Much progress has been made in the power and energy scaling of mid-infrared lasers based on transition metal ions, such as Cr2 + , Co2 + , and Fe2 + , in zinc and cadmium chalcogenides. Still, the exploration of the physics of these devices is incomplete. In this work, we analyze absorption spectra collected from Fe2 + ions in several binary, ternary, and quaternary host crystals at temperatures from a few degrees Kelvin to room temperature. We use the zero-phonon lines of the low-temperature spectra to calculate the value of the crystal field energy of Fe2 + ions in these hosts. We plot these crystal field energies with respect to the anion–cation distance of the host crystal and show that their crystal field strengths deviate somewhat from the trend predicted by crystal field theory. We use a model which we previously developed to describe the upper state lifetime of Fe2 + ions to predict the steady-state radiative efficiency of Fe:II–VI materials with respect to temperature. The impact of relative crystalline disorder on the output characteristics of lasers based on Cr:ZnS, Cr:ZnSe, Fe:ZnSe, and Fe:CdMnTe is explored. The effect of decreased long-range order of the host crystal is observed in the broadening of the absorption spectra of Fe2 + -doped ternary and quaternary alloys, the broadening of the spectral linewidth of continuous-wave Fe:II–VI lasers, and a reduction in the portion of the Cr:ZnSe emission spectrum accessible for modelocked lasing. This survey provides a richer picture of the tradespaces that can be leveraged when producing laser devices based on transition metal chalcogenides.
Fe:ZnSe and other transition metals have broad upper and lower energy manifolds that give rise to broad absorption and fluorescence bands in the mid-infrared spectral region. Energy transfer between Fe2 + ions via re-absorption of fluorescence (due to the spectral overlap of these bands) and phonon-assisted energy transfer (due to the lattice dynamics of ZnSe) becomes more probable with increasing Fe2 + concentration. Here, we treat these processes as additional terms in the rate equations that govern the spontaneous decay of the Fe2 + ion. This treatment gives insight into anomalous behavior seen in the thermal lifetime of the Fe:ZnSe system. We also apply the model to other transition metal-doped II–VI materials.
Much progress has been made in power scaling mid-infrared lasers based on transition metal ions such as Cr2+, Co2+, and Fe2+ in zinc and cadmium chalcogenides. Still, the exploration of the physics of the devices is incomplete. In this work, we analyze absorption spectra from Fe2+ in several binary and ternary hosts at low temperatures. We examine the effect of host ion size and mass on the zero-phonon energy of these spectra and further develop our previous model for the upper state lifetime of Fe2+ in these materials. The effect of the relative disorder in the crystalline environment on the lasing characteristics of Cr:ZnS, Cr:ZnSe, Fe:ZnSe, and Fe:CdMnTe laser devices is explored. We show that increasing disorder of the crystal host is easily observed in broadening of the absorption spectra and the spectral linewidth of the laser output, and the reduction in the portion of the emission spectrum accessible for mode locking. Practical design guidelines for laser devices are developed.
Fe:ZnSe and other transition metals have broad upper and lower energy manifolds which give rise to broad absorption and fluorescence bands in the mid-IR spectral region. Energy transfer between Fe2+ ions via re-absorption of fluorescence (due to the spectral overlap of these bands) and phonon-assisted energy transfer (due to the lattice dynamics of ZnSe) becomes more probable with increasing Fe2+ concentration. Here we treat these processes as additional terms in the rate equations which govern the spontaneous decay of the Fe2+ ion. This treatment gives insight into anomalous behavior seen in the thermal lifetime of the Fe:ZnSe system. We also apply the model to other transition metal doped II-VI materials.
This paper describes using a hot isostatic pressing (HIP) to improve II-VI crystal characteristics and diffuse metal ions into laser host crystals. Thin layers of metal are sputtered onto the surface of zinc selenide and zinc sulfide crystals prior to being HIP treated. The pre and post treatment optical properties for these materials are measured using various methods and at a variety of dopant concentrations.
We describe a variety of technological advances in the development of efficient, powerful, and continuously tunable Cr:ZnSe lasers operating in the 2.3-2.7 μm spectral region. This includes the development of compact "single chip" waveguide Cr:ZnSe lasers, waveguide mode-locked Cr:ZnSe lasers, and the creation of homogeneously broadened laser material.
In addition to the well-established 5I7 to 5I8 transition at 2.09 μm in holmium doped laser materials, there also exists a less energetic transition from the 5I6 level to 5I7 at 2.95 μm. As there has been a recent increase in interest and applications for 3.0 μm light, this material stands to be a viable alternative to other rare earth doped laser systems. Unfortunately, the wavelength required to directly pump the 5I6 level at 1.13 μm is not convenient for commercial laser diodes. Furthermore, the emission lifetime of the 5I7 state is longer than the 5I6 level, leading to a suppression of lasing due to “bottlenecking” in the material. To overcome these effects, we investigated the activation and deactivation of holmium doped yttrium aluminum garnet (YAG) using ytterbium and praseodymium respectively. By including ytterbium ions in the host material, readily available 914 nm diode light can be used to resonantly excite the 5I6 level in holmium. Similarly, the presence of praseodymium resonantly de-excites the 5I7 state, reducing its lifetime, and making the material more suitable for lasing. Here, we report the absorption and photoluminescence spectra of this triply doped Yb,Ho,Pr:YAG crystal. In addition, the emission lifetime for both the 2.09 μm and 2.95 μm transitions are reported and compared to a Yb,Ho:YAG control sample.
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