Transition metal-doped zinc chalcogenides: spectroscopy and laser demonstration of a new class of gain media

Abstract

The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, midinfrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr2+, CO'+, Ni2+, or Fe,'+ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise.The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 pm which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 pm for Cr and from 2.8-4.0 pm for Co. Cr luminesces strongly at room temperature; CO exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures. Cr2+ is estimated to have the highest quantum yield at room temperature among the media investigated with values of -75-100%.Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgFL pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 pm, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the CrL+ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalogenides; CO'+ may also serve usefully, but laser demonstrations yet remain to be performed.

Laser crystals and ceramics: recent advances

“…In particular, these chalcogenides doped with Cr 2+ ions have already been shown to produce highly efficient and broadly tunable SE in different lasing modes in the 2-3 µm spectral region [52][53][54]. As before, activated semiconductor crystals, especially of the II-VI family, stimulate the imagination and foster corresponding activity of researchers in the development of SSLs with "electrical" pumping (see, e.g.…”

“…11). The Cr 2+ ion is the latest TM lasant activator to be used in crystals [227]. Among several known laser crystals containing these 3d 4 ions ( Table 9) the most promising for obtaining broadly tunable and ultra-short-pulsed generation in the mid-IR with LD pumping is ZnSe:Cr 2+ [53,234,235].…”

Ultrashort pulse generation in the mid-IR

“…Based on the smooth and broad emission cross-section exhibited by these materials [68,102,103] (see Fig. 8), it is clear that those gain media would be highly suitable for mode-locked operation.…”

“…The crystal used for this one-of-akind laser was so hygroscopic that it had to be kept in a dry atmosphere with [59,60,61,62,63,64,65,66,67] -were only produced with sufficient quality, and made to lase, in the mid 1990s at Lawrence Livermore National Laboratory [68]. The first lasing action in Cr 2+ :CdSe was reported in 2007 [69] and complete spectroscopic characterization of Cr 2+ :CdS has been reported only this year [70].…”

High Power Tunable Tm3+-fiber Lasers and Its Application in Pumping Cr2+:ZnSe Lasers

“…This provides Cr:ZnSe with the highest gain among vibronic lasers and enables efficient room-temperature operation. The remarkable characteristics of the ultrabroadband (~1000 nm) Cr 2+ :ZnSe crystal, such as the high emission cross section of the order of 10 -18 cm 2 [96], the negligibly low excited state absorption (ESA) [97], the fairly good chemical and mechanical stability and the thermal conductivity nearly as high as in sapphire, gives this material enormous potential as a laser medium for diode-pumped tunable MIR lasers. ZnSe laser make it possible to produce 1~2 optical-cycle ultra-short laser pulses, which will find great potential applications in the femtosecond laser regime.…”