Divalent (Cr2+), trivalent (Cr3+), and tetravalent (Cr4+) chromium ion-doped tunable solid-state lasers operating in the near and mid-infrared spectral regions

Abstract

The chromium ion is among the most widely explored and used laser-active ions. Depending on the charge state of the laser-active chromium ion in the host, tunable chromium-doped lasers can be categorized under three groups as Cr2+, Cr3+, and Cr4+ lasers. In this paper, we provide a comprehensive overview of recent research conducted with chromium ion-doped tunable solid-state lasers, covering primarily the last 2 decades. After an introduction of the key physical parameters of tunable solid-state lasers, recent experimental results obtained with Cr3+, Cr4+, and Cr2+ ion-doped lasers are presented with an emphasis on alexandrite (Cr3+:BeAl2O4), Cr:LiCAF (Cr3+:LiCaAlF6), Cr:LiSAF (Cr3+:LiSrAlF6), Cr:LiSGaF (Cr3+:LiSrGaF6), Cr4+:forsterite (Cr4+:Mg2SiO4), Cr4+:YAG (Cr4+:Y3Al5O12), Cr2+:ZnSe, and Cr2+:ZnS lasers. For each laser system, recent developments involving power scaling, different excitation schemes, continuous-wave power performance, Q-switched/gain-switched operation, mode-locked operation, and emerging scientific/technological/biomedical applications are discussed. The paper is concluded with an overall assessment of these laser media and discussion about possible directions of research in future.