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MgO:LiNbO3 Nonlinear Crystal

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
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

  • SHG

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

  • Waveguide modulator

  • As a Q-switching in Nd: YAG lasers

  • Being used in frequency doubling at room temperature for 1064nm laser light

  • Electro-optic modulator

  • Range finder

  • Laser radar

  • Mobile telephones

CONTACT DETAILS
Nanjing Crylink Photonics Co.,Ltd
No.3, Hengda Road, Economic and Technological Development Zone, Nanjing, China
No.200,Zhaoxian Road,Jiading District,Shanghai City
Nanjing
Jiangsu
210038
China
Tel: (86)025-68790684
Fax: (86)025-68790685
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