KTP – Potassium titanyl phosphate
350 nm - 4400 nm
KTP (KTiOPO4) is very popular biaxial crystal. It is often grown using either flux or hydrothermal method, however flux growing is approximately 4 times cheaper. This crystal is one of the least expensive options for second harmonic generation (SHG).
- Features and Advantages
Second-Harmonic-Generation (SHG) and Sum-Frequency Mixing (SFM)
- Nd-doped lasers. KTP is most common crystal used for frequency doubling in Nd-doped low and medium power density laser systems.
Optical-Parameter-Oscillators (OPA), Optical-Parameter-Amplifiers (OPA), Optical-Parameter-Generators (OPG)
- For Visible light to middle-infrared (mid-IR) 600 nm to 4500 nm Tunable Output
- Optical Switches;
- Directional Couplers.
- PP-KTP (Periodically-poled KTP) – has transparency range of KTP, but without phase-matching limitations of KTP. Effective non-linear coefficient is approximately 3 times larger than typical phase matched crystal. Usually used in Second Harmonic Generation (SHG) of 946 nm to 473 nm and 1064 nm to 532 nm.
- HGTR/SKTP (high Gray track resistant KTP/ Super high quality KTP) crystals have gray tracking resistance and are suitable for high power applications, thus enabling higher average power density for Second Harmonic Generation (SHG)
- Flux grown – low cost compared to KTA, BBO and LBO;
- Wide transparency range (350 nm to 4.4 µm);
- Broad type II non-critical phase-matching range;
- Hydrothermally grown gray tracking resistant KTP crystals are available upon request;
- Large non-linear optical (NLO) and high electro-optical (E-O) coefficients;
- Efficient frequency conversion (1064nm SHG conversion efficiency of about 80% can be achieved);
- Non-hygroscopic, good chemical and mechanical properties (stability).
KTP crystals grown by flux method usually have “gray tracking” effect. Crystal is starting to become gray thus resulting lower transmission. The effect is accumulative – it starts appearing slowly, but it takes a lot of time to vanish (KTP must “rest” to “recover” original specifications)
The effect can be softened by keeping crystal in 70-80° C or working in that temperature. Higher temperature does not affect the recovery speed. The ovens are available upon request.
Gray tracking effects appears especially quickly in Continues-Wave (CW) regime or using long pulses.
Hydrothermal-grown KTP minimizing “gray tracking” effect, however they are at least 4 times more expensive and growth process is much slower.
Flux-grown KTP have water absorption line at 2940 nm. Water line prevents effective use of this crystal for tunable parametric generation close to 3 µm.