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Barium Borate (BBO) Crystal

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bbo1.GIF (13685 bytes)CASIX engineers have been growing and fabricating BBO crystal since it was discoveried in China. Using a newly improved flux method, CASIX now produces high quality Beta-Barium Borate (b-BaB2O4 or BBO) crystal boule with size up to f135 x 32 mm3. The finished BBO crystal devices produced by CASIX are expected to be as large as 20x20x25 mm3 with high optical homogeneity.

CASIX's BBO Features:

u Broad phase-matchable SHG range from 409.6 nm to 3500 nm;
u Wide transmission region from 190 nm to 3500 nm;
u Large effective second-harmonic-generation (SHG) coefficient;
u High damage threshold of 10 GW/cm2 for 100 ps pulse-width at 1064 nm;
u High optical homogeneity with Dn 10-6/cm;
u Wide temperature-bandwidth of about 55oC. (for type I SHG 1064 nm);
u Good mechinical and physical properties;

CASIX's BBO has been Applied to:

Q Second, third, fourth and fifth harmonic generations of Nd:lasers;
Q Frequency-doubling, -tripling and -mixing of Dye lasers;
Q Second, third & fourth harmonic generations of Ti:Al2O3 and Alexandrite lasers;
Q Optical parametric amplifiers (OPA) and optical parametric oscillators (OPO);
Q Frequency-doubling and -tripling of ultrashort pulse Ti:Sapphire and Dye lasers;
Q Frequency-doubling of Argon ion, Cu-vapor and Ruby lasers;
Q External intracavity SHG.

CASIX provides:

v Strict quality control;
v Crystal length from 0.01 mm to 25 mm and size up to 20x20x25 mm3;
v P-coatings, AR-coatings, mounting, housing and repolishing services;
v Strong technical supports;
v Mass production line to support OEM applications;
v Unbeatable price and special OEM discount;
v Fast delivery, in-stock crystals in a large quantity for next-day delivery;
v NEW! Super BBO for OPO & OPA UV Generation;
v NEW! Ultra-thin BBO crystals down to 0.01 mm thickness;
v NEW! Special mounts for Ultra-thin crystals.

Basic Properties

1. Structural and Physical Properties

Crystal Structure

Trigonal, space group R3c

Cell Parameters

a = b = 12.532Å, c = 12.717Å, Z = 6

Melting Point

1095±50C

Transition Temperature

925± 50C

Optical Homogeneity

Delta n » 10-6/cm

Mohs Hardness

4.5

Density

3.85 g/cm3

Linear Absorption Coefficients

a<0.001 cm-1 ( l =1064 nm)
a<0.01 cm-1 ( l=532nm)
a<0.5 cm-1 ( l=2550nm)

Hygroscopic Susceptibility

Low

Resistivity

> 1011 ohm-cm

Relative Dielectric Constant

eT11/e0: 6.7, eT33/e0: 8.1
Tan delta, < 0.001

Thermal Expansion Coefficients
(in the range of 250C - 9000C)

a, 4 x 10-6/K
c, 36 x 10-6/K

Thermal Conductivity

c, 1.2 W/m/K; ïçc, 1.6 W/m/K

2. Linear Optical Properties

Transparency Range:
189 - 3500 nm, See Transparency Curve

BBO-T-Curve.GIF (16107 bytes)

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

Therm-Optic Coefficients:
dno/dT = - 9.3 x 10-6/0C
dne/dT = -16.6 x 10-6/0C

Sellmeier Equations:
N20(l) = 2.7359+0.01878/(l2-0.01822)-0.01354 x l2 ( l in mm, T=200C)
N2e(l) = 2.3753+0.01224/(l2-0.01667)-0.01516 x l2 ( l in mm, T=200C)

3. Nonlinear Optical Properties

Phase-Matchable Output Range

189 - 1750 nm

NLO Coefficients

d11 = 5.8 x d36(KDP)
d31 = 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
at 0.266 mm

5 GW/cm2 (10 ns); 10 GW/cm2 (1.3 ns);
1 GW/cm2 (10 ns); 7 GW/cm2 (250 ps);
120 MW/cm2 (8ns).

Applications in Nd:YAG Lasers

BBO is an efficient NLO crystal for second, third and fourth harmonic generations of Nd:YAG lasers, and the only NLO crystal which can be used to produce the fifth harmonic generation (5HG) at 0.213mm. Conversion efficiencies of more than 70% for SHG, 60% for THG and 50% for 4HG, and 200 mW output at 213 nm (5HG) have been obtained respectively. Because of BBO's high efficiency, not hygroscopic after AR-coated (or P-coated), and large size available, it replaces KD*P in most of frequency doubling of Nd:YAG Laser. The comparisons of BBO and KD*P crystals in a Spectra-Physics DCR-2 Nd:YAG laser, and the basic nonlinear optical properties from SHG to 5HG are listed in Table 1 and Table 2, respectively.

Table 1: Harmonic generations using BBO and KD*P crystals

Crystal

1w
(mJ)

SHG
(mJ)

THG
(mJ)

4HG
(mJ)

5HG
(mJ)

BBO

220
600

105
350

39
140

18.5
70

5
20

KD*P

600

270

112.5

45

/

Table 2: Relevant NLO properties for type I BBO crystals

Fundamental Wavelength: 1064 nm

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 (degree)

3.2

4.1

4.9

5.5

Temperature Acceptance (oC)

51

16

4

/

BBO is an efficient crystal for intracavity SHG of high power Nd:YAG lasers. For intracavity SHG of an acousto-optic Q-switched Nd:YAG laser, more than 15 W average power at 532 nm was generated in CASIX's AR-coated BBO crystal.

BBO is also an excellent crystal to be applied to frequency-double, -triple and -quadruple the high power acousto-optic and electro-optic Q-switched and mode-locked Nd:YAG and Nd:YLF lasers. More than 4 W UV output at 355 nm and 2 W output at 266 nm are stably generated. Using specially designed optical system, conversion efficiency > 50% is obtained for frequency doubling 532 nm. In addition, greater than 1 W cw output at 266nm was commerically produced from doubling 532 nm laser with a Brewster-angle-cut BBO crystal in an external resonant cavity, the Deltatrain, an all-solid state laser system made by LAS Laser Analytical Systems GmbH (Germany).

Because of BBO's small acceptance angle and large walk-off, good laser beam quality (small divergence, good mode condition, etc.) is important for BBO to obtain high conversion efficiency. Tightly focusing of laser beam using sphere lens is not recommended by CASIX's engineers.

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 has been obtained in type I BBO, and 36% conversion efficiency was achieved for the XeCl-laser or Nd:YAG laser pumped Dye lasers (e.g. Lambda Physik, models FL 3000 and LPD 3000) with the power of 150KW. The conversion efficiency is about 4 - 6 times higher than that of ADP. The shortest SHG wavelength of 204.97 nm with efficiency of about 1% has been generated.

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 to 197 nm and the pulse energy of 95 mJ at 193 nm and 8 mJ at 189 nm have been obtained respectively.

2. Ultrashort Pulse Laser

Frequency-doubling and -tripling of ultra-fast lasers, for example, femtosecond (fs) Ti:Sapphire lasers, are the applications in which BBO shows superior properties compared with KDP and ADP crystals. Now, CASIX can provide as thin as 0.01 mm BBO for this purpose. A laser pulse as short as 2 fs can be efficiently frequency-doubled with a thin BBO by considering both phase-velocity and group-velocity matching. Standard ultra-thin BBO crystals is listed for your selection.

3. Ti:Sapphire and Alexandrite Lasers

UV output in the region 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 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 were also obtained for THG and 4HG of Ti:Sapphire lasers.

4. Argon Ion and Copper-Vapor Lasers

BBO is most suitable NLO crystals for directly frequency doubling wavelength less than 532 to generate UV output. 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 UV at 255.3 nm with maximum 8.9% conversion efficiency has been achieved for the SHG of Copper-Vapor laser at 510.6 nm.

OPO and OPA

BBO's OPO and OPA are the powerful tool for generating the widely tunable coherent radiation from UV to IR. The tuning angles of type I and type II BBO OPO and OPA have been calculated and shown as following respectively.

fig16.GIF (24889 bytes)

Type I OPO Tuning Curves of BBO

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Type II OPO Tuning Curves of BBO

By using CASIX's BBO crystals, Spectra-Physics MOPO-700 Series OPO Systems can generate more than 100 mJ pulse energy with wavelength tunable from 400 to > 2000 nm. The wavelength range can be further extended from 200 - 3000 nm by using BBO or KDP crystal. 　

Type II BBO can be used to decrease linewidth near degenerate points. Linewidth as narrow as 0.05nm and usable conversion efficiency of 12% were obtained. However, long (>15mm) BBO should be normally used to decrease the oscillation threshold when the type II phase-matching scheme is employed.　

Pumping with picosecond Nd:YAG at 355 nm, narrow-band (< 0.3 nm), high energy (> 200mJ) and wide tunable (400 nm to 2.0 mm) pulse have been produced by BBO's OPA. BBO's OPA, with more than 50% conversion efficiency, is superior to common Dye lasers in efficiency, tunable range and maintenance, and is easy to design and operate. 　

opo.GIF (11371 bytes)BBO's OPO pumped by fourth harmonic of a Nd:YAG laser (at 266nm) has been observed to cover the whole range of 330 - 1370 nm. The Nd:YAG at 266nm pumped OPO is commerically available by OPOTEK (CA, USA). The special design system is able to generate wavelength tunable from 300nm -500nm with 8mJ/pulse output power at 10Hz.

Others

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. Super BBO crystals were specially developed in CASIX for OPO and OPA applications. They are of large size and high quality.

Standard Size

The standard size crystals recommended by CASIX's engineers for various applications are listed as follows (assuming the laser beam diameter upon crystal is f2 mm to f3 mm):

1. Harmonic generations of Nd:YAG lasers

1064nm-->  Type I, 4 x 4 x 7 mm, 22.8°-cut --532nm
Type I, 4 x 4 x 7 mm, 31.3°-cut
Type II, 4 x 4 x 7 mm, 38.6°-cut 		--355nm
Type I, 4 x 4 x 7 mm, 47.6°-cut --266nm
Type I, 4 x 4 x 7 mm, 51.1°-cut --213nm

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

532nm--> Type I, 4 x 4 x 12 - 15 mm, 21°-cut --680nm - 2600 nm
355nm--> Type I, 6 x 4 x 12 - 15 mm, 30°-cut
Type II, 7 x 4 x 15 - 20 mm, 37°-cut		 --410nm - 2600 nm
266nm--> Type I, 6 x 4 x 12 - 15 mm, 39°-cut --295nm - 2600 nm

3. Frequency-doubling of Dye lasers

670 - 530 nm --> Type I, 6 x 4 x 7 mm, 40°-cut --335 - 265 nm
600 - 440 nm --> Type I, 8 x 4 x 7 mm, 55°-cut --300 - 220 nm
444 - 410 nm --> Type I, 8 x 4 x 7 mm, 80°-cut --222 - 205 nm

4. Harmonic generations of Ti:Sapphire lasers

700 - 1000 nm --> Type I, 7 x 4 x 7 mm, 28°-cut 350 - 500 nm
700 - 1000 nm --> Type I, 8 x 4 x 7 mm, 42°-cut 240 - 330 nm
700 - 1000nm --> Type I, 8 x 4 x 7 mm, 66°-cut 210 - 240 nm

5. Frequency-doubling and -tripling of Alexandrite lasers

720 - 800 nm --> Type I, 4 x 4 x 7 mm, 31°-cut 360 - 400 nm
720 - 800 nm --> Type I, 7 x 4 x 7 mm, 48°-cut 240 - 265 nm

6. Intracavity SHG of Ar+ laser with Brewster-angle-cut BBO

514 nm --> Type I, 4 x 4 x 7 mm, 51° B-cut 257 nm
488 nm --> Type I, 4 x 4 x 7 mm, 55° B-cut 244 nm

Ultra-Thin BBO for Ultra-fast Laser Application

Frequency Conversion of Ultrafast Lasers

For frequency conversion of ultrafast lasers with femtosecond (fs) pulse width, the main concern is fs pulse broadening induced by group velocity mismatching (GVM) or group velocity dispersion of NLO crystal. In order to keep efficiency frequency conversion without significant pulse broadening, the suggested thickness (LGVM) of crystals is less than Pulse Width divides GVM. 　

Based on advanced crystal technology, CASIX is proud to provide as thin as 0.02 mm BBO crystals for frequency conversion of ultrafast lasers.

Application (Type I)
BBO Crystals

SHG of 700 nm

SHG of 800 nm

SHG of 900 nm

THG of 700 nm

THG of 800 nm

THG of 900 nm
deff (pm/V)

1.296

1.365

1.408

0.893

1.101

1.221
GVM (ps/cm)

2.721

1.922

1.401

8.497

5.676

4.079
LGVM @ 10fs (micron)

40

50

70

10

20

30
Damage threshold
@ 10fs (GW/cm2)

20

25

30

10

15

20

Ultra-fast Ti:Sapphire Laser Optics Kits

Frequency Doubling Crystal

Substrate

Clear Aperture

Thickness

Part No.

BBO

>f 3.5 (mm)

0.02 (mm)

UTO8211

BBO

>f 3.5 (mm)

0.03 (mm)

UTO8213

BBO

>f 3.5 (mm)

0.05 (mm)

UTO8215

BBO

>f 3.5 (mm)

0.1 (mm)

UTO8210

BBO

>f 3.5 (mm)

0.5 (mm)

UTO8201

BBO

>f 9.0 (mm)

0.5 (mm)

UTO8203

BBO

>f 3.5 (mm)

1.0 (mm)

UTO8204

Frequency Tripling Crystal

Substrate

Clear Aperture

Thickness

Part No.

BBO

>f 3.5 (mm)

0.02 (mm)

UTO8311

BBO

>f 3.5 (mm)

0.03 (mm)

UTO8313

BBO

>f 3.5 (mm)

0.05 (mm)

UTO8315

BBO

>f 3.5 (mm)

0.1 (mm)

UTO8310

BBO

>f 3.5 (mm)

0.3 (mm)

UTO8301

BBO

>f 9.0 (mm)

0.3 (mm)

UTO8303

BBO

>f 3.5 (mm)

1.0 (mm)

UTO8304

Frequency Quadrupling Crystal

Substrate

Clear Aperture

Thickness

Part No.

BBO

f 3.5 (mm)

0.02 (mm)

UTO8411

BBO

f 3.5 (mm)

0.03 (mm)

UTO8413

BBO

f 3.5 (mm)

0.05 (mm)

UTO8415

BBO

f 3.5 (mm)

0.1 (mm)

UTO8410

BBO

f 3.5 (mm)

0.3 (mm)

UTO8403

BBO

f 3.5 (mm)

0.5 (mm)

UTO8404

BBO

f 3.5 (mm)

1.0 (mm)

UTO8401

Mounting

Super polished or coated crystals's surfaces are very easy to be damaged during transportation or handling when needed, especially for thin crystals. In order to prevent crystals from damaging or to be easily operated, CASIX provides three kinds of mount to install different dimension crystals. The sketches of them are listed following for your reference, custom made mounts or holders are also available.

Figure

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Part No.

0101-0100

0101-0500

0101-0300

F C (mm)

25.4

25.4

25.4

T (mm)

5

9.5, 13.5

9.5

Crystal Aperture(mm)

4X4 ~10X10

4X4~10X10

8X8~10X10

Crystal Length (mm)

0.1~2

4 ~10

3~6

CASIX'S Warranty on BBO Specifications

Transmitting wavefront distortion

less than l/8 @ 633nm

Dimension tolerance

(W± 0.1 mm) x (H± 0.1 mm) x (L + 0.2 mm/-0.1 mm)

Clear aperture

> 90% central area

Flatness

l/8 @ 633nm

Surface Quality

10/5 Scratch/Dig per MIL-O-13830A

Parallelism

better than 20 arc seconds

Perpendicularity

15 arc minutes

Angle tolerance

deltaq < 0.5o, deltaf < 0.5o

Quality warranty period

one year under proper use

COATINGS

1. Protective Coating (P-coating)

The polished surfaces of BBO are relatively easy to be fogged in humid air because of its low hygroscopic susceptibility. The protective coating (P-coating) was developed by CASIX to prevent BBO from exposure to moisture. The P-coating is featured by:
Long durability: More than 6 months at 95% humidity and much longer at lower humidity.
High damage threshold: Over 7 GW/cm2 with laser pulse-width 30ps at 1064nm.
Better transmittance: Transmittance of P-coated BBO is better than that of uncoated BBO over a wide wavelength range from 200 nm-3500 nm.

Note: The P-coated BBO with a mount is simpler and better than BBO with housing.

2. Anti-Reflective Coatings (AR-coatings)

CASIX supplies single-band and dual-band AR-coatings for BBO at 1064 nm and 532 nm. The AR-coatings are characterized by low reflectance (less than 0.2% at 1064 nm and 0.4% at 532 nm), high damage threshold (over 7 GW/cm2 with laser pulse-width of 30 ps and 1GW/cm2 with laser pulse-width 10 ns and repetition rate of 10Hz), anti-moisture and long durability. High damage threshold AR-coatings for 4HG of Nd:YAG or Nd:YLF laser are recently developed with R < 0.2% at 532 nm and R < 0.4% at 266 nm. AR-coatings at other wavelengths are also available upon request.

BBO-p-coatingcurve.GIF (19893 bytes)

P-Coating @ 800 nm

BBO-AR-coatingcurve.GIF (20417 bytes)

AR-Coating @532 &1064 nm

Note

1. BBO has a low susceptibility to moisture. Users are advised to provide dry conditions for both use and preservation of BBO.

2. BBO is soft and therefore the protection of its polished surfaces requires precautions.

3. When angle adjusting is necessary, keep in mind that the acceptance angle of BBO is small.

4. CASIX's engineers can select and design the best crystal for you if parameters of your laser are provided, for example, energy per pulse, pulse width and repetition rate for a pulsed laser, power for a cw laser, laser beam diameter, mode condition, divergence and wavelength tuning range, etc.

5. Keep BBO crystals in a certain temperature, it will increase the damage threshold.

6. CASIX provides mounts and sealed housing for BBO crystals.

Copyright  1998 CASIX, Inc. All rights reserved. Last Revised: May. 8, 1999
Web Page maintained by : Contact@CASIX.com

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