Abstract:  A collinear dual pulse laser induced breakdown spectroscopy (DP-LIBS) has been used for trace element
 analysis in aluminum alloy. The dependence of signal intensity on the inter-pulse delay time
has been carefully investigated, which gives an optimized delay time of about 8$\sim$9 $\mu$s.
For the two selected analytical lines Cu I 324.75 nm and Cr I 425.43 nm, more than 10 folds
enhancement of line intensities have been obtained compared to that of single-pulse laser
induced breakdown spectroscopy(SP-LIBS). Calibration curves for quantitative measurement of
Cu and Cr were derived using both SP-LIBS and DP-LIBS techniques. The limit of detection (LOD)
of elements Cu and Cr are found to be 21.46 and 4.26 $\mu$g/g respectively with DP-LIBS,
while the LOD of elements Cu and Cr are 169.5 and 94.5 $\mu$g/g with SP-LIBS.

Key words: dual pulse laser induced breakdown spectroscopy,  , Cr,  , Cu,   , limit of detection