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||ɛeff = 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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