threshold and excellent optical homogeneity. Therefore,
it provides an attractive solutions for various nonlinear optical applications.

**BBO crystal physical properties**

**BBO crystal chemical properties**

**Availability:**

Aperture: | 1x1 ~12x12mm |

Length: | 0.05 ~ 25mm |

Phase matching angle θ and φ: | Determined by different kinds of harmonic generation. |

Phase matching type: | Type I or Type II |

End configuration: | Flat or Brewster or Specified |

Coating: | Determined by different kinds of harmonic generation. |

**Typical Specification and Tolerance:**

Angle tolerance: | Δθ< ± 0.5°; Δφ< ±0.5° |

Dimension tolerance: | (W ± 0.1mm) x (H ± 0.1mm) x (L + 0.2mm/-0.1mm) |

Flatness: | λ/8 @ 633nm |

Scratch/Dig code: | 10/5 Scracth/dig per MIL-O-13830A |

Parallelism: | better than 20 arc seconds |

Perpendicularity: | 5 arc minutes |

Wavefront distortion: | less than l/8 @ 633nm |

Clear aperture: | > 90% central area |

Crystal Structure | trigonal, space group R3c |

Cell Parameters | a = b = 12.532Ä, c = 12.717Ä, Z = 6 |

Melting Point | 1095 +/-5°C |

Transition Temperature | 925 +/-5°C |

Optical Homogeneity | Dn ≈10-6/cm |

Hardness | 4.5 Mohs |

Density | 3.85 g/cm3 |

Absorption Coefficient | < 0.1%/cm (at 1064 nm) |

Hygroscopic Susceptibility | low |

Resistivity | > 1011 ohm-cm |

Relative Dielectric Constant |
eT11/e0: 6.7, eT33/e0: 8.1 Tan d, < 0.001 |

Thermal Expansion Coefficients(in the range of 25°C- 900°C) |
a, 4 x 10-6/K c, 36 x 10-6/K |

Thermal Conductivity |
^c, 1.2 W/m/K; ||c, 1.6 W/m/K |

Phase-matchable SHG range | 189-1750nm |

NLO coefficients | d11 = 5.8 x d36(KDP) d11 = 0.05 x d11, d22< 0.05 x d11 |

Electro-Optic Coefficients | g11 = 2.7 pm/V, g22, g31< 0.1 g11 |

Half-Wave Voltage | 48 KV (at 1064 nm) |

Damage Threshold at 1.064 mm at 0.532 mm |
5 GW/cm2 (10 ns); 10 GW/cm2 (1.3 ns)1 GW/cm2 (10 ns); 7 GW/cm2 (250 ps) |

Transparency Range | 189 - 3500 nm |

Refractive Indices at 1.0642 mm at 0.5321 mm at 0.2660 mm |
ne = 1.5425, no = 1.6551 ne = 1.5555, no = 1.6749 ne = 1.6146, no = 1.7571 |

Therm-Optic Coefficients |
dno/dT = - 9.3 x 10-6/°C dne/dT = -16.6 x 10-6/°C |

Sellmeier Equations: | no2(l) = 2.7359+0.01878/(l2-0.01822)-0.01354 l 2 ne2(l) = 2.3753+0.01224/(l2-0.01667)-0.01516 l 2 |

As a result of large thermal acceptance bandwidth, high damage threshold and small absorption BBO well suits for frequency conversion of high peak or average power laser radiation. The large spectral transmission range as well as phase matchability, especially in UV range, makes BBO perfectly suitable for frequency doubling of Dye, Ar+-ion and Copper vapour laser radiation, effective cascade harmonic generation of wide spread Nd:YAG as well as of Ti:Sapphire and Alexandrite laser radiation. Both angle tuned Type 1 (oo-e) and Type 2 (eo-e) of phase matching can be obtained increasing a number of advantages for different applications. SHG phase matching angle dependence on input radiation wavelength is shown in fig. 2

Both Type 1 and 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. Type 1 of interaction gives a larger tuning range and higher parametric amplification rate comparing to type 2 of interaction, while using type 2 interaction you are obtaining narrower bandwidth of output. Parametric gain in BBO is about 10 times higher then in KDP in case of 355 nm pump for 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 406-3170 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.

**Applications of BBO crystal in nonlinear (SHG,
THG) and OPO/OPA**

**BBO Crystal** is of particular importance in the visible and far UV. A wide variety of phase-matching applications are possible, including the following:

- Second, third, fourth and fifth harmonic generation of Nd doping lasers;

- Second harmonic generation to generate wavelengths as short as 204.8 nm

- Shorter wavelengths (193nm) can be generated by sum frequency mixing

- Frequency-doubling, -tripling and -mixing of Dye lasers;

- Second, third and fourth harmonic generation of Ti:Sapphire lasers;

- Optical parametric amplifier (OPA) and optical parametric oscillators
(OPO);

- Frequency-doubling of Argon ion, Cu-vapor and Ruby lasers.

- Transverse field Pockel cells made from BBO useful when high average powers or short wavelengths used.

**Application in SHG and SFG**

Because of a small acceptance angle and large walk-off, good laser beam quality (small divergence, good mode condition, etc.) is the key for BBO to obtain high conversion efficiency. Tight focus of laser beam is not recommended. BBO is the only NLO material which can be used to produce the fifth harmonic generation (5HG) of Nd:YAG lasers at 213 nm.

Relevant NLO properties for type I BBO crystal:

SHG | THG | 4HG | 5HG | |

Effective NLO Coefficient (d_{36}(KDP)) |
5.3 | 4.9 | 3.8 | 3.4 |

Acceptance Angle (mrad-cm) | 1.0 | 0.5 | 0.3 | 0.2 |

Walk-off Angle (°) | 3.2 | 4.1 | 4.9 | 5.5 |

**Application in Ultrafast Pulse (Ti:sapphire) Laser **

Frequency-doubling and -tripling of ultrashort-pulse lasers are the applications in which BBO shows superior properties to KDP and ADP crystals. As thin as 0.02mm BBO for this purpose is available.. A laser pulse as short as 10 fs can be efficiently frequency-doubled with a thin
BBO, in terms of both phase-velocity and group-velocity matching.

**Application in OPO and OPA **

The OPO and OPA of BBO are powerful tools for generating a widely tunable coherent radiation from the UV to IR. The tuning angles of type I and type II BBO OPO and OPA have been calculated, with the results shown in
following, respectively.

**BBO crystals with different angle cut for various applications are listed as follows:
**1) Harmonic generations of Nd:YAG lasers:

1064nm SHG --> 532nm: Type I , q=22.8°, f=0°;

1064nm THG --> 355nm: Type I, q=31.3°, f=0°; Type II q=38.6°, f=30°

1064nm 4HG --> 266nm: Type I, q=47.6°, f=0°;

1064nm 5HG --> 213nm: Type I, q=51.1°, f=0°;

2) OPO and OPA pumped by harmonics of Nd:YAG lasers

532nm Pump --> 680-2600nm: Type I, q=21°, f=0°;

355nm Pump --> 410-2600nm: Type I, q=30°, f=0°; Type II, q=37°, f=30°;

266nm Pump --> 295-2600nm: Type I, q=39°, f=0°;

3) Frequency doubling of dye lasers

670-530nm SHG --> 335-260nm: Type I, q=40°, f=0°;

600-440nm SHG --> 300-220nm: Type I, q=55°, f=0°;

444-410nm SHG --> 222-205nm: Type I, q=80°, f=0°;

4) Harmonic generations of Ti:Sapphire lasers

700-1000nm SHG --> 350-500nm: Type I, q=28°, f=0°;

700-1000nm THG --> 240-330nm: Type I, q=42°, f=0°;

700-1000nm FHG --> 210-240nm: Type I, q=66°, f=0°;

5) Frequency doubling and tripling of alexandrite lasers

720-800nm SHG --> 360-400nm: Type I, q=31°, f=0°;

720-800nm THG --> 240-265nm: Type I, q=48°, f=0°;

6) Intracavity SHG of Ar+ laser with brewster angle cut

514nm SHG --> 257nm: Type I, q=51°, f=0°, B-cut;

488nm SHG --> 244nm: Type I, q=55°, f=0°, B-cut;

**Mounting:**

In order to prevent crystals from damaging or to be easily operated, we provide three kinds of mount of holder to install different dimension crystals. Please contact our sales for more information.

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