3. Light Sources
A light source is anything that makes light,
whether natural and artificial. Natural light
sources include the Sun and stars. Artificial
light sources include lamps, Lasers Bulbs
etc.
3
4. Introduction
Without light sources we could not see
the world around us, however not every
object we can see is a light source. Many
objects simply reflect light from a light
source.
The source should have a readily
detectable output of radiation over the
wavelength region for which the
instrument is designed to operate.
4
Fig:
5. Source of visible light
Light or visible light is electromagnetic
radiation within the portion of
the electromagnetic spectrum that
is perceived by the human eye.
Source of visible light visible (Vis) region
is actually a very small part of the
electromagnetic spectrum, and it can be
seen by the human eye. The visible region
extends from the near-ultraviolet region
(380 nm, deep violet) to about 780 nm (far
red)
5
7. Lamp as a Source of light
Lamps and lasers are frequently used as
source of particular wavelength range of
light.
The most commonly used source for the
visible region is a quartz tungsten–halogen
(QTH) lamp. Wavelength range is from
about 325 or 350 nm to 25 μm, so it can also
be used in the near-ultraviolet and near-
infrared regions.
It has been utilized in the photo-catalytic
reactor.
7
Fig: Quartz Tungsten–halogen lamp
8. LED as a Source of light
LEDs are very power-efficient light sources a
white LED is composed of a blue InGaN
(Indium gallium nitride) LED emitting at
450 nm that is coated with a broadband
phosphor that has peak emission in the
green, at 550 nm;
blue LED and a phosphor emits primarily in
the green but extends into red, with the
wavelength ranges from 425–700 nm
Intensity of radiation.
8
Fig: LEDs of different colours
9. Source of UV-Visible
The ultraviolet region extends from 10 to 380 nm. The most
analytically useful region is from 190 to 380 nm called the near-
ultraviolet or quartz UV region. Below 190 nm, air, notably oxygen
absorbs appreciably and so the instruments are operated under a
vacuum; hence, this wavelength region is called the vacuum-
ultraviolet region.
9
10. Deuterium Discharge Lamps
Deuterium bulbs are a low-pressure,
gas-discharge lamp that is filled with
deuterium gas at carefully controlled
pressures.
They emit a nearly continuous
spectrum of light, ranging from UV
wavelengths of 180nm to 370nm.
10
Figure: Deuterium Discharge lamp
11. LASER as a Source of light
A laser is a device that emits light through a
process of optical amplification based on
the stimulated emission of electromagnetic
radiation. The word "laser" is an acronym for
"light amplification by stimulated
emission of radiation“.
Lasers are intense monochromatic sources,
being frequently used for fluorescence
excitation.
11
13. IR radiations as Source of light
The infrared (IR) region extends from
about 0.78 μm (780 nm) to 300 μm, but
the range from 2.5 to 15 μm is the most
frequently used for analysis Infrared
radiation is essentially heat, and so hot
wires, light bulbs, or glowing ceramics
are used as sources.
13
14. Fourier transform infrared instrument
For Fourier transform infrared instrument
typical infrared source is the Nernst glower. A
rod consisting of a mixture of rare-earth
oxides. It has a negative temperature
coefficient of resistance and is nonconducting
at room temperature. Therefore, it must be
heated to excite the element to emit radiation,
but once in operation it becomes conducting
and furnishes maximum radiation at about 1.4
μm, or 7100 cm−1 (1500 to 2000◦C).
14
Fig: FTIR Spectroscopy
15. Globar
Another infrared source is the Globar.
A Globar is used as thermal light source
for infrared spectroscopy. This is a rod of
sintered silicon carbide heated to about 1300
to 1700◦C. Its maximum radiation occurs at
about 1.9 μm (5200 cm−1), and it must be
water-cooled. The Globar is a less intense
source than the Nernst glower, but it is more
satisfactory for wavelengths longer than 15 μm
because its intensity decreases less rapidly.
15
Fig: Globar diagram
16. Used in Characterization instruments
UV-VIS
• UV-VISIBLE
SPECTROSCOPY
• For band gap
evaluation
PL
• PHOTOLUMINESCEN
CE EMISSION
SPECTROSCOPY
• For studying
optical properties
FTIR
To understand
the functional
group of the
material.
Photo-catalytic
reactor
For water degradation
process
17. Summary
Lasers are intense monochromatic sources, being frequently
used for fluorescence excitation.
As the demands on automotive lighting grow increasingly
complex, LED and laser light sources will inevitably play an
increasing role. After all, LED lamps have proven durable,
long-lasting, and energy-efficient, and single diode laser
modules are already proving themselves on the road in
automotive headlight applications.
By tailoring the spatial and spectral properties of cavity
resonances, the number of lasing modes, the emission
profiles, and the coherence properties can be controlled.
17
18. Hanulia, T., Oleszko, M., Tomala, R., & Strek, W. (2021). Investigation of
coherence properties of white light emission of tungsten lamp additionally
excited with laser radiation. AIP Advances, 11(2), 025119.
Horne, S., Smith, D., Besen, M., Partlow, M., Stolyarov, D., Zhu, H., & Holber,
W. (2010, April). A novel high-brightness broadband light-source technology
from the VUV to the IR. In Next-Generation Spectroscopic Technologies
III (Vol. 7680, pp. 105-111). SPIE.
Jansen, M., Carey, G. P., Carico, R., Dato, R., Earman, A. M., Finander, M. J.,
... & Umbrasas, A. (2007, February). Visible laser sources for projection
displays. In Projection Displays XII (Vol. 6489, pp. 50-55). SPIE. Moselund, P.
M., Petersen, C., Dupont, S., Agger, C., Bang, O., & Keiding, S. R. (2012, May).
Supercontinuum: broad as a lamp, bright as a laser, now in the mid-infrared.
In Laser Technology for Defense and Security VIII (Vol. 8381, pp. 265-270).
SPIE.
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References
