Polishing the surface of a z-cut KDP crystal by neutralized argon ions

The sputtering yield and dynamics of the surface roughness of the potassium dihydrogenphosphate—KH2PO4 (KDP) crystal z-cut was initially polished by precision micromilling with a diamond cutter, after which surface treatment by neutralized Ar ions was studied. The sputtering yield turned out to be noticeably higher than the values for materials that are amenable to ion polishing (fused silica, ULE, Zerodur, etc.), but the polishing effect at angles of incidence of 0°, 30°, and 45° was found. A record value of the effective surface roughness in the spatial frequencies range of ν∈[4.9·10−2–6.3·101  μm−1]σeff=0.61  nm was obtained.