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Laser Induced Breakdown Spectroscopy

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by

Rob Shalloo

on 4 August 2014

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Transcript of Laser Induced Breakdown Spectroscopy

Thank you. Questions!
Objectives
Introduction to Laser Induced Breakdown Spectroscopy (LIBS)

Background Theory

Applications of LIBS

Ambient Air experiment

Optical Cavity experiment

Future work
LIBS Thesis Project
Objectives of Project:
Become familiar with basic physics of laser induced plasmas, as well as their experimental treatment

Set up, align and conduct a LIBS experiment

Measure "Breakdown Spectra" for air and identify components

Trap laser plasma emission in an optical cavity and interpret the results
In Air Results
A time resolved LIBS spectra was successfully obtained
Elemental Oxygen and Nitrogen identified (singly and multiply ionized)
Emission Spectra of Air
Time Resolved Spectra With LIBS
Experimental Setup - No Cavity
Experimental Setup - With Cavity
Temporal Profile of Plasma in Cavity
Potential/Working Explanation
Credit: www.youtube.com
Credit: NASA & JPL/Caltech
Adding an Optical Cavity
Only certain frequencies resonate
Re-absorption into blackbody


Use LIBS plasma as a light source for absorption spectroscopy




Future Work
Further investigation of plasmas temporal profile in cavity

Systematic optimization of laser and cavity parameters

Follow up on promising absorption spectra for applications in trace gas detection
Applications of LIBS
What is LIBS
These Properties allow for its use in a wide variety of applications

Mars Curiosity Rover

Nanoparticle production

Compositional mapping

Industrial Solid Analysis

...Trace gas detection in air?
How does it work
An atomic emission spectroscopy technique in which a high powered
pulsed laser is used as an excitation source
Credit: Encyclopedia of Spectroscopy and Spectrometry
Multi-Photon ionization (MPI)

Emitted light consists of:
Discrete emission lines characteristic of the sample - Relatively long lived
Overlying continuum - free to free collision - Relatively short lived

Can be approximated by blackbody spectrum
Laser can ionize the gas phase in two main ways
Inverse Bremsstrahlung (IB)
Properties
Requires no physical contact with sample
Requires no sample preparation making it perfect as field research technique
Produces data in real time

Summary
Credit: howstuffworks.com
Credit: intechopen.com
LIBS:
A laser is focused down such that the high intensity sparks a plasma. This plasma emits light characteristic of the material
A simple LIBS experiment was established and elemental Oxygen and Nitrogen identified


The microplasma emission was successfully coupled into the cavity and sustained
The time resolved spectrum was obtained and interpreted
This light was then used as a source for absoption spectroscopy
No Cavity
Cavity
Laser Induced Breakdown Spectroscopy
BSc Physics (Single Honours) Thesis Project 2014: Robert Shalloo

Supervisor Dr. Albert Ruth
Credit: wikipedia.com
Credit: Fundamentals of Photonics
Possible Issues
What happens if we create the LIBS spark in an optical cavity
Why?
Azulene Absorption Spectrum
Special Thanks to:
Krishnakumar Chullipalliyalil
Karen Acheson
Dr. Ranjini Raghunandan
Dr. Albert Ruth


March 27th 2014
Light was successfully sustained within the cavity
Interesting temporal profile of plasma discovered
Potential Oxygen absorption lines detected
Potential Azulene absorption lines detected when
air surrounding plasma seeded

Cavity Results
Full transcript