G. Baldacchini

Radiation trapping and self-quenching analysis in Yb3+, Er3+, and Ho3+ doped Y2O3

Abstract The combined case of self-trapping and self-quenching in the lifetime analysis of Yb, Er, and Ho doped Y 2 O 3 single crystal fiber is studied. After deconvoluting theoretically the measured lifetime points, it is shown that self-quenching, for a rather large doping range, is well described by a limited diffusion process within the doping ion subsystem towards impurities analogous to the doping ions themselves. Fast diffusion towards intrinsic non-radiative centers cannot explain the observed results. As an application, a simple quantitative method for optimizing the gain material concentration for amplifiers and lasers is proposed and performed.

Experimental and theoretical investigation of self‐broadening and self‐shifting of ammonia transition lines in the ν2 band

We have measured self‐broadenings and self‐shiftings of several rotovibrational transitions of the ν2 band of NH3. We have found smaller broadenings and bigger shifts with respect to the known data of the inversion spectrum in the microwave region. The experimental results are compared with the Anderson original line broadening theory, successively extended in order to calculate the shift also. The agreement between experiments and theory is quite good so that it is possible to select the right procedure among those usually adopted in order to avoid divergences occurring in the Anderson’s perturbative treatment of the molecular collision matrix.

Soft x-ray submicron imaging detector based on point defects in LiF

The use of lithium fluoride (LiF) crystals and films as imaging detectors for EUV and soft-x-ray radiation is discussed. The EUV or soft-x-ray radiation can generate stable color centers, emitting in the visible spectral range an intense fluorescence from the exposed areas. The high dynamic response of the material to the received dose and the atomic scale of the color centers make this detector extremely interesting for imaging at a spatial resolution which can be much smaller than the light wavelength. Experimental results of contact microscopy imaging of test meshes demonstrate a resolution of the order of 400nm. This high spatial resolution has been obtained in a wide field of view, up to several mm2. Images obtained on different biological samples, as well as an investigation of a soft x-ray laser beam are presented. The behavior of the generated color centers density as a function of the deposited x-ray dose and the advantages of this new diagnostic technique for both coherent and noncoherent EUV so...

LIF FILMS : PRODUCTION AND CHARACTERIZATION

Abstract LiF films were produced by thermal evaporation onto amorphous substrates kept (during evaporation) at temperatures ranging from ambient up to 350°C. The evolution through two polycrystalline states was analysed by X-ray diffraction techniques, which also revealed that the LiF film lattice parameter is equal to that of LiF crystal. The refractive index of the produced films was measured by transmission optical interferometry. Talisurf-6 profilometer measurements on the film surface show sharp edges and very smooth surfaces, which reflect the substrate surfaces.

Colored LiF: an optical material for all seasons

Colored LiF salt has been always considered a singular optical material among alkali halides and other dielectric crystals for its peculiar characteristics, which in due time have been applied with success in thermoluminescence and laser technology. Lately, while the two previous topics have been revived, new relevant results have been obtained in the optoelectronic field by using both bulk crystals and newly characterized thin films. In practice, miniaturized photoluminescent patterns can be produced rather easily by using low-energy electron beams and soft X-rays. So, LiF salt is becoming a new interesting photonic material with promising developments in basic reasearch and applications as well.

New perspectives of coloured LiF for optoelectronic devices

Colour centre lasers (CCL) based on LiF crystals have been operating at room temperature (RT) in the visible and in the near infrared since many years. On the other hand little is known about LiF films treated by low energy electrons, which are promising candidates for the realisation of miniaturised broad band active optical devices, like waveguide and microcavity amplifiers and lasers. The high concentration of defects produced in these optically confined active structures does not seem to affect appreciably the numerical value of the gain coefficients, although complex mechanisms of losses should be taken into account. Interactions among several types of defects in extremely coloured samples should be further investigated in crystals and films. The formation of different kind of centres could be controlled by a careful choice of irradiation conditions and growth parameters in the polycrystalline films.

LiF films: absorption and luminescence of colour centres

Abstract LiF films 1 μm thick have been produced by thermal evaporation on amorphous silica substrates. X-ray diffraction has shown the existence of a polycrystalline structure. The films were subjected at room temperature to electron beam irradiation of energy 3 keV and current 120 μA on anea of about 0.5 cm2. This irradiation produced F2 and F3+ centres stable at room temperature that were observed by light absorption measurements. Although the concentration of the centres was much higher than that obtained usually in bulk crystals, luminescence was also observed.

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.

Photoluminescence of LiF crystal colored by a focused electron beam

Abstract The absorption, emission and excitation optical spectra of F2 and F+3 color centers generated in LiF through low energy (30 keV) electron beam irradiation were measured at room temperature by pumping with an Ar+ laser the resulting thin colored layer. A quenching of the emission intensity of the F+3 centers versus the pump power was observed, with characteristics similar to bulk colored crystals. The analysis of the photoemission spectra showed a new band, which has been discovered previously also in bulk crystals colored and treated in different ways. The possibility of applications of the colored ribbon for miniaturized laser devices is commented.

Scanning near-field optical microscopy images of microradiographs stored in lithium fluoride films with an optical resolution of λ∕12

Here we show a new, simple method to observe soft x-ray microradiographs of biological material. A thin film of lithium fluoride (LiF) works as image detector, storing the microradiograph obtained exposing biological samples to extreme ultraviolet and soft x-ray radiations. To read the stored image, collecting the optically stimulated visible luminescence emitted by the LiF active color centers locally produced by the x rays, a scanning near-field optical microscope is used with an optical aperture of 50nm, i.e., λ∕12, where λ is the wavelength of the collected photoluminescence.