Saturable absorption properties at 1.54 µm of Cr²⁺:ZnS prepared by thermal diffusion at hot isostatic pressing

Polycrystalline zinc sulfide (ZnS) samples obtained by chemical vapour deposition were doped with Cr²⁺ ions using hot isostatic pressing (at 100 MPa/1250 °C). Their structure was studied by means of x-ray diffraction, SEM and Raman spectroscopy. The Cr²⁺:ZnS samples exhibited excellent transparency in the near-IR. Absorption saturation of Cr²⁺:ZnS is demonstrated at 1.54 µm (⁵T₂(⁵D)  →  ⁵E(⁵D) transition of Cr²⁺ ions in tetrahedral sites) for ns-long pulses yielding a saturation fluence of 0.16  ±  0.03 J cm⁻². The laser-induced damage threshold is 6.0  ±  0.5 J cm⁻². The synthesized polycrystalline Cr²⁺:ZnS is promising for passive Q-switching of erbium lasers emitting at 1.5–1.7 µm. (letter)