Unifying Frequency Combs in Active and Passive Cavities: Temporal Solitons in Externally Driven Ring Lasers.

Frequency combs have become a prominent research area in optics. Of particular interest as integrated comb technology are chip-scale sources, such as semiconductor lasers and microresonators, which consist of resonators embedding a nonlinear medium either with or without population inversion. Such active and passive cavities were so far treated distinctly. Here we propose a formal unification by introducing a general equation that describes both types of cavities. The equation also captures the physics of a hybrid device-a semiconductor ring laser with an external optical drive-in which we show the existence of temporal solitons, previously identified only in microresonators, thanks to symmetry breaking and self-localization phenomena typical of spatially extended dissipative systems.

Direct thermo-optical tuning of silicon microresonators for the mid-infrared.

We use light from a visible laser diode to directly tune silicon-on-chip microresonators by thermo-optical effect. We show that this direct tuning is local, non invasive and has a much smaller time constant than global temperature tuning methods. Such an approach could prove to be highly effective for Kerr comb generation in microresonators pumped by quantum cascade lasers, which cannot be easily tuned to achieve comb generation and soliton-mode locked states.

Achromatic Metalens over 60 nm Bandwidth in the Visible and Metalens with Reverse Chromatic Dispersion.

In this Letter, we experimentally report an achromatic metalens (AML) operating over a continuous bandwidth in the visible. This is accomplished via dispersion engineering of dielectric phase shifters: titanium dioxide nanopillars tiled on a dielectric spacer layer above a metallic mirror. The AML works in reflection mode with a focal length independent of wavelength from λ = 490 to 550 nm. We also design a metalens with reverse chromatic dispersion, where the focal length increases as the wavelength increases, contrary to conventional diffractive lenses. The ability to engineer the chromatic dispersion of metalenses at will enables a wide variety of applications that were not previously possible. In particular, for the AML design, we envision applications such as imaging under LED illumination, fluorescence, and photoluminescence spectroscopy.

Super-Dispersive Off-Axis Meta-Lenses for Compact High Resolution Spectroscopy.

Metasurfaces have opened a new frontier in the miniaturization of optical technology by allowing exceptional control over the wavefront. Here, we demonstrate off-axis meta-lenses that simultaneously focus and disperse light of different wavelengths with unprecedented spectral resolution. They are designed based on the geometric phase via rotated silicon nanofins and can focus light at angles as large as 80°. Due to the large angle focusing, these meta-lenses have superdispersive characteristics (0.27 nm/mrad) that make them capable of resolving wavelength differences as small as 200 pm in the telecom region. In addition, by stitching several meta-lenses together, we maintain a high spectral resolution for a wider wavelength range. The meta-lenses have measured efficiencies as high as 90% in the wavelength range of 1.1 to 1.6 µm. The planar and compact configuration together with high spectral resolution of these meta-lenses has significant potential for emerging portable/wearable optics technology.

Multispectral Chiral Imaging with a Metalens.

The vast majority of biologically active compounds, ranging from amino acids to essential nutrients such as glucose, possess intrinsic handedness. This in turn gives rise to chiral optical properties that provide a basis for detecting and quantifying enantio-specific concentrations of these molecules. However, traditional chiroptical spectroscopy and imaging techniques require cascading of multiple optical components in sophisticated setups. Here, we present a planar lens with an engineered dispersive response, which simultaneously forms two images with opposite helicity of an object within the same field-of-view. In this way, chiroptical properties can be probed across the visible spectrum using only the lens and a camera without the addition of polarizers or dispersive optical devices. We map the circular dichroism of the exoskeleton of a chiral beetle, Chrysina gloriosa, which is known to exhibit high reflectivity of left-circularly polarized light, with high spatial resolution limited by the numerical aperture of the planar lens. Our results demonstrate the potential of metasurfaces in realizing a compact and multifunctional device with unprecedented imaging capabilities.

Polarization-Insensitive Metalenses at Visible Wavelengths.

In this Letter, we demonstrate highly efficient, polarization-insensitive planar lenses (metalenses) at red, green, and blue wavelengths (λ = 660, 532, and 405 nm). Metalenses with numerical apertures (NA) of 0.85 and 0.6 and corresponding efficiencies as high as 60% and 90% are achieved. These metalenses are less than 600 nm-thick and can focus incident light down to diffraction-limited spots as small as ∼0.64λ and provide high-resolution imaging. In addition, the focal spots are very symmetric with high Strehl ratios. The single step lithography and compatibility with large-scale fabrication processes make metalenses highly promising for widespread applications in imaging and spectroscopy.

Early childhood caries underweight or overweight, that is the question.

AIM: The purpose of this retrospective case study is to describe the body mass index in a group of children, from 3 to 6 years old with ECC and a similar group of caries-free children. MATERIALS AND METHODS: This case-control analysis involves two groups of children: the first was of 244 healthy children, 3 to 6 year-old and caries-free; the second was of 586 otherwise healthy children, same age, with Early Childhood Caries divided into three subgroups according the AAPD definition. Demographics, dmft, number teeth with pulpal involvement, BMI percentile, weight at birth, weight and height of both parents were measured during the clinical evaluation. Statistical analyses were performed using standard statistical software (SPSS Version 13). BMI distribution of the subjects with caries was graphically compared with the use of confidence intervals to a similar caries-free sample. RESULTS: Results are expressed as mean ± SD and frequencies (percentages), depending on the data type. The distribution of BMI percentiles of the ECC group was: underweight = 10%; normal weight = 55.90%; at risk of overweight = 22.22 %; overweight = 11.11%. Significantly, more children in the case group were underweight than in the control group (10% vs. 4.94%). CONCLUSION: The ECC population does not have a typical weight distribution, and the underweight finding in a significant number of Severe ECC (S-ECC) children may be due to the chewing alteration related to the dental pain due to caries and to missing teeth after hard tissues breakdown.

[Oral health and pregnancy: promotion of oral health during the pre-natal training in the Latina province]. / Salute orale e gravidanza: promozione sanitaria nei consultori di Latina e provincia.

The aim of this study, conducted in the Province of Latina, was to verify knowledge, attitudes, and lifestyles in relation to oral health in a sample of pregnant women, assessing their subjective perception of oral health, and highlight prenatal dental prevention need specialist in the area and provide adequate information on the importance of good oral hygiene in order to achieve a better health level both of the mother and the child. The study was conducted on a sample of pregnant women between the 26th and 39th gestational week, in the period from June to October 2009, during the childbirth training courses in the Province of Latina. Each patient was administered a questionnaire for the assessment of oral habits during pregnancy and for the definition of specific knowledge on and perception of themselves and their own oral condition. The survey shows that more than one third of the sample reported visiting a dentist only in case of pain, over half (56.9%) did not undergo any dental visit during the gestational period, only 24 subjects (33.3%) having applied to a dental hygienist for professional oral hygiene and that only 7 out of 72 women had been prescribed a dental checkup by a gynecologist. The study showed that knowledge about dental problems that may arise during pregnancy is insufficient to guarantee a good threshold to oral health care for the mother hence the need to promote information programs, oral health and pregnancy prevention and training in the territory mainly directed to health-care specialists (gynecologists and obstetricians) and to pregnant women.

Slow light nanocoatings for ultrashort pulse compression.

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays' performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications.

Dynamics of actively mode-locked Quantum Cascade Lasers.

The impact of upper state lifetime and spatial hole burning on pulse shape and stability in actively mode locked QCLs is investigated by numerical simulations. It is shown that an extended upper state lifetime is necessary to achieve stable isolated pulse formation per roundtrip. Spatial hole burning helps to reduce the pulse duration by supporting broadband multimode lasing, but introduces pulse instabilities which eventually lead to strongly structured pulse shapes that further degrade with increased pumping. At high pumping levels gain saturation and recovery between pulses leads to suppression of mode locking. In the absence of spatial hole burning the laser approaches single-mode lasing, while in the presence of spatial hole burning the mode locking becomes unstable and the laser dynamics does not reach a steady state anymore.

Band-gap engineering: from physics and materials to new semiconductor devices.

Band-gap engineering is a powerful technique for the design of new semiconductor materials and devices. Heterojunctions and modern growth techniques, such as molecular beam epitaxy, allow band diagrams with nearly arbitrary and continuous band-gap variations to be made. The transport properties of electrons and holes can be independently and continuously tuned for a given application. A new generation of devices with unique capabilities, ranging from solid-state photomultipliers to resonant tunneling transistors, is emerging from this approach.

Quantum mechanical actuation of microelectromechanical systems by the Casimir force.

The Casimir force is the attraction between uncharged metallic surfaces as a result of quantum mechanical vacuum fluctuations of the electromagnetic field. We demonstrate the Casimir effect in microelectromechanical systems using a micromachined torsional device. Attraction between a polysilicon plate and a spherical metallic surface results in a torque that rotates the plate about two thin torsional rods. The dependence of the rotation angle on the separation between the surfaces is in agreement with calculations of the Casimir force. Our results show that quantum electrodynamical effects play a significant role in such microelectromechanical systems when the separation between components is in the nanometer range.

Quantum cascade laser.

A semiconductor injection laser that differs in a fundamental way from diode lasers has been demonstrated. It is built out of quantum semiconductor structures that were grown by molecular beam epitaxy and designed by band structure engineering. Electrons streaming down a potential staircase sequentially emit photons at the steps. The steps consist of coupled quantum wells in which population inversion between discrete conduction band excited states is achieved by control of tunneling. A strong narrowing of the emission spectrum, above threshold, provides direct evidence of laser action at a wavelength of 4.2 micrometers with peak powers in excess of 8 milliwatts in pulsed operation. In quantum cascade lasers, the wavelength, entirely determined by quantum confinement, can be tailored from the mid-infrared to the submillimeter wave region in the same heterostructure material.

Self-mode-locking of quantum cascade lasers with giant ultrafast optical nonlinearities.

We report on the generation of picosecond self-mode-locked pulses from midinfrared quantum cascade lasers, at wavelengths within the important molecular fingerprint region. These devices are based on intersubband electron transitions in semiconductor nanostructures, which are characterized by some of the largest optical nonlinearities observed in nature and by picosecond relaxation lifetimes. Our results are interpreted with a model in which one of these nonlinearities, the intensity-dependent refractive index of the lasing transition, creates a nonlinear waveguide where the optical losses decrease with increasing intensity. This favors the generation of ultrashort pulses, because of their larger instantaneous intensity relative to continuous-wave emission.

School-age dental screening: oral health and eating habits.

AIM: the study has the purpose to evaluate the association between clinical data collected from dental screening carried out on children and their eating habits. Materials and methods: The dental screening was carried out on a sample of eight-year-old children attending the third grade of the elementary schools of Gaeta (Latina). Clinical data and periodontal status indexes were recorded. The descriptive statistics (mean, standard deviation, frequency) of all data were calculated and anova analysis and chi square test have been performed. RESULTS: On the sample of 70 children the results showed an average of 1.4 decayed teeth per child (sd ± 2.3) with a slightly higher average in females. More than 68% of the sample had poor or insufficient oral hygiene conditions with plaque presence in 64% of cases. Moreover, 57% of children had class II malocclusion with increased overjet and oral breathing respectively in 37% and 30% of cases. Only 24% were breastfed in the first months of life and more than 40% maintained a bad habit for over two years of age. About eating habits, more than 80% of the sample consumed sweets or sweet drinks every day. The analysis of the data showed as children consume several snacks throughout the day, and 47% eat them watching TV. CONCLUSIONS: The results of this study showed how prevention program carried out through the School is more effective on children for learning of content especially when the acquisition of knowledge follows the application and verification of theoretical and practical skills in terms of oral health.

Cannabidiol, extracted from Cannabis sativa, selectively inhibits inflammatory hypermotility in mice.

BACKGROUND AND PURPOSE: Cannabidiol is a Cannabis-derived non-psychotropic compound that exerts a plethora of pharmacological actions, including anti-inflammatory, neuroprotective and antitumour effects, with potential therapeutic interest. However, the actions of cannabidiol in the digestive tract are largely unexplored. In the present study, we investigated the effect of cannabidiol on intestinal motility in normal (control) mice and in mice with intestinal inflammation. EXPERIMENTAL APPROACH: Motility in vivo was measured by evaluating the distribution of an orally administered fluorescent marker along the small intestine; intestinal inflammation was induced by the irritant croton oil; contractility in vitro was evaluated by stimulating the isolated ileum, in an organ bath, with ACh. KEY RESULTS: In vivo, cannabidiol did not affect motility in control mice, but normalized croton oil-induced hypermotility. The inhibitory effect of cannabidiol was counteracted by the cannabinoid CB1 receptor antagonist rimonabant, but not by the cannabinoid CB2 receptor antagonist SR144528 (N-[-1S-endo-1,3,3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide), by the opioid receptor antagonist naloxone or by the alpha2-adrenergic antagonist yohimbine. Cannabidiol did not reduce motility in animals treated with the fatty acid amide hydrolase (FAAH) inhibitor N-arachidonoyl-5-hydroxytryptamine, whereas loperamide was still effective. In vitro, cannabidiol inhibited ACh-induced contractions in the isolated ileum from both control and croton oil-treated mice. CONCLUSIONS AND IMPLICATIONS: Cannabidiol selectively reduces croton oil-induced hypermotility in mice in vivo and this effect involves cannabinoid CB1 receptors and FAAH. In view of its low toxicity in humans, cannabidiol may represent a good candidate to normalize motility in patients with inflammatory bowel disease.

The role of endocannabinoids in the regulation of gastric emptying: alterations in mice fed a high-fat diet.

BACKGROUND AND PURPOSE: Endocannabinoids (via cannabinoid CB(1) receptor activation) are physiological regulators of intestinal motility and food intake. However, their role in the regulation of gastric emptying is largely unexplored. The purpose of the present study was to investigate the involvement of the endocannabinoid system in the regulation of gastric emptying in mice fed either a standard diet (STD) or a high-fat diet (HFD) for 14 weeks. EXPERIMENTAL APPROACH: Gastric emptying was evaluated by measuring the amount of phenol red recovered in the stomach after oral challenge; CB(1) expression was analysed by quantitative reverse transcription-PCR; endocannabinoid (anandamide and 2-arachidonoyl glycerol) levels were measured by liquid chromatography-mass spectrometry. KEY RESULTS: Gastric emptying was reduced by anandamide, an effect counteracted by the CB(1) receptor antagonist rimonabant, but not by the CB(2) receptor antagonist SR144528 or by the transient receptor potential vanilloid type 1 (TRPV1) antagonist 5'-iodoresiniferatoxin. The fatty acid amide hydrolase (FAAH) inhibitor N-arachidonoyl-5-hydroxytryptamine (but not the anandamide uptake inhibitor OMDM-2) reduced gastric emptying in a way partly reduced by rimonabant. Compared to STD mice, HFD mice exhibited significantly higher body weight and fasting glucose levels, delayed gastric emptying and lower anandamide and CB(1) mRNA levels. N-arachidonoylserotonin (but not rimonabant) affected gastric emptying more efficaciously in HFD than STD mice. CONCLUSIONS AND IMPLICATIONS: Gastric emptying is physiologically regulated by the endocannabinoid system, which is downregulated following a HFD leading to overweight.

The hallucinogenic herb Salvia divinorum and its active ingredient salvinorin A reduce inflammation-induced hypermotility in mice.

The hallucinogenic plant Salvia divinorum has been used for medical treatments of gastrointestinal disorders. Here, we evaluated the effect of a standardized extract from the leaves of Salvia divinorum (SDE) and of its active ingredient salvinorin A on motility in vivo, both in physiological states and during croton oil-induced intestinal inflammation. SDE (1-100 mg kg(-1)) significantly inhibited motility only in inflamed, but not in control, mice. In control mice, salvinorin A (0.01-10 mg kg(-1)) significantly inhibited motility only at the highest doses tested (3 and 10 mg kg(-1)) and this effect was not counteracted by naloxone or by the kappa-opioid receptor (KOR) antagonist nor-binaltorphimine. Inflammation significantly increased the potency of salvinorin A (but not of the KOR agonist U-50488) in reducing motility. The inhibitory effects of both salvinorin A and U-50488 in inflamed mice were counteracted by naloxone or by nor-binaltorphimine. We conclude that salvinorin A may reduce motility through activation of different targets. In physiological states, salvinorin A, at high doses, inhibited motility through a non-KOR mediated mechanism. Gut inflammation increased the potency of salvinorin A; this effect was mediated by KOR, but it was not shared by U-50488, thus suggesting that salvinorin A may have target(s) other than KOR in the inflamed gut.

The hallucinogenic herb Salvia divinorum and its active ingredient salvinorin A inhibit enteric cholinergic transmission in the guinea-pig ileum.

Salvia divinorum is a widespread hallucinogenic herb traditionally employed for divination, as well as a medicament for several disorders including disturbances of gastrointestinal motility. In the present study we evaluated the effect of a standardized extract from the leaves of S. divinorum (SDE) on enteric cholinergic transmission in the guinea-pig ileum. SDE reduced electrically evoked contractions without modifying the contractions elicited by exogenous acetylcholine, thus suggesting a prejunctional site of action. The inhibitory effect of SDE on twitch response was abolished by the opioid receptor antagonist naloxone and by the kappa-opioid antagonist nor-binaltorphimine, but not by naltrindole (a delta-opioid receptor antagonist), CTOP (a mu-opioid receptor antagonist), thioperamide (a H(3) receptor antagonist), yohimbine (an alpha(2)-receptor antagonist), methysergide (a 5-hydroxytryptamine receptor antagonist), N(G)-nitro-L-arginine methyl ester (an inhibitor of NO synthase) or apamin (a blocker of Ca(2+)-activated K(+) channels). Salvinorin A, the main active ingredient of S. divinorum, inhibited in a nor-binaltorphimine- and naloxone-sensitive manner electrically induced contractions. It is concluded that SDE depressed enteric cholinergic transmission likely through activation of kappa-opioid receptors and this may provide the pharmacological basis underlying its traditional antidiarrhoeal use. Salvinorin A might be the chemical ingredient responsible for this activity.