Laser Induced breakdown spectroscopy in Water for elemental analysis. Satyanarayan Ray Pitambar Mohapatra Project Guide: Dr. R.K. Thareja

Advantages of LIBS technique Can be used for rapid and remote analysis. Real time analysis possible. Complete elemental coverage can be achieved. The analysis spot size is small. Relatively low detection limit ( ppm/ppb).

Possible application Detection of elements in nuclear reactors. Detection of elements inside deep sea. Space mission; detection of elements in other planets. Environmental monitoring (soil contamination, particulates) . Materials analysis (metals, plastics).   Forensics and biomedical studies (teeth, bones analysis).   Military and safety needs (explosive particles, chemical and biological warfare agents e.g. Anthrax).   Art restoration/conservation (pigments, precious/ancient metals).  

LIBS on Mars ! A 300 mJ laser pulse can detect from 25m away. A 2 J laser pulse can detect from 100m away. photo credit: Chemistry Division , Los Alamos National Laboratory

Set up

Setup specification Wavelength of laser radiation = 355 nm Energy of laser radiation = 18 mJ Focal length of Plano-convex quartz lens = 10 cm Pulse repetition rate = 10 Hz Gate width for time integrated spectra = 2 micro second Gate width for time- resolved spectra = 500 ns Gate delay with respect to laser pulse = 300 ns

Advantages of water based test samples Relatively low conc. Solution (ppm) can be prepared. Solution in water are more homogeneous than solid ( so spatial variation of concentration is not there).

Why Na ? Easily available element to start with. To determine the concentration of Na in sea ice. Na concentration in blood and cells.

Typical sodium lines time integrated Na I 589 nm ( 3s 2S-3p 2P0)( J = 1) D1 line Na I 589.6 nm ( 3s 2S-3p 2P0)( J = 0) D2 line

Time resolved data for concentration = 38 ppm

Time resolved observation for concentration = 102 ppm, gate delay = 300 ns

Time resolved data of Sodium line for Concentration = 409 ppm, gate delay = 300 ns

Calibration curve D2 line Detection limit = 3σ /m Detection limit observed = (123 + 17) ppm

Calibration curve for D1 line Detection limit = 3σ/m Detection limit observed = (116+13) ppm

Calibration curve D2 line Detection limit = 3σ/m Detection limit observed = (19+ 5) ppm

Calibration curve for D1 line Detection limit = 3σ/m Detection limit observed = (7.8+3) ppm

Detection limit optimization Two types of background noise; plasma continuum & detector noise. Optimization Optimum gating time & optimum position of detector. Study of temporal and spatial expansion of plasma in air.

Problems to be fixed and future plans An actual set up should have the capability to distinguish among several elements. For that suitable wavelength of laser radiation to be decided. Suitable energy of laser radiation to be determined. Plasma parameters (plasma temperature, plasma density) to be determined for different elements. The LIBS method should be compared with other standard authentic methods. Salt solution of sodium and magnesium in the form of ice cubes to be analyzed.