Quality and spatial intensity distribution characteristics of short-exposure spot images of a supercontinuum laser in a turbulent atmosphere.

In this study, considering the combined effects of atmospheric attenuation and turbulence, we examine the spot quality and spatial intensity distribution characteristics of a supercontinuum (SC) laser propagating in a turbulent atmosphere using the multi-layer phase-screen method. An increase in turbulence strength or a decrease in the initial beam radius resulted in a greater impact of the atmospheric turbulence on the SC laser. A decrease in source coherence results in the deterioration of the image quality of the far-field spot. Under moderate to strong turbulence, the scintillation index decreased as the source coherence decreased; however, the opposite trend was observed under weak turbulence. These results are significant for the advancement and optimization of SC laser systems.

Evaluation for the effects of nutritional education on Chinese elite male young soccer players: The application of adjusted dietary balance index (DBI).

OBJECTIVES: To evaluate the effect of nutrition education on Chinese elite male young soccer players through the knowledge, attitude, behavior (KAP) survey and an adjusted dietary balance index (DBI). METHODS: 30 Chinese elite male young soccer players were randomly divided into two groups: lecture group (N = 15, Age: 16.7 ±â€¯1.8 years, Height: 173.9 ±â€¯9.0 cm; Weight: 62.4 ±â€¯13.0 kg; Training years: 5.6 ±â€¯2.7 years) and non-lecture group (N = 15, Age: 16.8 ±â€¯1.7 years, Height: 175.5 ±â€¯7.9 cm; Weight: 62.5 ±â€¯12.3 kg; Training years: 6.2 ±â€¯3.3). The comics book was given to the non-lecture group, while the a four-week nutritional quality education along with comic books were given to the lecture group. Before and after 4 weeks nutritional education, dietary nutritional status of both groups was assessed. The main outcome measurements included the scores for each part of the KAP survey, diet status (food-weighing method) and the dietary index in the adjusted DBI-07 system (DBI-low bound score, LBS; DBI-high bound score, HBS; and DBI-diet quality distance, DQD). RESULTS: In the lecture group, significant differences were found in the scores of general nutrition knowledge, sports nutrition knowledge and total scores of KAP dietary questionnaire after 4 weeks nutritional education (P < 0.01). However, there is no significant difference in dietary attitude and dietary behavior (P > 0.05) on both two groups. There is no significant change in the DBI-low bound score (LBS), DBI-high bound score (HBS) and DBI-diet quality distance (DQD) of dietary quality index (P > 0.05) in both two groups. CONCLUSIONS: Four weeks nutritional quality education improved the understanding of dietary nutrition among Chinese elite male young soccer players.

CaOH Molecular Emissions in Underwater Laser-Induced Breakdown Spectroscopy: Spatial-Temporal Characteristics and Analytical Performances.

Recently, molecular emissions from the laser-induced plasma in ambient gas have gained increasing interest; however, very little is known about the case in water solutions. In this work, we investigated the spatiotemporal characteristics of molecular emissions, CaOH for instance, in underwater laser-induced breakdown spectroscopy (LIBS) by using time-resolved spectroscopy, spectral-resolved imaging, and shadowgraph techniques. It was shown that clear CaOH molecular bands can be observed in the spectrum at very early times after the laser pulse and presented a much longer lifetime and more homogeneous emission distribution compared with the Ca I and Ca II lines. Such unique characteristics of CaOH molecular emission inspired us to improve the performances of underwater LIBS by using the CaOH molecular bands instead of Ca I and Ca II lines. We demonstrated the excellent quantification results of CaOH with higher stability, less self-absorption, and reduced matrix effect. Meanwhile, the limit of detection (LOD) of Ca with the CaOH molecular band (2.46 ppm) is comparable to that with the atomic line of Ca I (2.07 ppm), and much lower than that with the ionic line of Ca II (13.81 ppm), indicating a good sensitivity of CaOH. This work gives not only some insights into the molecule formation mechanisms in underwater plasmas, but also provides new ideas to improve the analytical performances of underwater LIBS.

Investigation of laser-induced plasma characteristics in bulk water under different focusing arrangements.

Laser-induced breakdown spectroscopy (LIBS) has drawn more attention as a new technique for in situ detection of seawater, especially for hydrothermal areas. In order to evaluate the focusing geometry effect on laser-induced plasma in bulk water, four focusing arrangements were tried out with a single lens as well as with a double-lens combination. We demonstrated that, for the same transmission distance in water, the double-lens combination with shorter effective focal length generated more condensed plasma, as shown by the spectroscopic and fast imaging results. Accordingly, the moving breakdown phenomenon significantly decreased with well-improved LIBS intensity, signal-to-noise ratio, and stability. The plasma emissions evidently attenuated along the laser transmission due to the strong absorption effect of the water medium. Based on the acquired results, the performance of a practical detection window was evaluated by combining the regular lens with a customized lens-shaped optical window, and a positive outcome was also reached. The obtained results suggested that improved LIBS detection could be easily achieved via settling another lens window to LIBS system, which is considered helpful for better in situ submarine application.

[Study on the Spatial Distribution of Laser Induced Plasma Emission Underwater with Different Laser Energies].

Laser-induced breakdown spectroscopy (LIBS), as a promising in-situ underwater detection technology, has received extensive attention in the field of ocean exploration. Improving the remote sensing ability of LIBS is crucial in bringing this technology into practical applications, hence higher laser energies, i.e. over threshold, are required. To characterize the plasma induced with super threshold energies and have a better understanding of resulted moving breakdown process, some extensive investigations into KCl water solution have been carried out with spectra-image jointed analysis. The spatial span and the brightest spot position of plasma radiation, with different laser energies from 1 to 20 mJ, were determined from the recorded plasma images. It was found that the plasma stretched from 0.49 to1.83 mm, as the laser pulse energy increased from 1 to 20 mJ, with a center position shift of 0.79 mm towards the incident laser beam. The obvious power dependence has also been observed from the obtained spatial resolved atomic spectra. Although the axial distributions at different energies were similar, both the position and the intensity of potassium atomic emission maximum varied. The optimal laser energy was determined to be 5 mJ with the emission intensity maximum higher than that at any other investigated energies. The obtained results suggested that the power dependence of atomic emission should be taken into account on increasing laser energy to meet the needs of stand-off LIBS applications. The FWHM and signal to background ratio of K Ⅰ 769.90 nm under different laser energies have also been investigated.