Use of dual-pulse laser-induced breakdown spectroscopy with an orthogonal spark orientation is presented as a technique for trace metal analysis in bulk aqueous solutions. Two separate Q-switched Nd:YAG lasers operating at their fundamental wavelengths are used to form a subsurface, laser-induced plasma in a bulk aqueous solution that is spectroscopically analyzed for the in situ detection of Ca, Cr, and Zn. Optimizing the key experimental parameters of proper spark alignment, gate delay (t d ), gate width (t b ), and interpulse timing (ΔT) allowed experimentally determined detection limits of the order of micrograms per milliliter and submicrograms per milliliter. We present supporting evidence of a sampling mechanism that involves the formation of a cavitation bubble with the first pulse (E1) followed by analysis of that bubble with a second pulse (E2). The plasma created by E2 contains the analytically relevant information from the aqueous sample and often represents >250-fold enhancement over a single laser pulse with energy equal to E1 alone.
© 2003 Optical Society of America
Original Manuscript: February 20, 2003
Revised Manuscript: July 11, 2003
Published: October 20, 2003
William Pearman, Jon Scaffidi, and S. Michael Angel, "Dual-pulse laser-induced breakdown spectroscopy in bulk aqueous solution with an orthogonal beam geometry," Appl. Opt. 42, 6085-6093 (2003)