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Description

Zinc germanium phosphide (ZnGeP₂) is an excellent mid-IR nonlinear crystal with many outstanding fundamental properties. ZnGeP2 (ZGP) crystal has large nonlinear susceptibility (d36~75 pm/V), which is approximately 160 times that of KDP. ZGP exhibits good optical transparency over the 0.74–12 um wavelength region and relatively high laser damage threshold, and is therefore well suited for producing tunable laser output in the near infrared. ZGP is a very promising material for applications such as SHG, SFG, OPO, and OPG/OPA in the mid-infrared region.

             Note: The Transmission spectra of 15 mm long AR coated ZnGeP₂ crystal  

Features

• Wide transmission region from 0.74 um to 12um

• Large nonlinear coefficient

• Good mechanical and physical properties

• Relatively high damage threshold 

• Phase matchable over a broad spectral region

• High thermal conductivity

Applications

• Second, third, and fourth harmonic generation of CO₂ laser

• Optical parametric generation (OPO) with pumping at a wavelengths of 2.05-2.94 µm and possibility to generate effectively 3-10 µm ranges

• Second harmonic generation of CO-laser

• Producing coherent radiation in sub-millimeter-range from 70.0 µm to 1000 µm - terahertz range

• Generation of combined frequencies of CO₂- and CO-lasers radiation and other lasers are working in the crystal transparency region

Chemical and Physical Properties  

Property	Value
Chemical formula	ZnGeP2
Crystal structure	Tetragonal,`42m
Lattice Parameter	a=b=5.467Å, c=12.736Å
Mass density	4.16 g/cm3
Moh hardness	5.5
Melting point	About 1040°C
Thermal conductivity	180 W/m/K
Thermal expansion coefficient	ß?,5x10-6/K; ß?,7.8x10-6/K
Birefringence	positive uniaxial

Linear Optical Properties

Property	Value
Transparency Range	0.74 - 12 um
Absorption Coefficient:	a<0.05cm-1 @2050-2100 nm
Refractive Indices @ 2.05 um  @ 2.79 um  @ 5.30 um  @ 10.6 um	no = 3.1478, ne = 3.1891 no = 3.1333, ne = 3.1744 no = 3.1136, ne = 3.1547 no = 3.0729, ne = 3.1143
Sellmeier Equations(? in µm)	no2(?) = 4.64467+5.10087/(?2-0.13656)+4.27777?2/(?2-1653.89) ne2(?) = 4.71539+5.26358/(?2-0.14386)+2.37310?2/(?2-1000.82)

Nonlinear Optical Properties

Property	Value
SHG Phase Matchable Range	3177 ~ 10357nm (Type I)
NLO coefficients	d36=75 ± 8 pm/V Type ? deeo=d36 sin2?cos2f Type ? doeo=deoo=d36 sin?sin2f
Damage Threshold at 2.79 um at 10.6 um	30 GW/cm2 (150 ps) 1 GW/cm2 (2 ns)

Figure 2. OPO tuning curves of ZGP with pump light of 2090 nm

Figure 3. OPO tuning curves of ZGP with pump light of 2800 nm

Figure 4. SHG curves of ZGP (TypeI (eeo))

Polishing Specification

Property	Value
Orientation Tolerence	< 0.5°
Thickness/Diameter Tolerance	±0.05 mm
Surface Flatness	<?/8@632 nm
Wavefront Distortion	<?/4@632 nm
Surface Quality	10/5
Parallel	30?
Perpendicular	15´
Clear Aperture	>90%
Chamfer	<0.2×45°

Standard products

Crystal dimension/mm	Application	Orientation Theta/Phi deg	Coatings
7x5x15	OPO @ 2.1-> 3.5-5 µm	54/0	AR@2.1µm+BBAR@3.5-5µm
7x5x20	OPO @ 2.1-> 3.5-5 µm	54/0	AR@2.1µm+BBAR@3.5-5µm
7x5x25	OPO @ 2.1-> 3.5-5 µm	54/0	AR@2.1µm+BBAR@3.5-5µm

Q&A

Q: What is phase mismatching?

A: A group of techniques for achieving efficient nonlinear interactions in a medium. Many phase-sensitive nonlinear processes, in particular parametric processes such as frequency doubling, sum and difference frequency generation, parametric amplification and oscillation, and also four-wave mixing, require phase matching to be efficient. Essentially, this means ensuring that a proper phase relationship between the interacting waves (for optimum nonlinear frequency conversion) is maintained along the propagation direction. Only if that condition is fulfilled, amplitude contributions from different locations to the product wave are all in phase at the end of the nonlinear crystal.

Q: What is Second harmonic generation (SHG)?

A: SHG is a nonlinear optical process, in which photons with the same frequency interacting with a nonlinear material are effectively "combined" to generate new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons.