N A Timofeeva

High-energy room-temperature Fe2+:ZnS laser

Characteristics of a room temperature laser on polycrystalline ZnS:Fe2+ subjected to diffuse doping from two sides were investigated. The sample was pumped by a non-chain electrodischarge HF laser with the FWHM duration of the radiation pulse of ~140 ns. The diameter of the pumping radiation spot on the surface of the crystal was 3.8 mm. Further increases in the size of the pumping spot were limited by parasitic generation arising due to a high concentration of Fe ions in the near-surface layer of the sample at a relatively small depth of doping (short length of active medium). The generation energy of 25.5 mJ was obtained at a slope efficiency of 12% with respect to the energy incident on the sample. Characteristics of lasers on polycrystalline ZnS:Fe2+ and ZnSe:Fe2+ have been compared in equal pumping conditions. The slope efficiencies of ZnSe:Fe2+ and ZnS:Fe2+ lasers with respect to the absorbed energy were 34% and 20%, respectively. At equal pumping energy absorbed in the samples, the duration of the ZnSe:Fe2+ laser radiation pulse was longer than that of the ZnS:Fe2+ laser. Possibilities of increasing the efficiency of ZnS:Fe2+ laser operation at room temperature by improving the technology of sample manufacturing and reducing the duration of the pumping pulse are discussed in this letter.

Room-temperature laser on a ZnSe : Fe2+ polycrystal with undoped faces, excited by an electrodischarge HF laser

Characteristics of a laser on a ZnSe : Fe2+ polycrystalline active element with undoped faces (the concentration of Fe ions was maximal inside the crystal and zero at the faces) were studied. The laser was pumped by a non-chain electrodischarge HF laser at room temperature of the crystal. The active element was fabricated by the method of diffuse doping, which prevented the iron film newly deposited to a ZnSe substrate from interacting with atmospheric air (moisture and oxygen) and hindered the subsequent penetration of oxygen into the ZnSe matrix in the course of the high-temperature annealing of the sample. This method was used instead of those employed earlier for doping polycrystalline samples; it noticeably increased the efficiency and generation energy of a ZnSe : Fe2+ laser at room temperature of the crystal. The generation energy was 298 mJ at the slope efficiency of η slope = 45% and the total efficiency with respect to the absorbed energy of η abs = 40%.

Room-temperature laser on a ZnS:Fe2+ polycrystal with a pulse radiation energy of 0.6 J

A laser on polycrystalline ZnS:Fe2+ samples pumped at room temperature by a pulsed electrodischarge HF laser was investigated. Samples of zinc sulphide grown by the method of chemical vapour deposition (CVD) were doped with iron ions from two sides by the diffusion method. The doping of the crystals was performed using the process of hot isostatic pressing (HIP treatment) at an argon pressure of 100 MPa and a temperature of 1265 °С. A longer duration of HIP treatment resulted in a greater depth of sample doping and higher slope efficiency of the laser. For a crystal subjected to HIP treatment for 151 h, a generation energy 660 mJ was obtained. The values of the slope and total efficiency of the energy absorbed in an active element were, respectively, η slope = 36% and η abs ≈ 26%. Based on the results obtained, and data from earlier published works, a conclusion has been made that to enhance the generation characteristics of a ZnS:Fe2+ laser it is necessary to increase the temperature of the HIP treatment of CVD ZnS.

The energy and spectral characteristics of a room-temperature pulsed laser on a ZnS:Fe2+ polycrystal

The energy and spectral characteristics of a laser on a ZnS:Fe2+ polycrystal operating at room temperature have been studied. The laser was pumped by a non-chain electro-discharge HF laser with a full-width at half-maximum pulse duration of ~140 ns. The diameter of the pumping radiation spot on the crystal surface was 3.8 mm. The two-sided diffuse doping of a polycrystalline CVD-ZnS sample with the surfaces preliminarily coated by high-purity iron films was performed in the process of hot isostatic pressing (HIP) in an argon atmosphere at a pressure of 100 MPa and temperature of 1290 °С. Increasing the duration of the HIP treatment from 54 h to 72 h made it possible to obtain twice the doping depth, and correspondingly, twice the length of active medium. As a result, the slope laser efficiency with respect to the absorbed energy was raised by a factor of 1.75 as compared to the value obtained in our earlier work with a polycrystalline sample. The generation energy was 25 mJ at a slope efficiency of η slope = 35%. It was established that the generation spectra of the laser with a non-selective resonator have a linear structure with intervals between the neighboring lines of δ λ ≈ 6 ÷ 8 nm, which is spurious for solid-state lasers. The spectral structure observed is not related to the elements inside the resonator, which might form Fabry–Perot interferometers.

Production and Laser Characteristics of Fe 2+ :ZnS x Se 1− x Polycrystals

A method is developed for producing active laser elements (spectrum range 4 to 5 μm) based on polycrystalline solid solutions ZnSxSex-1 doped with iron ions. Bilateral diffusion doping of the elements by Fe2+ ions is performed during hot isostatic pressing. Spectral and energy characteristics of the laser are investigated with the Fe2+:ZnS0.1Se0.9 active element kept at room temperature. It is found that the absorption band of the Fe2+:ZnS0.1Se0.9 crystal is blueshifted with respect to the Fe2+:ZnSe absorption band, while the lasing spectra of the Fe2+:ZnSe and Fe2+:ZnS0.1Se0.9 lasers and their energy parameters are almost identical. The lasing energy of 580 mJ is obtained at the slope efficiency with respect to the absorbed energy of 46%. Further increase in the lasing energy is limited by development of transversal parasitic oscillation at a large size of the pump beam spot.

Recrystallization Behavior of CVD ZnSe during Fe Diffusion Doping

This paper examines the effect of diffusion doping with divalent Fe ions in different atmospheres on the microstructure of polycrystalline CVD ZnSe. The activation energy for the recrystallization process in Fe2+:ZnSe is determined in the temperature range 900–1150°C, and the mechanisms underlying the effect of the dopant on grain growth in Fe2+:ZnSe are discussed.