KTP - Potassium Titanyl Phosphate
- KTP is the most commonly used material for SHG of Nd-doped lasers, and also for SFG to generate blue&red light. In addition to these functions, it is also applied to OPO, E-O devices and waveguides.
Potassium Titanyl Phosphate (KTiOPO4 or KTP) is widely used in both commercial and military lasers including laboratory and medical system, 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 20 × 20 × 40 mm3 and maximum length of 60 mm
- Quick delivery (15 working days for polished only, 20 working days for coated)
- Unbeatable price and quantity discount
- Technical support
- AR-coating, mounting and re-working service
Table 1. Chemical and Structural Properties
|Crystal Structure||Orthorhombic, Space group Pna21, Point group mm2|
|Lattice Parameter||a = 6.404 Å, b = 10.616 Å, c = 12.814 Å, Z = 8|
|Melting Point||About 1172 ℃|
|Thermal Conductivity||13 W/m/K|
|Thermal Expansion Coefficients||αx = 11 × 10-6 /℃, αy = 9 × 10-6 /℃, αz = 0.6 × 10-6 /℃|
Table 2. Optical and Nonlinear Optical Properties
|Transparency Range||350-4500 nm|
|SHG Phase Matchable Range||497-1800 nm (Type Ⅱ)|
|Therm-optic Coefficient ( λ in μm)||dnx/dT = 1.1×10-5 /℃|
|dny/dT = 1.3×10-5 /℃|
|dnz/dT = 1.6×10-5 /℃|
|Absorption Coefficients||< 0.1% /cm at 1064 nm, < 1% /cm at 532 nm|
|For Type Ⅱ SHG of a Nd:YAG laser at 1064 nm||Temperature Acceptance||24 ℃·cm|
|Spectral Acceptance||0.56 nm·cm|
|Angular Acceptance||14.2 mrad·cm (Φ)；55.3mrad·cm (θ)|
|Walk-off Angle||0.55 °|
|NLO Coefficients||deff (Ⅱ) ≈ (d24 - d15) sin2Φ sin2θ - (d15 sin2Φ + d24 cos2Φ) sinθ|
|Non-vanished NLO Susceptibilities||
d31 = 6.5 pm/V d24 = 7.6 pm/V
d32 = 5 pm/V d15 = 6.1 pm/V
d33 = 13.7 pm/V
|Sellmeier Equations (λ in μm)||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|
Low frequency (pm/V) High frequency (pm/V)
|Dielectric Constant||?eff = 13|
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. Up to now, Nd:lasers that use KTP for intra-cavity and extra-cavity frequency doubling have become a preferred pumping sources for visible dye lasers and tunable Ti:sapphire lasers as well as their amplifiers. They are also used as green sources for many research and industry applications.
Close to 80% conversion efficiency and 700 mJ green laser were obtained with a 900 mJ injection-seeded Q-switch Nd:YAG lasers by using extra-cavity KTP.
8 W green laser was generated from a 15 W LD pumped Nd:YVO4 with intra-cavity KTP.
KTP is also being used for intracavity mixing of 0.81 µm diode and 1.064 µm Nd:YAG laser to generate blue light and intracavity SHG of Nd:YAG or Nd:YAP lasers at 1.3 µm to produce red light.
Fig. 1 Type Ⅱ KTP SHG in XY Plane
Fig.2 Type Ⅱ 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 (600 nm) to mid-IR (4500 nm), 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 1064 nm Nd:YAG laser has generated as high as above 66% efficiency for degenerately converting to 2120 nm.
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 0.7 µm to 1 µm, the output can cover from 1.04 µm to 1.45 µm (signal) and from 2.15 µm to 3.2 µm (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 features, KTP also has promising E-O and dielectric properties that are comparable to LiNbO3. These excellent properties make KTP extremely useful to various E-O devices. Table 1 is a comparison of KTP with other E-O modulator materials commonly used:
Table 3. Electro-Optic Modulator Materials
From Table 1, 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 (?15 GHZ), 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 2 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 waveguide have been applied to the type Ⅰ quasi-phase-matchable SHG of a tunable Ti:Sapphire laser in the range of 760-960 mm, and directly doubled diode lasers for the 400-430 nm outputs.
Table 4. Electro-Optic Waveguide Materials
|Materials||r (pm/V)||n||εeff (ε11ε33)1/2||n3r/εeff (pm/V)|
Table 5. Specifications
|Dimension Tolerance||(W ± 0.1 mm) × (H ± 0.1 mm) × (L + 0.5/-0.1 mm) (L≧2.5 mm)(W ± 0.1 mm) × (H ± 0.1 mm) × (L + 0.1/-0.1 mm) (L＜2.5 mm)|
|Clear Aperture||Central 90% of the diameter|
|Internal Quality||No visible scattering paths or centers when inspected by a 50 mW green laser|
|Surface Quality (Scratch/Dig)||10/5 to MIL-PRF-13830B|
|Flatness||≦ λ/8 @633 nm|
|Transmitted Wavefront Distortion||≦ λ/8 @633 nm|
|Parallelism||20 arc sec|
|Perpendicularity||≦ 15 arc min|
|Angle Tolerance||≦ 0.25 °|
|Chamfer||≦ 0.2 mm × 45 °|
|Chip||≦ 0.1 mm|
＞1 GW/cm2 @1064 nm, 10 ns, 10 Hz (AR-coated)
＞0.3 GW/cm2 @532 nm, 10 ns, 10 Hz (AR-coated)
|Quality Warranty Period||One year under proper use.|
CASTECH provides the following AR-coatings:
- Dual Band AR-coating (DBAR) of KTP for SHG of 1064 nm; low reflectance (R<0.2% @1064 nm and R<0.5% @532 nm)
- High reflectivity coating: HR 1064 nm & HT 532 nm, R?99.8% @1064nm, T?90% @532 nm
- Broad Band AR-coating (BBAR) of KTP for OPO applications
- High damage threshold (?300 MW/cm2 at both wavelengths)
- Long durability
- Other coatings are available upon request
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