Laser gain measurements at 193 nm in a small discharge cell containing ArF excimer laser gas mixtures

Spatial and temporal gain profiles as well as the peak net gain at 193 nm have been measured in X-ray preionized discharges excited by a single pulse electrical system working in the charge transfer mode. Ar- and F2-containing laser gas mixtures with He or Ne as a buffer gas have been used. With a pumping pulse duration of ~ 100 ns (FWHM) and a specific peak power deposition of ~ 1 MW cm-3 bar-1 in a gas mixture containing F2 : Ar : He (0.1%:5%:94.9%), at 2 bar total pressure, a very high peak net gain coefficient of ~30% cm-1 was measured in the gas discharge. The FWHM of the gain waveform was ~ 60 n

Photo-electric effects in X-ray preionization for excimer laser gases

We present detailed measurements on the x-ray preionization electron density in a discharge chamber filled with different gases relevant to discharge pumped high-pressure excimer lasers. By comparing experimental results with the theoretical electron densities, we conclude that the observed preionization is inconsistent with the standard picture of direct ionization through x-ray absorption in the gas. We conclude that depending on the gas pressure, type of gas, and the gap length between the discharge electrodes used, x-ray preionization in excimer gases is, to a significant extent or even dominantly, based on a different mechanism. We identify that this mechanism is based on fast photoelectrons emitted by the cathode into the discharge chamber

Reading tea leaves worldwide: decoupled drivers of initial litter decomposition mass-loss rate and stabilisation

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

Preionization and gain studies in fluorine based excimer laser gas discharges

Fluorine-based excimer gas lasers are powerful sources of coherent radiation in the UV and VUV part of the electro-magnetic spectrum. Due to their short wavelengths and high output power they are widely employed in high resolution material processing like micromachining and in lithography. In this field pattern sizes several times shorter than the used wavelength can be achieved using an immersion technique. However due to the short duration of the laser pulse (typically of few tens of ns for commercially available fluorine-based excimer lasers), the laser pulse makes only a few round-trips inside the laser resonator cavity. As the result, the optical quality of the laser beam of such an excimer laser is poor, leading to non optimal focusing conditions. The purpose of this work was to investigate different methods and techniques to produce excimer lasers, based on fluorine containing gas mixtures, emitting optical pulse lengths of 100 ns or longer. In order to achieve this goal we have studied different gas discharge excitation techniques in a small scale discharge chamber (0.5 – 4 cm discharge gap, 5 cm electrodes diameter) at gas pressures varying from 2 to 5 bar. We have thoroughly investigated a pre - main pulse gas discharge pumping scheme with X-ray preionization and a single pulse excitation scheme with X-ray preionization. As preionization source we investigated two homemade X-ray sources. We have developed a high voltage open barrier discharge device producing a fast electron beam directly in the gas. It was shown that it was possible to generate soft X-ray radiation (10 – 100 keV) directly in gases by means of this beam. With this and with an earlier developed traditional X-ray source the produced electron densities in different gases and gas mixtures have been measured. During our experiments we discovered that, apart from the well known direct electron generation in the gas, a substantial part of the measured preionization electrons were generated indirectly by the Xrays via the photo-electric effect at the electrode. With the single pulse excitation scheme we succesfully ignited a homogeneous discharge and were able to sustain it as a stable, homogeneous pulsed gas discharge in gas mixtures typically containing 5 % of Ar and 0.1 % of F2 at a total gas pressure of 2 bar and an electrode distance of 1 cm. In this laser gas mixture the typical achieved peak power deposition density was 1 – 2 MW cm-3 with a pulse duration (FWHM) of ~ 100 ns. Under these conditions the observed spontaneous emission intensity was 119 kW cm-3 at the ArF* excimer wavelenth (193 nm). The width of this emission signal was ~ 60 ns (FWHM). With a probe laser (λ = 193 nm) the amplification of the probe signal in the excited laser medium was measured. Under the same conditions a net gain was measured of ~ 34±20 % cm-1 with a FWHM of ~ 60 ns. The combination of such high gain and the reasonably long optical pulse duration makes our gas discharge excitation system a promising device for the development of small scale fluorine-based excimer gas lasers. The short resonator length of several cm will result in a higher number of the intra cavity round-trips and thus to a better beam quality compared to the usual excimer lasers

Development of in-pile Power Monitoring System Based on the Calorimetric Gamma-Detector

In this analytical overview, domestic and foreign scientific and technical publications focusing on research of different types of in-core detectors and in-core instrumentation systems (ICIS) are considered. The issues of ICIS development are discussed and a novel nonconventional concept of reactor monitoring is suggested.В аналітичному огляді розглядаються вітчизняні та зарубіжні науково-технічні публікації стосовно проблеми дослідження різних типів детекторів активної зони і систем внутрішнього реакторного контролю (СВРК). Обговорюються проблеми розвитку СВРК і пропонується нетрадиційна концепція контролю роботи реактора.В аналитическом обзоре рассматриваются отечественные и зарубежные научно- технические публикации по проблеме исследования различных типов детекторов активной зоны и систем внутреннего реакторного контроля (СВРК). Обсуждаются проблемы развития СВРК и предлагается нетрадиционная концепция контроля работы реактора

Soft x-ray generation in gases by means of a pulsed electron beam produced in a high-voltage barier discharge

A large area pulsed electron beam is produced by a high-voltage barrier discharge. We compare the properties of the x-rays generated by stopping this beam of electrons in a thin metal foil with those generated by stopping the electrons directly in various gases. The generation of x-rays was investigated in He, Ne and Ar with and without an Al foil in the discharge chamber. It appears that, for voltages of up to 15 kV used in our experiments, x-rays are produced by the 'bremsstrahlung' mechanism and that characteristic x-ray radiation does not play an important role. The x-ray intensity strongly depends on the parameters of the electron beam (electron energy and current density) and the stopping material properties (Z-number). The energy of the x-ray photons is comparable to the applied voltage. The highest obtained energy in the x-ray spectrum depends on the electron energy (~10 keV in the investigated case) and the lowest energy is determined by the transmittance of the output window and the window of the detector