Researchers at East China Normal University have developed a trio of techniques to elevate the sensitivity of ultrafast laser-induced breakdown spectroscopy (LIBS). The techniques — plasma grating-induced breakdown spectroscopy (GIBS), multidimensional plasma grating-induced breakdown spectroscopy (MIBS), and filament and plasma grating-induced breakdown spectroscopy (F-GIBS) — improve the excitation laser source. This enables higher laser intensity and a better signal-to-noise ratio (SNR). In addition, the methods provide broader detection capabilities than traditional LIBS and broaden the range of detectable elements. According to the researchers, the GIBS, MIBS, and F-GIBS techniques will make it possible to adapt breakdown spectroscopy to mobile operations in harsh field conditions to achieve noncontact, online, in situ detection. The researchers believe that these technologies will be extensively applied in mineral exploration, environmental monitoring, water science, life sciences, and other fields. Breakdown spectroscopy is a valuable tool for determining elements in solids, liquids, and gases. LIBS in particular demonstrates a quick response, enables direct analysis without the need for complex pretreatment, and supports multiple elemental analysis capabilities. However, traditional nanosecond LIBS elicits a powerful thermal effect, a plasma shielding effect, and a complicated matrix effect, which can lead to low repeatability, weak SNR, and challenges in taking molecular measurements. These drawbacks reduce the accuracy and sensitivity of nanosecond LIBS, affecting the quantitative analysis. In filament-induced breakdown spectroscopy (FIBS), constraints to peak power can affect sensitivity. The researchers’ improvements focus on the optimization of spectral signals to enhance the intensity of the signals, improve the SNR, and reduce the effect of the matrix, as well as other effects. To surmount limitations to peak power and enhance the electronic density of the excitation in breakdown spectroscopy, the researchers developed GIBS, which uses two noncollinearly coupled filament pulses to form a plasma grating. This enables GIBS to overcome interference from plasma shielding. To further enhance the effects of excitation, the researchers then developed MIBS. The MIBS method uses three noncollinear and noncoplanar femtosecond pulses, which interact with the sample to generate plasma grating. The effect of diffraction causes the plasma grating in MIBS to change from 1D to 2D. The periodic structure and higher-order nonlinear effects of the 2D plasma grating enhance the density of the plasma and enhance the peak power, enabling greater detection sensitivity. The researchers also found that the increase in MIBS’ laser energy enhances the spectral line signal obtained by MIBS. Further, since only the excitation source needs to be modified, MIBS retains the speed, simplicity, and convenience of LIBS technology, enabling in situ, real-time detection for specific scenarios. Building on the success of multibeam pulse laser coupling demonstrated by MIBS, the researchers combined the FIBS and GIBS techniques to create F-GIBS, specifically for solution detection. The researchers achieved a dual excitation effect for solution detection with this technique by setting a reasonable impact delay between the filament and plasma grating. As a result, F-GIBS can overcome issues with bubbles and splashing, typically encountered when breakdown spectroscopy is used in solution detection, and improve the sensitivity and accuracy of solution detection. The work of the team to advance breakdown spectroscopy from nanosecond to femtosecond, from beams to filaments, from single filaments to nonlinear plasma gratings, and finally to triple filament asynchronous noncollinear coupling was successfully applied to identify various samples in the laboratory and outdoor environments with high sensitivity and a good SNR. In the process of enhancing breakdown spectroscopy, the researchers resolved the influence of the matrix and the plasma shielding. They improved long-distance detection and resolved the effect of intensity clamping on breakdown spectroscopy detection. The research was published in Ultrafast Science (www.doi.org/10.34133/ultrafastscience.0013).
