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ANALYTICAL CHEMISTRY
LASER SPECTROSCOPYAyesha Abdul Ghafoor
MS Chemistry
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
FLASHES OF BRILLIANCETHE HISTORY OF THE LASER
04/11/2023
“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
L.A.S.E.R
Light Amplification by Stimulated Emission of Radiation
BASIC LASER
Light Sources Gain medium Mirrors
R = 100% R < 100%
I0 I1
I2I3 Laser medium
I
R. Trebino
GAIN MEDIUM
E1
E2
BN1I = rate of Stimulated absorption
Einstein Coefficients
E2
E1
E2
E1
BN2I = rate of Stimulated emission
AN2 = rate of Spontaneous emission
E = hν
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
OBTAINING POPULATION INVERSION
satI
d NBIN BI N AN A N
dt
2
d NBI N AN A N
dt
1 /
1 /sat
sat
I IN N
I I
Laser Transition
Pump Transitio
n
Fast decay
Fast decay
1
2
3
0
2
1
N2
N1
Laser
Fast decay
Laser Transition
Pump Transitio
n1
23
2-level system
3-level system
4-level system
1 / sat
NN
I I
d NBIN BI N A N
dt
/
1 /sat
sat
I IN N
I I
Population Inversion is obtained for ΔN < 0 (ΔN = N1 – N2)
LASER SYSTEM
Active MediumActive medium can be of following types Liquid Solid gases
Pumping Source Optical pumping Chemical pumping Nuclear pumping Discharge technique Laser pumping Electron beam pimping
Resonators Transverse Mode Longitudinal mode
Laser Transition
Pump Transitio
n
Fast decay
Fast decay
1
2
3
0
Tunnable Laserswavlength of operation can be altered in controlled manner.
Dye lasers use complex organic dyesGas 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
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.
LASER SPECTROSCOPY INSTRUMENTATION
LASER as Source of Light Gratings and Monochromators Interferometers
Michelsons Interferometers Fourier Transform Spctrometer
Dtectors Thermal Detectors Flourescent detectors etc.
Recorder
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.
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.
Fig: LIBS Spectra for identification of different elements in sample
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.
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).
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.
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.
APPLICATIONS OF LASER SPECTROSCOPY
Medical field Analytical Chemistry Industrial Applications Environmental Applications
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
IDENTIFICATION OF BACTERIALCONTAMINATION 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)
toexcite LIF» Scattered light also measured» Certain thresholds for both signals
REAL-TIME MONITORING OF HEMODIALYSISReal-time monitoring 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
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 orphotodestruction
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
MOLECULES STUDIED IN BREATH BY LASER SPECTROSCOPY
Molecule MethodsAcetaldehyde LIBS , TDLASAcetone CRDSAmmonia PAS, TDLAS, OFC-CEASCarbon dioxide CRDS, TDLAS, CALOS, OFC-
CEASCarbon monoxide TDLASCarbonyl sulfide TDLAS, CALOSD/H isotopic ratio TDLASEthane LIBS , OA-ICOS, TDLAS, PASMethylamine, CRDS
LASER SPECTROSCOPY OF BREATH IS LIMITED TO SMALL MOLECULES single vibration-rotation
lines are measured -the lines have a certainlinewidth (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 cannotusually be used (typical p =
0.05 – 0.2 atm)
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
FIG :RAMAN SPECTRUM OF NATURAL DIAMOND
ARTS ( STUDY OF PAINTING)
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…
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
THANKS FOR LISTNIN
Questions???Glad to Answer your Questions
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