Waveguide lasers based on dielectric materials

Fifty years since the invention of the laser have been witness of the development of many different laser systems and designs. Among them, miniaturized versions of solid sate lasers based on rare-earth-doped dielectric materials have been proposed and demonstrated during the last 20 years. They are based on confined radiation provided by optical waveguide structures. Although many materials and techniques have been studied for producing planar and channel waveguides, only a few of them have shown to be adequate routes for fabricating waveguide lasers. Here we summarize the theory and specific technologies developed for characterizing waveguide structures, and we present some common fabrication techniques already successfully applied to fabricate dielectric waveguide lasers, where relevant examples of demonstrated working devices are outlined.     

Optical spectroscopy of Dy ions in LiNbO3

A systematic spectroscopic study of Dy³⁺ doped LiNbO₃ is presented. The energy position of the Stark levels and their symmetry character is given for most of the multiplets. Luminescence of this system has been investigated in the visible and infrared. The only emitting state in this region is the metastable 4F_9/2 multiplet whose life time is temperature independent and with a value of 186 μs. Evidence about Dy³⁺ multicentres is also discussed.     

Quantum Dot‐Based Thermal Spectroscopy and Imaging of Optically Trapped Microspheres and Single Cells

Laser‐induced thermal effects in optically trapped microspheres and single cells are investigated by quantum dot luminescence thermometry. Thermal spectroscopy has revealed a non‐localized temperature distribution around the trap that extends over tens of micrometers, in agreement with previous theoretical models besides identifying water absorption as the most important heating source. The experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping wavelength exists for biological applications close to 820 nm. This is corroborated by a simultaneous analysis of the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. This quantum dot luminescence thermometry demonstrates that optical trapping with 820 nm laser radiation produces minimum intracellular heating, well below the cytotoxic level (43 °C), thus, avoiding cell damage.     

Properties of Nd3+-doped and undoped tetragonal PbWO4, NaY(WO4)2, CaWO4, and undoped monoclinic ZnWO4 and CdWO4 as laser-active and stimulated raman scattering-active crystals

Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.     

Neodymium‐Doped LaF3 Nanoparticles for Fluorescence Bioimaging in the Second Biological Window

The future perspective of fluorescence imaging for real in vivo application are based on novel efficient nanoparticles which is able to emit in the second biological window (1000–1400 nm). In this work, the potential application of Nd³⁺‐doped LaF₃ (Nd³⁺:LaF₃) nanoparticles is reported for fluorescence bioimaging in both the first and second biological windows based on their three main emission channels of Nd³⁺ ions: ⁴F_3/2→⁴I_9/2, ⁴F_3/2→⁴I_11/2 and ⁴F_3/2→⁴I_13/2 that lead to emissions at around 910, 1050, and 1330 nm, respectively. By systematically comparing the relative emission intensities, penetration depths and subtissue optical dispersion of each transition we propose that optimum subtissue images based on Nd³⁺:LaF₃ nanoparticles are obtained by using the ⁴F_3/2→⁴I_11/2 (1050 nm) emission band (lying in the second biological window) instead of the traditionally used ⁴F_3/2→⁴I_9/2 (910 nm, in the first biological window). After determining the optimum emission channel, it is used to obtain both in vitro and in vivo images by the controlled incorporation of Nd³⁺:LaF₃ nanoparticles in cancer cells and mice. Nd³⁺:LaF₃ nanoparticles thus emerge as very promising fluorescent nanoprobes for bioimaging in the second biological window.     

Transient charging currents in annealed bulk polyethylene

Transient charging currents resulting from the application of a low constant voltage, up to 2×10⁴ V cm^–1, are investigated in melt crystallized samples of high density polyethylene. Three distinct regions can be clearly distinguished in the current-field characteristic curves at a given time after application of a voltage: (a) a linear region at a low electric field, (b) a negative resistance region in which the slope is negative at a medium electric field, (c) a superlinear region at a high electric field. At low electric fields and for charging times less than 10³ sec the law of dielectric response, l t ^–n , is obeyed. It is shown that the type of cooling process, after annealing at temperatures near 75° C, markedly influences the current decay. Annealing at this temperature is associated with a partial rearrangement of the lamellar microstructure. The current is enhanced after quenching while it decreases after slow cooling. Various mechanisms to explain the obtained data are considered.     

Quantum Dots Emitting in the Third Biological Window as Bimodal Contrast Agents for Cardiovascular Imaging

Physicians are demanding innovative technologies for multimodal imaging of the cardiovascular system that would lead to the appearance of advanced diagnosis and therapy procedures. This implies the simultaneous development of new imaging techniques and contrast agents whose synergy would make it possible. Optical coherence tomography (OCT) has recently emerged as a versatile and high‐resolution clinical technique for cardiovascular imaging. Unfortunately, the lack of adequate contrast agents impedes the use of OCT for intracoronary multimodal imaging. In this work, the hitherto unexplored capability of semiconductor quantum dots (IR‐QDs) emitting in the third infrared biological window (1.55–1.87 µm) to act as multimodal agents for intracoronary imaging is demonstrated. Under single line laser excitation at 1.3 µm, IR‐QDs are capable of providing simultaneous backscattering contrast and efficient luminescence at 1.6 µm. In this work, backscattered radiation is successfully employed to construct OCT images in both fluids and tissues whereas the infrared luminescence of the IR‐QDs provides the possibility for simultaneous acquisition of high penetrating fluorescence images. The first multimodal (fluorescence + OCT) imaging of an artery using IR‐QDs as contrast agents is provided herein demonstrating their outstanding potential for future clinical applications.     

Fifteen years after September 11: Where is the medical research heading? A scientometric analysis

The attacks of 9-11 have been not only the cause of the deaths of thousands of people but have also had an enormous impact on the health of the survivors, the rescue workers, the fire fighters and many more people worldwide. This study aims to depict a representative global picture of the research output of 15 years after the attacks of 9-11 by analyzing the bibliometric data of the overall publications with particular focus on medical topics. This study subsequently deepens the scientometric approach of the overall terrorism research of Magnone in 2014, also published in Scientometrics. The USA has published the most by far, taking the absolute numbers into account. When evaluating citation or socio-economic ratios, Israel takes first place. The main collaborating partner of the USA is the UK, followed by Canada. The share of European countries is rising over time, linked with the terror attacks in European cities. There are only a few other countries involved. Prospective study approaches should be concentrated on international performances as a contribution in dealing with terrorism, its causes and its consequences. The improved access and involvement of other countries’ scientists in the research and publication processes by a greater network would be an important component in facing international terrorism.     

Instantaneous In Vivo Imaging of Acute Myocardial Infarct by NIR‐II Luminescent Nanodots

Fast and precise localization of ischemic tissues in the myocardium after an acute infarct is required by clinicians as the first step toward accurate and efficient treatment. Nowadays, diagnosis of a heart attack at early times is based on biochemical blood analysis (detection of cardiac enzymes) or by ultrasound‐assisted imaging. Alternative approaches are investigated to overcome the limitations of these classical techniques (time‐consuming procedures or low spatial resolution). As occurs in many other fields of biomedicine, cardiological preclinical imaging can also benefit from the fast development of nanotechnology. Indeed, bio‐functionalized near‐infrared‐emitting nanoparticles are herein used for in vivo imaging of the heart after an acute myocardial infarct. Taking advantage of the superior acquisition speed of near‐infrared fluorescence imaging, and of the efficient selective targeting of the near‐infrared‐emitting nanoparticles, in vivo images of the infarcted heart are obtained only a few minutes after the acute infarction event. This work opens an avenue toward cost‐effective, fast, and accurate in vivo imaging of the ischemic myocardium after an acute infarct.