Search

We report the use of lithium fluoride fluorescent radiation imaging crystal detectors, read by an optical confocal laser microscope, to register the transmitted X-ray beams by polycapillary optics combined with a table-top Xray source. Polycapillary optics can control X-ray beams propagation and allows obtaining quasi-parallel beam (halflens) or focused beams (full-lens). Confocal laser fluorescence microscopy of X-ray irradiated LiF crystal detectors based on the photoluminescence of X-ray induced colour centres enables advanced characterization of these complex optics. Two-dimensional (2D) high spatial resolution images of X-rays transmitted through either a semi-lens or a full-lens were obtained. Moreover, the photoluminescent colour center volumes produced by X-rays in LiF crystals in a single exposure process have been used to provide threedimensional (3D) information about transmitted X-ray beams. The use of LiF crystal plates as X-ray imaging luminescent detectors represent a versatile and promising tool to characterize the operation of polycapillary optics.

Irradiation of lithium fluoride (LiF) crystals by low energy (few keV) electron beams gives rise to the efficient formation of stable laser active colour centres, mostly F2 and F3+ aggregate defects, on their surface. The presence of primary and aggregate point defects induces a local increase of the refractive index of the thin irradiated layer in the green-red spectral range, where the F3+ and F2 visible emissions are located. The use of electron-beam lithography techniques allows for the definition of coloured strips, so miniaturised optical active channel waveguides may be fabricated by a direct-writing process. We report on the observation of amplified spontaneous emission of the red light from LiF:F2 centres in active waveguides realised with different irradiation doses in a LiF crystal, in order to determine the influence of this fundamental parameter on the amplification properties of these optical confining structures. Low pumping power densities have been used in quasi-continuous-wave regime at room temperature; the appreciable values of the gain coefficient, several cm−1, with an exciting power density of few hundreds mW/cm2, make this material a good candidate for the realisation of active integrated optical devices.

We present broadband X-ray lensless projection imaging experiments performed at the TopoTomo beamline of the ANKA synchrotron facility by using innovative solid-state detectors based on the formation of stable photoluminescent colour centres (CCs) in lithium fluoride (LiF) films and crystals. The peculiar features of these detectors, like very high spatial resolution (standard 250 nm) across a large field of view (> 1 cm2), wide dynamic range (> 103), versatility and easiness of use combined with the high sensitivity of the optical fluorescence microscopy reading technique, make them very attractive as recording plates for X-ray imaging. High-resolution X-ray images of a metallic test pattern were recorded and acquired with good contrast both in LiF crystals and thin LiF films. The stored CCs fluorescence images show edge-enhancement effects ascribable to diffraction processes occurring during the X-ray beam propagation after its interaction with the samples. The experimental data concerning films and crystals based LiF-detectors will be discussed and compared with computer simulations of X-ray intensity distributions. The LiF film performances are very encouraging for the exploitation of these solid-state detectors for X-ray lensless imaging applications.

Fluorescent lithium fluoride detectors for X-ray projection imaging F. Bonfigli, M.A. Vincenti, R.M. Montereali ENEA, C.R. Frascati, Photonics Micro- and Nano-structures Lab., UTAPRAD-MNF, Via E. Fermi 45, 00044 Frascati (Rome), Italy E. Nichelatti ENEA, C.R. Casaccia, Optical Devices Laboratory, UTTMAT-OTT, Via Anguillarese 301, 00123 S. Maria di Galeria, Rome, Italy F. Somma, S. Heidari Bateni Università degli Studi Roma Tre, Dip. di Fisica E. Amaldi, Via della Vasca Navale 84, 00146 Rome, Italy A. Cecilia, T. Baumbach Institute for Photon Science and Synchrotron Radiation (IPS)/ANKA, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. Abstract The possibility of detecting high quality images of materials, devices and biological samples in the soft and hard X-ray spectral ranges with high spatial resolution and contrast and by using simple exposing configuration is a topical task nowadays. For this purpose, we propose the use of versatile imaging detectors based on the radiation sensitivity of lithium fluoride (LiF) to extreme ultraviolet, soft and hard X-rays [1, 2]. X-rays generate stable point defects in LiF, known as colour centres (CCs), which emit broad-band photoluminescence at visible wavelengths under optical pumping. The high dynamic response of the material to the received dose together with the atomic scale of the CCs make LiF plates, in form of thin films or crystals, extremely attractive as high-spatial-resolution radiation-imaging detectors both in absorption and phase contrast imaging configurations [1, 3]. The latent images are subsequently read by using optical fluorescence microscopes, which in the case of advanced techniques can reach spatial resolutions well below 100 nm [4]. We present lensless imaging experiments in projection mode at the TOPO–TOMO beamline of the synchrotron light source Anka (Karlsruhe, Germany) by using LiF crystals and thin films irradiated in the energy range 6–40 keV. Stable fluorescent images were formed in LiF detectors by scattered X-rays after an object had been positioned between the X-ray source and the detectors. The object used in this work is the commercial test pattern X500-200-30 (Xradia, Pleasanton, CA, USA) consisting of a gold mask (thickness 3 m) deposited on a (500500) μm2 Si3N4 window (thickness 330 nm). The LiF detectors were crystals and 1 m thick polycrystalline films deposited on glass substrates. To imprint the X-ray image of the sample on the LiF detectors, the test pattern was irradiated with several exposure times between 1 s and 60 s. The X-ray micro-radiographies were optically read with a confocal laser scanning microscope (CLSM, Nikon Eclipse 80i-C1) operating in fluorescence mode. It is worth pointing out that a 1 m LiF film was able to store high-quality and well contrasted fluorescence images of the test pattern, although X-ray attenuation length in LiF varies between 0.02-12 mm for X-ray energies in the investigated range. The stored images show edge-enhancement effects that are ascribable to diffraction processes occurring during the X-ray beam propagation after its interaction with the sample. A computer simulation was performed to calculate the incoming X-ray intensity distribution across the detector. A fairly good agreement with experimental data evidences a linear optical fluorescence response of LiF-film based detectors under the investigated conditions. This linear behaviour has been confirmed by measurements of the PL signals of F2 and F3+ CCs detected with a CLSM system for several X-ray irradiation times. Further investigations are in progress to study the exploitation of solid-state LiF detectors for X-ray lensless projection imaging experiments and applications. References [1] G. Baldacchini, F. Bonfigli, A. Faenov, F. Flora, R.M. Montereali, A. Pace, T. Pikuz, L. Reale, J. Nanoscience and Nanotechnology 3, 6 483-486, (2003). [2] S. Almaviva, F. Bonfigli, I. Franzini, A. Lai, R.M. Montereali, D. Pelliccia, A. Cedola, S. Lagomarsino, Appl. Phys. Lett. 89, 54102, (2006). [3] F. Bonfigli, A. Cecilia, S. Heidari Bateni, E. Nichelatti, D. Pelliccia, F. Somma, P. Vagovic, M.A. Vincenti, T. Baumbach and R.M. Montereali, Radiation Measurements 56, 277-280, (2013). [4] A. Ustione, A. Cricenti, F. Bonfigli, F. Flora, A. Lai, T. Marolo, R.M. Montereali, G. Baldacchini, A. Faenov, T. Pikuz, L. Reale, Appl. Phys. Lett. 88, 141107 (2006).

The depth refractive index profiles of broadband visible-emitting planar waveguides produced in LiF crystals with 1.5- and 2-MeV He+ ions at different doses have been derived from mode analysis. They show that there are two competitive mechanisms responsible for positive and negative modifications of the refractive index in the irradiated volume associated with different processes of energy deposition of the incident ions, so as to induce a complex coloration profile along the penetration direction, which is strongly dependent on the irradiation dose.

In this paper, the use of lithium fluoride (LiF) as imaging radiation detector to analyse living cells by single-shot soft X-ray contact microscopy is presented. High resolved X-ray images on LiF of cyanobacterium Leptolyngbya VRUC135, two unicellular microalgae of the genus Chlamydomonas and mouse macrophage cells (line RAW 264.7) have been obtained utilizing X-ray radiation in the water window energy range from a laser plasma source. The used method is based on loading of the samples, the cell suspension, in a special holder where they are in close contact with a LiF crystal solid-state X-ray imaging detector. After exposure and sample removal, the images stored in LiF by the soft X-ray contact microscopy technique are read by an optical microscope in fluorescence mode. The clear image of the mucilaginous sheath the structure of the filamentous Leptolyngbya and the visible nucleolus in the macrophage cells image, are noteworthiness results. The peculiarities of the used X-ray radiation and of the LiF imaging detector allow obtaining images in absorption contrast revealing the internal structures of the investigated samples at high spatial resolution. Moreover, the wide dynamic range of the LiF imaging detector contributes to obtain high-quality images. In particular, we demonstrate that this peculiar characteristic of LiF detector allows enhancing the contrast and reveal details even when they were obscured by a nonuniform stray light.

Lithium fluoride is a well known material used for dosimetry. In the last years it was proposed and tested also as imaging detector for X-ray microscopy. Optical microscopy represents the oldest and most used imaging technique for medicine and cell biology investigations; later other imaging techniques, including electron microscopy, were introduced. The recent technological developments in the soft X-ray field, concerning sources, optics and detectors, have been increased the interest of physicians and biologists for X-ray microscopy, mainly to obtain in vivo imaging of cells. An innovative imaging detector has been proposed and tested by researchers of C.R. ENEA Frascati, as handy, versatile and compact plate for soft X-ray imaging with very high spatial resolution, wide dynamic range, large field of view and easy to read by an optical microscope. Scientific and technological applications can be foreseen in several fields, as nanotechnologies, materials, photonics, life science and microscopy (including cell imaging, also in vivo).

Confocal Laser Scanning Microscope (CLSM) is a versatile and powerful optical instrument which is gaining a strong increase of interest for biological investigations and also for the characterization of materials, microstructures and devices. We exploit its capability for the characterization of light‐emitting micro and nano‐structures based on color centers in lithium fluoride. CLSM was successfully used as an advanced optical reading system to detect X‐ray micro‐radiographies of biological specimens stored in LiF imaging detectors.

X-ray microradiographs of small biological objects, such as animals and plant materials at micrometric resolution, are currently performed by various methods, all of which are limited by the resolution or the dynamic range of the image detectors. Here a novel X-ray image detector is discussed, in which the previous limitations have been overcome. A film of lithium fluoride salt is used as a detector, in which the stored biological image is read by observing the optically stimulated visible luminescence of the active color centers, efficiently produced by the X-rays.

ray microscopy and tomography is a field in rapid expansion, due to strong improvements in x-ray sources, optics and detectors. For high spatial resolution (of the order of few hundreds nanometers and below) in the hard x-ray region, highly demanding optical elements are in general required. For use with laboratory sources, conditions are obviouslymore stringent due to low flux. In this contribution we will present a simple, relatively inexpensivemethodwhich allows collecting high spatial resolution (about 250 nm) images with a laboratorymicrosource using Lithium Fluoride (LiF) films as imaging detectors in contact mode. LiF has a crystalline f.c.c. structure and, under exposure to ionizing radiation, can host different types of Color Centers (CC), electronic point defects in the lattice matrix [1]. Some of them (in particular the F2 and F + 3 CCs’ which are aggregates of the primary F centers), are optically active, with broad absorption and emission bands in the visible spectral range [2,3] and stable at room temperature. The CCs’ are extremely localized (around 1 nm), and are therefore well suited to record x-ray images with high spatial resolution. After exposure to x-rays, the images stored in LiF films were read with a confocal optical microscope. We present in this contribution examples of images which demonstrate a resolution of the order of 250 nm, a limit essentially dictated by the optical resolution of the reading instrument. Clear advantages of the LiF detector are the intrinsic high spatial resolution (far beyond the limit shown here), the wide dynamic range, the large field of view, the easiness of use, as it is insensitive to visible light and it doesn’t need any development after exposure, and finally the relatively low cost. Discussion about its potentialities in x-ray microscopy will be discussed

Novel X-ray imaging detectors based on photoluminescence of colour centres in lithium fluoride (LiF) have been proposed and tested for extreme ultraviolet, soft and hard X-rays up to 10 keV. For the first time we present the optical characterisation of LiF crystals and thin films irradiated at the TOPO-TOMO beamline of synchroton light source Anka (Karlsruhe, Germany) in the energy range 6-40 keV for different exposure times. Absorption and photoluminescence spectra were analysed to study the optical response of the LiF-based detectors. High resolved X-ray imaging of commercial test patterns has been obtained on LiF crystals and films by optical readout with a confocal laser scanning fluorescence microscope. © 2012 Elsevier B.V.

Calciphylaxis is a rare, but potentially life-threatening condition usually observed in patients with end-stage chronic renal disease and characterized by small- and medium-sized blood vessel calcification leading to tissue ischemia. The clinical features are primarily cutaneous, consisting of skin necrosis and ulceration, mostly located in the lower extremities. We report a case of a 56-year-old woman with a previous history of renal disease and atypical lobular hyperplasia of the right breast, who developed painful skin necrosis on both breasts. Differential diagnosis comprises acute bacterial infection with ulceration, cutaneous vasculitis, cancer and calciphylaxis.

Scanning near-field optical microscopy (SNOM) makes it routinely possible to overcome the fundamental diffraction limit of standard (far-field) microscopy. Recently, aperture-based infrared SNOM performed in the spectroscopic mode, using the Vanderbilt University free electron laser, started delivering spatially-resolved information on the distribution of chemical species and on other laterally-fluctuating properties. The practical examples presented here show the great potential of this new technique both in materials science and in life sciences. (C) 2004 Elsevier B.V. All rights reserved.

Recent investigations have demonstrated the relevance of the emission properties of laser active color centers (CCs) in lithium fluoride (LiF) films to design new miniaturized solid state sources. Among them, optical microcavities hold technological promises for the realization of all-solid, low-threshold, high-directional emitters and lasers. The peculiar structure of the microcavities changes the characteristics of local electromagnetic field and consequently the spatial, spectral and temporal properties of the active center emissions. In this work we will show significant changes in the emission behavior of F2 CCs in LiF films placed inside a microcavity, i.e. light intensity enhancement, spectral narrowing, spatial redistribution and alteration of spontaneous decay time, as compared to a no-cavity structure.

Lithium fluoride (LiF) films irradiated by low energy electrons were employed as active spacers in all-solid, dielectric optical microcavities emitting in the visible spectral range. We present the results of optical characterization of the spontaneous emission from F 2 color centers embedded in a LiF layer confined inside a planar microcavity. These structures seem promising for the realization of novel kinds of solid-state miniaturized emitting devices.