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 line480 500 520 540 560 580 600 620 640

0

1000

2000

3000

4000

5000

6000

29 Sept. 2003

D2

D1

Sodium lines

Inte

nsi

ty -

-->

Pixel ( wavelength) --->

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

0 200 400 600 800

0

500

1000

1500

2000

2500

3000

3500

4000

29 Sept. 2003

Resolution limit = 3/m = 123 ppm

D2 line of Na

Inte

nsity

(as

num

ber o

f cou

nts)

--->

Conc. in ppm --->

Calibration curve for D1 line

0 200 400 600 800

0

1000

2000

3000

4000

5000

6000

29 Sept. 2003

limit of resolution = 3/B =116

D1 line of NaInte

nsi

ty (

as

nu

mb

er

of c

ou

nts

) --

->

Conc. in ppm --->

• Detection limit = 3σ/m

• Detection limit observed = (116+13) ppm

Calibration curve D2 line

• Detection limit = 3σ/m

• Detection limit observed = (19+ 5) ppm

0 10 20 30 40 50 601200

1400

1600

1800

2000

2200

2400

31 October, 2003

Conc. in ppm

Inte

nsi

ty (

as

nu

mb

er

of

cou

nts

)D2 line of Na

Calibration curve for D1 line

• Detection limit = 3σ/m

• Detection limit observed = (7.8+3) ppm

0 10 20 30 40 50 602000

2200

2400

2600

2800

3000

3200

31 October, 2003

D1 line of Na

Inte

nsity

( a

s nu

mbe

r of

cou

nts)

Conc. in 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.