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 Quality20/10
Parallel30〞
Perpendicular15ˊ
Clear Aperture＞90%
Chamfer＜0.2×45°
Polishing Specification for Laser Grade Ⅱ
Orientation Tolerence＜0.2°
Thickness/Diameter Tolerance±0.02 mm
Surface Flatnessλ/10 @632nm
Wavefront Distortion＜λ/8 @632nm
Surface Quality10/5
Parallel10〞
Perpendicular5ˊ
Clear Aperture＞90%
Chamfer＜ 0.2×45°


Variation of Refractive Index with Temperature


355nm406nm532nm633nm1064nm
Lithium Niobate25°C2.401792.326312.236222.203512.15714
50°C2.403432.328072.237652.204582.15757
75°C2.407222.330802.239402.206072.15884
Magnesium Doped Lithium Niobate25°C2.384822.312482.225302.193232.14757
50°C2.387782.314412.226442.194242.14861
75°C2.391522.317182.228192.195672.14966


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

01466±2
0.81479±20.304
2.01486±10.301
3.31485±10.303
4.61480±2
Congruent LN

014110.316
>51486
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]none
0.43582.38632.2802
0.49162.34032.2416
0.54612.31142.2172
0.57702.29882.2068
0.57902.29802.2062
0.63282.28162.1922
0.69432.26782.1805
0.84002.24602.1622
1.06422.22722.1463


Experimental Values of Refractive Indices for Crystal with 5 mol% MgO and Mole Ratio Li/Nb=0.946 (congruent melt)

λ[µm]noneλ[µm]none
0.40472.42472.31110.57902.29822.2056
0.40782.42022.30730.58932.29452.2027
0.43582.38632.27950.62342.28402.1938
0.48612.34412.24440.65632.27562.1867
0.49162.34042.24120.69072.26812.1802
0.49622.33762.23890.69432.26692.1793
0.54612.31122.21671.06402.22372.1456
0.57702.29892.2063



Nonlinear Refractive Index

λ[µm]γ×1015[cm2/W]Note
0.782.0±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⇒0.532174.55mol% MgO, congruent LN
765mol% MgO
76.55mol% MgO, Li/Nb=0.97
82.37mol% MgO
1.0795⇒0.5397575.15mol% MgO, congruent LN
1.0796⇒0.5398745mol% MgO, Li/Nb=0.97
1.3414⇒0.6707545mol% 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⇒0.523575.3
1.0642⇒0.532125.40.6mol% MgO, congruent LN
78.57mol% MgO, along X
85–109>5mol% MgO
1075mol% MgO
1105mol% MgO
110.65mol% MgO
110.87mol% MgO
1.0795⇒0.539751155mol% 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⇒0.532120760.063
5mol% MgO
25.490
0.680.6mol% MgO
107902.160.735mol% MgO
110.690
0.735mol% MgO


Laser-induced Damage Threshold

λ[μm] τp[ns]Ithr[GW/cm2]Note
0.5321CW>0.0021mol% MgO, Li/Nb=1.38

>0.0022mol% MgO, Li/Nb=1.0

0.0025mol% MgO, congruent LN

>0.0061.8mol% MgO, Li/Nb=0.96–0.99
≈200.345mol% MgO
0.7780.002>107mol% MgO
0.780.00015>15
0.78–0.840.0001>1301kHz, 7mol% MgO
1.064225>0.0250.6mol% MgO, congruent LN
≈200.615mol% MgO
20>0.03910Hz, 5mol% MgO
0.04>0.80.6mol% MgO, congruent LN
0.03>0.145Hz, 5mol% MgO
1.560.00008>1.361kHz, 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]
0.53210.02
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]
0.5397516.66372.763
0.632812.12164.866
1.07954.35654.190
1.34145.89552.665
Dependence of Coercive Field Value for 5mol% MgO-doped Congruent LiNbO3 on Crystal Temperature
T[K]P[kV/mm]
2984.5
3532.4
3931.8
4431.3


Features


Applications

Compact 532nm microchip laser array utilizing optical contact Nd:YVO4/PPMgOLN