New class of diode-pumped mid-IR broadly tunable lasers based on TM2+ ions in Td coordination: Cr2+:ZnX (X=S,Se)

A new class of room-temperature, diode-pumped solid state lasers, that are broadly tunable in the mid-IR spectral region, has been conceptualized and demonstrated. These lasers are based on intra-ion transitions of divalent transition metals placed in substitutional cation sites of tetrahedral symmetry in large bandgap chalcogenide semiconductor crystals. These combinations of laser-ions and host crystals are seen to provide favorable radiative and non-radiative transition processes for the realization of the desired laser performance characteristics. Spectroscopic data for candidate schemes are reviewed and divalent chromium doped zinc chalcogenides are identified as potentially superior laser candidates. Preparation of laser quality Cr2+:ZnSe crystals is described and experimental results to date for a diode-pumped laser are given. Remaining laser development issues are discussed briefly.