Dental caries-related quality of life and socioeconomic status of preschool children, Bauru, SP

AIM: To evaluate oral health-related quality of life of preschool children of Bauru, State of São Paulo, Brazil, and associate it with socioeconomic profile of households. METHODS: The sample consisted of 229 preschool children between 3 and 5 years and the dmft (decayed, missing due to caries, filled teeth) index was adopted for assessment children's dental caries in accordance with the standards recommended by the World Health Organization. Questionnaires were used for evaluation oral health-related quality of life (Early Childhood Oral Health Impact Scale) and socioeconomic profile of parents or guardians of the preschool children. Statistical analysis was performed descriptively by relative and absolute frequencies and by Spearman's correlation and Kruskal-Wallis test (p <0.05). RESULTS: A dmft of 1.65 (± 2.87) and a Sic Index 4.88 (± 3.20) were found, indicating the polarization of dental caries in the studied group. It was verified low influence of oral health on quality of life of the children examined. With respect to socioeconomic classification, 66.38% of families were in the lower middle class. Linear and statistically significant correlation was found between dmft and oral health-related quality of life for the overall score and domains of the questionnaire (p<0.001). CONCLUSIONS: It was found low influence of oral health on quality of life of the preschool children and the assessment of socioeconomic conditions of the children's families may guide practices aiming to reducing inequalities in the distribution of dental caries in the population

Gating attosecond pulse train generation using multicolor laser fields

The process of high-order harmonic generation leads to the production of a train of attosecond-duration extreme ultraviolet (XUV) pulses, with one pulse emitted per optical half-cycle. For attosecond pump-probe experiments, a single, isolated attosecond pulse is preferable, requiring an almost continuous spectrum. We show experimentally and numerically that the addition of a second laser field, and later a third, at a noncommensurate frequency relative to the driving field can modify the subcycle shape of the electric field, leading to the appearance of additional spectral components between the usual odd harmonics and in some cases a quasicontinuum. We perform a parametric study of the frequency ratio between the two first laser fields, the result of which is in good agreement with theoretical selection rules. We also show numerically that using three laser frequencies from an optical parametric amplifier can achieve a single attosecond pulse from a 24-fs laser pulse.La g\ue9n\ue9ration d\u2019harmoniques d\u2019ordre \ue9lev\ue9 m\ue8ne \ue0 la production d\u2019un train d\u2019impulsions de rayonnement ultraviolet extr\ueame (UVX) de l\u2019ordre de l\u2019attoseconde par l\u2019\ue9mission d\u2019une impulsion par demi-cycle optique. Dans le cas des exp\ue9riences de pompe-sonde de l\u2019ordre de l\u2019attoseconde, une impulsion d\u2019une attoseconde isol\ue9e est pr\ue9f\ue9rable, ce qui n\ue9cessite un spectre pratiquement continu. Nous montrons, par la voie exp\ue9rimentale et num\ue9rique, que l\u2019ajout d\u2019un deuxi\ue8me champ laser, suivi d\u2019un troisi\ue8me, \ue0 une fr\ue9quence incommensurable comparativement au champ d\u2019entra\ueenement peut modifier la forme des sous-cycles du champ \ue9lectrique et mener \ue0 l\u2019apparition de composantes spectrales suppl\ue9mentaires entre les harmoniques impaires habituelles, et dans certains cas \ue0 un quasicontinuum. Nous avons r\ue9alis\ue9 une \ue9tude param\ue9trique du rapport de fr\ue9quence entre les deux premiers champs laser, dont le r\ue9sultat concorde bien avec les r\ue8gles de s\ue9lection th\ue9oriques. Nous montrons \ue9galement par la voie num\ue9rique que l\u2019utilisation de trois fr\ue9quences laser provenant d\u2019un amplificateur param\ue9trique optique peut permettre d\u2019obtenir une seule impulsion attoseconde \ue0 partir d\u2019une impulsion laser de 24 fs.Peer reviewed: YesNRC publication: Ye

High-order harmonic generation experiments with IR laser pulses

We report on the first experiments of high-order harmonic generation done with the 100 Hz high-energy optical parametric amplifier (OPA) of the Advanced Laser Light Source. Using krypton and argon as targets, we show that the OPA's signal beam - with a wavelength range from 1200 nm to 1600 nm, 1.3 mJ to 0.8 mJ of pulse energy and 100 fs pulse duration - can generate fully tunable XUV radiation down to a wavelength of 15 nm. We have also started to investigate the use of the OPA pulses for molecular imaging. Inducing molecular alignment with 800 nm, 70 fs pulses, we have measured the high harmonics spectra generated with 1300 nm pulses from nitrogen molecules oriented at various angles with respect to the ionizing field, in order to study for the first time the technique of molecular orbital tomography with a laser wavelength different than 800 nm.Peer reviewed: YesNRC publication: Ye

High harmonic cutoff energy scaling and laser intensity measurement with a 1.8 μm laser source

High harmonic generation in gas targets leads to the production of attosecond pulses. The process of high harmonic generation requires that the gas be ionized by an intense femtosecond laser field. The highest photon energy produced is related to the laser intensity times the wavelength squared. This cutoff is reached only if good phase matching is achieved. Using a laser with a wavelength of 1800 nm, we estimate the laser intensity in the gas jet by recording the ion yield, and simultaneously record the high harmonic spectrum. We show that the cutoff energy matches the measured intensity, confirming that good phase matching is achieved to 100 eV. We also use the ion collector to characterize the spatial size of the gas jet and to measure the confocal parameter of the laser beam, parameters that are useful for numerical modelling

High harmonic generation with a spatially filtered optical parametric amplifier

Numerous applications of high harmonic generation (HHG), such as attosecond pulse synthesis, depend on the ability to increase the electron recollision energy, which is a quadratic function of the driver wavelength. High-energy infrared pulses obtained from an optical parametric amplifier (OPA) are thus attractive for driving the HHG process, thereby offering the opportunity to yield shorter attosecond pulses. However, the increase in driver wavelength is often outweighed by the poor spatial quality of the OPA source. In this paper, we demonstrate that HHG using OPA signal pulses is significantly improved by spatial filtering in a hollow-core fibre prior to focusing in the gas target in comparison with the unfiltered case. Ion yield measurements in combination with beam profile monitoring in the far field enabled control over the interaction volume. For similar interaction volumes, we observe that with less than half the energy per pulse, the HHG yield can increase by one order of magnitude with spatial filtering. The comparison between the harmonic yields in argon and krypton, and their respective dependence on the peak laser intensity, provide experimental evidence that strongly suggests that the enhancement is due to improved phase matching.Peer reviewed: YesNRC publication: Ye

Laser-Induced Electron Tunneling and Diffraction

Molecular structure is usually determined by measuring the diffraction pattern the molecule impresses on x-rays or electrons. We used a laser field to extract electrons from the molecule itself, accelerate them, and in some cases force them to recollide with and diffract from the parent ion, all within a fraction of a laser period. Here, we show that the momentum distribution of the extracted electron carries the fingerprint of the highest occupied molecular orbital, whereas the elastically scattered electrons reveal the position of the nuclear components of the molecule. Thus, in one comprehensive technology, the photoelectrons give detailed information about the electronic orbital and the position of the nuclei.Peer reviewed: YesNRC publication: Ye

Wavelength scaling of high harmonic generation efficiency

Using longer wavelength laser drivers for high harmonic generation is desirable because the highest extreme ultraviolet frequency scales as the square of the wavelength. Recent numerical studies predict that high harmonic efficiency falls dramatically with increasing wavelength, with a very unfavorable \u3bb-(5-6) scaling. We performed an experimental study of the high harmonic yield over a wavelength range of 800\u20131850 nm. A thin gas jet was employed to minimize phase matching effects, and the laser intensity and focal spot size were kept constant as the wavelength was changed. Ion yield was simultaneously measured so that the total number of emitting atoms was known. We found that the scaling at constant laser intensity is \u3bb-6.3\ub11.1 in Xe and \u3bb-6.5\ub11.1 in Kr over the wavelength range of 800\u20131850 nm, somewhat worse than the theoretical predictions.Peer reviewed: YesNRC publication: Ye