Zinc Germanium Phosphide (ZGP) exhibits a large nonlinear coefficient, high laser damage threshold, and high thermal conductivity. The properties make ZGP ideally suited to high power applications. Most commonly, ZGP is used in OPOs, OPAs, and OPCPAs pumped with holmium and thulium fiber lasers to generate high power, tunable output between 3.0µm and 6.0µm, though other processes are also possible. ZGP is mechanically robust and stable over a wide operating temperature range.

ZGP single crystals are grown at Inrad Optics via the horizontal gradient freeze method and are available in lengths up to 25 mm. Our post-processing techniques drastically reduce absorption in the near infrared—a critical parameter for determining viable pump wavelengths.


Material Properties 
Chemical ZnGeP2
Crystal Symmetry and Class tetragonal, -42m
Lattice Parameters a =  5.467 Å 
c = 12.736 Å
Density 4.162  g/cm3
Mohs Hardness 5.5
Optical Class Positive uniaxial
Userful Transmission Range 2.0 μm - 10.0 μm
Thermal Conductivity  
@ T= 293 K
35 W/m∙K (⊥c)
36 W/m∙K ( ∥ c)
Thermal Expansion
@ T = 293 K to 573 K
17.5 x 106 K-1 (⊥c)
15.9 x 106 K-1 ( ∥ c)


Standard cross sections are 6 x 8 mm and 8 x 12 mm. Crystal lengths range from 1 to 25 mm. Custom sizes are also available on request.


  • Crystals can be fabricated with a 30-arcmin wedge in the non-tuning direction.
  • Anti-reflective coatings are available for OPO crystals.


The standard ZGP crystal orientation is for type I phasematching at an angle of θ = 54°, which is suitable for use in OPOs pumped at wavelengths between 2.05µm and 2.1µm to generate mid-infrared output between 3.0µm and 6.0µm. Custom orientations are available on request.

Download Data Sheet Download White Paper