The generation characteristics of a laser with a Fe:CdTe single crystal grown by a modified vertical gradient freeze method and subjected to high-temperature treatment as an active element have been studied. The possibility of efficient pumping using Fe:ZnSe or deuterium fluoride laser has been demonstrated. The broadband generation in the range of 5.3-6.0 $\mu \mathrm{m}$ with a maximum energy of up to 0.35 J per pulse has been obtained.

The record value of the output energy of Fe:CdTe laser, as well as the slope and total efficiency in terms of absorbed energy of 350 mJ, 57% and 42%, respectively, were obtained at the room temperature of the active element. An Fe:CdTe single crystal was pumped by a nonchain electric discharge deuterium fluoride laser operated in the spectral range of 3.6–4.06 μ m. The pump pulse full duration at half maximum was 220 ns. The output energy of the Fe:CdTe laser was limited by the development of transverse parasitic oscillations for pump spot diameters on the crystal surface of more than 11 mm. A laser with a non-selective cavity generated in the ranges of 5.5–6.0 μ m and 5.3–5.5 μ m at the output mirror reflectances of 53% and 21%, respectively.

The operation at room temperature of a single-crystal Fe:CdTe laser excited by a nonchain electric-discharge DF laser was studied. The output energy of 29 mJ was obtained with a slope efficiency in terms of absorbed energy of 30%. The development of transverse parasitic oscillation at large pump spot sizes on the crystal surface limited the laser output energy. The laser with a nonselective cavity operated in the range of 5.3–5.9 μ m; the total width of the generation spectrum was about 600 nm. Comparison of the Fe:CdTe generation spectra, obtained by pumping the crystal with DF and Fe:ZnSe lasers, confirmed the shift of the generation spectrum to the long wavelength region with increasing pump wavelengths. The maximum generation wavelength of the Fe:CdTe laser with a nonselective resonator excited by the Fe:ZnSe laser was 6.02 μ m with a total width of the generation spectrum of about 370 nm. Ways are discussed for further increasing the room-temperature output energy of a Fe:CdTe laser.

A technology for obtaining high-quality single-crystal active elements for a Fe:CdTe laser was described, which includes growing a single crystal from a melt using a modified vertical gradient freeze method followed by high -temperature treatment to remove free charge carriers. The room-temperature lasing and luminescence charac-teristics of a Fe:CdTe single crystal with a Fe2+ ions concentration of 6.1 x 1018 cm-3 were studied. The upper laser level lifetime, the output energy and a slope efficiency with respect to absorbed energy of the Fe:CdTe laser excited by the Fe:ZnSe laser were 340 ns, 13.5 mJ and 32%, respectively. The lasing spectrum of the Fe:CdTe laser with a nonselective cavity was located within the range 5.63-6.02 mu m. It was noted the possibility to control the lasing spectrum by changing the pump laser spectrum (shifting the Fe:ZnSe laser spectrum to the short-or long-wavelength region by changing the quality factor of the cavity). Ways are discussed for further increasing the output energy of a Fe:CdTe laser at room temperature of the active element, in particular, by using a non -chain electric-discharge DF laser for pumping.

The paper describes a method of fabrication of Cr2+:CdSe active elements by high-temperature diffusion. On test samples, repetitively pulsed laser generation was obtained at a wavelength of about 2.65 mu m with an efficiency of up to 69% in terms of absorbed power.

A technique was presented for obtaining laser media based on polycrystalline zinc selenide doped with iron from spray pyrolysis deposited films in the solid-phase diffusion process. The effect of the ligature film composition and the high-temperature treatment conditions on the lasing characteristics of Fe:(In):ZnSe active elements was investigated. Lasing with an energy of 100 mJ at a differential absorbed energy efficiency of 42% was obtained on 20 mm disk Fe:ZnSe element pumped by a pulsed electric-discharge HF laser.

The paper discusses the results of experimental studies of the Fe 2+ :ZnSe and Fe 2+ :ZnS lasers based on polycrystalline bulk active elements created using solid-state diffusion bonding of pre-alloyed CVD-ZnSe(S) plates and hot isostatic pressing method.

We investigated room-temperature pulsed lasing in heavily doped Fe:ZnSe single crystals. The active elements were pumped by a Q-switched Cr3+:Yb3+:Ho3+:YSGG laser operating at 2.87 μm. Our results show that the generation of short laser pulses has a deep high-frequency modulation associated with relaxation dynamics in Fe:ZnSe. The lasing regime obtained in this study provides a straightforward way to generate mid-IR single nanosecond pulses at moderate pump energies. Moreover, we found a relation between the lasing pulse duration and the concentration of Fe2+ doping ions, and we experimentally demonstrated pulse shortening in heavily doped active crystals. Single-pulse lasing with an FWHM pulse duration of ~2.8 ns was achieved in ZnSe crystals doped with 2.3 · 1019 cm-3 Fe2+ ions. The demonstrated single-pulse lasing regime is applicable for seeding high-power mid-IR laser systems.

Compact and portable diode-pumped solid-state MIR lasers with active and passive Q-switching based on Er:YAG, Er,Cr:YSGG and Ho,Yb,Cr:YSGG crystals have been designed and investigated. Those lasers provided the following parameters: pulse width 60 ns, peak power up to 1 MW and repetition rate 50 Hz. Geometrical sizes our lasers were just 75 mm diameter and 200 mm length. The Fe 2+ :ZnSe(ZnS) crystals pumping by radiation of designed lasers with the optical conversion efficiency near 40% was demonstrated.

The methods for suppressing transverse parasitic oscillation (TPO) at room temperature in Fe:ZnSe and Fe:ZnS lasers based on polycrystals doped using high-temperature diffusion have been considered. When active elements of this type are used, the development of TPO at large pump spots is due to the high dopant concentration on the surface of element end face and small length of the active medium as a whole (i.e., typical disk laser geometry). The TPO suppression methods under consideration are based on the fact that undoped Fe:ZnSe and Fe:ZnS exhibit significant absorption at the corresponding lasing wavelengths. Thus, the TPO development can be excluded by simple increase in the transverse size of active element and growth of active elements with several inner doped layers or an inner doped layer (layers) in the form of a meniscus. The problems of damage of active elements at large pump spots are discussed, and the potential of further increase in the radiation energy of Fe:ZnSe and Fe:ZnS lasers with room-temperature active elements is predicted.

The luminescence of Cr2+ and Fe2+ in Cr:Fe:ZnSe polycrystals excited at room temperature by pulsed lasers at wavelengths of 2.09 and 2.94 proportional to m was studied. For comparison, we also studied the luminescence in single crystals and polycrystals of Fe:ZnSe with iron ion concentration in the range from 5.6 x 10(18) to 5.7 x 10(19) cm(-3). Doping of the polycrystalline samples was carried out using a high-temperature diffusion process with subsequent control of the dopants concentration distribution over the crystal depth. The dependence of the luminescence lifetime tau lt of Fe2+ ions on the dopants concentration in crystals excited at a wavelength of 2.94 proportional to m was obtained. It was found that chromium quenches the luminescence of Fe2+ no less actively (if no more) than iron itself. The tau lt values were measured for Fe:ZnSe excited at a wavelength of 2.94 proportional to m and Cr:Fe:ZnSe samples with the same maximum Fe2+ ions concentrations (approximate to 0.9 x 10(19) cm(-3)) at wavelengths of 2.94 proportional to m and 2.09 proportional to m. A noticeable increase in tlt value and luminescence rise time was observed in Cr:Fe:ZnSe crystals excited at a wavelength of 2.09 proportional to m (tau lt approximate to 460 ns) compared to 2.94 proportional to m (tau lt approximate to 240 ns). For comparison, the value of tau lt in Fe:ZnSe was about 340 ns. The obtained results confirm the fast energy transfer in Cr:Fe:ZnSe crystals from excited chromium ions to iron ions. The output characteristics of lasers on Fe:ZnSe and Cr:Fe:ZnSe polycrystalline active elements with pumping by HF laser radiation were compared. The slope efficiency with respect to the absorbed energy of Cr:Fe:ZnSe lasers was significantly lower, and the generation threshold was two times higher than for Fe:ZnSe lasers. The prospects for creating a room temperature laser, in which the excitation of iron ions will be carried out through energy transfer from chromium ions, are analyzed.

The characteristics of a laser based on Fe:Cr:ZnSe polycrystals, excited at room temperature by a non-chain HF laser (2.6 to 3.1 µm) have been investigated. High-temperature diffusion doping of zinc selenide (CVD ZnSe plates) with chromium and iron was applied. Two active elements were studied. In one of them, iron and chromium were introduced into the crystal through one of the ZnSe plate surface; i.e., the Cr2+ and Fe2+ concentration profiles were overlapped in the crystal. When fabricating the second element, iron and chromium were introduced from the opposite plate surfaces, and their concentration profiles were spaced. It is established that co-doping of zinc selenide with chromium and iron reduces significantly the slope efficiency and increases essentially the lasing threshold with respect to the absorbed energy in comparison with similar parameters of lasers based on Fe2+:ZnSe crystals, fabricated by the same technology. One of the main causes of the deterioration of lasing characteristics of the Fe:Cr:ZnSe laser in comparison with the Fe2+:ZnSe laser is the absorption of radiation at the lasing wavelengths in the range of 4 to 5 µm in chromium-containing crystals. The prospects of designing a laser with an active element operating at room temperature, in which iron ions should be excited due to the energy transfer from chromium ions, are discussed.

An Fe2+:ZnSe laser on a polycrystalline active element with an inner doped layer in the form of a meniscus operating at room temperature was investigated. The active element was manufactured using the solid-state diffusion bonding (SSDB) technique. The billets, in the form of plano-concave and plano-convex ZnSe lenses with a radius of curvature of 200 mm, were subjected to diffusion bonding. Before bonding, zinc selenide was doped with Fe2+ ions by diffusion through spherical lens surfaces by the process of hot isostatic pressing (HIP). After the SSDB procedure, the prepared sample was subjected to an additional HIP treatment. An Fe2+:ZnSe polycrystal was pumped by an electric-discharge hydrogen fluoride (HF) laser. The use of the active element with an inner doped layer in the form of the meniscus permitted an increase in the pump spot diameter, at which there was not yet any reduction in laser output energy associated with the development of transverse parasitic oscillation. This increase was ~19% (compared to samples with a single flat doped layer). The output energy of 480 mJ was achieved at a total efficiency (with respect to absorbed energy) of 38% on the 20 mm diameter Fe2+:ZnSe sample with the meniscus inner doped layer.

Characteristics of a Fe:ZnSe laser are studied at room temperature. The laser active elements are heavily doped single crystals with the $$\hbox {Fe}^{2+}$$ ion concentration $$n=0.64\times 10^{19}-5.7\times 10^{19}\hbox {cm}^{-3}$$ , grown from melt by the Bridgman method. The generated energy of 870 mJ is obtained at the total efficiencies with respect to the absorbed and incident energies $$\eta _{\mathrm{{abs}}}=43\%$$ and $$\eta _{\mathrm{{inc}}}\approx 35\%$$ , respectively. The laser slope efficiency with respect to the absorbed energy is $$\eta _\mathrm{{slope}}\approx 50\%$$ . In a heavily doped active element with the $$\hbox {Fe}^{2+}$$ concentration $$n=5.7\times 10^{19}\hbox {cm}^{-3}$$ , in which the medium excitation depth is just a part of the total element dimension along the optical axis (the element is completely non-transparent for the pumping radiation), the radiation spectrum of the Fe:ZnSe laser shifts to the long-wavelength range by more than 300 nm as compared to spectra of the laser on crystals excited along the whole element length. It is shown that Fe:ZnSe lasers on heavily doped single-crystal elements can be efficiently excited by a radiation of a Cr:ZnSe laser without tuning the spectrum of the latter to the longer wavelength range.

The characteristics of a laser based on Fe:Cr:ZnSe polycrystals, excited at room temperature by a non-chain HF laser (2.6 to 3.1 µm) have been investigated. High-temperature diffusion doping of zinc selenide (CVD ZnSe plates) with chromium and iron was applied. Two active elements were studied. In one of them, iron and chromium were introduced into the crystal through one of the ZnSe plate surface; i.e., the Cr 2+ and Fe 2+ concentration profiles were overlapped in the crystal. When fabricating the second element, iron and chromium were introduced from the opposite plate surfaces, and their concentration profiles were spaced. It is established that co-doping of zinc selenide with chromium and iron reduces significantly the slope efficiency and increases essentially the lasing threshold with respect to the absorbed energy in comparison with similar parameters of lasers based on Fe 2+ :ZnSe crystals, fabricated by the same technology. One of the main causes of the deterioration of lasing characteristics of the Fe:Cr:ZnSe laser in comparison with the Fe 2+ :ZnSe laser is the absorption of radiation at the lasing wavelengths in the range of 4 to 5 µm in chromium-containing crystals. The prospects of designing a laser with an active element operating at room temperature, in which iron ions should be excited due to the energy transfer from chromium ions, are discussed.

Представлены результаты экспериментального и численного исследований прохождения излучения нецепного HF(DF)-лазера через монокристаллы германия (Ge) различной толщины и удельного сопротивления.На основе экспериментальных данных для спектра генерации HF(DF)-лазера сделаны оценки коэффициента двухфотонного поглощения в Ge-K 2 = 55 ± 10 cm/GW для λ = 2.8 µm.Результаты хорошо согласуются с теорией.Разработанная программа обработки данных эксперимента позволила численно исследовать прохождение мощного излучения с λ = 2.6-3 µm через Ge в любой момент воздействия лазерного импульса.Показано, что для мощного лазерного излучения с λ = 2.6-4 µm тонкие покрытия из Ge могут эффективно выравнивать распределение энергии по апертуре пучка.

The characteristics of an Fe2+:ZnSe laser at room temperature and its active elements with undoped faces were studied. Polycrystalline elements with one or two diffusion-doped internal layers were obtained by the solid-state diffusion bonding technique applied to chemical vapor deposition grown ZnSe plates preliminary doped with Fe2+ ions in the process of hot isostatic pressing. A non-chain electric-discharge HF laser was used to pump the crystals. It was demonstrated that increasing the number of doped layers allows increasing the maximum diameter of the pump radiation spot and the pump energy without the appearance of transversal parasitic oscillation. For the two-layer-doped active element with a diameter of 20 mm an output energy of 480 mJ was achieved with 37% total efficiency with respect to the absorbed energy. The obtained results demonstrate the potential of the developed technology for fabrication of active elements by the solid-state diffusion bonding technique combined with the hot isostatic pressing treatment for efficient IR lasers based on chalcogenides doped with transition metal ions.

A new method was developed and used for fabricating active elements on the basis of solid solutions of ZnS x Se 1-x doped with iron ions for lasing in the spectral range of 4 to 5 μm. It was found out that the absorption band of the synthesized samples was blueshifted with respect to the absorption band of the Fe 2+ :ZnSe crystal, while the lasing spectra and energy parameters of the Fe 2+ :ZnSe and Fe 2+ :ZnS 0.1 Se 0.9 lasers were almost identical.

Some results of experimental and numerical studies on the transmission of a nonchain high-frequency (HF) laser beam through germanium (Ge) single crystals of differing thickness and specific resistance are presented. Based on the experimental data for the HF(DF) lasing spectrum, the coefficient of two-photon absorption in germanium has been estimated as K2 = 55 ± 10 cm/GW at λ = 2.8 μm. The results are in good agreement with theory. The developed experimental data-processing software has enabled the numerical study of the transmission of a high-power beam with λ = 2.6–3 μm through Ge at any laser-pulse-impact moment. It has been shown that thin germanium coatings can efficiently smoothen the distribution of energy over the beam aperture for high-power laser radiation with λ = 2.6–4 μm.