The role of laser wavelength on dual pulse laser-breakdown spectroscopy

Summary form only given. Laser-induced breakdown spectroscopy (LIBS) provides multi-elemental in-situ sample analysis down to trace concentrations for many elements, including most light elements (H, C, O, N). The LIBS technique is useful for a variety of applications including elemental analysis, detecting airborne biological agents, quantitative analysis of aerosols, etc. Although LIBS is suited for various applications, this technique possesses a lower sensitivity and precision than the other forms of elemental analysis, such as ICP-MS. Improving the sensitivity of LIBS can be achieved by either enhancing the signal strength or reducing the background noise. Double-pulse (DP) excitation is more promising among the various methods proposed for improving the detection sensitivity of LIBS. The term “double-pulse” refers to two laser pulses used for LIBS excitation, each separated by delay time ranging from a few nanoseconds to several microseconds. It has been recently noticed that a combination of UV and NIR wavelengths in double pulse experiments provides significantly higher sensitivities compared to same wavelength DP experiments. We used a combination of Nd:YAG (both fundamental and harmonics) and a TEA CO₂ laser to improve the sensitivity of LIBS. The role of wavelengths, the delay times, and energies of the preheating and reheating pulses on the LIBS sensitivity improvements are studied and discussed.