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A solar-pumped laser (SPL) that converts sunlight directly into a coherent and intense laser beam generally requires a large concentrating lens and precise solar tracking, thereby limiting its potential utility. Here, we demonstrate a fully-planar SPL without a lens or solar tracking. A Nd3+-doped silica fiber is coiled into a cylindrical chamber filled with a sensitizer solution, which acts as a luminescent solar collector. The body of the chamber is highly reflective while the top window is a dichroic mirror that transmits incoming sunlight and traps the fluorescence emitted by the sensitizer. The laser-oscillation threshold was reached at a natural sunlight illumination of 60% on the top window. Calculations indicated that a solar-to-laser power-conversion efficiency could eventually reach 8%. Such an SPL has potential applications in long-term renewable-energy storage or decentralised power supplies for electric vehicles and Internet-of-Things devices. Solar-pumped laser systems are attractive for applications including hydrogen generation and space propulsion, but current technologies are cumbersome and rely on accurate tracking of the sun’s light. Here, lasing is achieved using a planar, luminescent solar collector removing the need for lenses or tracking.

The polarization states of a resonator made of anisotropic mirrors are shown to coalesce into a single eigenstate at the exceptional point and to eliminate spatial hole burning, thereby promoting single mode laser operation.

Anisotropic mirrors are used to form a laser resonator exhibiting non-Hermitian, parity-time (PT) symmetric, polarization states. The relative angle of the two mirrors principal axes is used to control the degree of non-hermiticity. A sharp symmetry-breaking transition is observed at a specific angle, called the exceptional point, where the two states coalesce into a single polarization state and the interference pattern produced by counter-propagating (CP) waves vanishes. At a smaller angle, in the unbroken PT symmetry regime, the polarization state experiencing higher losses is suppressed. In the broken symmetry regime, the two polarization states coexist, but the orthogonality of the CP waves favors single longitudinal mode emission by suppressing the interference pattern of the standing wave. The two regimes meet at the exceptional point, where a unique polarization state exists in a resonator free from interference intensity pattern. Microchip PT-symmetric lasers operating at the exceptional point are thus an attractive solution to achieve single mode operation from a miniature monolithic device without any intra-cavity element., 29 pages, 5 figures

Helically-structured mirrors producing circular Bragg reflection, used as laser mirrors for the twisted-mode operation of compact single frequency microchip lasers, offer better suppression of dual polarization oscillation than linear birefringent nanostruchrred mirrors.

We demonstrate a solar-powered laser (SPL) that does not rely on any concentrator optics or solar tracking system. We believe that the utility of such “unconcentrated” SPLs has considerably increased for energy conversion applications. The proposed SPL consists of a Nd3+-doped fiber as an active medium, a liquid sensitizer, and a housing in which the transmittance of the front window is tailored to work as a luminescent solar collector. The very simple structure of the proposed SPL can be mass-produced easily at a low cost. The lasing threshold is 0.07 W/cm2 (70% of natural sunlight) which is four orders of magnitude smaller than those of conventional SPLs, and the output power at the pumping intensity of 0.1 W/cm2 is 0.25 mW. The SPL exhibits several lasing peaks between 1095 and 1105 nm.

Multimode laser emission generally takes place in homogeneously broadened gain media placed inside a standing-wave resonator due to spatial hole burning. Solutions proposed to eliminate this phenomenon have so far involved the use of intracavity elements, such as an etalon, wave plates or saturable absorbers. We propose a monolithic solution, wherein birefringent layers of T i O 2 are deposited on both laser mirrors. This solution enables one to control the contrast of the interference pattern of the standing wave inside the resonator, and thus the strength of the spatial hole burning, by rotating one mirror around the optical axis. A monochromatic laser emission is demonstrated in a quasi-continuous-wave laser-diode-pumped Y b 3 + : Y A G laser experiment.

The concept of the twisted-mode laser operation, which suppresses spatial hole burning and produces single-mode operation in a standing-wave resonator, is revisited for the case of optically anisotropic laser mirrors presenting arbitrary birefringent and dichroic properties. Our analysis clarifies the relationship between the mirrors’ optical properties and the proximity of the polarization states of the counterpropagating waves, which determines the contrast of the standing-wave pattern inside the resonator. The intensity of the principal mode and the population of the upper laser level as a function of the pumping rate are then determined analytically, which enables estimates of the slope efficiency and threshold of multimode emission for a given contrast value of the standing wave. The inversion density is found to reach an upper bound as a function of the pumping rate for every value of the contrast except unity. The design rules for anisotropic mirrors to produce single-frequency operation are provided that are less strict than those to achieve pure twisted-mode operation.

Background There is a growing interest in the effects of probiotics for the prevention and treatment of skin diseases due to their immunomodulatory and antiinflammatory properties. Objective To assess a mixture of five bacterial strains in the prevention of chronic skin inflammation in mice. Methods Hairless SKH-1 mice received daily oral treatment with the probiotic mixture at the dose of 1x109 Colony-Forming Unit (CFU)/day (or vehicle) for three weeks. Chronic skin inflammation was induced by repeated applications of 12-O-tetradecanoylphorbol-13- acetate (TPA; control mice received acetone). Macroscopic and microscopic evaluations of skin lesions were performed and serum levels of interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, IL-17, IL-22, IL-10 and IL-4 measured at the end of the study. Results Treatment with the probiotic mixture significantly limited the induced chronic skin inflammation at both the macroscopic and microscopic levels. This limitation was consistent with downregulated levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, IL- 17 and IL-22) and up-regulated levels of the anti-inflammatory cytokines, IL-10 and IL-4. Conclusion The results suggest that the probiotic mixture tested could help in preserving skin integrity and homeostasis and that its use could be beneficial in dermatological conditions such as atopic dermatitis and psoriasis.

We present the design and experimental characterization of nanostructured laser mirrors aimed at suppressing spatial hole burning (SHB) of a standing wave resonator. The dielectric Bragg mirrors were made by GLancing Angle Physical Vapor Deposition. Two designs are presented. First, helically-nanostructured materials that produce circular Bragg resonance at the wavelength matching the helical period. Second, thick anisotropic coatings deposited on ordinary mirrors, which act as half-wave plates to produce twisted mode laser operation. Both designs enable single longitudinal mode laser operation by suppressing SHB.

A Monte Carlo ray-tracing simulation was developed for a transversely excited solar-pumped fiber laser without focusing optics. To make this possible, the fiber is immersed in a liquid sensitizer and sandwiched between highly reflective mirrors. The top reflector is dichroic to transmit solar radiation but reflect fluorescence to confine photons that match the absorption band of the active fiber. Simulation was used to evaluate the validity of the concept and optimize device performance. For comparison with the calculations, preliminary experiments were conducted by illuminating a 30 cm aperture, laser module with a solar simulator. The observed gains were in good agreement with the calculations for various conditions, such as sensitizer concentration and mirror reflectivity. Finally, we show that the predicted output power reaches 29 mW when the fiber length is optimized, and it will be enhanced to 150 mW with 0.21% solar-to-laser efficiency under the assumption of a reabsorption-free sensitizer.

The neodymium-doped optical fiber operated at 1.1 μm is a very promising material for the solar-pumped laser without concentrator because of its strong absorption bands in the visible region and its extremely low optical losses. It is generally considered a true four-level system owing to the large energy gap of the lower level of the laser transition to the ground level. In this study, the exquisitely small thermally excited population in the I11/24 Stark level is shown to be primarily responsible for the absorption losses at the laser wavelength at room temperature. Thanks to its long geometry, the absorption cross section and linestrength of the laser transition could be directly measured, allowing easier estimation of the emission cross section than with usual methods relying on fluorescence decay time and quantum efficiency measurements, or a Judd–Ofelt analysis. Our measurements are corroborated by McCumber’s reciprocity principle. The small-signal gain spectrum measured in an amplifier experiment matches well with the emission cross section. Order-of-magnitude loss reduction is demonstrated by lowering the temperature to −34°C, implying substantial reduction of the laser oscillation threshold in cold solar-pumping environments.

A study on Laguerre-Gaussian (LG) modes selection in cw and pulsed Nd:YAG or Yb:YAG ceramic lasers pumped by diodes or an external laser source was carried out. Methods of scalar and vector LG modes selection from low to high orders, involving shaping of the pump profile, usage of intra-cavity lenses, uniaxial crystals and polarization selective mirrors, are considered. CCD camera images of beam profiles of hollow scalar LGpm modes (p -radial, m -azimuth indices) of record high-orders and Bessel-like multi-ring modes with highly directional propagation properties are presented. CW and pulsed ceramic lasers with radially or azimuthally polarized LG vector modes of low and high orders are also demonstrated. Applications of the developed laser schemes and LG beams are discussed. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A polarizing laser mirror made with glancing angle deposition of TiO2 could withstand a train of 2.7 ns pulses with peak power density of around 800 MW/cm2 and a polarization extinction ratio of 1000 when used as an output coupler of a passively Q-switched (Yb0.1Y0.9)3Al5O12 ceramic laser.

Probiotics have been shown to have preventive and therapeutic effects on diarrhea. Because effects tend to be strain specific, benefit of a strain or mixture has to be substantiated by experimental evidence. The aim of this study was to investigate the antidiarrheal and antinociceptive effects of a probiotic mixture (Lactibiane Imedia®, PiLeJe). Castor oil-induced diarrhea test was performed in Wistar rats following oral administration of probiotics (20 × 109, 30 × 109 or 40 × 109 CFU/kg), loperamide (5 mg/kg) or vehicle (water; 10 mL/kg). Time to initial evacuation, number of feces and diarrheal feces, fresh weight and water content of the feces and body weight loss were monitored. Behavioral parameters (eye closing, abnormal posture, activity, fur aspect) were used as pain indices. Probable mechanisms of action were evaluated by using the castor oil-induced enteropooling and charcoal meal transit tests. Probiotics significantly and dose-dependently delayed onset time to first feces and had a beneficial effect on all other parameters (p 90%) at the two highest doses tested (30 × 109 or 40 × 109 CFU/kg) without completely blocking defecation (65.7% at 30 × 109 CFU/kg). Behavioral parameters were improved with probiotics compared to vehicle, improvement that was not observed with loperamide. Probiotics significantly and dose-dependently decreased the volume of intestinal fluid (p

Over the last twenty years, diode pumping of solid-state lasers has opened new prospects for the mode control and formation of Laguerre-Gaussian (LG) beams, enabling a large variety of applications. Experiments on scalar and vector LG modes selection in Nd3+- and Yb3+-doped ceramics and crystal lasers carried out at the Institute for Laser Science, Tokyo are reviewed. Selection of LG modes from low to high orders using intra-cavity elements, polarization-selective mirrors, or shaping the pump beam profile, is considered. Illustrations of record-high-order LG hollow modes, multiring modes with highly directional propagation properties, characteristics of cw and pulsed lasers with radially or azimuthally polarized beams of high polarization purity are presented. General solutions of the wave equation for the axi-symmetric electric field, which describe LG beams of various profiles, are proposed for data analysis. In parallel, a short review on LG modes selection studies carried out at other laboratories is given.

We report an experimental investigation on the thermal effects in a Nd3+:Y3Al5O12 nanocrystalline-powder random laser with a one-mirror structure by quasi-continuous-wave laser diode pumping. Extremely low thermal conductivity in powder and significant temperature dependence of the narrow emission spectrum of Nd3+:Y3Al5O12 leads to a laser line redshift and gain reduction with a higher heat deposit. Mode drifting induced by the temperature dependence of the refractive index is also discussed.

Room-temperature cw laser oscillations at 1030 and 1075 nm wavelengths were demonstrated for the TEM00 mode with Yb3+:Y2O3 ceramics by LD-pumping. A maximum extraction efficiency of 72% at 1075 nm lasing wavelengths and of 45% at 1030 nm lasing wavelengths were observed.

A polarizing laser mirror was made of an alternating sequence of low and high refractive index layers of titanium oxide using glancing angle deposition (GLAD). Large refractive index contrast and large birefringence, reaching 0.5 and 0.1, respectively, could be obtained from one single raw material by changing the deposition conditions. The laser mirror could withstand a train of 2.7 ns, single-mode pulses at 680 Hz, λ=1030 nm, and peak power density of 670 MW/cm2 when used as an output coupler of a passively Q-switched (Yb0.1Y0.9)3Al5O12 ceramic laser. The polarization extinction ratio was found to be better than 30 dB both in continuous-wave and pulsed regimes. These results indicate that polarizing laser mirrors made from nanostructured thin films with GLAD, in addition to being simple to fabricate, can withstand high pulse energy density.

Bulk laser damage thresholds of doped and undoped ceramic Y3Al5O12 (YAG) materials are reported. These materials were found to resist 100 J/cm2, 4-ns pulses at 1.064 µm wavelength. Single-crystal YAG materials of similar composition yielded similar damage thresholds. Hence, ceramic microstructure does not contribute to lower damage threshold. Beam-size dependence of damage threshold fluence was also studied by repeating the experiment using a lens with a longer focal length. The evolution of damage probability with laser fluence was found to strongly depend on the beam diameter; however, damage threshold was not found to vary significantly with beam diameter.

In a recent clinical study, we demonstrated in the general population that Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 (PF) taken in combination for 30 days decreased the global scores of hospital anxiety and depression scale (HADs), and the global severity index of the Hopkins symptoms checklist (HSCL-90), due to the decrease of the sub-scores of somatization, depression and anger-hostility spheres. Therefore, oral intake of PF showed beneficial effects on anxiety and depression related behaviors in human volunteers. From there, it is interesting to focus on the role of this probiotic formulation in the subjects with the lowest urinary free cortisol levels at baseline.This addendum presents a secondary analyse of the effects of PF in a sub-population of 25 subjects with urinary free cortisol (UFC) levels less than 50 ng/ml at baseline, on psychological distress based on the percentage of change of the perceived stress scale (PSs), the HADs and the HSCL-90 scores between baseline and f...

In a previous clinical study, a probiotic formulation (PF) consisting ofLactobacillus helveticusR0052 andBifidobacterium longumR0175 (PF) decreased stress-induced gastrointestinal discomfort. Emerging evidence of a role for gut microbiota on central nervous system functions therefore suggests that oral intake of probiotics may have beneficial consequences on mood and psychological distress. The aim of the present study was to investigate the anxiolytic-like activity of PF in rats, and its possible effects on anxiety, depression, stress and coping strategies in healthy human volunteers. In the preclinical study, rats were daily administered PF for 2 weeks and subsequently tested in the conditioned defensive burying test, a screening model for anti-anxiety agents. In the clinical trial, volunteers participated in a double-blind, placebo-controlled, randomised parallel group study with PF administered for 30 d and assessed with the Hopkins Symptom Checklist (HSCL-90), the Hospital Anxiety and Depression Scale (HADS), the Perceived Stress Scale, the Coping Checklist (CCL) and 24 h urinary free cortisol (UFC). Daily subchronic administration of PF significantly reduced anxiety-like behaviour in rats (P P P P P P P P P L. helveticusR0052 andB. longumR0175 taken in combination display anxiolytic-like activity in rats and beneficial psychological effects in healthy human volunteers.

A new animal model of travelers' diarrhea has been developed by infecting rats orally with a strain of enterotoxigenic Escherichia coli in order to assess the efficacy of three probiotic formulations for the prevention of travelers' diarrhea. Five groups of six rats were given daily (by oral gavage) either a placebo (negative and positive control groups), the suspension of bacterial probiotics called FF1, the yeast probiotic Saccharomyces boulardii, or a combination of both, called Protecflor(TM). After 14 days of treatment, all groups except the negative control one were infected by oral administration of E. coli. Body temperature, body weight, food and water consumption, stools consistency, behavior, and cytokines secretion were disturbed following E. coli infection. Probiotics-treated groups generally displayed less-pronounced symptoms, the combination of probiotics Protecflor(TM) being the most effective.

The photoconductivity of high Yb-concentration YAG and Y2O3 samples has been measured, confirming the occurrence of up-conversion in these materials. High intensity pumping reveals a very broad emission spectrum that exhibits avalanche behaviour.

Neodymium-doped silica glass fiber is pumped by a Xe arc lamp as a simulated solar light. The fiber is immersed in rhodamine 6G solution to enhance the photon flux at the 588 nm absorption band of the Nd3+. The chamber that contains the active fiber and dye solution is made of a pair of reflectors. The bottom reflector is highly reflective over the entire visible spectrum, while the top reflector is a short-pass dichroic mirror whose cutoff wavelength is set at 580 nm. As a result, the dye fluorescence of the absorption band is confined by the multiple reflections, like a “greenhouse effect”. The expected confinement factor as a function of the angular-dependent reflectivity of the reflectors is discussed. The highest gain observed is 1.0 ×10-2 m-1 when the lamp light intensity is 2.7 W/cm2.

We present a device that can modulate the orbital angular momentum (AOM) of a laser beam The proposed design can be scaled up to several GHz using existing commercial devices, while the output power can also be scaled to values determined by state-of-the-art high-power lasers. This device will find applications in laser processing and for the characterization of metamaterials.