22 May 2019 Description
MgO:LiNbO3 – A kind of nonlinear crystal optimize the performance of LiNbO3
One of the most important drawbacks of popular LiNbO3 crystal is its susceptibility to photorefractive damage (optically induced change of refractive index, usually under exposure with blue or green CW light). The usual way to eliminate this effect is to keep LN crystals at elevated temperatures (400K or more). Another way to prevent photorefractive damage is MgO-doping (usually at levels of around 5 mol% for congruent LN). What is good is that such MgO-doped congruent LiNbO3 crystals have a much lower coercive field value than undoped LN crystals.Recently, it was shown that stoichiometric LiNbO3 crystals, doped with only 1 mol% MgO, possess higher photorefractive damage threshold than 5 mol% MgO-doped congruent LN samples.
Pure LiNb03 (LN) is a good candidate for various optical devices, but has a major disadvantage due to its low threshold optical damage. MgO-doped LN(congruent compositions) is one of the possible solutions to deal with this problem. MgO doping has played an important role in LN and shown an increased threshold laser beam strength by 100 times. An interesting point is that every physical property of MgO-doped LN (e.g. transition temperature, activation energy, optical band , optical absorption spectra, shift of OH- vibration frequency, density, and electric activation energy based on our previous measurements4) has threshold composition at just above 5 mole% of MgO concentration.
Parameter
Polishing
| Polishing Specification for Laser Grade Ⅰ |
| Orientation Tolerence |
＜0.5° |
| Thickness/Diameter Tolerance |
±0.1 mm |
| Surface Flatness |
＜λ/8@632nm |
| Wavefront Distortion |
＜λ/4@632nm |
| Surface Quality |
20/10 |
| Parallel |
30〞 |
| Perpendicular |
15ˊ |
| Clear Aperture |
＞90% |
| Chamfer |
＜0.2×45° |
| Polishing Specification for Laser Grade Ⅱ |
| Orientation Tolerence |
＜0.2° |
| Thickness/Diameter Tolerance |
±0.02 mm |
| Surface Flatness |
λ/10 @632nm |
| Wavefront Distortion |
＜λ/8 @632nm |
| Surface Quality |
10/5 |
| Parallel |
10〞 |
| Perpendicular |
5ˊ |
| Clear Aperture |
＞90% |
| Chamfer |
＜ 0.2×45° |
Variation of Refractive Index with Temperature
| |
355nm |
406nm |
532nm |
633nm |
1064nm |
|
| Lithium Niobate |
25°C |
2.40179 |
2.32631 |
2.23622 |
2.20351 |
2.15714 |
| 50°C |
2.40343 |
2.32807 |
2.23765 |
2.20458 |
2.15757 |
| 75°C |
2.40722 |
2.33080 |
2.23940 |
2.20607 |
2.15884 |
| Magnesium Doped Lithium Niobate |
25°C |
2.38482 |
2.31248 |
2.22530 |
2.19323 |
2.14757 |
| 50°C |
2.38778 |
2.31441 |
2.22644 |
2.19424 |
2.14861 |
| 75°C |
2.39152 |
2.31718 |
2.22819 |
2.19567 |
2.14966 |
Curie Temperature and UV Absorption Cutoff at α =20cm−1 as a Function of MgO Concentration (in mol%) in Stoichiometric and Congruent LN Crystals
| [MgO] |
Tc[K] |
λcutoff[μm] |
| Stoichiometric LN |
|
|
| 0 |
1466±2 |
|
| 0.8 |
1479±2 |
0.304 |
| 2.0 |
1486±1 |
0.301 |
| 3.3 |
1485±1 |
0.303 |
| 4.6 |
1480±2 |
|
| Congruent LN |
|
|
| 0 |
1411 |
0.316 |
| >5 |
1486 |
|
| Transparency range at “0” transmittance level for congruent LN crystals: 0.32–5µm |
Experimental Values of Refractive Indices for Crystal with 5 mol% MgO and Mole Ratio Li/Nb=0.97
| λ[µm] |
no |
ne |
| 0.4358 |
2.3863 |
2.2802 |
| 0.4916 |
2.3403 |
2.2416 |
| 0.5461 |
2.3114 |
2.2172 |
| 0.5770 |
2.2988 |
2.2068 |
| 0.5790 |
2.2980 |
2.2062 |
| 0.6328 |
2.2816 |
2.1922 |
| 0.6943 |
2.2678 |
2.1805 |
| 0.8400 |
2.2460 |
2.1622 |
| 1.0642 |
2.2272 |
2.1463 |
Experimental Values of Refractive Indices for Crystal with 5 mol% MgO and Mole Ratio Li/Nb=0.946 (congruent melt)
| λ[µm] |
no |
ne |
λ[µm] |
no |
ne |
| 0.4047 |
2.4247 |
2.3111 |
0.5790 |
2.2982 |
2.2056 |
| 0.4078 |
2.4202 |
2.3073 |
0.5893 |
2.2945 |
2.2027 |
| 0.4358 |
2.3863 |
2.2795 |
0.6234 |
2.2840 |
2.1938 |
| 0.4861 |
2.3441 |
2.2444 |
0.6563 |
2.2756 |
2.1867 |
| 0.4916 |
2.3404 |
2.2412 |
0.6907 |
2.2681 |
2.1802 |
| 0.4962 |
2.3376 |
2.2389 |
0.6943 |
2.2669 |
2.1793 |
| 0.5461 |
2.3112 |
2.2167 |
1.0640 |
2.2237 |
2.1456 |
| 0.5770 |
2.2989 |
2.2063 |
|
|
|
Nonlinear Refractive Index
| λ[µm] |
γ×1015[cm2/W] |
Note |
| 0.78 |
2.0±0.3 |
[100] direction |
| 2.0±0.3 |
[010] direction |
Experimental Values of Phase-matching Angle (T =293K)
| Interacting wavelengths[μm] |
Φexp [deg] |
Note |
| SHG, o+o ⇒ e |
|
|
| 1.0642⇒0.5321 |
74.5 |
5mol% MgO, congruent LN |
| 76 |
5mol% MgO |
| 76.5 |
5mol% MgO, Li/Nb=0.97 |
| 82.3 |
7mol% MgO |
| 1.0795⇒0.53975 |
75.1 |
5mol% MgO, congruent LN |
| 1.0796⇒0.5398 |
74 |
5mol% MgO, Li/Nb=0.97 |
| 1.3414⇒0.6707 |
54 |
5mol% MgO, congruent LN |
| Note: The PM angle values are strongly dependent on melt stoichiometry. |
Experimental Values of NCPM Temperature
| Interacting wavelengths[μm] |
T[℃] |
Note |
| SHG, o+o ⇒ e |
|
|
| 1.047⇒0.5235 |
75.3 |
|
| 1.0642⇒0.5321 |
25.4 |
0.6mol% MgO, congruent LN |
| 78.5 |
7mol% MgO, along X |
| 85–109 |
>5mol% MgO |
| 107 |
5mol% MgO |
| 110 |
5mol% MgO |
| 110.6 |
5mol% MgO |
| 110.8 |
7mol% MgO |
| 1.0795⇒0.53975 |
115 |
5mol% MgO, congruent LN |
| Note: The PM temperature values are strongly dependent on melt stoichiometry. |
Experimental Values of Angular and Temperature Bandwidths
| Interacting wavelengths[μm] |
T[℃] |
θpm[deg] |
Δθint[deg] |
ΔT[℃] |
Note |
| SHG, o+o ⇒ e |
|
|
|
|
|
| 1.0642⇒0.5321 |
20 |
76 |
0.063 |
|
5mol% MgO |
| 25.4 |
90 |
|
0.68 |
0.6mol% MgO |
| 107 |
90 |
2.16 |
0.73 |
5mol% MgO |
| 110.6 |
90 |
|
0.73 |
5mol% MgO |
Laser-induced Damage Threshold
| λ[μm] |
τp[ns] |
Ithr[GW/cm2] |
Note |
| 0.5321 |
CW |
>0.002 |
1mol% MgO, Li/Nb=1.38 |
| |
>0.002 |
2mol% MgO, Li/Nb=1.0 |
| |
0.002 |
5mol% MgO, congruent LN |
| |
>0.006 |
1.8mol% MgO, Li/Nb=0.96–0.99 |
| ≈20 |
0.34 |
5mol% MgO |
| 0.778 |
0.002 |
>10 |
7mol% MgO |
| 0.78 |
0.00015 |
>15 |
|
| 0.78–0.84 |
0.0001 |
>130 |
1kHz, 7mol% MgO |
| 1.0642 |
25 |
>0.025 |
0.6mol% MgO, congruent LN |
| ≈20 |
0.61 |
5mol% MgO |
| 20 |
>0.039 |
10Hz, 5mol% MgO |
| 0.04 |
>0.8 |
0.6mol% MgO, congruent LN |
| 0.03 |
>0.14 |
5Hz, 5mol% MgO |
| 1.56 |
0.00008 |
>1.36 |
1kHz, 5mol% MgO |
| Note: Under CW 0.532-µm irradiation, the bulk photorefractive damage was investigated. |
Absolute Values of Second-order Nonlinear Coefficients for 5mol% MgO:LiNbO3
|d31(0.852µm)|=4.9pm/V
|d33(0.852µm)|=28.4pm/V
|d31(1.064µm)|=4.4pm/V
|d33(1.064µm)|=25.0pm/V
|d31(1.313µm)|=3.4pm/V
|d33(1.313µm)|=20.3pm/V
Other Properties
| Linear Absorption Coefficient |
|
| λ[µm] |
α [cm-1] |
|
| 0.5321 |
0.02 |
|
| 1.0642 |
<0.01 |
|
| <0.003 |
|
| Temperature derivatives of refractive indices for 5 mol% MgO-doped congruent LiNbO3 |
| λ[µm] |
dno/dT×106[ K-1] |
dne/dT×106[ K-1] |
| 0.53975 |
16.663 |
72.763 |
| 0.6328 |
12.121 |
64.866 |
| 1.0795 |
4.356 |
54.190 |
| 1.3414 |
5.895 |
52.665 |
| Dependence of Coercive Field Value for 5mol% MgO-doped Congruent LiNbO3 on Crystal Temperature |
| T[K] |
P[kV/mm] |
|
| 298 |
4.5 |
|
| 353 |
2.4 |
|
| 393 |
1.8 |
|
| 443 |
1.3 |
|
Features
-
Homogeneity is high
-
Transparency range is wide
-
The value of damage threshold is high
-
Good electro-optical properties
-
Good photoeleastic properties
Applications
Compact 532nm microchip laser array utilizing optical contact Nd:YVO4/PPMgOLN
|
