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Beta Barium Borate (b -BaB2O4 or
BBO) is one of the most outstanding nonlinear optical crystals which
has the unique properties: wide transparency region (0.19m m in
UV and 3.5m m in NIR) and phase matching range (0.41-3.5m m),
larger nonlinear coefficient, high damage threshold (>
10GW/cm2 for 1.3 ps 1.064m m), excellent optical
homogeneity (D n» 10-6/cm) and large thermal
acceptable bandwidth (» 55oC).
As a result of the above obvious advantages, BBO
perfectly suits frequency conversions of high peak or average power
laser radiation and harmonic generations in VIS and UV. Typical
applications are listed as follows: · SHG, THG, 4HG and 5HG harmonic
generations of Nd: YAG and Nd:YLF 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. Both Type I and Type II phase-matching can be obtained by
angle-tuning. The BBO phase-matching angles of frequency doubling
dependence on input radiation wavelength is shown in Fig. 1.
Wide transparency range and high effective nonlinearity
make BBO one of the most suitable materials for applications in
broadly tunable optical parametric amplifiers (OPA) and optical
parametric oscillators (OPO).
By using improved flux
growth methods, Beijing Gospel OptoTech Co. (GOT) has
grown up to f 130x30mm BBO crystal boules of high quality. As large as
15x15x20 mm3 finished devices with high optical quality are
fabricated and supplied steadily. Advanced techniques of crystal
growth and fabrication, strong production capability as well as strict
quality control system, ensure us the first choice and reliable
supplier to not only R&D users but commercial and industrial customers
in global market.
Basic
Properties
Density : 3.84
g/cm3
Crystal
Structure : Trigonal; Point group 3m, Space group R3c
Lattice
Parameters : a=b=12.532 A, c=12.717 A
Mohs Hardness :
4.5±5
Melting Point :
1095±5° C
Transition
Temperature : 925 ±5° C
Resistivity : >1011ohm-cm
Optical
Homogeneity : D n » 10-6/cm
Absorption
Coefficient : <0.1%/cm @1.064 m m
Thermal
Conductivity : K1 =K 2 =1.2W/m/K; K3
= 1.6 W/m/K
Thermal Expansion
Coefficient : a 1=a 2=4x10-6/K, a
3=36x10-6/K
Relative
Dielectric Constant : e 11T/e 0=6.7,
e 33T/e 0=8.1; Tand <0.001
Hygroscopisity :
low
Optical and NLO Properties
Transparency
Region : 0.19 m m ~ 3.5 m m
Phase Matching
Range : 0.41 m m ~ 3.5 m m
Nonlinear
Coefficients :d11=5.8 x d36(KDP)
(@ 1.064 m m) d31=0.05 x d11,
d22<0.05 x d11
Effective SHG
Coefficients :
deff = d31sinq
+ (d11cos3f - d22sin3f )cosq (Type I)
deff = (d11sin3f
+ d22cos3f )cos2q (Type II)
(where q and f are polar angles
referring to Z and X axis)
Refractive Indexes : no ne
1.6551 1.5425 (@1.064 m
m)
1.6750 1.5555 (@0.532 m
m)
1.7055 1.5775 (@0.355 m
m)
1.7571 1.6146 (@0.266 m
m)
1.8465 1.6742 (@0.213 m
m)
Sellmeier Equations :
no2 =
2.7359+0.01878/(l 2-0.01822)-0.01354l
2(l in m m
)
ne2 =
2.3753+0.01224/(l 2-0.01667)-0.01516l
2
Therm-optic Coefficients :
dno/dT = -9.3 x 10-6/°
C
dne/dT = -16.6 x 10-6/°
C
Electro-optic Coefficients :
g 11 = 2.7 pm/V
g 31, g 22
< 0.1 g 11
Damage Threshold :
> 5GW/cm2 (10 ns) and >
10GW/cm2 (1.3 ns) @1.064 m m
> 1GW/cm2 (10 ns) and > 7GW/cm2
(250 ps ) @0.532 m m
Main Applications of BBO Crystals
Applications in Nd:YAG Lasers
Due to its superior optical and NLO properties, BBO is
the most attractive material applied for SHG, THG, 4HG of Nd:YAG
lasers. More than 70% for SHG, 60% for THG and 50% for 4HG conversion
efficiencies have been reached. Moreover, BBO is the sole crystal
which can produce 5HG (200 mW 0.213μm output obtained). Basic NLO
properties from SHG to 5HG of Type I BBO crystal are listed in
Table 1. Please refer to Table 2, the harmonic generation
results of BBO and KD*P crystals.
· BBO is a very
efficient crystal for intracavity SHG of high power Nd: YAG laser. For
example, more than 15 W average power at 532 nm was obtained in an
AR-coated BBO crystal, in intracavity SHG of an acousto-optic
Q-switched Nd:YAG laser.
· From a
Brewster-angle-cut BBO in an external resonant cavity, 66 mW output
was produced when pumped by 600 mW SHG ouput of a mode-locked Nd:YLF
laser.
Due to BBO's small acceptance angle and large walk-off
angle, good laser beam quality (such as low divergence, good mode
condition, etc.) is required to obtain high conversion efficiency.
Tight focus of laser beam is NOT recommended.
Applications in Tunable Lasers
· With over 10% SHG
efficiency (l ³ 206 nm) in Type I BBO, efficient UV output (205 -
310 nm) and 36% conversion efficiency have been achieved for a
XeCl laser pumped Dye lasers (such as Model FL3000 and LPD 3000
in Lambda Physik) with power of 150 KW. The conversion efficiency is
about 4 - 6 times higher than that of ADP. Furthermore, the shortest
SHG wavelength (204.97 nm) with efficiency of about 1 % has been
generated.
· With SFG of 780 - 950
nm and 248.5 nm (SHG output of 495 nm Dye laser) in Type I BBO,
the shortest UV outputs range (l88.9 - 197 nm) and the pulse
energy of 95 μJ at 193 nm and 8 μJ at 189 nm have been obtained
respectively
· 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.
· > 50% SHG conversion
efficiencies in Ti:Sapphire lasers have been generated. High
conversion efficiencies were also obtained for THG and 4HG of
Ti:Sapphire lasers.
· In the intracavity
frequency-doubling of an Argon Ion laser with all lines output
power of 2 W, the maximum 33 mW at 250.4 nm and thirty-six
lines of deep UV wavelengths range (228.9 - 257.2 nm) were
generated in a Brewster-angle-cut BBO crystal.
· Up to 230 mW average
power in UV at 255.13 nm with maximum 8.9% conversion
efficiency has been achieved for the SHG of Copper-Vapor laser
at 510.6 nm.
· Less than 10 fs pulse
width laser can be efficiently frequency-doubled by 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 employing 0.02 mm doubling BBO crystal. Now 0.01 mm up to
1 mm thickness BBO wafers produced and supplied by GOT
are widely used in frequency-doubling, -tripling and autocorrelation
measurement of ultrashort pulse lasers, for example, fs Ti:Sapphire
lasers.
Applications in OPO and OPA
Wide transparency range and excellent NLO properties
make BBO 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. Both Type I and
Type II phase matching are used in BBO's OPO and pumped at different
harmonics (up to 5HG) of Nd:YAG lasers (shown in Fig. 2 and
Fig. 3).
Type I interaction gives a larger tuning range and
higher parametric amplification rate comparing to Type II interaction,
while Type II interaction can produce narrower bandwidth (0.05 nm)
output near degenerate points. Generally long BBO (>15mm) shall be
used to decrease the oscillation threshold when employing the type II
phase-matching scheme. In order to get high efficient conversion,
input laser radiation with good beam quality and low divergence is
required because of small acceptance angle and large walk-off. Typical
application results of OPO and OPA are listed:
·
Pumping with Nd:YAG lasers,
Spectra-Physics' OPO Systems generate higher than 100 mJ pulse
energy in the tunable wavelength range from 400 nm to
more than 2000 nm. A maximum 30 % conversion efficiency in the tuning
range of 400 〜
3100 nm and higher than 18 % conversion efficiency over the wavelength
range from 430 nm to 2000 nm have been achieved.
· Pumped by a 1 mJ, 80
fs Dye laser at 615 nm, OPA with two BBO crystals yields
more than 50 μJ (maximum 130 μJ), < 200 fs ultrashort pulse over
800-2000 nm
· Up to 30% energy
conversion efficiency has been obtained using 12 mm length BBO crystal
in OPO device synchronously pumped at 532 nm, which outputs at
406 -3170 nm.
· Parametric gain of
BBO is about ten times higher than that of KDP in case of 355nm pump
for Type I interaction. Pumped by ps Nd:YAG at 355 nm,
narrow-band (< 0.3 nm), high energy (> 200μJ) and wide tunable (400
〜 2000 nm) 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.
· . Tunable OPO with
signal wavelengths between 422 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 nm - 1.37 m m.
· Furthermore, coherent
radiation from 205 nm to 3500 nm can be generated by BBO's OPO or OPA
plus BBO's SHG.
Standard Specifications of BBO Crystals
Dimensional
Tolerance :
(W ± 0.1mm) x (H ± 0.1mm) x (L
+0.5/-0.1 mm)
Wavefront Distortion
: < l /4 @633 nm
Angle Tolerance : D
q < ± 0.2° , D f < ± 0.2°
Scratch/Dig Code :
10/5 per MIL-O-13830A
Clear Aperture : >
Central 90%
Flatness : l /10
@633 nm
Parallelism : < 20
arc seconds
Perpendicularity : <
5 arc minutes
Coating Types :
Protective-coating, AR and BBAR coatings
Coating Specifications of BBO Crystals
Protective Coating (P-coating)
GOT's coating engineers
have developed the protective coating which can prevent the polished
surfaces of BBO from exposure to moisture, considering the fact the
polished surfaces are very easy to be fogged in humid air due to its
low hygroscopic susceptibility. P-coated BBO with a mount is much
simpler and better to use than BBO with housing. The significant
advantages of protective coating are:
Long lifetime: over 6 months
at 95% humidity and much longer at lower humidity
Better transmission: better
than that of uncoated BBO over its all transparency range
High damage threshold: > 7 GW/cm2
at 1.064 m m (30 ps pulse width)
Anti-Reflective
Coatings (AR-coatings)
GOT can manufacture and
supply single-band, dual-band and broad-band AR-coatings for BBO at
versatile applications (extra- and intracavity SHG, THG, 4HG, SFG, OPO,
etc.), featured by anti-moisture and long durability, low reflectance,
and high damage threshold.
Typical AR-coatings and results are listed below for
reference. AR-coatings at other wavelengths are available upon
customers' request.
Single-band: AR@ 1.5,
1.064, 0.85, 0.532, 0.355 m m, etc. (R< 0.05〜0.15%)
Dual-band: AR@ 1.34/0.67,
1.064/0.532, 1.053/0.527, 1.047/0.523, 0.946/0.473, 0.8/0.4,0.532/0.266
m m (Rw <0.1〜0.2%, R2w <0.2〜0.4%)
Broad-band: AR@ 0.7〜1.0
m m, 0.8〜0.95 m m/0.4〜0.475
m m, 0.4〜0.75 m m/0.355 m m, etc.
Special Notes for BBO Crystals
· BBO is a soft crystal
and required to protect the polished surfaces carefully.
· BBO is easy to be
deliquesced and required the dry environment while using and keeping
it.
· In order to render
better service to customers, GOT prepares lots of BBO of
standard dimensions (Harmonic generations of Nd:YAG lasers -
4x4x7 mm; Frequency-doubling and tripling of
tunable lasers - 4x4x7, 6x4x7 or 8x4x7 mm;
OPO and OPA pumped by harmonics of Nd:YAG
lasers - 4x4x12〜15
mm, 6x4x12〜15 or
7x5x15〜20 mm;
etc.) with coatings in stock, and can deliver goods within 24 hours.
· 0.05 mm up to 1 mm
BBO wafers (Type I, SHG or THG of 800 nm; P-coated, with 1" mounts)
for frequency conversion and autocorrelation measurement of ultrafast
lasers with fs pulse are in stock to meet urgent delivery requirement.
As thin as 0.01 mm BBO wafers are available.
· Our engineers will
provide the specific designs to meet your requirement and save your
cost, if your laser's parameters (power for a cw laser or energy per
pulse, pulse width and repetition rate for a pulsed laser, laser beam
diameter, mode condition, divergence and wavelength tuning range,
etc.) are given, and offer you the latest technical information of BBO
crystal.
·
Special quantity
discounts for OEM customers! |
