The phase transition and optical properties of Cr2+-doped ZnSe under high pressure

The phase transition pressure, electronic structure, optical properties and stability for ZnSe and Cr2+:ZnSe with different doping concentrations were calculated by first-principles calculation based on density-functional theory. The phase transition pressure was calculated by enthalpy-pressure relation. The introduction of dopant (Cr2+) reduces the phase transition pressure, and the phase transition pressure decreases with the increase of doping concentration. The high pressure enhances the degeneracy of Cr-d orbitals. Under the high-pressure conditions, the absorption peak positions of Cr2+:ZnSe have obvious blue-shift. Meanwhile, the stability of structures for ZnSe and Cr2+:ZnSe were further confirmed by defect formation energy and elastic constants. Keywords: Phase transition pressure, Optical properties, Cr2+:ZnSe, First-principles calculatio

Mid-infrared Fe2+:ZnSe semiconductor saturable absorber mirror for passively Q-switched Er3+-doped ZBLAN fiber laser

A mid-infrared (mid-IR) semiconductor saturable absorber mirror (SESAM) based on Fe2+:ZnSe for passively Q-switched Er3+-doped ZBLAN fiber laser has been demonstrated. Fe2+:ZnSe SESAM was fabricated by electron beam evaporation method. Fe2+ was innovatively doped into the reflective Bragg stack, in which ZnSe layer served as both doped matrix and high refractive layer during the fabricating process. By using the Fe2+:ZnSe SESAM, stable passively Q-switched pulses with the minimum pulse width of 0.43 μs under a repetition rate of 160.82 kHz were obtained. The recorded maximum average output power of 873 mW with a peak power of 12.59 W and pulse energy of 5.43 μJ were achieved. The results demonstrated a new method for fabricating Fe2+:ZnSe SESAM, which can be used in compact mid-IR Q-switched fiber laser

Femtosecond laser induced nano-meter size surface structures on ZnSe film

We realize femtosecond laser-induced high spatial frequency nano-meter size periodic surface structures with a periodicity about 140nm-170 nm on ZnSe film in one step. Compared with bulk ZnSe, the periodicity and fluence threshold of the surface structure on ZnSe film are smaller and lower. We propose the shortened melting duration, which caused by the higher thermal conductivity of the sapphire substrate, is the origin of the difference between the bulk ZnSe and ZnSe film. Surface capillary wave is easier frozen with shorter melting duration leaves smaller periodicity. Meanwhile, we also found stripes on the surface of sapphire with much lower threshold than previously reported values. The results can benefit advanced optoelectronic device fabrication and fundamental research