RESUMO
Mode conversion based on adiabatical mode evolution in a two-core configuration is investigated. The configuration can convert all the launching modes to higher-order modes from one port and convert all the launching modes to lower-order modes from another port. Mode conversion between the two degenerated high-order modes is also demonstrated numerically. The mode conversion feature is only dependent on the relationship between the effective mode indices of the two cores in the configuration, which shows the characteristics of high flexibility and large fabrication tolerance.
RESUMO
It is quick and accurate to on-line monitor the sample condition of laser cleaning by means of laser-induced plasma spectrum in air. In the present article, the echelle grating spectrometer was used to detect the plasma spectral lines induced by pulsed laser interaction with copper coin samples with or without contamination. The spectrogram showed that there were clear Cu I spectrum lines and air atom spectrum lines of N I and O I. In order to eliminate the uncertainty of single measurement, the statistical regularity of N I and O I spectrum lines was analyzed. Their intensity distribution laws were consistent and their relative standard deviations were the same basically. So a single measurement spectrum could be used to monitor cleaning process. The spectra of copper samples with contamination consisted of many elements atomic spectral lines and continuous spectral lines. But there are Cu I spectral lines in the spectra of clean copper samples. As a result, the authors could detect the change of spectral lines to judge whether the laser cleaning samples were clean.
