Potassium titanyl phosphate

Potassium titanyl phosphate (KTiOPO₄) or KTP is a nonlinear optical material which is commonly used for frequency doubling diode pumped solid-state lasers such as Nd:YAG and other neodymium-doped lasers. The material has a relatively high optical damage threshold (~15 J/cm²), a great optical nonlinearity and excellent thermal stability in theory. In practice, KTP crystals needs to have stable temperature to operate if they are pumped with 1064 nm (infrared, to output 532 nm green). However, it is prone to damage (called grey tracking) during high-power 1064 nm second-harmonic generation which tends to limit its use to low- and mid-power systems. It is used to produce "greenlight" to perform some laser prostate surgery.

It is also frequently used as an optical parametric oscillator for near IR generation up to 4 µm. It is particularly suited to high power operation as an optical parametric oscillator due to its high damage threshold and large crystal aperture. The high degree of birefringent walk-off between the pump signal and idler beams present in this material limit its use as an optical parametric oscillator for very low power applications.

KTP is also used as an electro-optic modulator, optical waveguide material, and in directional couplers.

KTP has orthorhombic crystal structure. It is highly transparent for wavelengths between 350–2700 nm with a reduced transmission out to 4500 nm where the crystal is effectively opaque. Its second harmonic generation (SHG) coefficient is about three times higher than KDP. It has a Mohs hardness of about 5.

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