Fe²+:ZnSe saturable absorbers (SA) are ideal materials for passive Q-switches of solid-state lasers operating in the spectral range of 2.5-4.0 μm.These lasers (e.g. 3.0 μm Er:YAG/YSGG/YLF) are used for pumping middle-infrared Optical Parametric Oscillators and for numerous medical and dental applications. Fe:ZnSe or Iron(Ferrum) doped Zinc Selenide (Fe2+:ZnSe) is also one of the most effective crystals used to design lasers in middle (thermal) infrared. It is considered to be the most effective laser medium to obtain 3~5um mid-infrared lasers with high performance and wide tuning range because of long output wavelength, wide absorption band and emission band.Such high-performance mid-infrared lasers have important application value in the field of military confrontation,biological safety and environmental sciences. Applications: As a gain material in compact laser systems; As passive Q-switch for 2800 – 3400 nm nm lasers; Source for pumping middle infrared (MIR) optical parametric oscillators (OPO); Spectroscopy; Infrared (IR) missile countermeasure systems (ship and aircraft based); Free space communications; Gas tracing and analysis; Chemical warfare detection; Non-invasive medical diagnostics; Medical surgeries; Cavity ring down (CRD) spectroscopy