Non-linear crystal KNbO3 for second-harmonic generation of near infrared pulsed laser light

KNbO3 crystal is an oxygen octahedra ferroelectric with perovskite structure. Is a good candidate for nonlinear frequency conversion using QPM, due to its large nonlinear optical coefficient (d31=15.8 pm/V;d32=18.3 pm/V), wide transparency range (0.4~5 mm) and freedom from photorefractive effects. KNbO3 crystals have an average refractive index of 2.2.The theoretical value of normal incident reflectivity is 14% and the theoretical transmittance is more than 80%. Because of its high second-order (nonlinear) coefficients and favorable phase-matching properties KNbO3 is the material of choice for doubling low-power laser diodes in the wavelength region near 860 nm, Ti: sapphire lasers in the range 850-1000 nm, and Nd:YAG lasers at 1064 nm. In addition, KNbO3 can be used for optical parametric oscillation when pumped by Nd:YAG lasers at either the fundamental or the second-harmonic wavelength, producing tunable radiation in the near-IR spectral region between 0.7 and 3 μm.

The solid-state blue-green laser has stable performance, compact structure and integrability, which makes it has a good application prospect in optical storage, optical communication and laser medical instrument, etc. It is a research hotspot in the world at present. A feasible way to achieve this goal is to realize blue and green light output by semiconductor near infrared laser frequency doubling. Currently, the crystal that can octave the semiconductor near infrared laser frequency is potassium niobate (KNbO3). KNbO3 is an interesting nonlinear material for optical and electro-optical applications. Second-harmonic generation, sum frequency mixing, and optical parametric oscillation are important processes for converting available laser wavelengths into the blue-green and the near-IR spectral regions.


Chemical formulaKNbO3
Crystal structureOrthorhombic,mm2
Lattice Parametera = 5.6896Å, b = 3.9692Å, c = 5.7256Å
Mass density4.617 g/cm3
Melting Point1333 K
Curie temperature498 K
Assignment of dielectric and crystallographic axes X, Y, Z ⇒ b, a, c
Specific heat capacity cp at P = 0.101325MPacp = 767 J/kgK
Thermal conductivity coefficientκ > 3.5 W/mK
Thermal Expansionaa=5.010×10-6/℃; ab=1.410×10-5/℃; ac=5.010×10-7/℃
Transparency Range400-5500 nm
IR cutoff wavelength 5.5 μm
Absorption loss<=1%/cm at 1064 nm
Damage Threshold<=4 J/cm2 at 527 nm(500ps,single pulse)
<=6 J/cm2 at 1054 nm(700ps,single pulse)
Nonlinear Optical Coefficientd31=-15.8 pm/V, d32=-18.3 pm/V at 1064 nm
The shortest SHG wavelength425 nm(typeⅠ NCPM,y-cut or a-cut)
Acceptance Angle for typeⅠSHG of 1064 nmDq=0.24 mrad/cm(internal)
Acceptance Temperature for  typeⅠSHG of 1064 nmDT=0.3 ℃/cm
XY planedeeo = d32 sin2 φ + d31 cos2 φ
YZ planedooe = d32 sin θ
XZ plane, θ <Vzdoeo = deoo = d31 sin θ
XZ plane, θ > Vzdooe = d31 sin θ
KNbO3 nonlinear crystal Temperature CRYLINKKNbO3 nonlinear crystal index CRYLINK
KNbO3 nonlinear crystal transmission CRYLINKKNbO3 nonlinear crystal Optical CRYLINK
KNbO3-Transmittance SpectrumKNbO3-Optical-Absorbance

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