KTP is a nonlinear optical (NLO) material which is known for its high NLO coefficient, high electrooptical coefficient, wide transparency range, small walk off angle, good chemical and mechanical properties, and a moderate optical damage threshold. These properties make KTP very attractive for different nonlinear optical applications.
Applications:
 Frequency Doubling (SHG) of Nddoped Lasers for Green/Red Output
 Frequency Mixing of Nd Laser and Diode Laser for Blue Output
 Parametric Sources (OPG, OPA and OPO) for 0.6mm4.5mm Tunable Output
 EO Modulators and Optical Switches
Phase Matching Angles:
Figure 1 & 2 show type II SHG phase matching angles vs. fundamental wavelengths in both XY and XZ planes. In XY plane the slope ∂(Δk)/∂θ is small, which ensures a large acceptance angle and a small walk off. In XZ plane the slope ∂(Δk)/∂λ is almost zero around the wavelength 2.0um, which ensures a large spectral acceptance. These two techniques are known as noncritical phase matching (NCPM).



Figure 1: KTP type II phasematching angles vs. wavelengths in XY plane




Figure 2: KTP type II phasematching angles vs. wavelengths in XZ plane




Figure 3: KTP OPO tuning curve in XY plane




Figure 4: KTP OPO tuning curve in XZ plane

Figure 3 & 4 show OPO tuning curve in both XY and XZ planes with a pump wavelength 532nm. As an efficient OPO crystal, KTP generates tunable parametric sources from visible (0.6um) to midIR (4.5um). Due to the development of NCPM, KTP OPO/OPA pumped by a tunable laser such as Ti:Sapphire could generates new wavelengths from 1.04um to 1.45um at a fixed KTP orientation.

Crystal Structure 
Orthorhombic



lattice constant (Å) 
a = 6.404, b = 10.616, c = 12.814



Melting Point (°C) 
1172



Mohs Hardness 
≈ 5



Density (g/cm^3) 
3.02



Absorption Coefficient (/cm) 
α<0.001 at 1064nm & 532nm


Hygroscopic Susceptibility 
No



Relative Dielectric Constant 
ε_{eff} = 13 

Linear Coefficient of Thermal Expansion (100°C) ( /K)

a1: 8.7X10^{6} a2: 10.5X10^{6} a3: 0.2X10^{6}



Transmission Range (nm) 
350~4500



Damage Threshold (MW/cm^{2})

10 at 1064nm 


Constant of Dispersion (dn/dT) (/°C) 
dnx/dT = 1.1X10^{5} dny/dT = 1.3X10^{5} dnz/dT = 1.6X10^{5}



Refractive Indices 
nx = 1.7377, ny = 1.7453, nz = 1.8297 at 1064 nm nx = 1.7780, ny = 1.7886, nz = 1.8887 at 532 nm 


Sellmeier Equations (λ in um)

nx^{2 }= 3.0065+0.03901/(λ^{2}0.04251)0.01327×λ^{2} ny^{2 }= 3.0333+0.04154/(λ^{2}0.04547)0.01408×λ^{2} nz^{2 }= 3.3134+0.05694/(λ^{2}0.05658)0.01682×λ^{2} 


Nonlinear Optical Coefficients (pm/V) (at 1064nm)

d_{31}=2.54, d_{32}=4.35, d_{33}=16.9, d_{24}=3.64, d_{15}=1.91 d_{eff}(II)=(d_{24}d_{15})sin(2Φ)sin(2Θ)(d_{15}sin^{2}(Φ)+d_{24}cos^{2}(Φ)sin(θ) 


Table 1: KTP Properties


