Zinc germanium phosphide (ZGP) crystals have garnered significant attention for their nonlinear properties, making them good candidates for powerful mid-IR optical parametric oscillators and second-harmonic generators. A ZnGeP2 single crystal was treated by deep magnetorheological processing (MRP) until an Angstrom level of roughness. The studies presented in this article are devoted to the experimental evaluation of the influence of deep removal (up to 150 μm) from the surface of a ZnGeP2 single crystal by magnetorheological polishing on the parameters of optical breakdown. It was shown that the dependence of the ZnGeP2 laser-induced damage threshold on MRP depth is a smooth monotonically decreasing logarithmic function. The obtained logarithmic dependence indicates the thermal nature of optical breakdown and the dependence of the ZnGeP2 laser-induced damage threshold on the concentration of surface absorbing defects.
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