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  • Position: Home >> Products >> Crystals >> Nonlinear Optical Crystals >> LBO
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  • Beta-Barium Borate (�-BaB2O4 or BBO)

    Beta-Barium Borate (�-BaB2O4 or BBO) is one of the most excellent NLO crystals. Using a newly improved flux method, AOTK now produces high-quality BBO crystal with high optical homogeneity, no inclusion and lower defects, lower absorption, high damage threshold and better laser performance. AOTK supplies the crystal length from 0.005mm to 20mm with various aperture and coating.



    		  
    AOTK's BBO Advanced Properties
     ? Broad phase-matchable range from 409.6 nm to 3500 nm
     ? Wide transmission region from 190 nm to 3500 nm
     ? High damage threshold of 10 GW/cm2 for 100 ps pulse-width at 1064 nm
     ? Large effective second-harmonic-generation (SHG) coefficient
     ? Wide temperature-bandwidth of about 55�C
     ? High optical homogeneity with ?n > 10-6/cm
     ? Good mechanical and physical properties

    Typical Applications of BBO
     ? SHG, THG, 4HG and 5HG harmonic generations of Nd: lasers
     ? SHG, THG, and 4HG harmonic generations of Ti:Sapphire and Alexandrite lasers
     ? Frequency-doubling, -tripling and -mixing of Dye lasers
     ? Frequency-doubling and -tripling of ultrashort pulse Ti:Sapphire and Dye lasers
     ? Frequency-doubling of Argon ion, Cu-vapor and Ruby lasers
     ? Optical parametric amplifiers (OPA) and optical parametric oscillators (OPO)

    Basic Properties

    1. Structual and Physical Properties

    Crystal Structure
    Trigonal Point group 3m, Space group R3c
    Lattice Parameters
    a=b=12.532Å, c=12.717Å, z=6
    Density
    3.84 g/cm3
    Mohs Hardness
    4.0
    Melting Point
    1095 � 5oC
    Transition Temperature
    925 � 5oC
    Resistivity
    >1011 ohm-cm
    Absorption Coefficient
    a<0.1%/cm @1064 nm; a<1%/cm @532 nm
    Optical Homogeneity
    ?n � 10-6/cm
    Hygroscopic Susceptibility
    Low
    Thermal Conductivity Coefficient
    ?c, 1.2W/m/K; //C,  1.6W/m/K
    Thermal Expansion Coefficient
    a1=a2=4x10-6/oC, a3=36x10-6/oC
    Relative Dielectric Constant
    eT11/e0=6.7, eT33/e0=8.1; Tan d<0.001

    2. Linear Optical Properties

    Transparency Region
    189 - 3500 nm
    Refractive Indexes at 1064nm
    at 1064 nm
    at 532 nm
    at 355 nm
    at 266 nm
    at 213 nm
     
    no = 1.6551       ne = 1.5425
    no = 1.6750       ne = 1.5555
    no = 1.7055       ne = 1.5775
    no = 1.7571       ne = 1.6146
    no = 1.8465       ne = 1.6742
    Therm-Optic Coefficients
    dno/dT = -9.3 x 10-6/oC
    dne/dT = -16.6 x 10-6/oC
    Sellmeier Equations (? in �m, T=20 �C)
    no2=2.7359+0.01878(?2-0.01822)-0.01354?2
    ne2=2.3753+0.01224(?2-0.01667)-0.01516?2

    3. Nonlinear Optical Properties

    Phase Matching Output Wavelength
    189 - 1750 nm
    Nonlinear Coefficients
    d11 = 5.8 x d36(KDP)
    d31 = 0.05 x d11
    d22 < 0.05 x d11
    Effective SHG Coefficients
    Type I: deff = d31sin?+(d11cos3F-d22sin3F)cos?
    Type II: deff = (d11sin3F+d22cos3F)cos2?
    (where ? and F are polar angles referring to Z and X axis respectively)
    Electro-Optic Coefficients
    g11 = 2.7 pm/V, g22, g31 < 0.1 g11
    Half-Wave Voltage
    48 KV (at 1064 nm)
    , ,
    Damage Threshold
    at 1064 nm
    at 532 nm
    at 266 nm
     
    5GW/cm2 (10 ns), 10GW/ cm2 (1.3 ns)  
    1GW/cm2 (10 ns), 7GW/ cm2 (250 ps )
    120MW/cm2 (8 ns)

    Main Applications

    I. Applications in Nd:YAG Lasers

    Base on its superior optical and NLO properties, BBO is the most efficient NLO crystal used for SHG, THG, 4HG of Nd:YAG lasers. Moreover, BBO is the ONLY NLO crystal which can produce 5HG at 213 nm. More than 70% for SHG, 60% for THG and 50% for 4HG conversion efficiencies have been obtained respectively, and output 200 mW at 213 nm. Basic NLO properties from SHG to 5HG of Type I BBO crystal are shown in Table 1, and Table 2 shown the harmonic generation results of BBO and KD*P crystals.

    Table 1. Relevant NLO Properties of Type I BBO Crystal

    Fundamental Wavelength: 1064 nm
    SHG
    THG
    4HG
    5HG
    Effective NLO Coefficient (d36(KDP))
    5.3
    4.9
    3.8
    3.4
    Angular Acceptance (mrad-cm)
    1.0
    0.5
    0.3
    0.2
    Walk-off Angle (Degree)
    3.2
    4.1
    4.9
    5.5
    Temperature Acceptance (�C)
    51
    16
    4
    /

    Table 2. Harmonic Generations using BBO and KD*P Crystal

    Crystal
    1? (mJ)
    SHG (mJ)
    THG (mJ)
    4HG (mJ)
    5HG (mJ)
    BBO
    220
    105
    39
    18.5
    5
    600
    350
    40
    70
    20
    KD*P
    600
    270
    112.5
    45
    /

    Both type I and type II phase-matching can be reached by angle-tuning. The phase matching angles of frequency doubling determined by input radiation wavelength is shown in Fig. 1. 

    BBO is a very efficient crystal for intracavity SHG of high power Nd:YAG lasers. For example, greater than 15 W average power at 532 nm was obtained in intracavity SHG of an acousto-optic Q-switched Nd:YAG laser with AR-coated BBO crystal.
    		  

    Good laser beam quality (such as: small divergence, good mode condition, etc.) is the key for BBO to obtain high conversion efficiency, due to BBO's small acceptance angle and large walk-off. Tight focus of laser beam is not recommended.

    II. Applications in Tunable Lasers

    Dye Lasers

    Efficient UV output (205 - 310 nm) with a SHG efficiency of over 10% at wavelength of more than 206 nm was obtained in type I BBO, and 36% conversion efficiency have been achieved for a XeCl-laser pumped Dye laser (for example, Lambda Physik's Model LDP3000 and FL 3000) with power 150KW. The conversion efficiency is about 4 - 6 times higher than that of ADP. Furthermore, the shortest SHG wavelength 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.

    With sum-frequency of 780 - 950 nm and 248.5 nm (SHG output of 495 nm dye laser) in Type I BBO, the shortest UV outputs ranging from 188.9nm to 197 nm and the pulse energy of 95 mJ at 193 nm and 8 mJ at 189 nm have been obtained respectively.

    Ultrafast Pulse Laser

    A laser pulse as short as 10 fs pulse can be efficiently frequency-doubled with very thin BBO wafer which shows its superior properties compared with KDP and ADP crystals, considering both phase-velocity and group-velocity matching. It has been reported that 10fs 438 nm ultrafast laser has been achieved by 0.01 mm doubling BBO crystal wafer. Now as thin as 0.01 mm thickness BBO wafers fabricated and supplied by AOTK are widely used in frequency-doubling, -tripling and autocorrelation measurient of ultrafast pulse lasers.

    Alexandrite and Ti:sapphire Lasers

    UV output in the region of 360 - 390 nm with pulse energy of 105mJ (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 BBO SHG and THG of an Alexandrite laser.

    Greater than 50% of SHG conversion efficiency in a Ti:Sapphire laser has been obtained. High conversion efficiencies were also obtained for THG and 4HG of Ti:Sapphire lasers.

    Argon Ion and Copper-Vapor Laser

    By using the intracavity frequency-doubling technique in an Argon Ion laser with all lines output power of 2W, 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 UV at 255.3 nm with maximum 8.9% conversion efficiency has been obtained for the SHG of Copper-Vapor laser at 510.6 nm.

    III. Applications in OPO and OPA

     

     

    Fig. 2. Type I OPO Turing curves of BBO

     Fig. 3. Type II OPO Turing curves of BBO


    BBO is one of the most suitable materials for optical parametric oscillators (OPO) and optical parametric amplifiers (OPA), to generate the widely tunable coherent radiation from UV to IR. Type I and Type II phase matching are applied in BBO's OPO and OPA shown in Fig. 2 and Fig. 3.
    Generally long BBO (>15mm) shall be used to decrease the oscillation threshold when employing the type II phase-matching scheme. In order to obtain high efficient conversion, input laser radiation with good beam quality and low divergence is required because of small acceptance angle and large walk-off. Type I gives a larger tuning range and higher parametric amplification rate comparing to Type II, However, Type II interaction can produce narrower bandwidth (0.05 nm) output near degenerate points.

    BBO OPO can generate more than 100mJ with wavelength tunable from 400nm to 2000nm by Nd:YAG laser. Meanwhile, BBO OPO system cover the tuning range from 400nm to 3100nm. A maximum of 30% conversion efficiency can be obtained from 400nm to 3100nm, and more than 18% conversion efficiency over the wavelength range from 430nm to 2000nm.

    Pumped by picosecond Nd:YAG at 355 nm, narrow-band (< 0.3 nm), high energy (> 200mJ) and wide tunable (400nm ~ 2000nm) pulse have been produced by BBO's OPA. With > 50% conversion efficiency, BBO's OPA is superior to common Dye lasers in efficiency, tunable range and maintenance, and is easy to design and operate. 

    With a 1 mJ, 80 fs Dye laser at 615 nm pumping, OPA using two BBO crystals yields more than 50 mJ (maximum 130 mJ), < 200 fs ultrashort pulse over 800 nm ~2000 nm.

    Parametric gain of BBO is over ten times higher than that of KDP at 355 nm pump for Type I interaction.

    Tunable OPO with signal wavelengths between 422 nm and 477 nm has been generated by angle tuning a type I BBO crystal pumped with XeCl excimer laser at 308 nm.

    BBO's OPO pumped by fourth harmonic of a Nd:YAG laser (at 266 nm) has been observed to cover the whole range of 330 - 1370 nm.

    IV. BBO's E-O Applications

    BBO can also be used for E-O applications. It has wide transmission range from UV to about 3500nm and it has much higher damage threshold than KD*P or LiNbO3, More than 80W output power and 50KHz repetition rate have been reached by using AOTK�s E-O BBO crystals and Nd:YVO4 crystals as gain media. At 5KHz, its pulse has width as short as 6.4ns,and energy of 5.7mJ or peak power of 900 KW. It has advantages over the commercial A-O Q-switched one, including a very short pulse, high beam quality and size compact as well. Although it has a relative small electro-optic coefficient, the Half-wave voltage is very high (48KV at 1064nm), long and thin BBO can reduce the voltage requirements. AOTK now can supply 20mm long and 1mm thin high optical quality of BBO crystal with Z-cut, AR-coated and Gold/Chrome plated on the side faces.