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Einführung (in Englisch)

YCOB crystal was first found in 1990s. Because it has good nonlinear optical properties and high temperature piezoelectric properties and it is easy to grow large size crystal with high quality, it attracts attention new in recent years.

Compared with Lithium Tetraborate (LBO) crystals, which are commonly used in high power laser system, it has the following advantages:

no deliquescence,
larger effective NLO susceptibilities,
larger Temperature Acceptance,
similar laser induce damage threshold,
less parametric luminescence (three orders less),
smaller thermal expansion coefficient,
less anisotropy,
better processability,
shorter growth period by Cz method and cheaper to make larger aperture element.

YCOB crystal is suitable for applications in high energy and high power laser fields，including

Laser wavelength conversion: second-harmonic generation (SHG) and third-harmonic generation (THG),
optical parametric oscillator (OPO),
optical parametric amplification(OPA),
optical parametric chirped-pulse amplification (OPCPA).
Another application is in the field of piezoelectric devices at high temperature.

YCOB crystal has very high electric resistivity that can be fabricated as piezoelectric sensors working at the temperature as high as 1000ºC in aerospace engines.

Chemical and Structural Properties of YCOB Crystal

Crystal Structure	Monoclinic, Point group m
Lattice Parameter	a = 8.0770 Å, b = 16.0194 Å , c = 3.5308 Å , β = 101.167º, Z = 2
Melting Point	About 1510 ℃
Mohs Hardness	6 ~ 6.5
Density	3.31 g/cm³
Thermal Conductivity	2.6 W/m/K (║X), 2.33 W/m/K (║Y), 3.1 W/m/K (║Z)
Thermal Expansion Coefficient	a_x = 10.8•10^-5/K, a_y = -8.8•10^-5/K, a_z = 3.4•10^-5/K

Optical and Nonlinear Optical Properties of YCOB compared with LBO

Properites	YCOB	LBO
Transparency Range	210 ~ 2600 nm	160 ~ 2600 nm
SHG Phase Matchable Range	724 ~ 2600 nm (Type I) 1030 ~ 2150 nm (Type II)	551 ~ 2600 nm (Type I) 790 ~ 2150 nm (Type II)
Thermo-optic Coefficient (T in [°C], λ in [μm])		dn_x/dT=-9.3•10^-6 dn_y/dT=-13.6•10^-6 dn_z/dT=(-6.3 - 2.1λ)•10^-6
Absorption Coefficient	<0.1% cm^-1 at 1064nm	<0.1% cm^-1 at 1064nm <0.3% cm^-1 at 532nm
Angle Acceptance	0.062 º-cm (θ, Type I,1064 SHG)	0.19 º-cm (φ, Type I,1064 SHG)
Temperature Acceptance	112°C-cm (Type I, 1064 SHG)	4.7 °C-cm (Type I, 1064 SHG)
Spectral Acceptance	1.19 nm-cm (Type I, 1064 SHG)	1.0 nm-cm (Type I, 1064 SHG)
Walk-off Angle	1.26° (Type I 1064 SHG)	0.60° (Type I 1064 SHG)
NLO Coefficients	deff(I)=d₁₃sinΦ (Type I in XY plane) deff(I)=d₁₃ sin2θ d₁₂cos2θ (Type I in YZ plane) deff(I)=d₁₂cosθ- d₃₂sinθ (Type I in XZ plane, VZ>θ>0, Ф=0º) deff(I)=d₁₂cosθ d₃₂sinθ (Type I in XZ plane, VZ>θ>0, Ф=180º)	deff(I)=d₃₂cosΦ (Type I in XY plane) deff(I)=d₃₁cos2θ d₃₂sin2θ (Type I in XZ plane) deff(II)=d₃₁cosθ (Type II in YZ plane) deff(II)=d₃₁cos2θ d₃₂sin2θ (Type II in XZ plane)
Non-vanished NLO susceptibilities	d₁₂ = 0.24 pm/V; d₁₃ = -0.73 pm/V d₃₁ = 0.41 pm/V; d₃₂ = 2.35 pm/V; d₃₃ = -1.60 pm/V	d₃₁ = 1.05 ± 0.09 pm/V d₃₂ = -0.98 ± 0.09 pm/V d₃₃ = 0.05 ± 0.006 pm/V
Sellmeier Equations(λ in μm)	n_x² = 2.7697 0.02034 / (λ² - 0.01779) - 0.00643λ² n_y² = 2.8741 0.02213 / (λ² - 0.01871) - 0.01078λ² n_z² = 2.9107 0.02232 / (λ² - 0.01887) - 0.01256λ²	n_x² = 2.454140 0.011249 / (λ²- 0.011350) - 0.014591λ² - 6.60•10^-5λ⁴ n_y² = 2.539070 0.012711 / (λ²- 0.012523) - 0.018540λ² - 2.0•10^-4λ⁴ n_z² = 2.586179 0.013099 / (λ²- 0.011893) - 0.017968λ² - 2.26•10^-4λ⁴

Piezoelectric Properties of YCOB

Recommended literature (e.g.):

FaPeng Yu et al.: Rare-Earth Calcium Oxyborate Piezoelectric Crystals ReCa4O(BO3)3: Growth and Piezoelectric Characterizations; Crystals 2014,4(3),241-261.

See http://www.mdpi.com/2073-4352/4/3/241/htm

Yttrium Calcium Oxoborat (YCOB)

Anwendung	Größe [mm]	Theta	Phi	d_eff [pm/V]
2^nd Harmonic Generation (SHG)	30x30x15	30.8°	180°	1.14
3^rd Harmonic Generation (THG)	4x4x7	106°	77.2°	NA
Optical Parametric Amplifier (OPA)	15x15x20	28°	180°	1.32

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