The case of BBO crystasl in FHG application
Time：2019-12-08 18:23
266nm laser is a kind of ultraviolet laser. Compared with other laser markers, the deep ultraviolet laser marker has high photoelectric conversion efficiency.
Through the comparison of several common nonlinear crystal parameters in the table below.We can find that although the frequency doubling acceptance angle of the BBO crystal is small and the walk off angle is large in the Type 1 phase matching UV fourth harmonic generation process, BBO crystal has higher nonlinear coefficient in the UV band then other crystal.
| Comparison of Several Common Nonlinear Crystal Parameters | ||||
| Crystal | BBO | CLBO | LBO | |
| Transmittance range(nm) | 189-3500 | 180-2750 | 160-2600 | |
| Phase matching range(nm) | 409.6-3500 | Type1:477-2750 | Type1:554-2600 | |
| Type2:640-2750 | Type2:790-2150 | |||
| Damage threshold(GW/cm2)) | 10(1.3ns) | 25(1.3ns) | 25(1.3ns) | |
| SHG | 1064nm-532nm | Type 1 | Type 1 | Type 1 |
| Phase matching angle(deg) | 22.9 | 29.3 | 11.3（φ） | |
| Deff(pm/V) | 2.01 | 0.382 | 0.832 | |
| △θ△φ(mrad.cm) | 1.15 | 2.28 | 9.63（△φ） | |
| △λ(cm-1.m) | 38.95 | 84.31 | 75.9 | |
| △T(k.cm) | 40.67 | 57.48 | 7.04 | |
| Walk off [mrad] | 35.85 | 31.39 | 6.88 | |
| FHG | 532nm-266nm | Type 1 | Type 1 | Unavailable |
| Phase matching angle(deg) | 47.6 | 61.5 | ||
| Deff(pm/V) | 1.75 | 0.788 | ||
| △θ△φ(mrad.cm) | 0.37 | 1.08 | ||
| △λ(cm-1.m) | 5.8 | 10.14 | ||
| △T(k.cm) | 6.03 | 6.8 | ||
| Walk off [mrad] | 85.3 | 32.96 | ||
| Hygroscopy performance | Low | high | Very Low | |
Case - 1
By using a Q-switched Nd: YVO4 laser, KTP was used for SHG and BBO crystals was used for THG.
We obtained a CW ultraviolet 266nm laser wavelength of 296mW. Conversion efficiency of more 30.1% from 1064 to 532nm;Conversion efficiency of more more 10.1% from1064 to 266nm
Case -2
Nd:YAG, Output wavelength 1064nm, pulse width 6ns, repetition rate 1Hz-5Hz, output spot 8mm
KTP, Type 2 , Theta=90°,Phi=23.5°, Size: 3x3x9 ,Both side with AR/AR@1064+532nm
BBO, Type1, Theta=47.7°,Phi=0°, Size: 4x4x8, Both side with AR/AR@532+266nm
By using UVFS Dispersion spectroscopic prism to reduce the strong absorption of ultraviolet laser.
The first prism as a beam splitter, and the second prism as a compensating optical path.
When the Infrared output power is 14mJ, We obtained a 6.94mJ Green wavelength at 532nm and 2.26mJ UV laser wavelength at 266nm
Conversion efficiency of more is about 49.5% from 1064 to 532nm ;Conversion efficiency of more is about 16.1% from1064 to 266nm
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