Potassium Titanyl Phosphate (KTiOPO4 or KTP) is widely used in both commercial and military lasers including laboratory and medical systems, range-finders, lidar, optical communication and industrial systems.
CASTECH's KTP is featured by：
• Large nonlinear optical coefficient;
• Wide angular bandwidth and small walk-off angle;
• Broad temperature and spectral bandwidth;
• High electro-optic coefficient and low dielectric constant;
• Large figure of merit;
• Nonhydroscopic, chemically and mechanically stable.
• Strict quality control;
• Large crystal size up to 20x20x40mm3 and maximum length of 60mm;
• Quick delivery (2 weeks for polished only, 3 weeks for coated);
• Unbeatable price and quantity discount;
• Technical support;
• AR-coating, mounting and re-polishing service.
Table 1. Chemical and Structural Properties
Orthorhombic, space group Pna21,point group mm2
a=6.404Å, b=10.616Å, c=12.814A, Z=8
Thermal Conductivity Coefficient
Thermal Expansion Coefficient
ax=11x10-6/℃, ay=9x10-6/℃, az=0.6x10-6/℃
Table 2. Optical and Nonlinear Optical Properties
SHG Phase Matchable Range
497 ~ 1800nm (Type II)
Thermal-optic Coefficients (/°C)
<0.1%/cm at 1064nm <1%/cm at 532nm
For Type II SHG of a Nd:YAG laser at 1064nm
Temperature Acceptance: 24°C·cm
deff(II)≈(d24 - d15)sin2Φsin2θ - (d15sin2Φ + d24cos2Φ)sinθ
Non-vanished NLO Susceptibilities
d31=6.5 pm/V d24=7.6 pm/V
Low frequecy(pm/V) High frequency(pm/V)
(λ in μm)
Applications for SHG and SFG of Nd: lasers：
KTP is the most commonly used material for frequency doubling of Nd:YAG and other Nd-doped lasers, particularly when the power density is at a low or medium level. To date, extra- and intra-cavity frequency doubled Nd:lasers using KTP have become a preferred pumping source for visible dye lasers and tunable Ti:Sapphire lasers as well as their amplifiers. They are also useful green sources for many research and industry applications.
• More than 80% conversion efficiency and 700mJ green laser were obtained with a 900mJ injection-seeded Q- switch Nd:YAG lasers by using extra-cavity KTP.
• 8W green laser was generated from a 15W LD pumped Nd:YVO4 with intra-cavity KTP.
• 200mW green outputs are generated from 1W LD pumped Nd:YVO4 lasers by using CASTECH's 2x2x5mm3 KTP and 3x3x1mm3 Nd:YVO4 .
KTP is also being used for intracavity mixing of 0.81µm diode and 1.064µm Nd:YAG laser to generate blue light and intracavity SHG of Nd:YAG or Nd:YAP lasers at 1.3µm to produce red light.
Fig. 1 Type II KTP SHG in XY Plane Fig. 2 Type II KTP SHG in XZ Plane
Applications for OPG, OPA and OPO：
As an efficient OPO crystal pumped by a Nd:laser and its second harmonics, KTP plays an important role for parametric sources for tunable outputs from visible (600nm) to mid-IR (4500nm), as shown in Fig. 3 and Fig. 4. Generally, KTP's OPOs provide stable and continuous pulse outputs (signal and idler) in fs, with 108 Hz repetition rate and a miniwatt average power level. A KTP's OPO that are pumped by a 1064nm Nd:YAG laser has generated as high as above 66% efficiency for degenerately converting to 2120nm.
Fig. 3 OPO pumped at 532 in X-Z plane Fig. 4 OPO pumped at 532 in X-Y plane
The novel developed application is the non-critical phase matched (NCPM) KTP's OPO/OPA. As shown in Fig.5, for pumping wavelength range from 0.7µm to 1µm, the output can cover from 1.04µm to 1.45µm (signal) and from 2.15µm to 3.2µm (idler). More than 45% conversion efficiency was obtained with narrow output bandwidth and good beam quality.
Fig. 5 Type II NCPM OPO
Applications for E-O Devices：
In addition to unique NLO features, KTP also has promising E-O and dielectric properties that are comparable to LiNbO3. These advantaged properties make KTP extremely useful to various E-O devices. Table 3 is a comparison of KTP with other E-O modulator materials commonly used:
Table 3. Electro-Optic Modulator Materials
From Table 3, clearly, KTP is expected to replace LiNbO3 crystal in the considerable volume application of E-O modulators, when other merits of KTP are combined into account, such as high damage threshold, wide optical bandwidth (>15GHZ), thermal and mechanical stability, and low loss, etc.
Applications for Optical Waveguides：
Based on the ion-exchange process on KTP substrate, low loss optical waveguides developed for KTP have created novel applications in integrated optics. Table 4 gives a comparison of KTP with other optical waveguide materials. Recently, a type II SHG conversion efficiency of 20%/W/cm2 was achieved by the balanced phase matching, in which the phase mismatch from one section was balanced against a phase mismatch in the opposite sign from the second. Furthermore, segmented KTP waveguides have been applied to the type I quasi-phase-matchable SHG of a tunable Ti:Sapphire laser in the range of 760-960mm, and directly doubled diode lasers for the 400-430nm outputs.
Table 4. Electro-Optic Waveguide Materials
CASTECH provides the following AR-coatings：
• Dual Band AR-coating (DBAR) of KTP for SHG of 1064nm. low reflectance (R<0.2% at 1064nm and R<0.5% at="" high="" damage="" threshold="">300MW/cm2 at both wavelengths); long durability.
• Broad Band AR-coating (BBAR) of KTP for OPO applications.
• High reflectivity coating: HR1064nm&HT532nm, R>99.8%@1064nm, T>90%@532nm.
• Other coatings are available upon request.
CASTECH's Warranty on KTP Specifications：
• Dimension tolerance：(W±0.1mm)x(H±0.1mm)x(L+0.5/-0.1mm)(L≥2.5mm)
• Clear aperture: central 90% of the diameter
• No visible scattering paths or centers when inspected by a 50mW green laser
• Flatness: less than λ/8 @ 633nm
• Transmitting wavefront distortion: less than λ/8 @ 633nm
• Chamfer: ≤0.2mm@45°
• Scratch/Dig code: better than 10/ 5（MIL-PRF-13830B）
• Parallelism: better than 20 arc seconds
• Perpendicularity: ≤5 arc minutes
• Angle tolerance: △θ≤0.25°, △ф≤0.25°
• Damage threshold [GW/cm2 ]：>0.5 for 1064nm, TEM00, 10ns, 10HZ (AR-coated)
>0.3 for 532nm, TEM00, 10ns, 10HZ (AR-coated)
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