Description
Featured by：- Broad phase matchable range (409.6-3500 nm)
- Wide transmission region (190-3500 nm)
- Large effective second-harmonic-generation (SHG) coefficient about 6 times greater than that of KDP crystal
- High damage threshold
- High optical homogeneity with δn ≈ 10-6 / cm
- Wide temperature-bandwidth of about 55 ℃
- An efficient NLO crystal for the second, third, fourth, and even up to fifth harmonic generation of Nd doped lasers
- Widely applied in harmonic generation of ultrashort-pulse lasers
- Crystal down to 0.005 mm thick, up to 25 mm long and size up to 15 × 15 × 15 mm3
- P-coatings, AR-coating, mounts, and re-working services
Basic Properties：
| Table 1. Chemical and Structural Properties | |
| Crystal Structure | Trigonal, Space group R3c, |
| Lattice Parameter | a = b = 12.532 Å, c = 12.717 Å, Z = 6 |
| Melting Point | About 1095 ℃ |
| Mohs Hardness | 4 Mohs |
| Density | 3.85 g/cm3 |
| Thermal Conductivity | 1.2 W/m/K(⊥c); 1.6 W/m/K(∥c) |
| Thermal Expansion Coefficients | α11 = 4 × 10-6 /K, α33 = 36 × 10-6 /K |
| Table 2. Optical and Nonlinear Optical Properties | |
| Transparency Range | 190-3500 nm |
| SHG Phase Matchable Range | 409.6-3500 nm (Type Ⅰ) 525-3500 nm (Type Ⅱ) |
| Therm-optic Coefficient (/℃) | dno/dT = – 16.6 × 10-6
dne/dT = – 9.3 × 10-6 |
| Absorption Coefficients | < 0.1% /cm at 1064 nm, < 1%/cm at 532 nm |
| Angle Acceptance | 0.8 mrad·cm (θ, Type Ⅰ, 1064 SHG)
1.27 mrad·cm (θ, Type Ⅱ, 1064 SHG) |
| Temperature Acceptance | 55 ℃·cm |
| Spectral Acceptance | 1.1 nm·cm |
| Walk-off Angle | 2.7 ° (Type Ⅰ, 1064 SHG)
3.2 ° (Type Ⅱ, 1064 SHG) |
| NLO Coefficients | deff (I) = d31sinθ + (d11cos3Φ – d22sin3Φ) cosθ
deff (II) = (d11sin3Φ + d22cos3Φ) cos2θ |
| Non-vanished NLO Susceptibilities | d11 = 5.8 × d36 (KDP) =2.55 pm/V
d31 = 0.05 × d11 d22<0.05 × d11 |
| Sellmeier Equations (λ in μm) | no2 = 2.7359 + 0.01878 / (λ2 – 0.01822) – 0.01354 λ2
ne2 = 2.3753 + 0.01224 / (λ2 – 0.01667) – 0.01516 λ2 |
| Electro-optic Coefficients | γ22 = 2.7 pm/V |
| Half-wave Voltage | 7 KV（at 1064 nm, 3 × 3 × 20 mm3） |
| Resistivity | ˃1011 ohm·cm |
| Relative Dielectric Constant | ɛs11/ɛo: 6.7
ɛs33/ɛo: 8.1 Tanδ<0.001 |
BBO is a negative uniaxial crystal, with an ordinary refractive index (no) larger than the extraordinary refractive index (ne). Both type Ⅰ and type Ⅱ phase matching can be reached by angle tuning. The phase-matching angles of frequency doubling are shown in Fig. 2
Figure1. Transparency curve of BBO
Figure2. SHG tuning curves of BBO
Application in Nd:YAG Lasers：
BBO is an efficient NLO crystal for the second, third and fourth harmonic generation of Nd:YAG lasers, and the best NLO crystal for the fifth harmonic generation at 213 nm. Conversion efficiency of more than 70% for SHG, 60% for THG and 50% for 4 HG, and 200 mW output at 213 nm (5HG) have been obtained, respectively. BBO is also an efficient crystal for the intracavity SHG of high power Nd:YAG lasers. For the intracavity SHG of an acousto-optic Q-switched Nd:YAG laser, more than 15W average power at 532 nm was generated in a AR-coated BBO crystal. When it is pumped by the 600 mW SHG output of a mode-locked Nd:YLF laser, 66 mW output at 263 nm was produced from a Brewster-angle-cut BBO in an external enhanced resonant cavity.
Because of 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. Tightly focusing of laser beam is not recommended.
Applications in Tunable Lasers：
1. Dye lasers
Efficient UV output (205-310 nm) with a SHG efficiency of over 10% at wavelength of ≧206 nm was obtained in type Ⅰ BBO, and 36% conversion efficiency was achieved for a XeCl-laser pumped Dye laser with power 150KW which is about 4-6 times higher than that in ADP. The shortest SHG wavelength of 204.97 nm with efficiency of about 1% has been generated.
BBO is widely used in the Dye lasers. With type Ⅰ sum-frequency of 780-950 nm and 248.5 nm (SHG output of 495 nm dye laser) in BBO, the shortest UV outputs ranging from 188.9 nm to 197 nm and the pulse energy of 95 mJ at 193 nm and 8 mJ at 189 nm have been obtained, respectively.
2. Ultrafast Pulse Laser
Frequency-doubling and -tripling of ultrashort-pulse lasers are the applications in which BBO shows superior properties to KDP and ADP crystals. Now, we can provide as thin as 0.005 mm BBO for this purpose. 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.
3. Ti:Sapphire and Alexandrite lasers
UV output in the region 360-390 nm with pulse energy of 105 mJ (31% SHG efficiency) at 378 nm, and output in the region 244-259 nm with 7.5 mJ (24% mixing efficiency) have been obtained for type Ⅰ SHG and
THG of an Alexandrite laser in BBO crystal.
More than 50% of SHG conversion efficiency in a Ti:Sapphire laser has been obtained. High conversion efficiencies have been also obtained for the THG and FOHG of Ti:Sapphire lasers.
4. Argon Ion and Copper-Vapor lasers
By employing the intracavity frequency-doubling technique in an Argon Ion laser with all lines output power of 2 W, maximum 33 mW at 250.4 nm and thirty-six lines of deep UV wavelengths ranging from 228.9 nm to 257.2 nm were generated in a Brewster-angle-cut BBO crystal.
Up to 230 mW average power in the UV at 255.3 nm with maximum 8.9% conversion efficiency was achieved for the SHG of a Copper-Vaper laser at 510.6 nm.
BBO’s 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 Fig. 3 and Fig. 4, respectively.
Figure 3. Type I OPO tuning curves of BBO
Figure 4. Type II OPO tuning curves of BBO
1. OPO pumped at 532nm
An OPO output ranging from 680 nm to 2400 nm with the peak power of 1.6 MW and up to 30% energy conversion efficiency was obtained in a 7.2 mm long type Ⅰ BBO. The input pump energy was 40 mJ at 532 nm with pulse-width 75 ps. With a longer crystal, higher conversion efficiency is expected.
2. OPO and OPA pumped at 355nm
Using BBO crystal, the OPO system covers a turning range from 400 nm to 3100 nm, and over the wavelength range from 430 nm to 2000 nm the OPO system’s conversion efficiency reach 18%~30%. Type Ⅱ BBO can be used to decrease linewidth near the degenerated points. A linewidth as narrow as 0.05 nm and usable conversion efficiency of 12% were obtained. However, a longer (˃15 mm) BBO should normally be used to decrease the oscillation threshold when employing the type Ⅱ phase-matching scheme.
Pumping with a picosecond Nd:YAG at 355 nm, a narrow-band (<0.3 nm), high energy (˃200 µJ) and wide tunable (400-2000 nm) pulse has been produced by BBO’s OPAs. This OPA can reach as high as more than 50% conversion efficiency, and therefore is superior to common Dye lasers in many respects, including efficiency, tunable range, maintenance, and easiness in design and operation. Furthermore, coherent radiation from 205 nm to 3500 nm can be also generated by BBO’s OPO or OPA plus a BBO for SHG.
3. Others
A tunable OPO with signal wavelengths between 422 nm and 477 nm has been generated by angle tuning in a type Ⅰ BBO crystal pumped with a XeCl excimer laser at 308 nm. And a BBO’s OPO pumped by the fourth harmonic of a Nd:YAG laser (at 266 nm) has been observed to cover the whole range of output wavelengths 330-1370 nm.
When pumped by a 1 mJ, 80 fs Dye laser at 615 nm, the OPA with two BBO crystals yields more than 50 µJ (maximum 130 µJ), <200 fs ultrashort pulse, over 800 nm – 2000nm.
BBO’s E-O Applications ：
BBO can also be used for E-O applications. It has wide transmission range from UV to about 3500 nm. And it has much higher damage threshold than KD*P and LiNbO3. More than 100W output power and 1000 KHz repitition rate have been reached by using E-O BBO crystals and Nd:YVO4 crystals as gain media. At 5 KHz, its pulse has width as short as 6.4 ns, and energy of 5.7 mJ or peak power of 900 KW. It has advantages over the commercial A-O Q-switched one, including very short pulse, high beam quality and size compact as well. Although it has a relative small electro-optic coefficient, and its half-wave voltage is high (7 KV at 1064 nm, 3 × 3 × 20 mm3), long and thin BBO can reduce the voltage requirements. We now can supply 25 mm long and 1 mm thin high optical quality of BBO crystal with Z-cut, AR-coated and Gold/Chrome plated on the side faces.
Coatings：
Provides the following AR-coating for BBO:
- IBS, IAD coating methods are available upon request
- Low reflectance dual band and triple band AR-coating of BBO for SHG, THG and FOHG of 1064 nm
- Broad Band AR-coating (BBAR) of BBO for SHG of tunable lasers
- Broad Band P-coating of BBO for OPO applications
- High damage threshold Long durability
- Other coatings are available upon request
BBO’s Parameters：
| Table 3. Specifications | |
| Dimension Tolerance | (W ± 0.1 mm) × (H ± 0.1 mm) × (L + 0.5/-0.1 mm) × (L≧2.5 mm)
(W ± 0.1 mm) × (H ± 0. 1 mm) × (L + 0.1/-0.1 mm) × (L＜2.5 mm) |
| Clear Aperture | Central 90% of the diameter |
| Internal Quality | No visible scattering paths or centers when inspected by a 50 mW green laser |
| Surface Quality (Scratch/Dig) | 10/5 to MIL-PRF-13830B |
| Flatness | ≦λ/8 @633 nm |
| Transmitted Wavefront Distortion | ≦λ/8 @633 nm |
| Parallelism | 20 arc sec |
| Perpendicularity | ≦15 arc min |
| Angle Tolerance | ≦0.25° |
| Chamfer | ≦0.2 mm × 45° |
| Chip | ≦0.1 mm |
| Damage Threshold | ＞1.5 GW/cm2 @1064 nm, 10 ns, 10 Hz (polished only)
＞1 GW/cm2 @1064 nm, 10 ns, 10 Hz (AR-coated) ＞0.3 GW/cm2 @532 nm, 10 ns, 10 Hz (AR-coated) |
| Quality Warranty Period | One year under proper use. |
Note：
- BBO has a low susceptibility to the moisture. Users are advised to provide dry conditions for both application and preservation of BBO.
- BBO is relatively soft and therefore requires precautions to protect its polished surfaces.
- When angle adjusting is necessary, please keep in mind that the acceptance angle of BBO is small.
- Select and design the best crystal, based on the main parameters of your laser, such as energy per pulse, pulse width and repetition rate for a pulsed laser, power for a cw laser, laser beam diameter, mode condition, divergence, wavelength tuning range, etc.
- For thin crystals, we can provide free holders for you.
