Single-pulse and double-pulse optical emission spectroscopy(OES)analyses were carried out in air by using ultrashort laser pulses at atmospheric pressure.The aim of this work is to use spectroscopic methods to analyze the early phase of laser-induced plasma after the femtosecond laser pulse.The temporal behavior of emission spectra of air plasma has been characterized.In comparison with the single-pulse scheme,the plasma emission obtained in the double-pulse scheme presents a more intense continuum along with several additional ionic lines.As only one line is available in the single-pulse scheme,the plasma temperature measurements were performed using only the relative line-to-continuum intensity ratio method,whereas the relative line-to-line intensity ratio method and the relative line-to-continuum intensity ratio method were used simultaneously to estimate the electron temperature in the double-pulse scheme.The results reveal that the temperature values obtained by the two methods in the double-pulse scheme agree.Moreover,this shows that the relative line-to-continuum intensity ratio method is suitable for early phase of laser-induced plasma diagnostics.The electron number density was estimated using the Stark broadening method.In the early phase of laser-induced plasma,the temporal evolution of the electron number density exhibits a power law decrease with delay time.
Being as a plant of cross-pollination; the cultivar identification of alfalfa (Medicago sativa L.) is more difficult than other self-pollination plant because of the admixture genotypes within a cultivar. A preliminary study on alfalfa cultivar identification was conducted on native cultivars, bred cultivars, and cross cultivars using SSR markers. The results suggest that some nonspecific bands were avoided by using denatured gels for the separating of PCR products; the gene frequency of l4Sbp band of AFcal loci was much higher in Longmu series cultivars than that in other alfalfa cultivars, by which Longmu cultivars were identified among alfalfa cultivars. However, the gene frequency differences could not be used for other cultivar identification, because the differences among other alfalfa cultivars were small. Thus, it was very difficult to identify all alfalfa cultivars by using limited SSR markers. Some alfalfa cultivars could be identified by using the molecular marker associated with a specific trait of the cultivar.
We theoretically investigate the contribution of the excited state to the ellipticity of the harmonics from H+2 at different orientation angles irradiated by a linearly polarized laser pulse. It is found that the first excited state has a significant influence to the ellipticity of the harmonics, and the contribution of higher excited states to the ellipticity can be neglected.Moreover, the conclusion is not dependent on the laser intensity.
The ionization time in sequential double ionization with an elliptically polarized laser pulse has been examined theo-retically using a semiclassical method. The significant discrepancy between the ionization time for parallel and anti-parallel electron emission is predicted numerically for the first time. The impact of the carrier envelope phase offset is also studied in this work.
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