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The peculiar photoluminescence characteristics of radiation-induced colour centres in lithium fluoride (LiF), well known for applications in optically-pumped tuneable lasers and broad-band miniaturised light-emitting photonic devices operating at room-temperature, are under exploitation in passive imaging detectors and dosimeters based on visible radiophotoluminescence in LiF crystals and polycrystalline thin films. Their high intrinsic spatial resolution, wide dynamic range and large field of view, combined with easy handling, ambient-light operation and no development need, allow to successfully extend their use from X-ray imaging to proton-beam advanced diagnostics and dosimetry, even at those low dose values that are typical of hadrontherapy. After exposure, the latent images stored in LiF as local formations of F2 and F3 + aggregate defects are read with an optical fluorescence microscope under illumination in the blue spectral range. Their visible emission intensity was found to be linearly proportional to the dose over at least three orders of magnitude, so that bi-dimensional LiF solid-state dosimeters based on spectrally-integrated radiophotoluminescence reading can be envisaged. Taking advantage of the low thickness of LiF thin films, transversal proton beam dose mapping was demonstrated at low proton energies, even at high doses. Recent results and advances concerning LiF crystals and polycrystalline thin film characterisation in the linearity range are presented and discussed with the aim of highlighting challenges related to increasing the LiF film detector radiation sensitivity to both particles (protons) and photons (X-rays), although therapeutic dose values typical of clinical radiotherapy are still a big challenge.

Proton therapy uses proton beams to destroy cancer cells. Since the energy deposition of protons peaks at the end of the trajectory (Bragg peak), healthy tissues close to the target are partially spared. In clinical practice, beams of different energies are composed to obtain a broadened peak (SOBP, Spread Out Bragg Peak) to treat the entire lesion region in a uniform manner. In the framework of the TOP-IMPLART project (linear accelerator for proton therapy under construction at ENEA-Frascati), we present a semi-analytical method that allows to optimize SOBP uniformity for two different energy-modulation techniques, passive and active.

Lithium fluoride (LiF) films and crystals are versatile X-ray imaging detectors based on the optical reading of visible photoluminescence from radiation-induced electronic defects. Distinctive features of these detectors are their high spatial resolution across a large field of view, wide dynamic range and insensitivity to ambient light. These peculiarities of LiF detectors appear to be promising for monitoring the spatial intensity distribution of ultra-short, ultra-high pulses of the EUV-X-ray Free Electron Laser (XFEL) and could be exploited for coherent diffraction imaging experiments.

The concentrations of primary F centres and F2 and F3+ aggregate defects were evaluated as a function of the irradiation dose in broad-band light-emitting single-mode strip waveguides directly written with 12 keV electrons at the surface of a LiF crystal. From a careful best-fit procedure of the optical transmission spectra, measured on microstructures only few tens of micrometers wide, the spectral contributions of several types of colour centres were identified and quantified. This characterization provided useful information for the optimization of these confining microstructures and for the development of waveguide colour centre lasers.

The modal-field theory is applied to study the potential performances of an opticalplanar dielectric microcavity based on active color centers in a lithium-fluoride layer. Experimentalangular distributions of the emitted intensity for a low-energy-electron-irradiated lithium-fluoridemicrocavity are compared with theoretical predictions.

He+ ions with an energy of 1.5 -2 MeV and doses ranging from 6 ´ 1013 to 2.5 ´ 1016 ions/cm2 were used to produce primary and aggregate defects in Lithium Fluoride (LiF) crystals. The optical properties of the implanted samples and their dependence on ion dose were studied by means of optical absorption spectroscopy and Scanning Near-field Optical Microscopy (SNOM). The results show the formation, for high doses, of macrodefects such as lithium intrinsic nano-aggregates that could play an important role in the realisation of non-linear optical waveguides

Besides the extinction coe_cient, the refractive index of a dielectricmedium is modi_ed by the presence of resonant absorbing centres, too. Fully an-alytical expressions of the complex refractive index dispersions are derived for thecases of homogeneous and inhomogeneous absorption-line broadening. In both cases,we demonstrate that the modi_cation is such that the refractive index results asincreased at photon energies lower than the resonance absorption energy. If theabsorbing centres also emit Stokes-shifted radiation, the increase of refractive indexcan be exploited for passive and active waveguiding applications. An example isreported regarding active waveguides based on colour centres in a lithium uoridecrystal.Keywords: Absorbing centres, active waveguiding, colour centres, Gaussian line-shape, inhomogeneous line broadening, refractive index.