HF Laser Research Articles

Peculiarities of Formation of Plasma Structures in Working Mixtures of Electrochemical HF (DF) Lasers and Methods for Their Study

Peculiarities of Formation of Plasma Structures in Working Mixtures of Electrochemical HF (DF) Lasers and Methods for Their Study

Geochronology and geochemistry of zircon from Early to Middle Devonian granitic and felsic volcanic rocks from the Cashes Ledge igneous suite, central Gulf of Maine, USA

New zircon U–Pb, trace element, and Lu–Hf laser ablation inductively coupled mass spectrometry (LA-ICP-MS) data are presented for five Early to Middle Devonian granitic and felsic volcanic rocks from the Cashes Ledge igneous suite, central Gulf of Maine, USA. These samples were previously analyzed by U–Pb LA-ICP-MS and whole-rock geochemical methods and the new data generally corroborate the earlier results. Coarse-grained alkali-feldspar granite from northwest of the Fundy magnetic anomaly, the interpreted fault boundary in the offshore between Gondwanan microcontinents Ganderia to the northwest and Avalonia to the southeast, yielded a crystallization age of 414 ± 2 Ma. Southeast of the inferred fault, crystallization ages are 385 ± 3 Ma and 386 ± 3 Ma for two crystal tuff samples near the fault, 403 ± 3 Ma for an alkali-feldspar granite ~50 km southeast of the fault, and 399 ± 5 Ma for syenogranite ~25 km southeast of the fault, which also yielded inherited grains at ~1.3 Ga and between 613 ± 15 Ma and 558 ± 9 Ma. Lu–Hf LA-ICP-MS data for zircon retaining igneous crystallization ages have εHf(t) between 2.9 and 13.1 and model ages based on felsic sources between 0.52 and 1.04 Ga, reflecting a mix of late Mesoproterozoic (Avalonian?) basement and primitive melt, possibly in an extensional setting. Zircon Nb/Hf ratios generally greater than 0.001 indicate a predominately within-plate/anorogenic/rift setting, consistent with their whole-rock chemistry. U/Yb-Nb/Yb and U/Yb-Hf tectonic setting discrimination diagrams show ocean island to continental arc signatures, with a stronger continental arc signature for the syenogranite. Most zircon grains have Eu/Eu* values less than 0.1, indicating a crustal thickness of ~30 km or less at the time of their crystallization.

Improving bonding strength between Ni/Cu/Ag coatings and MgTiO3 ceramic resonator by alumina thin-film grown by atomic layer deposition

A layer of nano-sized alumina thin-film was grown on MgTiO3 based ceramic resonator using atomic layer deposition (ALD) to improve the bonding between resonator and electroless plated and/or electroplated metal coatings. The hydroxylation of resonator surface ensures the strong bonding between alumina film and ceramic substrate, indicating by the bonding score to 10 from 0. However, it will not result in the degradation of the insertion loss of metalized resonators. The signal insertion loss of metalized ceramic resonator with alumina thin-film intermediate layer is significantly lower than that of resonators treated by traditional HF solution corrosion and/or laser scanning to achieve strong bonding between resonator and metalized coatings. It could be promising to metalize ceramic resonators with highly complex intricate geometric shape.

Laser properties of active media based on ZnSe doped with Fe and In from spray pyrolysis deposited films

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.

Collimation of an anastigmat objective with three off-axis aspherical mirrors

Subject of study. Objectives for a wide variety of wavelengths from the visible to the mid-infrared are currently under development for use in small spacecraft. Because of advantages such as the ability to operate over a broad spectral range, the use of low-weight mirror fabrication technologies, and their smaller size, reflective objectives are preferred for space-based applications. This paper discusses the collimation of reflective objectives with off-axis aspheric mirrors (objectives with an off-axis field of view). Collimation of reflective objectives has traditionally been performed using interferometers operating in autocollimation mode, with collimation being verified using compensatory designs. In the case of compact multimirror objectives, it is not always possible to find space for the collimation equipment (either an interferometer with an auxiliary mirror or a holographic compensator). Method. An alternative technique was developed for sequential element-by-element collimation of a prototype multimirror objective, based on monitoring focal-spot shapes and comparing them against a calculated focal-spot shape. We discuss collimation of a four-mirror anastigmat objective, in which the first mirror is an off-axis concave ellipsoid, the second mirror is an off-axis convex hyperboloid, the third mirror is a flat, and the fourth mirror is an off-axis concave ellipsoid. The objective was collimated using a He-Ne laser (wavelength 0.63 µm), with the distribution of light in the focal spot being recorded with a television camera; collimation was verified using a continuously tunable CO laser (emission wavelength of 5.415 µm) and an HF laser (emission wavelength of 2.8–3.2 µm), and the distribution of light in the focal spots was measured with an InSb photodetector array. The focal spots were inspected using a microscope whose object plane coincided with the focal plane of the element being collimated. The entrance aperture of the objective was illuminated by a collimated laser beam parallel to the collimation axis. The quality of collimation was determined by comparing the shapes of the observed focal spots against those theoretically calculated for an ideally collimated objective. Main results. Our research revealed that a test collimation technique based on the shape of the focal spots is insufficiently sensitive to miscollimation of individual mirrors and scattering within a multiple-mirror system. In addition, the technique fails to provide the required collimation accuracy. Practical significance. The proposed technique will be used to develop specialized optoelectronic instrumentation for continuous, step-by-step verification of all optical elements in a four-mirror anastigmat to sufficient accuracy for collimation.

An Effective Pulsed-Periodic Chemical HF(DF) Laser

—A working process is proposed for an HF(DF) laser, in which evacuation of the reactor is completely excluded. The workflow consists of the following stages: (1) displacement of the reaction products, which are formed after initiation of the working mixture, by an inert gas and (2) subsequent displacement of the inert gas by the working mixture. A design solution is proposed for the system of gas puffing into the reactor. Gas is supplied through an annular slot at one of the reactor ends, which makes it possible to minimize the consumption of inert gas used for displacing the reaction products after initiation of the working mixture. The amount of residual HF(DF) gas in the reactor is incapable of affecting the generation energy in the next cycle. It has been experimentally shown that the displacement technology does not lower the lasing energy in comparison with the pumping technology, but significantly reduces the duration of the HF(DF)-laser operating cycle by approximately two orders of magnitude).

Dielectric and Design and Experimental Study of GIS Gas Chamber HF and Micro Water Dual Fiber Laser Detection System

HF gas and trace moisture content, as the primary characteristic by-products of SF6 gas decomposition reaction, are of great significance to the fault diagnosis of high voltage SF6 gas insulated high voltage power equipment. In this paper, the typical discharge fault types in GIS are analyzed, and the decomposition products corresponding to different discharge types are summarized. The physical and chemical mechanism of HF generation in the early dissociation process of SF6 and under certain micro water and micro oxygen conditions is explained, and the experimental platform is built to carry out the simulation generation experiment of HF gas and micro water. The results show that choosing the best target absorption line suitable for sensitive and selective gas sensing can eliminate interference, simplify the system and reduce the cost. Furthermore, under the experimental conditions, the self-developed TDLAS online detection technology is used to realize the effective detection of HF gas and trace water in GIS discharge room. The 1278nm and 1392nm laser sources are selected respectively, and the TDLAS technology based on dual fiber time-sharing multiplexing is feasible for HF and trace water measurement. The stability and reliability of the technology are verified, which can provide effective technical support for on-line detection of HF gas in GIS, and has good engineering application value.

Pure single line oscillation of HF lasers in fine atmospheric window

Pure single line oscillation of HF lasers in fine atmospheric window

Performance improvement of a Fe2+:ZnSe laser pumped by non-chain pulsed HF laser

The causes and suppression methods of parasitic lasing in transverse direction of Fe2+:ZnSe laser are analyzed theoretically and experimentally. For a crystal with given diameter, there exists a maximum pump spot diameter dmax, below which the parasitic lasing doesn’t occur. The effective maximum pump spot diameter dmax can be increased by coating graphite on the side of the laser crystal, and the average increase of dmax is about 1.7 times after coating. The thermoelastic stresses and deformations on the Fe2+:ZnSe crystal under pulsed pumping mode are modeled, with results showing that it is possible by choosing doping profile shape to significantly reduce optical distortions and increase pulse power.

Possibility of using tetrafluorohydrazine as an oxidiser in a supersonic cw chemical HF laser

We report a computational and experimental study of the possibility of replacing NF3 nitrogen trifluoride, which is used in the NF3 – D2 – He fuel composition in the atomic fluorine generator of a supersonic cw chemical HF laser, with N2F4 tetrafluorohydrazine. As a result of comparing the specific energy characteristics of an HF laser operating with each of the oxidisers, it is shown that the replacement of nitrogen trifluoride with tetrafluorohydrazine in the same laser model leads to an increase in the specific energy output by 13% – 15%. In this case, it is possible to reduce the specific mass of the oxidiser storage system (the ratio of the mass of the oxidiser storage system to the laser facility power), reduce the oxidiser tank dimensions, and simplify the active medium generator design by eliminating the ignition system of the NF3 oxidiser with a D2 primary fuel.

Уширение и сдвиг линий основной колебательно-вращательной полосы молекул фтористого водорода молекулами SF-=SUB=-6-=/SUB=- и H-=SUB=-2-=/SUB=-

Foreign gas broadening and shift of the vibration-rotation lines in the fundamental band of hydrogen fluoride have been investigated. Using mathematical modeling of measuring the absorption of radiation of an electric discharge HF laser, the possibility of correct calculations of both broadening and shift of HF lines by foreign gases were determined. Measurements for two foreign gases (Ar and N2 for which there are literature data) were made in order to test this approach. The obtained results have been well matched with existing literature data. After that, measurements were carried out on two transitions P(7) and P(8) for SF6 (for which neither broadening nor the shift are known) and for H2 (only broadening is known for overtone band). The obtained results were compared with scarce literature data.

Comparative analysis of characteristics of a supersonic cw chemical HF laser on molecular fluorine and nitrogen trifluoride

We have experimentally studied the characteristics of a supersonic cw chemical HF laser with a flat nozzle array based on a nozzle – nozzle reagent mixing scheme operating with the use of F2 – D2 – He and NF3 – D2 – He fuel compositions in an atomic fluorine generator. The active medium flow field pattern, its gas-dynamic characteristics, and the laser radiation spectrum are considered. The comparison of these characteristics has made it possible to establish a strong impact on the flow field (lasing zone length) of the chemical composition of the combustion products from the atomic fluorine generator. The gas-dynamic parameters of the active medium formed by using a NF3 – D2 – He fuel have turned out to be less acceptable in terms of the gas flow pressure recovery than in the case of F2 – D2 – He fuel, while the radiation spectrum was more preferable from the viewpoint of passing through the atmosphere.

Transversal parasitic oscillation suppression in high gain pulsed Fe2+:ZnSe laser at room temperature

The performance of a room temperature high gain solid-state Fe2+:ZnSe laser was investigated. Causes and affecting factors of Transversal Parasitic Oscillation (TPO) were analyzed theoretically. The results indicate that TPO could be suppressed by reducing pump spot size or coating graphite around the active element. Corresponding experiments were made on Fe2+:ZnSe laser pumped by a non-chain pulsed HF laser, and the results demonstrate that the combination of reducing spot size and coating graphite can successfully overcome gain depletion problem due to TPO in high gain Fe2+:ZnSe lasers. At room temperature, the output energy of Fe2+:ZnSe laser reached 502 mJ, and the slope efficiency, measured with respect to the input pump energy, was 32.6%. An average power of 21.7 W was obtained at a pulse repetition rate of 50 Hz.

Investigation on pulsed discharge mode in SF6-C2H6 mixtures

The non-chain chemical HF(DF) laser is one of the most powerful electrically-driven lasers operating in mid-infrared, in which SF6-C2H6 mixtures are often used as lasering media. Due to the electronegativity of SF6, the discharge in SF6-C2H6 presents a complicated discharge mode. To achieve reproducible pulsed laser output, pulsed discharge in SF6-C2H6 mixtures is investigated for discharge mode using plane electrodes assisted by array pre-ionization spark pins in cathode surface. Firstly, two modes can be distinguished. One mode is called the self-sustained volume discharge (SSVD), which is characterized by spatial uniformity in the discharge gap and pulse to pulse repeatability. On the contrary, another mode includes random arc passages in the discharge gap and therefore cannot conduct lasering. By varying discharge conditions (gap voltage, gas pressure, etc) two discharge modes are observed. Secondly, the holding scope of the SSVD mode is analyzed for the optimal mixture ratio of 20:1, and the boundary tend of the holding scope of SSVD indicates there exists maximum gas pressure and maximum charging voltage for SSVD. Finally, the peak current of SSVD relates positively to charging voltage, while negatively to gas pressure, from which it is drawn that synchronous electron avalanches initiated by the sliding array overlap spatially into SSVD and thus SSVD is essentially an α ionization avalanche.

Efficiency of using nitrogen trifluoride as an oxidiser in a supersonic continuous-wave chemical HF laser

We report the results of an experimental study of possible ways to increase the efficiency of using NF3 nitrogen trifluoride as an oxidiser in an atomic fluorine generator of a supersonic continuous-wave chemical HF laser with a flat nozzle block corresponding to the nozzle – nozzle reagent mixing scheme. As such ways, we consider increasing the residence time of reagents in the combustion chamber and rising temperature in the chemical reaction zone. Comparison of specific energy characteristics of an HF laser operating with the use of the studied (NF3) and ‘basic’ (F2) oxidisers shows that the replacement of molecular fluorine with nitrogen trifluoride during the burning with deuterium in the combustion chamber of an atomic fluorine generator with allowance for the proposed measures leads to a reduction in the specific laser energy output by no more than 23 % – 24 % at high burning completeness.

Energy characteristics of a supersonic continuous-wave chemical HF laser using hydrazine decomposition products

We report the results of calculations and experimental studies of specific energy characteristics of a supersonic cw chemical HF laser with a flat nozzle block corresponding to the nozzle – nozzle reagent mixing scheme, in which catalytic decomposition products of hydrazine N2H4 (H2 + N2 + NH3) are used as a secondary fuel. As a result of experiments with cold (300 K) model mixtures, the specific energy extraction of the laser is found to decrease in this case by 43 % compared with the laser utilising pure hydrogen. The calculations show that the main reason for a decrease in the specific energy of the laser is an increase in the temperature in the mixing zone of the oxidising gas and secondary fuel jets. A strong effect of ammonia is revealed. Taking into account the actual heating of the products (up to 1000 K) during the catalytic decomposition of N2H4 allows the level of specific energy extraction from the laser to approach that of energy extraction from the laser operated on pure hydrogen by 13 %, which will lead to a decrease in the specific energy extraction by only 30 % in the absence of NH3 decomposition products.

Tetrafluoroethylene as a fuel component for an atomic fluorine generator of a supersonic continuous-wave chemical HF laser

A cheap and widely accessible combination (one of non-saturated perfluorocarbons), i.e. C2F4 tetrafluoroethylene, is proposed as an alternative fuel component for an atomic fluorine generator of a supersonic cw chemical HF laser of self-contained type. Combustion products of the hypergolic F2 – C2F4 – He mixture do not contain active relaxants of vibrationally excited HF(v) molecules. According to estimates, the atomic fluorine yield under comparable conditions is about 70 % in relation to that of the atomic fluorine generator operating on the F2 – D2 – He mixture which is the ‘basic’ one for a HF laser. The specific power is reduced by 23 % with an improvement in a set of the fuel performance and a significant reduction in the cost of triggering the laser in the course of its bench tests.

Luminescent and lasing characteristics of polycrystalline Cr:Fe:ZnSe exited at 2.09 and 2.94 µm wavelengths

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 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 × 1018 to 5.7 × 1019 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 τlt of Fe2+ ions on the dopants concentration in crystals excited at a wavelength of 2.94 m was obtained. It was found that chromium quenches the luminescence of Fe2+ no less actively (if no more) than iron itself. The τlt values were measured for Fe:ZnSe excited at a wavelength of 2.94 m and Cr:Fe:ZnSe samples with the same maximum Fe2+ ions concentrations (≈0.9 × 1019 cm−3) at wavelengths of 2.94 m and 2.09 m. A noticeable increase in τlt value and luminescence rise time was observed in Cr:Fe:ZnSe crystals excited at a wavelength of 2.09 m (τlt ≈ 460 ns) compared to 2.94 m (τlt ≈ 240 ns). For comparison, the value of τlt 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.

Lasing Characteristics of Fe:Cr:ZnSe Polycrystals

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.

Self-Organization of Dissipative Structures in Gas-Discharge Plasma of Self-Initiated Volume Discharge

It is shown that the features of the development of the self-initiated volume discharge in gas mixtures of a non-chain electrochemical HF laser are caused by self-organizing processes of dissipative structures representing plasma diffusion channels. The formation features of diffusion channels in the gas-discharge plasma of the self-initiated volume discharge are determined.