wu5c14 by Adel Khamis
-
Upload
adel-khamis -
Category
Documents
-
view
216 -
download
0
Transcript of wu5c14 by Adel Khamis
-
8/14/2019 wu5c14 by Adel Khamis
1/10
Unit Five -129- Chapter Fourteen
Laser
Overview:
The word Laser means:
Emission
There are two kinds of emission:
.. Emission.
.. Emission.
Mechanism Spontaneous Emission:
When the electrons
rotate in its original
level, the atom is called
in .
state.
The higher energy levels are called levels.
When the atom gain photon (quantum) of energy equal to
., the electron transfer to , and the atom is
called at . state.
The atom remains at excited state for lifetime about 10-8 second, then it
.. state losing . In form of ...
Characteristics of Spontaneous Emission:
It occurs when the atom (excites / relaxes) from an .. state to a
state, emitting spontaneously the energy difference in the form of
.. without the effect of an external photon.
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
2/10
Unit Five -130- Chapter Fourteen
It occurs (after / before) the lifetime is over.
The emitted photons have (single / wide range of) wavelengths.
The emitted photons propagate (randomly / coherently).
It spreads: where its intensity (decreases / increase) by increase the
traveling distance, according to ... law.
It scatters: where it ..
This is the dominant radiation in ordinary sources.
Spontaneous Emission:
Mechanism Stimulated Emission:
When an excited atom at energy level E2 gain a photon of energy E2 E1
(after / before) the lifetime is over, it forced to return to the
state (absorbing / emitting) the original photon and the colliding photon
(stimulating and stimulated photons).
Characteristics of Stimulated Emission:
It occurs when an external
photon stimulates (ground
state / excited atoms) to
emit the energy difference
in the form of ..
It occurs (before / after)
the lifetime is over.
The emitted photons are .. wavelength.
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
3/10
Unit Five -131- Chapter Fourteen
The emitted photons are (coherent / not coherent) and propagate in (one /
all) direction as a collimated parallel beam
Its spreading is .: where it (obey / disobey) the inverse square law.
Its scattering is ..: where it is rarely to collide with other
particles.
This is the dominant radiation in laser sources.
Stimulated Emission:
..
Comparison between properties of a
laser beam and ordinary light:
Mono-chromaticity:
Ordinary light: consists of
wavelength, differ in
...
Laser beam: consists of ..
band, and the intensity is
., therefore it consider as
beam.
Collimation:
Ordinary light: characterized by
because it (obey /
disobey) the inverse square rule,
therefore the width of the light beam
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
4/10
Unit Five -132- Chapter Fourteen
(increase / decrease) by increasing the traveling distance, and the
intensity (increases / does not change / decrease).
Laser beam: characterized by .. because it (obey / disobey) the
inverse square rule, therefore the width of the laser beam (does / does
not) change by increasing the traveling distance, and the intensity will
(increase / not change / decrease).
Coherence:
Ordinary light: its photons propagate randomly at different instants of
time; therefore it is in (phase / phase difference).
Laser beam: its photons emit at the same time, therefore it is in (phase /
not in phase), which make the radiation intense and focused.
Intensity:
Ordinary light: it (obeys / disobeys) the inverse square rule, therefore its
intensity (increase / does not change / decrease) by increase the traveling
distance.
Laser beam: it (obeys / disobeys) the inverse square rule, therefore its
intensity (increase / does not change / decrease), how long the traveling
distance was.
Theory of the Laser Action:
The active medium must be in the state of ..
Where the number of excited atoms (less / exceed) than the number of
atoms at ground state.
Emission of radiating for the excited atom through the (spontaneous /
stimulated) emission.
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
5/10
Unit Five -133- Chapter Fourteen
The excited atom may produce ., or . emission, and
the laser action depends on the emission produced by (spontaneous /
stimulated) emission which required photon of energy E2 E1 to impact
with the (ground state / excited) atom.
Amplification of stimulated emission through the .
The number of photons (intensity of laser) is increase due to the
.. between two enclosing mirrors, where the photons impact with
more atoms at the (ground / excited) level, causing the number of
coherent photons to (increase/ decrease).
Main components of a laser:
Active medium:
It is the active medium to produce the laser beam, and it can be:
a) ....: such as ruby.
b) .....
c) .: such as water solution of organic dye.
d) ..: such as He Ne laser.
e) ..: such as CO2 laser.
Source of Energy:
It is responsible for . the active medium.
a) Electric energy: where there are two methods of excitation by electric
energy:
By using of ..
By using of ..
which is used in gas laser (e.g.: CO2 laser, Ar laser, He-Ne laser).
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
6/10
Unit Five -134- Chapter Fourteen
b) Excitation by optical energy: where
there are two methods of excitation by
optical energy:
By (e.g.: ruby laser).
By (e.g.: liquid dye laser)
Using of optical energy to cause the
excitation is called ...
c) Thermal Excitation:by using the thermal effect of the ..
energy of gases (e.g.: He-Ne laser).
d) Excitation by chemical energy: some kind of chemical reactions
produce huge amount of energy such
as the reaction between hydrogen and
fluorine or the reaction between
deuterium fluoride and CO2. That
energy can be used to the
active medium stimulating it to
produce laser.
Resonant Cavity:
It is the container and the activating catalyst for amplification. There are two
types of resonant cavity:
a) External resonant cavity: in form of ....
b) Internal resonant cavity: ..
..
(e.g.: ruby laser).
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
7/10
Unit Five -135- Chapter Fourteen
Helium Neon (He Ne) laser:
The two elements are selected due to
..
Active medium:
Gas atom, where:
Helium and Neon in ratio of (.: ) under pressure (.) mm Hg.
is the responsible gas to produce laser, while .. is
used to excite . to reach the popular inverse case.
Source of Energy:
Electric energy, where there are two methods:
.. from the outside.
.. inside the tube causing electric discharge
Resonant Cavity:
Internal resonant cavity: where Helium and Neon are placed in
The ends of the tube are polished to act as ; one of them is
nearly .% reflector, while the other is % reflector.
Operation:
1. Helium atoms are excited by ..
2. The excited helium atoms collide with , as
inelastic collisions casing the Neon atom to ..
3. The life time of the excited Neon atom is relatively long (10-3 sec),
therefore it called ... level, and that cause
. to be reached.
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
8/10
Unit Five -136- Chapter Fourteen
4. The excited Neon atom relaxes, and by (spontaneous / stimulated)
emission, it produces (random / coherent) photons travel in (one / all)
directions.
5. Photons at the direction of the axis of the tube suffer by
the two parallel mirrors, and cant escape from the tube.
6. During the propagation of photons, they may collide with Neon atoms at
.. level, causing (spontaneous / stimulated) emission, and
producing more photons (in phase / not in phase) and in the same
direction.
7. The previous step is repeated which causing the multiplies to increase the
number of photons that are in phase and in the same direction.
8. At certain intensity, part of the radiation the semitransparent
mirror, while the other part remains inside the tube to cause more of
stimulated emission.
9. Neon atoms that relax to lower energy level, loss the rest of their energy
to reach ground state, and be ready to collide .
10. Helium atoms that lose their energy due to collision, get excited again by
.
Laser applications:
Laser light covers different regions of the electromagnetic spectrum,
therefore it used in different fields:
I. Holography:
Image is formed by ...
Image information are:
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
9/10
Unit Five -137- Chapter Fourteen
1. of light wave.
2. . of light wave. Intensity is (directly / inversely)
proportional to the square of the amplitude.
3. ., which can
be indicated by the phase angle where:
..........
differencepath..........ediffereencphase =
Plane image (2D Image) carries information
about the .. only.
Recording the image at the holograph plate:
Holography is established by Gabor, where:
1. Part of coherence light beam (laser) fall at . and
reflect to the ...
2. Another part (.) fall at the holograph plate
directly.
3. Due to the interference between the two parts of the beam,
formed at the plate.
View the image:
by illuminate the plate by coherent waves of the same frequency of the
.. beam, two images are appear:
1. .. behind the plate.
2. at screen beside the plate.
The same plate can store more than one image; therefore it may used to
produce ..
Work Sheet 2007/2008
-
8/14/2019 wu5c14 by Adel Khamis
10/10
Unit Five -138- Chapter Fourteen
II. Laser in medicine:
Lasers are used to ., where the operation
takes less time and effort.
Lasers are used to treat cases of and ..
sightedness.
Lasers are used with optical fibers in .., for diagnosing and
surgery.
III. Other applications of laser:
Communications: where . carry the information instead
of wire caries ..
Industry: specially fine industries.
Military applications: (e.g.: guidance, smart bombs and laser radar
[LADAR]).
CD recording.
Laser printing.
Arts and laser shows.
Surveying.
Space research.
Work Sheet 2007/2008