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KN ( Potassium Niobate, KNbO3)
KN is a perovskite type negative
biaxial crystal. It has a large transmission range from visible to
mid-infrared and the largest nonlinear optical coefficients among the
commonly used inorganic crystals. Hence, it is normally used for frequency
doubling of low and medium power lasers, such as diode lasers, diode
pumped solid state lasers, Ti:Sapphire lasers and CW Nd:YAG lasers. It is
well suited to SHG of near infrared radiation. Temperature tuning over the
range -40oC
to 180oC
provides noncritical phase matching (NCPM) in the spectral range of diode
lasers, with phase matching for 860nm occurring at room temperature. KN may
also be prepared for photorefractive application. The photorefractive
properties of KN allow applications in modulators and phase conjugation
processes.
Please contact Newlight Photonics for the cut
angles, dimensions, and coatings of KN crystals for your applications.
Structural and Physical Properties
|
Crystal structure |
orthorhombic |
|
Point group |
mm2 |
|
Lattice parameters |
a=5.697Å
b=3.971Å
c=5.722 Å |
|
Melting point |
1050°C |
|
Thermal Expansion coefficient |
αa
=3.0x10-6/°C
αb
=1.410x10-5/°C
αc =5.010x10-7/°C |
|
Phase transition temperature |
-50°C, 220°C, 430°C |
|
Thermo-optic coefficient |
dna/dT=0.2X10-4
dnb/dt=-0.35x10-4
dnc/dT=-0.55x10-4
|
|
Thermal Conductivity coefficient |
3.5W/mK |
|
Density |
4.62 g/cm3
|
|
Mohs hardness |
5 |
|
Specific Heat |
0.767J/g K |
Optical Properties
|
Transmitting range |
350~4500 nm |
|
Refractive indices |
|
nx (nc) |
ny(na) |
nz(nb) |
|
1064 nm |
2.1194 |
2.2195 |
2.2576 |
|
860nm |
2.1338 |
2.2372 |
2.2784 |
|
532nm |
2.2022 |
2.3223 |
2.3819 |
|
Nonlinear Coefficients
|
d11
= 21.9 pm/V, d26 =
9.2pm/V
d12 = 8.9 pm/V, d35 = 13.0pm/V
d13 = 12.4 pm/V
( Defined in the dielectric xyz frame ) |
|
Damage
threshold |
~4J/cm2
at 527nm (500ps)
~6J/cm2 at 1054nm (700ps) |
|
Absorption coefficien |
< 0.1% cm at 1064nm |
Sellmeier equations
(
λ
in
µm)
|
nx2=4.4208
+ 0.10044/( λ2-0.054084)
- 0.019592λ2
ny2=4.8355
+ 0.12839/( λ2
-0.056342) - 0.025379λ2
nz2=4.9873
+ 0.15149/( λ2
-0.064143) - 0.028775λ2
|
Phase-matching Properties
|
The shortest SHG wavelength |
428nm (Type I NCPM along the y-axis at RT). |
|
NCPM wavelenghth @ RT |
982nm for z-cut crystal
858nm for y-cut crystal |
|
SHG of 1064nm @ RT |
θ =19°,
φ=0° .
|
|
NCPM for 1064nm SHG |
Temp. @ 188 °C,
θ=0deg.(z-cut) |
Wavelength range for Type I SHG
@ RT |
YZ plane:858-982nm |
XY plane:858-2000nm |
|
Effective nonlinearity |
deff=d31
sin2θ
+d32
cos2θ |
deff=d32
sinφ |
Handling of KN Crystals
 Due to the
small acceptance temperature, customers are advised to put KN crystal
into an oven with temperature stability better
than ± 0.1°C if stable output is required.
The domain
structure of KN may appear from shaking or stressing the crystals,
customers are advised to handle KN crystals very carefully.
Never cool KN
crystals below -40°C or heat it up over 210°C or the crystals will
experience phase transition and lose the nonlinearity.
Hot
Applications
SHG for middle and low
power Nd: lasers at 1064nm
SHG for the Nd: Lasers
at 914nm & 946nm for blue laser.
NCPM SHG for 860nm Laser
diode at room temperature
SHG for laser diode
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