Paolo Di Lazzaro

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.

Pattern recognition after image processing of low-contrast images, the case of the Shroud of Turin

We discuss the potentially misleading effect of software techniques for elaborating low-contrast images. In particular, we present the example of the stains embedded into one of the most studied archeological objects in history, the Shroud of Turin. We show for the first time that image processing of both old and recent photographs of the Shroud may lead some researchers to perceive inscriptions and patterns that do not actually exist, confirming that there is a narrow boundary between image enhancement and manipulation.

Coloring linens with excimer lasers to simulate the body image of the Turin Shroud

The body image of the Turin Shroud has not yet been explained by traditional science; so a great interest in a possible mechanism of image formation still exists. We present preliminary results of excimer laser irradiation (wavelength of 308 nm) of a raw linen fabric and of a linen cloth. The permanent coloration of both linens is a threshold effect of the laser beam intensity, and it can be achieved only in a narrow range of irradiation parameters, which are strongly dependent on the pulse width and time sequence of laser shots. We also obtained the first direct evidence of latent images impressed on linen that appear in a relatively long period (one year) after laser irradiation that at first did not generate a clear image. The results are compared with the characteristics of the Turin Shroud, reflecting the possibility that a burst of directional ultraviolet radiation may have played a role in the formation of the Shroud image.

Large-field high-resolution x-ray monochromatic microscope based on spherical crystals and high-repetition-rate laser-produced plasmas

The combination of a table-top laser produced plasma X-ray source and spherically bent crystals for the soft X-ray region is used in traditional X-ray microscopy schemes. The X-ray source is well localized both spatially (approximately 20 micrometer) and temporally (1 ps - 10 ns, it depends on the used laser) and it is spectrally tunable in a relatively wide range (6 - 19 angstrom). High quality monochromatic ((delta) (lambda) /(lambda) approximately 10-5 - 10-3) images with high spatial resolution (up to approximately 4 micrometer) and in a large field of view (few mm) are presented. For many applications, these low-cost compact systems can offer a simple alternative to the larger installations which are usually used. It was demonstrated that the spherically bent crystals can be efficiently used in a wide ((Theta) equals 40 - 90 degrees) range of reflection angles, thus allowing wide wavelength selection. A very efficient concentration of monochromatic X-Ray radiation into different spot shapes (line, circle spot, etc) is demonstrated.

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.

Superficial and Shroud-like coloration of linen by short laser pulses in the vacuum ultraviolet

We present a survey on five years of experiments of excimer laser irradiation of linen fabrics, seeking a coloration mechanism able to reproduce the microscopic complexity of the body image embedded onto the Shroud of Turin. We achieved a superficial, Shroud-like coloration in a narrow range of irradiation parameters. We also obtained latent coloration that appears after artificial or natural aging of linen following laser irradiations that, at first, did not generate any visible effect. Most importantly, we have recognized photochemical processes that account for both coloration and latent coloration.

Krypton as filter for ions, debris, and useless radiation in EUV projection lithography systems

The life time of the first multilayer mirror (the condenser) in optical systems for projection Extreme Ultra-Violet (EUV) lithography based on Laser Produced Plasmas (LPP) is limited both by the debris bombardment and by the EUV radiation photoablation. These problems can be dramatically reduced by using krypton as debris stopper, exploiting its high atomic weight (21 times the helium value) and its high transparency in the EUV region only between 60 and 90 eV. We demonstrate both theoretically and experimentally that by filling the laser-target interaction chamber with krypton at low pressure (a few mbar) it is possible to stop efficiently the small debris (having a size smaller than 1 micron, including ions, neutrals and clusters) while keeping a reasonable transmission of the EUV radiation in the 60-90 eV range. In particular, this is experimentally demonstrated for a solid target LPP based on a tantalum or copper tape target and pumped by a large energy (4 J - 120 ns) XeCl excimer laser. The poor transmission of krypton, out of the above mentioned spectral window, significantly reduces the exposition of the condenser mirror to useless radiation. This new technique for stopping the debris has recently been patented by our group. As far as the larger size debris is regarded, a dramatic reduction of their flux has been obtained by decreasing the laser intensity on the target, still keeping a laser to EUV energy conversion as high as 0.7 percent/eV/sr at 70 eV, from a Ta target, together with a shot to shot EUV pulse energy stability better than 1 percent.

Novel portable high-luminosity monochromatically tunable x-ray microscope

A novel experimental setup for transmission x-ray microscopy is presented. It is based on the use of a point isotropic x- ray source and a single spherical crystal. The x-ray beam intensity is modulated by the object attenuation, then monochromatized and enlarged using a spherical crystal and, lastly, imaged using a detector downstream of the crystal. We demonstrate by ray tracing technique and experimental testing that this system allows microscopy studies with image resolution better than the dimensions of the source, high magnification ratios, and great field of view. Microscopes using this model ca be easily built using different micro x-ray sources, like conventional x-ray tube generators, x-rays emitted by laser generated plasmas or synchrotron radiation. Utilization of spherically bent crystals to obtain high-resolution, large field, monochromatic images in a wide range of Bragg angles is demonstrated for the first time. High quality monochromatic images with high magnification about 15-35 times and spatial resolution over a large field of view were obtained. Some possible applications and preliminary experimental verification of the feasibility of the setup are also presented.

Hercules: an XeCl excimer laser facility for high-intensity irradiation experiments

Hercules is a XeCl excimer laser designed and constructed about ten years ago at the Laboratories of ENEA Frascati. It can deliver up to 10 J output energy at a repetition rate of 10Hz. Since 1992, Hercules is a laser facility available to check the feasibility of processes and/or the effects occurring to materials irradiated with ultraviolet radiation at very high energy fluence or at high intensity level or over a large area. Here we present a summary of the main mechanical, electrical and optical characteristics of Hercules, together with a selected list of irradiation experiments, including the generation of soft x-rays amorphous silicon.Hercules is a XeCI excimer laser (wavelength ?=308 nm) designed and constructed about ten years ago at the Laboratories of ENEA Frascati. It can deliver up to 10 J output energy at a repetition rate of 10Hz. Since 1992, Hercules is a laser facility available to check the feasibility of processes andlor the effects occurring to materials irradiated with ultraviolet radiation at very high energy fluence (up to 106 Jcm-2) or at high intensity level (up to 1014 Wcm-2) or over a large area (up to 50 cm2 per shot). Here we present a summary of the main mechanical, electrical and optical characteristics of Hercules, together with a selected list of irradiation experiments, including the generation of soft X-rays by laser-driven plasmas. the shock hardening of metals, the surface modification of textile fabrics, the crystallisation of

Atmospheric-pressure soft x-ray source for contact microscopy and radiobiology applications

A large volume non-conventional XeCl excimer laser (HERCULES) emitting long pulses (from 10 ns up to 120 ns at a wavelength of 308 nm) has been used to drive a soft x-ray plasma source. The x-rays pulse duration and the energy conversion efficiency in different spectral regions have been measured; x-rays emission lasting up to 100 ns has been obtained in the 70 eV region. The dependence of x-ray pulse duration on the size of the laser spot is discussed. The x- ray source can be operated both in vacuum and in helium at atmospheric pressure. This allows irradiating over a large area both for contact microscopy of living specimens (up to 1 mm2 windows) and for radiobiology (up to some cm2 windows). The experimental results obtained for these two applications as well as for radiographic images of living insects are discussed.