KTA crystal features large non-linear optical and electro-optical coefficients in comparison to KTP and has the added benefit of significantly reduced absorption in the 2 to 5 μm region. It has found more and more applications in second harmonic generation (SHG), sum and difference frequency generation (SFG)/(DFG), optical parametric oscillation/ amplification (OPO/OPA), and electro-optical Q-switching.
KTA features
Large nonlinear optical coefficients
Wide angular bandwidth and small walk-off angle
Broad temperature and spectral bandwidth
Large electro-optic coefficients
Lower absorption in the 3-4 μm range than KTP.
Nonhydroscopic, chemically and mechanically stable
High thermal conductivity
High damage threshold
KTA is a positive biaxial crystal, with the principal axes X, Y, and Z ( nz>ny>nx ) parallel to the crystallographic axes a, b, and c, respectively.
Structural and Physical Properties
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Crystal Structure |
Orthorhombic, space group Pna21, point group mm2
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Cell Parameters |
a=13.125?, b=6.5716?, c=10.786 ?, Z=8
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Melting Point |
1130oC |
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Curie Point |
880oC |
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Mohs Hardness |
~ 5 |
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Density |
3.45 g/cm3 |
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Color |
colorless |
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Hygroscopic Susceptibility |
No |
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Specific Heat |
0.687 J/g/K |
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Thermal Conductivity |
1.8 W/m/K |
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Electrical Conductivity
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0.7-3.4 x10-6 s/cm (c-axis, @22 oC, 1KHz)
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Linear Optical Properties:
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Transmitting Range
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350 nm - 5500 nm
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Refractive Indices:
1064nm
532nm
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nx ny nz
1.7818 1.7866 1.8680
1.8264 1.8331 1.9310
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Sellmeier Equations
(l in μm) |
nx2=1.90713+1.23522l2 /(l2-0.19692)-0.01025l2
ny2=2.15912+1.00099l2 /(l2-0.21844)-0.01096l2
nz2=2.14768+1.29559l2/(l2-0.22719)-0.01436l2 |
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Thermo-optic Coefficients
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dnx/dT=1.1x10-5/oC, dny/dT=1.3x10-5/oC
dnz/dT=1.6x10-5/oC |
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Absorption Coefficient
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a < 1% cm-1 @1064nm and 532nm
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Nonlinear Optical Properties:
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Phasematchable SHG Range |
542 - 1800nm |
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Nonlinear Optical Coefficients |
d31=2.8pm/v, d32=4.2pm/v,
d33=16.2pm/v,d24=3.2pm/v,
d15=2.3pm/v |
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Effective Nonlinearity Expressions
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deff(II)= (d24-d15)sin2fsin2q-(d15sin2f+d24cos2f)sinq
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Electro-optic Coefficients
( Low frequency ) |
r13= 11.5pm/V, r23=15.4pm/V, r33=37.5pm/V
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Dielectric Constant |
eeff=42
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Specifications for finished KTA
Wavefront distortion: less than l/4 @ 633 nm
Dimension tolerance: (W +/- 0.1 mm) x (H +/- 0.1 mm) x (L + 0.2 mm/-0.1mm)
Clear aperture: > 90% central area
Flatness: l/8 @ 633 nm
Scratch/dig: 10/5 to MIL-O-13830A
Parallelism: better than 20 arc seconds
Perpendicularity: 5 arc minutes
Angle tolerance: Dq< +/-0.25o, Df< +/-0.25o
Coating and Mount
Standard dual band anti-reflection (DBAR) coatings at 1064nm/1530 nm, 1064/3200nm, or 1320nm/660nm are available. Other coatings are also available upon request. Mounts may be provided free of charge.
 Nd:YAG rod Nd:YVO4 KTA Er:YAG (Nd, Ce):YAG Yb:YAG Cr4+:YAG KTP LBO BBO
Nd:GGG
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