**2. Materials and methods**

### **2.1 Experimental procedure**

An experimental setup, used to obtain LIBS spectra from various materials, generally consists of a high-intensity pulsed laser system, with nanosecond laser pulse duration, an experimental chamber, a collection optics, and a high-precision optical spectrometer. Plasma is generated by focusing the high-intensity laser pulses into the material; usually a Nd:YAG laser is applied at its fundamental laser wavelength of 1064 nm or its second harmonic 532 nm with different repetition rates from 1 Hz to a few kHz [25–27]. A schematic of the experimental LIBS setup is shown in **Figure 2**.

#### **2.2 LIBS setup**

For laser-induced breakdown, a Nd:YAG solid-state laser from Quantel was used. It was operated at the fundamental laser wavelength 1064 nm with 8.5 ns pulse duration and a laser energy of 300 mJ per pulse. The laser radiation was focused into the plane solid target surface, using a 10 cm focusing lens, to create the plasma. Optical emission from the plasma was collected perpendicularly via optical telescope, into the highresolution Echelle spectrograph (model Aryelle Butterfly from LTB Berlin), equipped with an ICCD detector. Optical emission from plasma has been collected from UV as well as from VIS parts; thus the total spectral window from 190 to 800 nm wavelength has been recorded. The spectral resolution capability is from 3 to 7 pm for the UV range and from 4 to 8 pm for the VIS range, thus providing spectral information of a

*Major Chemical Elements in Soot and Particulate Matter Exhaust Emissions Generated… DOI: http://dx.doi.org/10.5772/intechopen.90452*

**Figure 2.** *Layout of the laser-induced breakdown spectroscopy experimental setup [28].*

broad range with very high resolution and variability. The delay time for LIBS spectral signal was set to 1 μs and the time window for spectral acquisition to 2 μs. In early delay time, less than 1 μs, the black body radiation is dominating in the laser-produced plasma, while in later delay time, 3 μs, the atomic, ionic, and molecular emissions are more pronounced. The laser-induced plasma has been created in open air atmosphere under the normal atmospheric pressure and at room temperature.
