KTP crystal is the most commonly used for SHG(Frequency doubling) of Nd-doped laser for green/red output. JG Intl has finished the largest growing and processing line of KTP crystals and can supply more than 200,000pieces/year different dimension KTP crystals for the OEM and R&D requirement based on the good price,high quality and fast delivery.
Potassium Titanyl Phosphate (KTP) has the following exceptional properties that make it a very important nonlinear crystal:

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

High thermal conductivity

Moisture free

Minimum mismatch gradient

Low cost compare with BBO and LBO

KTP is a positive biaxial crystal, with the principal axes X, Y, and Z (n_z>n_y>n_x) parallel to the crystallographic axes a, b, and c, respectively.

KTP is a positive biaxial crystal, with the principal axes X, Y, and Z (nz>ny>nx) parallel to the crystallographic axes a, b, and c, respectively.
   
Structural and Physical Properties:

Crystal structure	Orthorhombic, space group Pna21,point group mm2
Cell parameters	a=6.404Å, b=10.616Å, c=12.814Å, Z=8
Melting point	1172¡ãC incongruent
Curie point	936°C
Mohs hardness	»5
Density	3.01 g/cm3
Color	colorless
Hygroscopic susceptibility	no
Specific heat	0.1643 cal/(g*°C)
Thermal conductivity	0.13 W/(cm*K-1)
Electrical conductivity	3.5x10-8 s/cm (c-axis, 22°C, 1KHz)

Linear Optical Properties:

Transmitting range:	350 nm - 4500 nm
Refractive indices:            1064nm            532nm	nx           ny          nz 1.7377   1.7453   1.8297 1.7780   1.7886   1.8887
Sellmeier equations: (l in mm)	nx2=3.0065+0.03901/(l 2-0.04251)-0.01327l 2 ny2=3.0333+0.04154/(l 2-0.04547)-0.01408l 2 nz2=3.0065+0.05694/(l 2-0.05658)-0.01682l 2
Therm-optic coefficients:	dnx/dT=1.1x10-5℃, dny/dT=1.3x10-5℃, dnz/dT=1.6x10-5℃
Absorption coefficient:	a < 1% cm-1 @1064nm and 532nm

Nonlinear Optical Properties:

KTP’s Applications:

Frequency doubling (SHG) of Nd-doped lasers for green/red outputs.

Frequency mixing (SFM) of Nd laser and diode laser for blue outputs.

Parametric sources (OPG, OPA and OPO) for 600nm-4500nm tunable outputs.

E-O modulators, optical switches, directional couplers.

Optical waveguides for integrated NLO and E-O devices.

Applications for SHG and SFG of Nd:lasers

KTP is the most commonly used material for frequency doubling of Nd:YAG lasers and other Nd-doped lasers, particularly at the low or medium power density. The following Table lists the major NLO properties of KTP for frequency-doubling of Nd:YAG laser.

To date, extra- and intra-cavity frequency doubled Nd:lasers using KTP have become a preferred green laser source for many R&D, medical, industrial and commercial applications. By using extracavity KTP SHG, over 80% conversion efficiency and 700mJ green laser were obtained with a 900 mJ injection-seeded Q-switched Nd:YAG laser.

Applied to diode-pumped Nd:laser, KTP is a basic NLO crystal for the construction of compact visible solid state laser systems. Recent advances in intracavity-doubled Nd:YVO4 and Nd:YAG lasers have increased the demand for compact green lasers used in display, construction, optical disk and laser printer. Over 200 mw TEM00 green outputs are available from LD pumped Nd:YVO4 and Nd:YAG lasers and 3 W TEM00, mode-locked green laser was generated by intracavity SHG in a 5.3 W mode-locked diode-laser pumped Nd:YAG laser. Moreover, 2.5mW green light was obtained from 50mW LD pumped and intracavity doubled Nd:YVO4 mini-lasers with a 9mm long cavity.

KTP is also a powerful crystal for SHG and SFG of laser with wavelength from about 1um to 3.4 um. The SHG phase-matching angle and effective SHG coefficients (deff) of KTP in XY plane (0.9 mm to 1.08 mm) and XZ plane (1.1 um to 3.3 um) are showed as the figtures. Although KTP cut in YZ plane can be phase-matched for SHG of 1 mm to 3.45 um, it is seldom used in practices because of the low deff.

Type ll SHG in XY Plane		Type ll SHG in XZ Plane		OPO Pumped at 1064 nm

OPG (OPA、OPO）

As an efficient OPO crystal pumped by the fundamental and second harmonics of a Nd:YAG or Nd:YLF laser, KTP plays an important role in parametric sources for tunable output from visible (0.6 um) to mid-IR (4.5 um). The phase-matching angles and effective NLO coefficient for OPO/OPA pumped at 532 nm and 1064 nm in XZ plane are showed as following figures. NCPM KTP OPO pumped by 1064 nm, the signal output is around eye safe wavelength, find applications in eye-safe devices. The OPO/OPA in XY and YZ is seldom employed because of their low effective nonlinear coefficients and other limitation.

KTP's OPO results in stable, continuous outputs of femtosecond pulse of 108 Hz repetition rate and miliwatt average power levels in both signal and idler outputs. KTP's OPO pumped by a 1064 nm Nd:laser has generated above 66% conversion efficiency for degenerate conversion from 1064 to 2120 nm.

The recently developed new application is the non-critical phase-matched (NCPM) KTP OPO/OPA pumped by the tunable lasers such as Ti:Sapphire, Alexandrite and Cr:LiSrAlF6 (see right figure). The NCPM KTP OPO keeps the KTP crystal fixed in X-axis and tunes the pumping wavelength. If a tunable Ti:Sapphire laser is used as a pumping source (0.7 um to 1 um), the output can cover the wavelength range from 1.04 um to 1.45 um (signal) and from 2.15 um to 3.2 um (idler). Due to the favorable NLO properties of NCPM KTP, as high as 45% conversion efficiency was obtained with narrow output bandwidth and good beam quality.

Quasi-Phase-Matched Waveguide

Recently, type II SHG conversion efficiency of 20%/W/cm2 was achieved by quasi-phase matched waveguide doubler, in which the phase mismatch from one section is balanced against a phase mismatch of the opposite sign from a second section. Furthermore, segmented KTP waveguides have been applied to type I quasi-phase-matchable SHG of 0.76-0.96 um for tunable Ti:Sapphire laser and directly doubled diode laser for 0.43-0.40 um output. Conversion efficiency in excess of 100%/W/cm2 has been obtained.

NCPM KTP for OPO

Efficiency of KTP elements in OPO 1064 - 1570 nm

The recently developed new application is the non-critical phase-matched (NCPM) KTP OPO/OPA application. The NCPM KTP OPO keeps the KTP crystal fixed in X-axis and tunes the pumping wavelength. If 1064nm pumping source, the output will be at 1.57um (signal) and 3.3 um (idler). Due to the favorable NLO properties of NCPM KTP, as high as 45% conversion efficiency was obtained with narrow output bandwidth and good beam quality.

Oven for heating KTP crystals:

Increasing the temperature of KTP crystal can enhance the damage threshold of KTP crystal. Therefore, for high power or high power density SHG of Nd lasers, heating KTP to a certain temperature (e.g., 80oC) is recommended. JG InterNational provides precision oven with temperature controller for heating KTP. A full assembly including KTP crystal, oven and temperature controller is also available.

KTP specifications:

Transmitting wavefront distortion: less than l/4 @ 633 nm

Dimension tolerance: (W ± 0.1 mm) x (H ± 0.1 mm) x (L + 0.2 mm/-0.1mm)

Clear aperture: > 90% central area

Flatness: l/8 @ 633 nm

Scratch/Dig code: 10/5 to MIL-O-13830A

Parallelism: better than 20 arc seconds

Perpendicularity: 5 arc minutes

Angle tolerance: Dq < ±0.5°, Df < ± 0.5°

AR coating: R< 0.2% at 1064nm and R<1.0% at 532 nm.

Standard Products: 

Part No.	Dimension	Application	Coating	Type
K23	2x2x3mm	SHG@1064nm	AR/HR coating	II
K25	2x2x5mm	SHG@1064nm	AR/AR coating	II
K35	3x3x5mm	SHG@1064nm	DBAR-coating	II
K310	3x3x10mm	SHG@1064nm	DBAR-coating	II
K75	7x7x5mm	SHG@1064nm	DBAR-coating	II
K85	8x8x5mm	SHG@1064nm	DBAR-coating	II
K97	9x9x7mm	SHG@1064nm	DBAR-coating	II
K720	7x7x20mm	OPO for 1064nm&1570nm	AR coating	II