1,354,746 research outputs found
Re-based inorganic-crystal nanofibers produced by electrospinning for photonic applications
No full textElectrospinning is an effective and inexpensive technique to grow polymer materials in nanofiber shape with exceptionally high surface-area-to-volume ratio. Although it has been known for about a century, it has gained much interest in the new millennium thanks to its low cost and versatility, which has permitted to obtain a large variety of multifunctional compositions with a rich collection of new possible applications. Rare-earth doped materials possess many remarkable features that have been exploited, for example, for diode pumped bulk solid-state lasers in the visible and near infrared regions, or for biomedical applications when grown in nanometric form. In the last few decades, electrospinning preparation of rare-earth-doped crystal nanofibers has been developed and many different materials have been successfully grown. Crystal host, crystal quality and nanosized shape can deeply influence the optical properties of embedded rare earth ions; therefore, a large number of papers has recently been devoted to the growth and characterization of rare earth doped nanofibers with the electrospinning technique and an up-to-date review of this rapidly developing topic is missing; This review paper is devoted to the presentation of the main results obtained in this field up to now with particular insight into the optical characterization of the various materials grown with this technique
Light in the darkness
No full textLaser light is usually limited to the same wavelength range as the spontaneous emission of the active material. A judicious choice of dielectric coatings on the cavity has now enabled laser emission far beyond the spectral range of the gain medium
Upconversion enhancement in Yb3+,Tm3+:BaY2F8 quasi-nanoparticles
No full textYb3+Tm3+:BaY2F8 single crystals have been milled to quasi-nanometric size. A complete characterization
of the quasi-nanoparticles has been compared with that of a bulk crystal with the same
composition. The emission spectra did not show any difference as for the shape and relative intensity
of the various peaks within each band, but the infrared lifetime of the quasi-nanoparticles is
significantly longer than that of the bulk crystal. In agreement with other literature results we
observed a strong increase of the upconverted luminescence intensity in the quasi-nanoparticles. An
explanation is given as the effect of radiation trapping of the pumping radiation that increases the
effective pump intensity in the volume of the quasi-nanoparticles with respect to the bulk crystal
Study of the evolution in space and time of water diffusion in a leaf through a sub-terahertz portable imaging system
No full textAmong the non-destructive techniques capable of obtaining information on biological systems even in vivo, terahertz-based techniques are emerging due to their specificity to the water content, which can represent an important indicator of the presence of microorganisms and, in general, of the health status, particularly in plants. Nevertheless, the analysis of the extracted data (especially for images) and the exploitation of the potential of the technique for the study of the complex phenomena that occur in living tissues are still almost unexplored fields. In this work, the hydration status of leaves both in vivo and ex vivo was monitored continuously and non-destructively by acquiring videos in the sub-terahertz range through a portable imaging system. A model for describing the water flow in space and time in the midvein of a leaf is obtained which is suitable for the analysis of the data extracted from the portable sub-terahertz imaging system. These results show that terahertz-based technology can be used to study biological phenomena even in vivo; moreover, they pave the way for the introduction of a general method for the analysis of terahertz data based on surface fits in space and in time as well
Spectroscopy and dynamic measurements of Tm,Dy : BaY2F8 crystal
No full textA Tm, Dy:BaY2F8 crystal is studied in order to develop a solid state laser device pumped by a diode laser. Spectroscopic results include the measurements of the absorption and fluorescence spectra of both Tm and Dy at various crystal temperatures. Moreover, we measured the lifetime and deduced the emission cross-section of the H-6(13/2) --> H-6(15/2) Dy transition in the 3 mu m wavelength region. We also calculated the radiative lifetime of the upper multiplet and estimated the phonon energy of the crystal. (C) 1999 Elsevier Science B.V. All rights reserved
Mid-infrared spectroscopy of Pr3+:Lu2O3 single crystal
No full textRare earth-doped crystals and fibers have long been used as laser active media in the UV, VIS, and NIR spectral regions, but only a limited number of materials have shown laser emission beyond 3 μm, mainly because of the competition between radiative and non-radiative processes that limit the emission efficiency of these materials at long wavelengths. The ideal material must have excellent crystal quality, good thermo-physical parameters, wide transparency region in the mid infrared (MIR) and low phonon energies. Most of the research has been focused on fluorides, bromides and chlorides [1], but these compounds are often hygroscopic and/or the optical quality of grown samples (especially chlorides and bromides) is low both for the presence of scattering centers and contamination with quenching centers
Picosecond Nd:BaY2F8 laser discretely tunable around 1 micron
No full textPassive mode-locking of a diode-pumped Nd:BaY(2)F(8) (Nd:BaYF) was achieved on four lines in the range 1040-1074 nm, employing a semiconductor saturable absorber mirror (SAM). Nearly Fourier-limited pulses with durations of 2.6 to 7.2 ps and output power a parts per thousand 50 mW were generated in a dispersion-controlled resonator using a single prism for wavelength selection, tuning and dispersion management
Spectroscopic characterization of Er,Yb:Y2Ti2O7 nanoparticles for forensic applications
No full textFingerprint identification technology has been widely utilized in the forensic field, given that the fingerprint is unique for each person and each finger and does not vary with age. In general, the fingerprints at a crime scene are latent and difficult to collect if the fingers were not contaminated with coloured materials, such as blood, ink or pigment. Moreover, the fingerprints on a smooth plane or transparent glass are hard to be visualized with traditional methods
Comparison of Tm-sensitized Ho:YAG and Ho:YLF crystals for a laser-pumped 2 mu m CW oscillator
No full textWe report on a comparison of YAG and YLF crystals for Tm,Ho based CW laser systems operating at 2 mu m. As pump source we have used both a Ti:Al2O3 laser and an array of diode lasers in order to quantitatively assess the relevance of the pump beam spatial features on the 2 mu m laser performance. The results are compared with the predictions of a computer simulation using a rate equation model
Mechanical oscillations in lasing microspheres
No full textThis is the preprint version of the paper available at: https://dx.doi.org/10.1063/1.4997182
A. Toncelli, N. E. Capuj, B. Garrido, M. Sledzinska, C. M. Sotomayor-Torres, A. Tredicucci, D. Navarro-Urrios. Mechanical oscillations in lasing microspheres. Journal of Applied Physics, 2017, 122:
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