Giovanni Schina

Compact three-electrodes excimer laser IANUS for a POPA optical system

A novel discharge configuration has been realized with the XeCl laser IANUS, which has been developed at the ENEA Frascati center as a 1:1 laser head prototype for the 1 kW average output power XeCl system EOLUS (EUREKA EU211 Project). The patented design of the discharge region consists of two active zones which are geometrically in parallel and electrically in series. The obvious advantages of this configuration are, the presence of the intermediate high impedance electrode, suitable for prepulse application, then the absence of current return bars, so improving the recirculating gas flow uniformity, and the automatic synchronization of the two discharges very useful for a compact oscillator-amplifier configuration (POPA). A number of measurements have been done on IANUS, to have an almost complete characterization; based on these results a generalized self-filtering unstable resonator (GSFUR) has been designed and realized on the smaller gap, leaving the other active medium for the high optical quality beam amplification, in the scheme of a POPA system. The GSFUR output beam results are 1.5 times the diffraction limit, with an energy of 9 mJ in a 87 ns FWHM pulse.

Excimer lamp pumped by a triggered longitudinal discharge

The ultraviolet (UV) radiation performance of an XeCl excimer lamp is measured as a function of the gas mixture composition (with and without neon as buffer gas) and pumping condition (longitudinal discharge with and without trigger). Both spatial distribution and spectral content of the emitted UV radiations are carefully determined including the contribution of the XeCl (B-X), XeCl (C-A), and Xe continuum emissions. A peak power density of up to 3 kW/cm/sup 2/ and an average power density of up to 0.2 W/cm/sup 2/ can be achieved when using a simple cylindrical aluminum reflector.

Parametric study of an x‐ray preionizer with plasma cathode

The construction characteristics and the performances of an x‐ray diode working at 200 Hz are described. The temporal behavior of both the plasma cathode emission and the diode discharge has been studied, including the measurements of vacuum effects on the repetition rate and lifetime capability, preionization versus electrical features, and ionization density versus dosage. This simple and low‐cost x‐ray diode has been used to uniformly preionize a half‐liter XeCl laser, delivering an output laser energy of 800 mJ/shot at a 100 Hz repetition rate.

Excimer laser development and applications at the ENEA Frascati Centre

In this paper we intend to present some recent result obtained in our laboratory on excimer laser development and applications. Even if the activity has been initiated as long as 15 years ago after 1986, following the European Eurolaser Initiative, the programs were strengthened and enlarged to accommodate more ambitious goals, according to the increased attention to this field. Actually the activity includes the following: (1) development of source, (2) computer models, 3) special devices, and (4) applications. The description of our activity is presented according to the above mentioned order, with special attention to the most recent results.

XUV generation from plasma produced by a XeCl excimer laser on a Cu target

SummaryWe present a detailed study of XUV and soft X-ray emission from Cu plasma produced by an excimer laser at intensitiesIL≦8·1011 W/cm2. The XeCl excimer laser (ψ≈308 nm) delivers pulses with energyEL≈2.3 J, temporal durationtL≈100 ns and brightnessB≧1014 W/cm2 sr. We recorded a spectral conversion efficiency η=0.5% eV−1 forIL=4·1011W/cm2 in the aluminium window at 73eV with a harder X-ray tail around ≈400eV. We also measured the dependence of X-ray signal on laser intensity and viewing angle. Experimental results have been compared with some analytical laser-plasma interaction models.

Industrial large-aperture XeCl laser for surface processing

In the frame of a large project on new materials technologies for photovoltaic and microelectronic applications (FOTO), the process of amorphous silicon (a-Si) transformation into polycrystalline silicon (poly-Si) by means of laser irradiation has been tested with a long-pulse (160 ns), 8 J/p XeCl source. Following the positive results, a laser source, having design parameters of 10 J/p, 120 ns, 10 Hz, has been designed and built, with the aim of realizing a laboratory line for the production of thin film transistors (TFTs) devices.

Pulsed x-ray generator for commercial gas lasers

We have designed and tested a 1-m-long x-ray diode based on innovative plasma cathodes, which exploit commercial spark plugs as electron emitters. Based on the results of a numerical study, we optimized both diode geometry (e.g., the angle between anode and cathode surfaces, the thickness of the Al window) and electrical circuitry (e.g., the capacitance in series to each spark plug, the peak voltage of the anode) of our x-ray generator. The overall result is a simple and efficient circuitry, giving a total diode current in excess of 2.1 kA with a breakdown voltage of 70 kV, which generates a 50 ns rise-time x-ray pulse with a spatially averaged dosage of up to 6×10−4 Gy when using a Pb-wrapped anode. The double-diode x-ray generator was operated for 1.5×106 shots at a repetition rate of up to 30 Hz, and the lifetime test was interrupted without any fault. During the lifetime test, it was not necessary to adjust any working parameter. At the end of the lifetime test, the x-ray emission uniformity was bette...

X-ray diode with spark plug plasma cathodes

We have tested a high-repetition-rate X-ray diode working in reflection geometry, which uses commercial spark-plugs as plasma cathode. The results show that the spark-plug plasma cathode is a reliable, high-current and long-lifetime electron gun. After more than 106 shots, the dose, uniformity and ionization rate of the emitted X-ray guarantee an effective preionization of XeCl excimer laser discharges. Due to the low cost, the long lifetime and the substantial absence of maintenance, this X-ray diode seems suitable to preionize commercial gas lasers, such as excimer and TEA CO2 lasers.

Operation of a 10-L discharge XeCl laser

A 1 0 liter active volume, x-ray preionized XeC1 laser has been operated with both a conventional spark-gap switched discharge and a x-ray triggered one. In the last case, 45 W average output power was obtained. A simple model has been developed to study the minimum conditions on the preionization source to drive a uniform switchiess discharge.

Applications of an x-ray plasma source driven by an excimer laser: in vivo microscopy, microradiography, and radiobiology

A high brightness x-ray source has been obtained by focusing the large aperture excimer laser HERCULES on a solid target with a laser intensity of more than 1013W/cm2. The characteristics of the x-ray source for different laser time evolution in the range 6-120 ns are investigated. Experimental result on specific applications of the source, like the soft x-ray contact microscopy and the low photon energy radiobiology will be presented.