1. ANALYTICAL CHEMISTRY
LASER SPECTROSCOPY
Ayesha Abdul Ghafoor
MS Chemistry

2. LASER SPECTROSCOPY
 LASER
 Principle of Laser
 Laser System
 Laser as spectroscopic Light source
 Spectroscopy
 LASER +Spectroscopy
 Laser Induced Breakdown Spectroscopy
 Laser Induced Fluorescent Spectroscopy
 Laser ablation inductively coupled plasma optical emission
spectroscopy (LA-ICP-OES)
 Raman Spectroscopy
 Applications of Laser Spectroscopy

3. 2013-2-26
FLASHES OF BRILLIANCE
THE HISTORY OF THE LASER
“A splendid light has dawned on me”
– Albert Einstein
 In 1917 Einstein published ideas on stimulated emission of radiation.
The laser is credited as being invented in 1958 by Charles H. Townes and
Arthur L. Schawlow. Townes coined the term “laser” with help from his
students.
 On May 16, 1960, Theodore H. Maiman operated the first functioning
laser i.e., a pulse mode operation of solid- state flash lamp -pumped

4. L.A.S.E.R
Light Amplification by Stimulated Emission of Radiation

5. BASIC LASER
 Light Sources
 Gain medium
 Mirrors
I
I0 I1
I3 Laser medium I2
R = 100% R < 100%
R. Trebino

6. GAIN MEDIUM
Einstein Coefficients
E2
AN2 = rate of Spontaneous emission
E1
E2
BN2I = rate of Stimulated emission
E1
E = hν
E2
BN1I = rate of Stimulated absorption
E1

7. TO ACHIEVE LASING:
 Stimulated emission must occur at a
maximum (Gain > Loss)
 Loss:
 Stimulated Absorption
 Scattering, Reflections
 Energy level structure must allow for
Population Inversion
E2
E1

8. OBTAINING POPULATION INVERSION
2-level system 3-level system 4-level system
3 3
Fast decay Fast decay
2 2
2 N2

I sat  Pump Laser Pump Laser

Laser Transition Transition Transition Transition
1 N1 1 1
Fast decay
0
d N d N d N
 2 BI N  AN  AN   BIN  BI N  AN  AN   BIN  BI N  AN
dt dt dt
N 1  I / I sat I / I sat
N  N  N N   N
1  I / I sat 1  I / I sat 1  I / I sat
Population Inversion is obtained for ΔN < 0 (ΔN = N1 – N2)

9. LASER SYSTEM
 Active Medium 3
Active medium can be of following types
 Liquid Fast decay
 Solid 2
 gases
 Pumping Source Pump Laser
 Optical pumping Transition Transition
 Chemical pumping
 Nuclear pumping
 Discharge technique 1
 Laser pumping Fast decay
 Electron beam pimping 0
 Resonators
 Transverse Mode
 Longitudinal mode

10. Tunnable Lasers
wavlength of operation can be altered in controlled manner.
Dye lasers use complex organic dyes
Gas lasers are pumped by current.
Solid-state lasers have lasing material distributed in a solid matrix
(such The Nd:YAG laser emits infrared light at 1.064 nm.
Semiconductor lasers, sometimes called diode lasers, are p-n
junctions. Current is the pump source. Applications: laser printers or
CD players.
Excimer lasers (from the terms excited and dimers) use reactive
gases, such as chlorine and fluorine, mixed with inert gases such as
argon, krypton, or xenon. Excimers lase in the UV.
Free electron Lasers is a laser that shares the same opical
properties as conventional lasers such as emitting a beam of
coherent EMR radiations which can reach high power
R. Trebino

11. SPECTROSCOPY
 Study of interaction of light with matter
 all atoms and molecules absorb and emit
light at certain wavelengths so we can
identify and read their properties
 In essence, every element has a unique
atomic "fingerprint" that takes the form of a
set of wavelengths, or a spectrum.

12. LASER SPECTROSCOPY INSTRUMENTATION
 LASER as Source of Light
 Gratings and Monochromators
 Interferometers
 Michelsons Interferometers
 Fourier Transform Spctrometer
 Dtectors
 Thermal Detectors
 Flourescent detectors etc.
 Recorder

13. LASER-INDUCED BREAKDOWN
SPECTROSCOPY (LIBS)
 advanc-ing significantly over the last decade.
 It can analyze solids, liquids and gases and
 can return results rapidly, with very little
damage to the sample.
 It can do its work from a distance, unlike
some analytical tools that require samples
being brought to a lab.

14. WORKING OF LIBS
 The laser, of course, Generally, LIBS systems use a
neodymium-doped yttrium aluminum garnet
(Nd:YAG) laser at fundamental wavelength of 1,064
nanometers
(but many different lasers have been used. The laser
doesn't blast the sample with a nonstop beam)
 The laser light passes through a lens, which focuses the
energy onto the sample.
 "laser spark” produced.
 Excitation
 Relaxation
 The spectrometer contains a prism and a camera to
photograph the spectra for further study.

16.  Fig: LIBS Spectra for
identification of
different elements in
sample

17. LASER ABLATION INDUCTIVELY COUPLED
PLASMA OPTICAL EMISSION SPECTROSCOPY
(LA-ICP-OES)
 The "P" in ICP stands for plasma, an ionized gas
consisting of positive ions and free electrons.
 The Plasma torch consists of three concentric tubes
of silica surrounded by a metal coil. A nozzle at the
end of the torch acts as an exit for the plasma.
 Now the instrument is ready to analyze a sample.
 In the laser-based version of ICP-OES, a
neodymium-doped yttrium aluminum garnet (Nd:YAG)
laser is used to cut, or ablate, a few microscopic
particles from the sample's surface. The ablated
particles are then carried to the pl-asma torch, where
they become excited and emit light.

19. LASER-INDUCED FLUORESCENCE (LIF)
 Laser-induced fluorescence (LIF) is a spectroscopic
method used for studying structure of molecules,
detection of selective species and flow visualization and
measurements.
 Experimental Method
The species to be examined is excited with a laser. The
wavelength is often selected to be the one at which the
species has its largest cross section . The excited species
will after some time, usually in the order of few
nanoseconds to microseconds, de-excite and emit light at
a wavelength longer than the excitation wavelength. This
fluorescent light is typically recorded with a
photomultiplier tube (PMT).

21. RAMAN SPECTROSCOPY
 C.V. Raman ,Indian scientist discovered Raman
spectroscopy
 Raman spectroscopy is a spectroscopic technique used to
study vibrational , rotational, and other low-frequency modes
in a system
 Principle: It relies on inelastic scattering , or Raman scattering,
of monochromatic light, usually from a laser in the visible ,
near infrared , or near ultraviolet range. The laser light
interacts with molecular vibrations, phonons or other
excitations in the system, resulting in the energy of the laser
photons being shifted up or down. This happens because the
laser light interacts with phonons. The shift in energy gives
information about the phonon modes in the system and
ultimately about the molecules present in the sample.

22.  Experimental Procedure: The
beam from an argon-ion laser is
directed by a system of mirrors
to a lens, which focuses
monochromatic light onto the
sample. Most of the light
bouncing off the sample
scatters at the same
wavelength as the incoming
light, but some of the light does
scatter at different wavelengths
and goes to detector This
happens because the laser light
interacts with phonons. we use
photomultiplier ,CCD detectors
etc. and determine vibrations
kinds and finally sample
molecule.

23. APPLICATIONS OF LASER SPECTROSCOPY
 Medical field
 Analytical Chemistry
 Industrial Applications
 Environmental Applications

24. LASER SPECTROSCOPY IN MEDICINE AND
BIOLOGY
 Medical diagnostics by breath trace gas analysis
 Real-time monitoring of exhaled gases (therapeutic monitoring,
toxicology, occupational health)
 Tissue analysis
 Mapping of drug delivery
 Insect studies
 Plant physiology

25. IDENTIFICATION OF BACTERIAL
CONTAMINATION OF PLATELETS (LIF)
 Blood transfusion carries a risk of
infection (hepatitis, HIV…) or
consequent sepsis
 every platelet concentrate should be
checked before use (after donation and
shortly before transfusion
» Fluorescent stain attaches to the DNA of
bacteria (platelets don’t contain DNA!)
» Frequency doubled Nd-laser (532 nm)
to
excite LIF
» Scattered light also measured
» Certain thresholds for both signals

26. REAL-TIME MONITORING
Real-time monitoring OF HEMODIALYSIS
of hemodialysis
» Hemodialysis is used
in treatment of renal
failure
» Urea, creatinine, etc.
removed
» Treatment 3 times a
week, 2-12 hours
» Over million patients
worldwide, growing fast

27. LIF SPECTROSCOPY OF TISSUES
There are cellular or
subcellular differences
between normal and
tumorous tissues
» LIF can be used to
visualize tissue
characteristics
and detection of anomalies
» Fluorescing compounds
or autofluorescence
» Non-invasive procedure,
no photosensitization or
photodestruction

28. RESPIRATION OF INSECTS
 Respiration of insects
 - real-time, on-line measurement of
CO2
 - very small quantities sensitive
detection method, small volume of
sample line and cell
 photoacoustic spectroscopy
 - mid-IR should be used if possible
(CO2 at 4.234 μm)
 - OPO (between 3.9 and 4.8 μm)
continuous-wave, single mode
operation
 - detection limit 0.7 ppb.
 - sporadic release of CO2 observed

29. MOLECULES STUDIED IN BREATH BY LASER
SPECTROSCOPY
Molecule Methods
Acetaldehyde LIBS , TDLAS
Acetone CRDS
Ammonia PAS, TDLAS, OFC-CEAS
Carbon dioxide CRDS, TDLAS, CALOS, OFC-CEAS
Carbon monoxide TDLAS
Carbonyl sulfide TDLAS, CALOS
D/H isotopic ratio TDLAS
Ethane LIBS , OA-ICOS, TDLAS, PAS
Methylamine, CRDS

30. LASER SPECTROSCOPY OF BREATH IS
LIMITED TO SMALL MOLECULES
 single vibration-rotation
lines are measured
 -the lines have a certain
linewidth (Voigt profile)
 -the bigger the molecules,
the more congested the
spectrum becomes(lines
start to overlap
each other)
 -typical laser wavelength 1.5
to 10 μm
 -sensitivity ppt – ppm
 -normal pressure cannot
usually be used (typical p =
0.05 – 0.2 atm)

31. IN ANALYTICAL CHEMISTRY
 Laser Spectroscopy in Analytical Chemistry
 Chemical Reactions
 Detection of Atoms
 Study of Transition States
 Separation of isotopes (In Nuclear Reactors)
 Study of Bond Energies and Angles
 Type of Material

32. FIG :RAMAN SPECTRUM OF NATURAL DIAMOND

33. ARTS ( STUDY OF PAINTING)

34. LIF SPECTROSCOPY OF INTERNAL COMBUSTION
ENGINES
 LIF spectroscopy of internal
combustion engines
 Goals: to improve combustion
efficiency to reduce emission of
pollutants
 how well air and fuel are mixed
 chemical intermediates
 rate constants of key reactions
 l = air/fuel ratio
 ArF ,KrF lasers
 Molecules:
NO, CO, CO2, hydrocarbons…

35. CONCLUDING THOUGHTS
The key to managing today’s rapidly evolving technology it to
constantly analyze how each advance affects us as individuals
and as a society as a whole. “
“Our Advancing Technology , if separated from the
human factor, I take to be part of the advance in the evolving
quality of existence, something that gives added meaning and
higher dimension to the human venture…”
- Roger Sperry
Neuroscientist and Nobel Laureate

36. Questions???
Glad to Answer your Questions
THANKS FOR LISTNIN