BBO Crystal 

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

Physical Properties

Crystal Structure trigonal, space group R3c
Cell Parameters a = b = 12.532, c = 12.717, Z = 6
Melting Point 1095 +/-5C
Transition Temperature 925 +/-5C
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 25C- 900C)
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

Chemical Properties

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: 

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 (d36(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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