Sana Shaikh is studying for her M.Sc in physical chemistry with a specialization in analytical chemistry. Her topic is on sources of electromagnetic radiation used in spectroscopy. There are two main types of sources - continuum sources that emit over a wide range of wavelengths like tungsten filament lamps, and line sources that emit discrete wavelengths like gas discharge lamps. Lasers are also described as precise line sources that are monochromatic and coherent.

1. Name: Sana Shaikh.
Roll no-3.
M.sc-Part one.
Specialization : Physical chemistry .
Subject: Analytical chemistry.
Topic : Sources.

2. Introduction to spectroscopy.
• Spectroscopy is the branch of science dealing
with the study of interaction of electromagnetic
radiation with matter.
• It is carried under the following heads.
 Atomic spectroscopy: This deals with of
interaction of electromagnetic radiation
with atoms.
 Molecular spectroscopy: This deals
with interaction of electromagnetic
radiation with molecules.

3. Energy of electromagnetic
radiation.
Region Wavelength range.
Radio waves 2 x 105 cm to 30 cm
Micro waves 30 cm to 10 -2 cm
Far infra red 200 µ to 15 µ
Infra red 15 µ to 2.5 µ
Near infra red 2.5 µ to 0.8 µ
Visible 800 nm to 400 nm
Ultra violet 400 nm to 200 nm
Far ultra violet 200 nm to 15 nm
X-rays 15 nm to 10 -2 nm
Γ-rays 10 -2 nm to 10 -3 nm

4. General instruments for
spectroscopy.

5. Sources of radiation .
• Properties :
• A source must generate a beam with
sufficient radiant power for easy detection
and measurement.
• Its output power should be stable for
reasonable periods.
• Intensity should not fluctuate over long
and short time intervals.

6. Types of radiation sources.
• Two types of radiation sources
• Continuum Sources
and
• Line Sources

7. Continuum Sources
• Emit radiation over a wide range of wavelengths
• Intensity of emission varies slowly as a function of wavelength
• Used for most molecular absorption and fluorescence
spectrometric instruments
• Examples
• Tungsten filament lamp (visible radiation)
• Deuterium lamp (UV radiation)
• High pressure Hg lamp (UV radiation)
• Xenon arc lamp (UV-VIS region)
• Heated solid ceramics (IR region)
• Heated wires (IR region)

8. Examples.
Tungsten filament lamp
Xenon arc lamp
Deuterium lamp

9. Line Sources
• - Emit only a few discrete wavelengths of light
• - Intensity is a function of wavelength
• - Used for molecular, atomic, and Raman spectroscopy
• Examples
• Hollow cathode lamp (UV-VIS region)
• Electrodeless discharge lamp (UV-VIS region)
• Sodium vapor lamp (UV-VIS region)
• Mercury vapor lamp (UV-VIS region)
• Lasers (UV-VIS and IR regions)

10. Hollow cathode lamp
Electrode less
discharge lamp
Lasers

11. • Tungsten Filament Lamp
• Glows at a temperature near 3000 K
• Produces radiation at wavelengths from 320 to 2500 nm
• Visible and near IR regions
• Dueterium (D2) Arc Lamp
• D2 molecules are electrically dissociated
• Produces radiation at wavelengths from 200 to 400 nm
• UV region

12. • Mercury and Xenon Arc Lamps
• Electric discharge lamps
• Produce radiation at wavelengths from 200 to 800 nm
• UV and Visible regions
• Silicon Carbide (SiC) Rod
• Also called globar
• Electrically heated to about 1500 K
• Produces radiation at wavelengths from 1200 to 40000 nm
• IR region

13. Laser
• Light Amplification by Stimulated Emission of
Radiation
• Produce specific spectral lines
• Used when high intensity line source is required
• Can be used for
• UV
• Visible
• FTIR

14. Why laser is better ?
• Incandesent lamp.
• Many wavelengths.
• Multidirectional.
• Incoherent.
• Laser light
• Monochromatic.
• Directional
• Coherent.

15. Types of laser.
• Solid state lasers.
• Gas lasers.
• Tunable lasers.
• Semiconductor lasers.

16. Solid state lasers
• Ruby laser.
• The first laser, one that is still
used.
• Ruby is synthetic aluminum
oxide, Al2O3, with 0.03 to
0.05% of chromium oxide,
Cr2O3, added to it. The Cr3+
ions are the active ingredient;
the aluminum and oxygen
atoms are inert.
• Pumping is by light from a
xenon flash tube.

17. Solid state lasers
• Neodymium: YAG
laser.
• The active ingredient is
trivalent neodymium, Nd3+,
added to an yttrium aluminum
garnet, YAG, Y3Al5O12.
• The Nd-YAG laser has a vary
high radiant power outpt at
1064nm.

18. Gas lasers.
• Gas lasers consist of a gas filled tube placed in the laser cavity. A
voltage (the external pump source) is applied to the tube to excite the
atoms in the gas to a population inversion. The light emitted from this
type of laser is normally continuous wave (CW).
• These device are of 4 types
• Neutral atom lasers (He & Ne).
• Ion laser (Ar+ and Kr+).
• Molecular laser (Co2 and N2 ).
• Excimer laser (ArF and XeCl ).

19. Tunable lasers.
• dye lasers: first tunable lasers
• parametric oscillator:
 more compact  less expensive
 easier to operate  tuning range much wider
Color center lasers: tuned over wide bands in the UV, the visible, and
the IR.
free-electron laser:
 high powers of the order of megawatts
 very efficient
 tuned through a wide range of wavelengths.

20. Semiconductor lasers.
• LED: light-emitting diode.
• Emit almost anywhere in the
spectrum, from the UV to the
IR
• An efficiency much higher
than with optical pumping .
• main application :
• waveguides
• integrated optics

21. Reference
• Principles of instrumental analysis by
skoog,holler and crouch (6th edition).
• Fundamentals of analytical chemistry
skoog,holler and crouch (9th edition).
• Image source:-
• www.google.com
THANK YOU