KNbO3

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KNbO3 (Potassium Niobate) crystal (KN for short) is one of the very important nonlinear optical crystals. Its nonlinear optical quality factor, d2 /n3, ranks first among all oxide crystals. The average refractive index of KN is 2.2. The theoretical value of reflectivity is 14%. The theoretical transmittance is 86%.

The crystal is chemically stable, has a large nonlinear optical coefficient, and direct frequency doubling (101 mW) of a semiconductor 860 nm laser has yielded nearly 40 mW of 430 nm blue light. Due to its special properties, the KN crystal is important in developing microlasers for this new application. The realization of blue lasers is a top priority, and KN crystals are one of the ideal materials for generating second harmonics and realizing blue lasers.

Features of KNbO3 (Potassium Niobate) Crystal:

  • Millisecond response time
  • Very low scattering loss
  • Large nonlinear optical coefficient
  • High nonlinear optical coefficient
  • Excellent photorefractive properties
  • High stability under light irradiation
  • Favorable phase matching characteristics

Physicochemical Properties

Chemical FormulaKNbO3
Crystal StructureRhombic，mm2
Lattice Constanta = 5.6896Å,
b = 3.9692Å,
c = 5.7256Å
Mass Density4.617 g/cm3
Melting Point1333 K
Curie Temperature498 K
Distribution of dielectric axis and crystallinity axis X, Y, Z ⇒ b, a, c
Specific heat CP at P = 0.101325MPacp= 767 J/kgK
Thermal Conductivityκ > 3.5 W/mK
Thermal Expansionaa=5.010×10-6 /℃;
ab=1.410×10-5/℃;
ac=5.010×10-7/℃

Nonlinear Optical Properties

AttributeNumerical
Nonlinear Optical Coefficientd31=-15.8 pm/V, d32=-18.3 pm/V @ 1064 nm
Shortest SHG Wavelength425 nm（Type I NCPM, y-cut or a-cut）
Type I SHG has an acceptance angle of 1064 nmDq = 0.24 mrad / cm（internal）
The acceptance temperature of type I SHG is 1064 nmDT=0.3 ℃/cm

Linear Optical Properties

AttributeNumerical
Transparent Range400-5500 nm
IR Cutoff Wavelength5.5 μm
Absorb Losses<=1%/cm @1064 nm
Damage Threshold<= 4 J/cm2 @527 nm（500ps，Single Pulse）
<= 6 J/cm2 @1054 nm（700ps，Single Pulse）

Phase Matching Angle Experimental Value (T=293K)

Interaction Wavelength[μm]φexp [deg]θexp [deg]
XY Plane，θ=90°
SHG, e + e ⇒ o
0.946 ⇒ 0.473≈30 
4.7599 ⇒ 2.3799569.9 
YZ Plane, φ = 90°
SHG, o + o ⇒ e
0.86 ⇒ 0.43 83.5
0.89 ⇒ 0.445 70.7
0.92 ⇒ 0.46 64
0.94 ⇒ 0.47 60.5
1.0642 ⇒ 0.5321 46.4
1.3188 ⇒ 0.6594 30.6
1.3382 ⇒ 0.6691 29.7
3.5303 ⇒ 1.76515 37.3
4.7291 ⇒ 2.36455 77.3
SFG, o + o ⇒ e
1.3188 + 0.6594 ⇒ 0.4396 62.3
1.3188 + 1.0642 ⇒ 0.5889 37.7
4.7762 + 3.1841 ⇒ 1.9105 46.6
5.2955 + 3.5303 ⇒ 2.1182 59.5
XZ Plane, φ = 0°, θ > Vz
SHG, o + o ⇒ e
1.0642 ⇒ 0.5321 70.4
1.3188 ⇒ 0.6594 56.8
1.3382 ⇒ 0.6691 56.2
3.5303 ⇒ 1.76515 58.8
SFG, o + o ⇒ e
1.3188 + 1.0642 ⇒ 0.5889 62.6
5.2955 + 3.5303 ⇒ 2.1182 86.1

Experimental Value of Temperature Bandwidth at T=295K

Interaction Wavelength[μm]θexp [deg]ΔT [◦C]
YZ Plane, φ = 90°
SHG, o + o ⇒ e
1.0642 ⇒ 0.532146.40.39
1.3382 ⇒ 0.669129.70.59
3.5303 ⇒ 1.7651537.12.3
SFG, o + o ⇒ e
5.2955 + 3.5303 ⇒ 2.118259.52.4
XZ Plane, φ = 0°, θ >Vz
SHG, o + o ⇒ e
1.0642 ⇒ 0.532171.40.77
1.3382 ⇒ 0.669156.22.2
3.5303 ⇒ 1.7651558.110.1

Spectrum

KNbO3 nonlinear crystal Temperature CRYLINKKNbO3 nonlinear crystal index CRYLINK
KNbO3-Temperature variation of the supporting phaseRefractive index dispersion of KNbO3 at room temperature
KNbO3 nonlinear crystal transmission CRYLINKKNbO3 nonlinear crystal Optical CRYLINK
KNbO3-Transmission SpectraKNbO3-Optical Absorption

References

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[2]  Kim J H ,  Yoon C S . Domain switching characteristics and fabrication of periodically poled potassium niobate for second-harmonic generation[J]. Applied Physics Letters, 2002, 81(18):3332-3334.
[3]  Zysset B ,  Biaggio I ,  Gunter P N . Refractive indices of orthorhombic KNbO3. I. Dispersion and temperature dependence[J]. Journal of the Optical Society of America B, 1992, 9(3).
[4]  Umemura N ,  Yoshida K ,  Kato K . Phase-Matching Properties of KNbO_3 in the Mid-Infrared[J]. Applied Optics, 1999, 38(6):991-994.
[5]  Uematsu Y . Nonlinear Optical Properties of KNbO3 Single Crystal in the Orthorhombic Phase[J]. Japanese Journal of Applied Physics, 1974, 13(9):1362-1368.
[6]  Baumert J C ,  Hoffnagle J ,  Gunter P . Nonlinear Optical Effects In KNbO3 Crystals At AlxGa1_xAs, Dye, Ruby And Nd:YAG Laser Wavelengths.[C]// European Conference on Optics. International Society for Optics and Photonics, 1985.
[7]  Yoshiguchi T ,  Ota T ,  Adachi N . Crystal Growth of KNbO 3 by Solution-Dropping Method[J]. Materials Science Forum, 2007, 544-545:697-700.
[8]  Yamanouchi K ,  Wagatsuma Y ,  ODaGawa H , et al. Single crystal growth of KNbO3 and application to surface acoustic wave devices[J]. Journal of the European Ceramic Society, 2001, 21(15):2791-2795.
[9] Shao-Yi, Yong-Qiang, Zhang, et al. First-principles study of structural, electronic, elastic, and optical properties of cubic KNbO3 and KTaO3 crystals[J]. Physica status solidi, B. Basic research, 2017, 254(5).
[10]  Grabowska E . Selected perovskite oxides: Characterization, preparation and photocatalytic properties—A review[J]. Applied Catalysis B Environmental, 2016, 186:97-126.
[11]  Comes R ,  Lambert M ,  Guinier A . The chain structure of BaTiO3 and KNbO3[J]. Solid State Communications, 1968, 6(10):715-719.
[12]  Zgonik M ,  Schlesser R ,  Biaggio I , et al. Materials constants of KNbO3 relevant for electro- and acousto-optics[J]. Journal of Applied Physics, 1993, 74(2):1287-1297.
[13] MD Fontana,  Metrat G ,  Servoin J L , et al. Infrared spectroscopy in KNbO3 through the successive ferroelectric phase transitions[J]. Journal of Physics C Solid State Physics, 1984, 17(3):483-514.
[14] A, Magrez, E, et al. Growth of Single-Crystalline KNbO3 Nanostructures.[J]. ChemInform, 2006, 37(15):no-no.
[15]  Tennery V J ,  Hang K W . Thermal and X‐Ray Diffraction Studies of the NaNbO3KNbO3 System[J]. Journal of Applied Physics, 1968, 39.
[16] Wu, Xing, and, et al. Progress in KNbO3 crystal growth[J]. Journal of Crystal Growth, 1986, 78(3):431-437.
[17]  Baumert J C , P Günter,  Melchior H . High Efficiency Second Harmonic Generation in KNbO3 Crystals[J]. Optics Communications, 1983, 48(3):215-220.
[18]  Currat R ,  Comes R ,  Dorner B , et al. Inelastic neutron scattering in orthorhombic KNbO3[J]. Journal of Physics C:Solid State Physics, 1974.
[19]  Matthews D G ,  Conroy R S ,  Sinclair B D , et al. Blue microchip laser fabricated from Nd:YAG and KNbO3[J]. Optics Letters, 1996, 21(3):198-200.
[20]  Krakauer H ,  Yu R ,  Wang C Z , et al. Dynamic local distortions in KNbO3[J]. Journal of Physics Condensed Matter, 1999, 11(18):3779.
[21] U, Flückiger, and, et al. On the preparation of pure, doped and reduced KNbO3 single crystals[J]. Journal of Crystal Growth, 1978.
[22]  Yang Y ,  Jung J H ,  Yun B K , et al. Flexible pyroelectric nanogenerators using a composite structure of lead-free KNbO(3) nanowires.[J]. Advanced Materials, 2012, 24(39):5357-5362.

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