Beta Barium Borate (b-BaB₂O₄ or BBO)

III. Main Applications

• Applications in Nd:YAG Lasers ( In tunable Lasers | In OPO and OPA )
  

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 0.213 m m 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.

Table 1 Basic NLO Properties of Type I BBO

SHG

THG

4HG

5HG

Effective SHG 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

Table 2 Harmonic Generations of BBO and KD^*P

Input

SHG

THG

4HG

5HG

1.064

0.532

0.355

0.266

0.213

BBO

220 mJ

105 mJ

39 mJ

18.5 mJ

5 mJ

600 mJ

350 mJ

140 mJ

70 mJ

20 mJ

KD^*P

600 mJ

270 mJ

112 mJ

45 mJ

/

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 ( In Nd:YAG Lasers | In OPO and OPA )
  

1. With over 10% SHG efficiency (l>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.

2. 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 mJ at 193 nm and 8 mJ at 189 nm have been obtained respectively.

3. 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.

4. > 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.

5. 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.

6. 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.

7. 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 iploying 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 measurient of ultrashort pulse lasers, for example, fs Ti:Sapphire lasers.
   
   

• Applications in OPO and OPA ( In Nd:YAG Lasers | In tunable Lasers )
  

Fig. 2  Type I BBO OPO Tuning Curves

Fig.3  Type II BBO OPO Tuning Curves

1. Pumping with Nd:YAG lasers, Spectra-Physics' OPO Systis generate higher than 100 mJ pulse energy in the tunable wavelength range from 400 nm to more than 2 mm. A maximum 30 % conversion efficiency in the tuning range of 400 nm ~ 3.1 mm and higher than 18 % conversion efficiency over the wavelength range from 430 nm to 2 mm have been achieved.

2. Pumped by a 1 mJ, 80 fs Dye laser at 615 nm, OPA with two BBO crystals yields more than 50 mJ (maximum 130 mJ), < 200 fs ultrashort pulse over 800 nm ~2 mm.

3. 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 nm ~ 3.17 mm.

4. Parametric gain of BBO is about ten times higher than that of KDP in case of 355 nm pump for Type I interaction. Pumped by ps Nd:YAG at 355 nm, narrow-band (< 0.3 nm), high energy (> 200mJ) and wide tunable (400nm ~ 2 mm) 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.

5. 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.

6. 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 mm.

7. Furthermore, coherent radiation from 205 nm to 3.5 mm can be generated by BBO's OPO or OPA plus BBO's SHG.