Echelle LIBS-Raman system: A versatile tool for mineralogical and archaeological applications

There are a number of analytical techniques used to study material related problems. Most of them imply experimental determination of parameters and functions by means of which elemental, optical and other properties of materials can be described. Laser Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are highly complementary spectroscopic techniques used for lab, in-situ, and remote analyses of materials. The LIBS-Raman system provides further information compared to other conventional techniques since it can detect the presence of low atomic number-elements, isotopic composition, hydration and structure of trace materials which may be present as surface layers etc., which are very difficult, if not impossible, by portable X-ray based systems. A setup for LIBS and Raman spectroscopy measurements in a single unit has been developed and reported recently by us using an echelle spectrograph system. The system utilizes a single nanosecond pulsed Nd:YAG laser (532 nm) and an ICCD coupled echelle spectrograph for both measurements. The unit has been successfully used for multipurpose applications such as identification of minerals, pigments etc and also for checking quality assurance. The combined atomic and molecular information from the same location on a sample, at several locations, can provide more comprehensive information regarding its properties than using either of these quantities taken singly. In many cases, it has been observed that the high resolution of the echelle spectrograph provides better quality Raman signals by virtue of the small degeneracy/crystal field splitting of many fundamental Raman bands. This can provide valuable information on inclusions in bulk samples, changes due to symmetry alteration or complex formation with surroundings, hydrogen bonding etc. The advantage of echelle system to identify natural and artificial pigments by identifying the minor and trace components by the spectra of the elements therein, is also helpful in many situations. In the present paper, the orthogonal use of LIBS and Raman spectroscopy is assessed and highlighted. The results clearly demonstrate the potential of echelle-based LIBS-Raman system in applications where more detailed information on complex samples like minerals, archaeological artifacts etc, is required with minimum sample damage or consumption.