Filament- and plasma-grating-induced breakdown spectroscopy (F-GIBS) was demonstrated as an efficient technique for sensitive detection of metals in water, where plasma gratings were established through synchronized nonlinear interaction of two noncollinear filaments and an additional filament was generated with another fs laser beam propagating along their bisector. A water jet was constructed vertically to the three co-planar filaments, overcoming side effects from violent plasma explosion and bubble generation. Three distinct regimes of different mechanisms were validated for nonlinear couplings of the third filament with plasma gratings. As the third filament was temporally overlapped with the two noncollinear filaments in the interaction zone, all the three filaments participated in synchronous nonlinear interaction and plasma grating structures were altered by the addition of the third filament. As the third filament was positively or negatively delayed, the as-formed plasma gratings were elongated by the delayed third filament, or plasma gratings were formed in the presence of plasma expansion of the ahead third filament, respectively. Using F-GIBS for trace metal detection in water, significant spectral line enhancements were observed.

Laser-induced breakdown spectroscopy (LIBS) is a useful tool for determination of elements in solids, liquids, and gases. For nanosecond LIBS (ns-LIBS), the plasma shielding effect limits its reproducibility, repeatability, and signal-to-noise ratios. Although femtosecond laser filament induced breakdown spectroscopy (FIBS) has no plasma shielding effects, the power density clamping inside the filaments limits the measurement sensitivity. We propose and demonstrate plasma-grating-induced breakdown spectroscopy (GIBS). The technique relies on a plasma excitation source—a plasma grating generated by the interference of two noncollinear femtosecond filaments. We demonstrate that GIBS can overcome the limitations of standard techniques such as ns-LIBS and FIBS. Signal intensity enhancement with GIBS is observed to be greater than 3 times that of FIBS. The matrix effect is also significantly reduced with GIBS, by virtue of the high power and electron density of the plasma grating, demonstrating great potential for analyzing samples with complex matrix.