KTA Crystals

KTA Crystals
KTA Crystals KTA Crystals KTA Crystals

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 wide applications in second harmonic generation (SHG), sum and difference frequency generation (SFG)/(DFG), optical parametric oscillation/ amplification (OPO/OPA), and electro-optical Q-switching involving MIR wavelengths.

Application examples:

55 ps pulse @2.95 μm from a KTA OPA for selective cutting of biological tissues
High average power ns OPO @ 1535 nm with NCPM KTA
Noncollinear OPCPA in KTA produces intense 160 fs pulses @1550 nm
KTA OPA pumped by 120 fs amplified pulses to generate intense 3-5 μm pulses

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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:

Crystal Structure  

Orthorhombic, space group Pna21, point group mm2

Cell Parameters  

a=13.125 Å, b=6.5716 Å, c=10.786 Å, Z=8

Melting Point  

1130 oC

Curie Point  

880 oC

Mohs Hardness  

 ~ 5


3.45 g/cm3



Hygroscopic Susceptibility


Specific Heat  

0.687 J/g/K

Thermal Conductivity  

1.8 W/m/K

Electrical Conductivity  

0.7-3.4 x10-6 s/cm (c-axis @ 22oC, 1 KHz)

Linear Optical Properties:

Transmitting Range      350 - 5000 nm      

Refractive Indices:
               532 nm               
             1064 nm
             3480 nm 

         nx             ny            nz
 1.8264      1.8331      1.9310 
     1.7818      1.7866      1.8680
1.7717      1.7763      1.8544
     1.7385      1.7411      1.8098

Sellmeier Equations
λ in μm)  
nx2=1.90713+1.23522λ2 /(λ2-0.19692)-0.01025λ2
ny2=2.15912+1.00099λ2 /(λ2-0.21844)-0.01096λ2
Thermo-optic Coefficients   dnx/dT=1.1x10-5 /oC, dny/dT=1.3x10-5 /oC
-5 /oC   
Absorption Coefficient    α < 1% cm-1 @ 1064nm and 532nm   

Nonlinear Optical Properties:

Phasematchable SHG Range 542 - 1800 nm  
Nonlinear Optical Coefficients d31=2.8 pm/V, d32=4.2 pm/V,
33=16.2 pm/V,d24=3.2 pm/V,
15=2.3 pm/V
Effective Nonlinearity Expressions  deff(II)= (d24-d15)sin2φsin2θ-(d15sin2φ+d24cos2φ)sinθ
Electro-optic Coefficients
(Low frequency)
 γ13= 11.5 pm/V, γ23=15.4 pm/V, γ33=37.5 pm/V
Dielectric Constant εeff=42  

NCPM Tuning Curve for 1064nm pumped OPO/OPA

With its excellent transmission at the MIR and the possibility to achieve NCPM when pumped with the common Nd lasers at 1064 nm, KTA is the crystal of choice for the effective generation of 3-5 μm through OPO/OPA.  The NCPM OPO/OPA can be temperature tuned by placing an x-cut crystal in an oven. The tuning curve is as follows,



Specifications for finished KTA:

Wavefront distortion: less than λ/6 @ 633 nm
Dimension tolerance: (W +/-0.1 mm) x (H +/-0.1 mm) x (L + 0.2/-0.1 mm)
Clear aperture: > 90% central area
Flatness: λ/8 @ 633 nm
Scratch/Dig: 20/10 to MIL-O-13830A
Parallelism: better than 20 arc seconds
Perpendicularity: 5 arc minutes
Angle tolerance:   Δθ < +/-0.25o, Δφ < +/-0.25o


Common dualband anti-reflection (DBAR) coatings at 1064/1535 nm, 1064/3480 nm,  1064/1650 nm, 1064/3000nm, or 1320/660 nm, 

Coatings for other specific applications are available upon request.


For customer convenience and protection of crystals,  crystals with T≤ 3.0 mm can be
mounted in a 1" anodized aluminum holder.

Thicker crystals are typically supplied unmounted, but water-cooled or uncooled mounts can be offered upon request.

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