KTP Crystal (KTiOPO4) — Potassium Titanyl Phosphate Nonlinear Optical Crystal Supplier, Type II SHG

Frequently Asked Questions

What is KTP crystal used for?

KTP (Potassium Titanyl Phosphate) crystal is primarily used for second harmonic generation (SHG) — converting 1064nm Nd:YAG/Nd:YVO4 infrared laser light into 532nm green light. It is also used for optical parametric oscillation (OPO) generating tunable mid-IR (1.5-4.5µm), electro-optic Q-switching, and quantum optics SPDC entangled photon generation. KTP is the crystal inside virtually every green laser pointer, DPSS module, and medical/aesthetic green laser worldwide.

What is KTiOPO4 crystal?

KTiOPO4 is the chemical formula for Potassium Titanyl Phosphate (KTP) — an orthorhombic (point group mm2) nonlinear optical crystal with chemical formula KTiOPO4. It is a biaxial positive crystal with high nonlinear coefficient (d33=16.9 pm/V, ~3× KDP), broad transparency (350-4500nm), and excellent electro-optic properties (r33=36.3 pm/V). KTiOPO4 is non-hygroscopic and chemically stable.

How does KTP crystal work?

KTP works through Type II phase matching: when 1064nm infrared light passes through a KTP crystal cut at θ=90°, φ=23.5°, the crystal's nonlinear susceptibility generates a 532nm second harmonic wave. The crystal's birefringence is engineered so that the fundamental and harmonic waves travel at the same phase velocity — enabling constructive interference and efficient energy transfer (>40% conversion). This is second harmonic generation (SHG).

What is SHG in KTP crystal?

SHG (Second Harmonic Generation) in KTP is the nonlinear process of frequency-doubling: two 1064nm photons combine in the KTP crystal to produce one 532nm photon (half the wavelength, double the frequency/energy). KTP's Type II SHG uses the d24 coefficient (7.6 pm/V) for this 1064nm→532nm conversion — the most efficient and widely used SHG configuration in green DPSS lasers.

Is KTP crystal hygroscopic?

No — KTP is non-hygroscopic and chemically stable, requiring no hermetic packaging. Unlike BBO (slightly hygroscopic) and DKDP (highly hygroscopic requiring sealed cells), KTP maintains optical performance in ambient air for years. This simplifies mounting, reduces system cost, and improves long-term reliability.

What is the laser damage threshold of KTP crystal?

KTP has a laser damage threshold of >500 MW/cm² at 1064nm with 10ns pulses at 10Hz (AR-coated). For CW and high-repetition-rate operation, HGTR (High Grey Track Resistance) KTP provides enhanced resistance to photochromic grey-tracking damage. The practical power limit for standard KTP is ~5W CW green output; specify HGTR for higher powers.

KTP crystal for green laser — why is it the standard?

KTP is the standard green laser SHG crystal because its combination of high deff (~3.5 pm/V), small walk-off (4.9mrad), and wide angular/temperature acceptance is uniquely forgiving of alignment — critical for mass-produced DPSS green modules. For green lasers <20W, KTP provides the optimal cost-performance ratio. For >100W green, LBO's higher damage threshold is preferred.

KTP crystal for lidar and range finder — which configuration?

For lidar and laser range finders, KTP is used both as: (1) SHG crystal for 532nm green output — visible wavelength improves detector sensitivity and eye-safety classification; (2) EO Q-switch crystal for generating ns pulses with r33=36.3 pm/V enabling compact, high-repetition-rate (>10kHz) Q-switched lasers. Princeton Powder supplies both SHG-cut and EO-grade KTP.

KTP crystal for optical parametric oscillator (OPO) — what's special?

For optical parametric oscillator (OPO) applications, KTP is cut for θ=90° non-critical phase matching (NCPM) — eliminating walk-off for the longest effective interaction length and widest tuning range. KTP OPO pumped at 1064nm generates tunable output from 1.5-4.5µm (signal 1.5-2.1µm, idler 2.4-4.5µm) for mid-IR spectroscopy and remote sensing.

KTP crystal vs LBO crystal — which for high-power?

KTP: higher deff (~3.5 pm/V), smaller walk-off, easier alignment — best for <20W green and non-hygroscopic stability. LBO: 50× higher damage threshold (25 GW/cm² vs >500 MW/cm²) and NCPM at 148°C with zero walk-off — best for >100W industrial green. Choose KTP for cost-effective low-to-medium power; choose LBO for high-power industrial. Princeton Powder supplies both.

KTP vs KDP crystal — which is better?

KTP is superior to KDP for most SHG applications: 3× higher nonlinear coefficient (d33=16.9 vs d36~0.5 pm/V), non-hygroscopic (KDP is highly hygroscopic requiring sealed cells), and higher damage threshold. KDP remains used only for very large aperture (>100mm) applications where KTP cannot be grown large enough. For 1064nm SHG below 20W, KTP is the clear choice.

Type I vs Type II KTP crystal — which phase matching?

Type II (o+e→e) is the standard for KTP SHG at 1064nm — using the d24 coefficient (7.6 pm/V) for maximum effective nonlinearity. Type II also produces orthogonally polarized signal and idler in SPDC — ideal for quantum entanglement. Type I KTP can be phase-matched at other wavelengths but offers lower deff for 1064nm. Princeton Powder supplies both Type I and Type II cuts.

Do you offer custom KTP crystal cutting and large size?

Yes — custom KTP crystal cutting for any phase-matching wavelength within 350-4500nm, and large size KTP crystals up to 20×20×40mm³. Provide your pump wavelength, target output wavelength, and phase-matching type — our engineers calculate the optimal cut angle (θ, φ) and crystal length. Custom AR coatings for any wavelength band available.