Fraunhofer-type absorption lines from a submerged Cu target by long-pulse laser-induced breakdown spectroscopy: toward non-gated detection

Abstract

The underwater Fraunhofer-type absorption signal from a plasma generated on an immersed Cu target was investigated using single-pulse laser-induced breakdown spectroscopy (LIBS). We found that clear underwater Fraunhofer-type absorption lines were observed with a long-pulse irradiation, while the signal observed with a short-pulse irradiation was quite indistinct. The time-resolved spectra show that both absorbance and line broadening gradually decrease with increasing delay time, i.e., Fraunhofer-type absorption occurs at the initial stage of the plasma. This enables us to obtain clear Fraunhofer-type absorption lines by a non-gated detection method, which can effectively simplify the LIBS equipment. The results not only provide some insights into the generation and evolution of underwater Fraunhofer-type absorption, but more importantly, suggest a new idea for underwater LIBS analysis, with a non-gated detection scheme.