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Potassium Titanyl  Phosphate (KTiOPO4 or KTP)

KTP is a nonlinear optical (NLO) material which is known for its high NLO coefficient, high electro-optical 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.


  • Frequency Doubling (SHG) of Nd-doped Lasers for Green/Red Output
  • Frequency Mixing of Nd Laser and Diode Laser for Blue Output
  • Parametric Sources (OPG, OPA and OPO) for 0.6mm-4.5mm Tunable Output
  • E-O 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 non-critical phase matching (NCPM).  



                                               Figure 1: KTP type II phase-matching angles vs. wavelengths in XY plane



                                               Figure 2: KTP type II phase-matching 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 mid-IR (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 εeff = 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/cm2)
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)
nx2 = 3.0065+0.03901/(λ2-0.04251)-0.01327×λ2
 ny2 = 3.0333+0.04154/(λ2-0.04547)-0.01408×λ2
 nz2 = 3.3134+0.05694/(λ2-0.05658)-0.01682×λ2
  Nonlinear Optical Coefficients (pm/V)
(at 1064nm)
d31=2.54, d32=4.35, d33=16.9, d24=3.64, d15=1.91
  Table 1: KTP Properties

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