KTP Crystals

KTP Crystals
KTP Crystals

Newlight KTP features, Large nonlinear optical coefficients Wide angular bandwidth and small walk-off angle Broad temperature and spectral bandwidth Nonhydroscopic, chemically and mechanically stable High thermal conductivity Flux grown, extremely low cost compared to KTA, BBO and LBO

These favorable features enables KTP to be widely used for frequency doubling (SHG) or sum frequency mixing (SFG) to generate Red/Green/Blue (RGB) outputs, and for optical parameteric oscillator (OPO) or optical parametric amplifier (OPA) to generate visible to mid-infrared tunable wavelengths. KTP is also used in many electro-optic (E-O) devices such as Q-switches and E-O modulators.

Hydrothermally grown gray tracking resistant KTP crystals are available upon request.

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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    1172oC in congruent
 Curie Point    936oC
 Mohs Hardness    ~ 5
 Density    3.01 g/cm3
 Color    Colorless
 Hygroscopic Susceptibility  No
 Specific Heat    0.687 J/g/K
 Thermal Conductivity    2 W/m/K
 Electrical Conductivity    3.5x10-8 s/cm (c-axis, @ 22oC, 1 KHz)

Linear Optical Properties:

 Transmitting Range     350 - 3500 nm      
 Refractive Indices
              1064 nm
               532 nm  
     nx             ny            nz
   1.7377       1.7453      1.8297
   1.7780       1.7886      1.8887
 Sellmeier Equations
 (λ in µm)  
 Thermo-optic Coefficients       dnx/dT=1.1x10-5 /oC, dny/dT=1.3x10-5 /oC
 dnz/dT=1.6x10-5 /oC   
 Absorption Coefficient      α < 1% cm-1 @1064 nm and 532 nm   

Nonlinear Optical Properties:

 Phase-matchable SHG Range  994 - 3600 nm  
 Nonlinear Optical Coefficients  d31=1.95 pm/v, d32=3.9 pm/v,
 d33=15.3 pm/v,d24=3.9 pm/v,
 d15=1.95 pm/v
 Effective Nonlinearity Expressions   deff(II)= (d24-d15)sin2φsin2θ-(d15sin2φ+ d24cos2φ)sinθ 
 For type II SHG of a Nd:YAG Laser at  1064 nm  PM angle: θ=90°, φ=23.5° 
 Effective SHG coefficient: deff=8.3xd36(KDP)  
 Angular acceptance: 20 mrad-cm
 Temperature acceptance: 25°C-cm
 Spectral acceptance: 5.6 Å -cm
 Walk-off angle: 4.5 mrad (0.26°)   

Application examples:

SHG 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 a Nd:YAG laser.

 PM Angle  θ=90o, φ=23.5o
 Effective SHG Coefficient  deff = 8.3xd36(KDP)
 Angular Acceptance  20 mrad-cm
 Temperature Acceptance  25 oC-cm
 Spectral Acceptance  5.6 Å-cm.
 Walk-off angle  4.5 mrad (0.26o)

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


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 non-critical phase-matched (NCPM) OPO/OPA with a X-cut KTP pumped by 1064nm is particularly useful as the signal output @1.57 um is eye safe.  NCPM KTP OPO/OPA pumped by the tunable lasers such as Ti:Sapphire, Alexandrite and Cr:LiSrAlF6 have also been reported with a high efficiency of 45%.

Specifications of KTP components:

Wavefront distortion: less than λ/8 @ 633 nm
Dimension tolerance: (W +/-0.1 mm) x (H +/-0.1 mm) x (L + 0.2/-0.1 mm)
(L+0.5/-0.1 mm) for large crystals.
Clear aperture: > 90% central area
Flatness: λ/8 @ 633 nm
Scratch/Dig: 10/5 to MIL-O-13830A
Parallelism: better than 20 arc seconds
Perpendicularity: 5 arc minutes
Angle tolerance:   Δθ < +/-0.25o, Δφ < +/-0.25o



For SHG of 1064 nm, the standard coating is dual band AR (DBAR) at 1064/532 nm with residual reflectivity < 0.2% @ 1064 nm and < 1.0% @ 532 nm per face. HR @ 1064 nm and HT @ 532 nm is available for compact laser-SHG devices.

Temperature-controlled oven:

KTP may suffer from optical damage known as "gray tracking". Maintaining KTP crystal at an elevated temperature ( e.g., 80oC) can help to reduce the formation of gray tracking.  Please refer here for more information on the oven for crystal heating.


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