Daniele Murra

High-contrast photoluminescent patterns in lithium fluoride crystals produced by soft x-rays from a laser-plasma source

A technique using soft x-rays and extreme ultraviolet light generated by a laser-plasma source has been investigated for producing low-dimensionality photoluminescent patterns based on active color centers in lithium fluoride (LiF) crystals. Strong visible photoluminescence at room temperature has been observed in LiF crystals from fluorescent patterns obtained by masking the incoming radiation. This technique is able to produce colored patterns with high spatial resolution on large areas and in short exposure times as compared with other coloration methods.

ACCURATE WAVELENGTH MEASUREMENTS AND MODELING OF Fe XV TO Fe XIX SPECTRA RECORDED IN HIGH-DENSITY PLASMAS BETWEEN 13.5 AND 17 A

Iron spectra have been recorded from plasmas created at three different laser plasma facilities: the Tor Vergata University laser in Rome (Italy), the Hercules laser at ENEA in Frascati (Italy), and the Compact Multipulse Terawatt (COMET) laser at LLNL in California (USA). The measurements provide a means of identifying dielectronic satellite lines from Fe XVI and Fe XV in the vicinity of the strong 2p → 3d transitions of Fe XVII. About 80 Δn ≥ 1 lines of Fe XV (Mg-like) to Fe XIX (O-like) were recorded between 13.8 and 17.1 A with a high spectral resolution (λ/Δλ ≈ 4000); about 30 of these lines are from Fe XVI and Fe XV. The laser-produced plasmas had electron temperatures between 100 and 500 eV and electron densities between 1020 and 1022 cm-3. The Hebrew University Lawrence Livermore Atomic Code (HULLAC) was used to calculate the atomic structure and atomic rates for Fe XV-XIX. HULLAC was used to calculate synthetic line intensities at Te = 200 eV and ne = 1021 cm-3 for three different conditions to illustrate the role of opacity: optically thin plasmas with no excitation-autoionization/dielectronic recombination (EA/DR) contributions to the line intensities, optically thin plasmas that included EA/DR contributions to the line intensities, and optically thick plasmas (optical depth ≈200 μm) that included EA/DR contributions to the line intensities. The optically thick simulation best reproduced the recorded spectrum from the Hercules laser. However, some discrepancies between the modeling and the recorded spectra remain.

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.

How many times is a laser beam diffraction-limited?

Abstract We present an approach to the definition and estimation of the “times diffraction limit” (TDL) of highly diffracted laser beams that takes into account the near- and far-field energy distribution of the real beam instead of an ideal Gaussian beam. We have used it to find the TDL factor of two hard-edge-unstable-resonator laser beams having different quality and spatial energy distributions. The results are compared with the widely used beam quality parameter M 2 . The discrepancy between our TDL and the M 2 coefficient becomes significant when the near-field energy distribution of a spatially coherent beam deviates from the pure Gaussian shape.

Luminescent patterns based on color centers generated in lithium fluoride by extreme ultraviolet radiation and soft X-rays

Primary and aggregate color centers in lithium fluoride (LiF) crystals and polycrystalline LiF films were produced by an innovative irradiation technique using extreme ultraviolet radiation and soft X-rays generated by a laser-plasma source. This irradiation facility allowed the efficient formation of active color centers on luminescent patterns with submicron spatial resolution on large areas and short exposure times. The method looks promising for the realization of low-dimensionality photonic devices. The optical characterization of the colored structures was performed by means of absorption and photoluminescence measurements on LiF samples colored under different irradiation conditions.

Analytical propagation of supergaussian-like beams in the far-field

Abstract The analytical propagation of coherent supergaussian (SG)-like beams was calculated after F. Gori [Optics Comm. 107 (1994) 335] by introducing a linear superposition of Laguerre-Gauss functions called “flattened gaussian beam”. Here we propose a new family of SG-like beams, written as the convolution of a gaussian with a rectangle function; then, the well known convolution theorem allows a straightforward and simple analytical calculation of the beam profile in the focal plane of an arbitrary focusing system. In addition, this method can be successfully applied to more complex cases, as the SG-like beams commonly emitted by hard-edged unstable resonators (beam energy distribution with a hole).

Rydberg transitions in the spectra of near-neon-like Cu and Zn ions in different laser-produced plasmas: observations and modeling

Abstract We present observations of high-n transitions in the spectra of neon-like Cu19+ and Zn20+ ions observed in a variety of laser-produced plasmas (LPPs). The spectra are recorded with spectral resolution λ/Δλ=3000–8000 from three different laser sources: a 15 ns -pulse length Nd:glass, a ps-pulse length Nd:glass, a 12 ns -pulse length XeCl laser. These spectral observations are used to classify the transitions in the 2p–nd and 2s–np Rydberg series of the Ne-like copper and zinc ions, and to derive their first and second ionization energies. The plasma X-ray emission is simulated with a steady-state collisional-radiative model that includes the effect of self-absorption on line intensities, and the effect of hot-electron populations on the ionization balance. These spectra, along with those in our other recent work, provide a comprehensive set of data that can be used to test the accuracy of atomic-structure calculations, and to demonstrate the importance of opacity and hot electron effects on high-n transitions.

Identification and precise measurements of the wavelengths of high-n transitions in N-, O-, and F-like Zn ions

We have observed spectra of highly charged zinc ions from a variety of laser-produced plasmas. High-precision measurements of transition wavelengths have been made in the range 6.7–8.6 A, with accuracies of ≈1 mA. Line identifications for high-n transitions (n ≤ 7) in the N-, O-, and F-like spectra of Zn XXIV, XXIII, XXII, respectively, are made by comparison with steady-state collisional–radiative models.

First results of high-resolution patterning by the ENEA laboratory-scale extreme ultraviolet projection lithography system

We report the high-resolution patterning achieved by the laboratory-scale micro-exposure tool for extreme ultraviolet projection lithography realized at the ENEA Frascati Research Center in the frame of a National Project. Such a result obtained using a laser-produced-plasma source, a couple of twin ellipsoidal collectors and a low-cost Schwarzschild-type projection optics shows that it is possible to attain a nanometer-scale spatial resolution using relatively inexpensive projection optics.