1. Visible & Infrared Laser Induced
Breakdown Spectroscopy of
Potassium based Energetic
Materials Deposited on Substrates
Keith Tukes
Hampton University
Department of Physics
Research Advisors:
Uwe Hommerich
EiEi Brown
Eric Kumi-Barimah

2. Outline
• Introduction
– Basic Idea of Laser Induced Breakdown Spectroscopy
– Structure and Spectroscopy of Atoms
– Structure and Spectroscopy of Molecules
• Research Objective
• Experimental Details
– Sample Preparation: bulk pellets, films on substrates
– Un-gated visible LIBS using a Miniature Spectrometer System
– Infrared LIBS setup
• Results and Discussion
– Pictures of prepared samples
– Visible LIBS spectra in air and element identification
– MIR LIBS spectra of bulk and thin film samples
– LWIR LIBS spectra of bulk and thin film samples
– Identification of IR atomic and molecular LIBS emissions
• Conclusions

3. What is LIBS?
Method of identifying the elemental
composition of a sample by
examining the spectrum of light
created by striking a sample with a
highly-focused laser pulse. The
spark that is created contains
blackbody, atomic, and molecular
emissions.
• Blackbody (Thermal radiation)
–> Broad-band emission (UV-VIS-IR)
• Atomic Emissions
–> Narrow line emission (UV-VIS & IR)
• Molecular Emissions
–> Broad-band emission (mainly IR)
Schematics of LIBS setup
[1]

4. Research Applications
LIBS is an especially valuable technique
for material identification but at the
present, only information about the UV-
Visible region has been collected.
Current applications of LIBS include:
• De-Mining- Detection and
identification of landmines and other
hazardous objects.
• Robotic LIBS- Using rovers to identify
materials on deep-space landings.
• Stand-off Detection of Explosive
materials
• Underwater LIBS- Specifically its use
in identifying archeological materials.
Advantages of LIBS
LIBS is used in many different ways
simply because of the versatility of the
technique, but it also boasts additional
advantages such as:
• Minimal Sample Preparation
• Spectra may be obtained from long
distances
• Ability to analyze solids, liquids, &
gases
• Minimal amount of material is
required for analysis
• Simple and rapid collection of data
and analysis
[3]
[4]
[2]

5. Blackbody Radiation
• Blackbody Radiation
– Thermal Radiation
– Any object based on its temperature
emits blackbody radiation
– Appears as broad-band spectra with
low resolution
– The peak amount of radiation occurs
at different wavelengths depending
on temperature
– Planck’s Equation gives the spectral
radiance distribution as a function of
the temperature T
– Blackbody emission is overlapping
LIBS atomic emissions
(-> gated spectroscopy needed)
1
1
*
2
)( /5
2

 kThc
e
hc
I 



T=300K T~5000K

6. Atomic Transitions
• Bohr’s Model: The atom looks like the solar
system.
• There exist discrete atomic energy levels
and states (orbits)
• Atomic Emission
– Occurs due to electrons being excited into higher
energy states (absorption)
– Following excitation, electrons return to the ground
state by emitting photons (Emission)
Figure 2: Bohr’s Atomic Model
2S+1
LJ
Spectroscopic notation
2
2
( 13.6 )n
Z
E eV
n
 
Z=1 for hydrogen

7. Molecular Transitions
• Molecular Emission
– Slowest emissions
– Broad bands (Infrared region)
• Molecular Transitions:
– Create the smallest changes in the total
energy of a molecule
– Total energy:
• Nuclear energy levels are quantized
• Vibrational Energy
• Rotational Energy
Etot
= Eele
+Enuc

8. • Schrodinger’s Equation is used to
identify the energy of electron in
atoms
– Quantum numbers can be derived
from Schrodinger’s Equation
• Quantum Numbers describe the
characteristics of electrons and
their orbitals
• Principal Quantum Number (n)
– Describes the amount of energy
the electron will have.
• Spectroscopic Notation
– Notation that uses quantum
numbers to describe an electron
• L: Total orbital angular
momentum
• S: Total Spin
• J: Total Angular Momentum
2S+1
LJ
Quantum Numbers and the Quantum
Mechanical Model
2
2
( 13.6 )n
Z
E eV
n
  hydrogen

9. Research Objectives
• Prepare bulk pellets and thin-films of potassium based
compounds used as energetic materials (e.g. KClO3, KClO4).
Use an air-spray technique to deposit films on substrate
including aluminum, cement, asphalt, and glass.
• Determine amount of deposited material necessary to obtain
sufficient emission signatures in LIBS.
• Use visible LIBS to identify atomic emissions from potassium
based compounds as bulk materials and then as thin films. Use
the NIST database to identify background emissions from
substrate materials.
• Extend visible LIBS to the infrared region and use the NIST
database to identify atomic and molecular emission
wavelengths from bulk and thin-film materials. Identify
background emissions from substrates. Use IR emission
signatures to assist material identification.

10. Sample Preparation
• Bulk Pellets
– Compressed pellets of
the energetic material
(i.e. KClO3)
Uncoated
Substrates
•Substrate Films
–Substrates coated with
energetic materials
Sample Press
(7 metric tons)
Bulk Pellet
(KClO3)
Energetic
Material
(KClO3)
Weighed 5.2 g for
each sample
Aqueous Solution
(2 g KClO3)
Spray Gun
Connected to Nitrogen gas tank
(25 psi)
Coated Substrates
Aluminum Substrate
Cement Substrate
Asphalt Substrate

11. ND:YAG
Laser
Boxcar
Averager
Oscilloscope Computer
Sample
Stage
Infrared
Spectrometer
C
F
Infrared
Detector
Visible LIBS
Spectrometer
Visible LIBS mount
and detector
CF
• Pulsed Nd:YAG laser beam is directed and focused onto sample surface
• Sample is struck by laser which results in ablation of material from surface
• Emitted light is collected using collimating lenses and focused onto fiber or spectrometer
• Visible LIBS:
• CaF2 Lenses, Optical fiber, miniature CCD array-spectrometer system, Ungated
• Infrared LIBS:
• ZnSe lenses, grating spectrometer, IR detector (InSb)
• Boxcar and Oscilloscope are use for gated LIBS detection
Experimental Details: UV-VIS & IR LIBS

12. Experimental Details: UV-VIS & IR LIBS
CaF2 Lenses
ZnSe Lenses
Sample Stage
UV-Vis-NIR Fiber Optic Detector
IR Spectrometer
Liquid Nitrogen Cooled IR Detector
Mounted Sample
ND:YAG Laser
Data Collecting Interface
Boxcar Averager
Spectrometer Controller
Sample Stage Controller

13. Visible-NIR LIBS spectrum of background air
Observed
 obs(nm)
Literature
*
lit (nm)
Element
399.5 399.5 N-II
403.9 403.9 Ar-II
444.9 444.9 Ar-II
500.6 500.7 N-II
567.7 567.9 N-II
795.1 795.1 O-I
868.4 868.3 N-I
300 400 500 600 700 800 900 1000 1100 1200
0
10000
20000
30000
40000
50000
60000
70000
Intensity(AU)
Wavelength (nm)
N-II 399.5 nm
Ar-II 403.9 nm
Ar-II 444.9 nm
N-II 500.6 nm O-I 795.1 nm N-I 868.4 nm
laser scatter
- Air spark shows a rich UV-VIS LIBS emission spectrum.
- Several atomic emissions were identified including those of
Nitrogen, Argon and Oxygen.
*NIST atomic database
AIR

14. Visible-NIR LIBS spectrum of bulk KClO3
Pressed pellets:
800
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Intensity
WaveLength (nm)
Aluminum
Sample2 KClO3 (0.0374g)
Sample3 KClO3 (0.0474g)
Sample1 KClO3 (0.0593)
766.490nm 769.896 nm
Dominant Potassium Emission Lines:
• Bulk KClO3 sample shows dominant potassium emission lines at
766.490nm and 769.896 nm (consistent with NIST database)
• Thin film of KClO3 also reveals potassium emission lines. In addition,
strong emission lines at ~395nm from aluminum substrate was observed
300 400 500 600 700 800 900 1000 1100 1200
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Intensity
WaveLength (nm)
(K) 766.5 nm
Air
Aluminum
KClO3
KClO3 on Aluminum

15. MIR (2-4 µm) LIBS spectrum of KClO3:
bulk sample and films on substrates
Pressed pellets
Film on Al-substrate
• MIR LIBS shows no emission features from background air.
• MIR LIBS shows distinct potassium MIR atomic emission lines from bulk
sample and from a thin film of KClO3 on aluminum substrate.
NIST database shows K-emissions at: 2.7µm, 3.2µm, 4.03µm
Al-substrate
2000 2500 3000 3500 4000 4500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Intensity
Wavelength (nm)
Pure KClO3
Air
KClO3 on Aluminum
Aluminum
~2.7µm
~4.0µm
~3.2µm

16. LWIR (4-12 µm) LIBS spectrum of KClO3:
bulk sample and films on substrates
4000 6000 8000 10000 12000
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
Intensity(a.u.)
Wavelength (nm)
Bulk KClO3
KClO3
film on Aluminum
Aluminum
FTIR spectrum
• Bulk pellet of KClO3 shows atomic and molecular LIBS emission features.
• The molecular emission at ~10500nm matches IR absorption of chlorate
anion (ClO3
-).
• Molecular emission of KClO3 films is only weak from film, due to small
sample amount.
~6.2µm
atomic
~10.5µm
molecular

17. Conclusions
• Bulk pellets and thin-film samples of KClO3 were prepared for UV-VIS and IR
LIBS studies. The thin-film samples were deposited on aluminum substrates
using an air-spray system.
• A combined UV-VIS and IR LIBS experimental setup was carefully aligned for
LIBS studies in air.
• Background air revealed strong UV-VIS atomic emission signatures from
oxygen, nitrogen, and argon. Observed UV-VIS atomic emissions were
identified using the NIST database. Background air did not reveal any
emission in the MIR region from 2000-4000nm.
• KClO3 pellets and thin films exhibited characteristic potassium emission lines
in the UV-VIS and IR region useful for sample identification.
• Initial LWIR LIBS were performed and showed indications of a molecular LIBS
emission at ~11000nm due to the ClO3- ion.
• Additional studies using different substrate materials and different sample
concentrations need to be carried out in the future.

18. Acknowledgment
• Dr. Hommerich
• Dr. Brown
• Dr. Kumi-Barimah
• Hampton University Physics Department
• Army Research Office
• National Science Foundation

20. Results and Discussion
– Visible LIBS spectrum of background air
– Visible LIBS spectra of KClO3 (bulk and film on
substrate)
– Infrared LIBS spectrum of air
– Infrared LIBS spectrum of KCLO3 (bulk and film on
substrate
– Identification of atomic and molecular emissions

21. Laser-Induced Breakdown Spectroscopy (LIBS) is a valuable tool for the
chemical analysis of materials. In this study we used LIBS to identify atomic
and molecular emissions of potassium-based energetic materials in the
ultraviolet-visible (UV-VIS) and mid-infrared (MIR) regions. LIBS has become
useful because of its ability to rapidly obtain information from a sample in
solid, liquid or gaseous form. LIBS has been applied to element identification
in planetary exploration, stand-off detection of dangerous chemicals and
explosives, and deep-sea geochemical studies. In this research, the samples
were prepared using an air-spray technique to deposit thin-films of
potassium-based energetic materials onto substrates. During analysis, the
substrate emissions were identified and subtracted from sample emissions
leaving only the relevant atomic and molecular LIBS features from the
energetic materials to be used for sample identification.
Abstract