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Файл:English for Optics Students. Английский для студентов, изучающих оптику. Учебное пособие
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Additional texts to Unit Optics
Text 1
Modern optics encompasses the areas of optical science and engineering
that became popular in the 20th century. These areas of optical science typically relate to the electromagnetic or quantum properties of light but do include other topics. A major subfield of modern optics, quantum optics, deals
with specifically quantum mechanical properties of light. Quantum optics is
not just theoretical; some modern devices, such as lasers, have principles of
operation that depend on quantum mechanics. Light detectors, such as photomultipliers and channeltrons, respond to individual photons. Electronic
image sensors, such as CCDs, exhibit shot noise corresponding to the statistics of individual photon events. Light-emitting diodes and photovoltaic
cells, too, cannot be understood without quantum mechanics. In the study of
these devices, quantum optics often overlaps with quantum electronics.
Specialty areas of optics research include the study of how light interacts with specific materials as in crystal optics and metamaterials. Other
research focuses on the phenomenology of electromagnetic waves as in singular optics, non-imaging optics, non-linear optics, statistical optics, and
radiometry. Additionally, computer engineers have taken an interest in integrated optics, machine vision, and photonic computing as possible components of the "next generation" of computers.
Today, the pure science of optics is called optical science or optical
physics to distinguish it from applied optical sciences, which are referred to
as optical engineering. Prominent subfields of optical engineering include
illumination engineering, photonics, and optoelectronics with practical applications like lens design, fabrication and testing of optical components,
and image processing. Some of these fields overlap, with nebulous boundaries between the subjects terms that mean slightly different things in different parts of the world and in different areas of industry. A professional
community of researchers in nonlinear optics has developed in the last
several decades due to advances in laser technology.
Text 2
Optical fiber
Optical fiber is the most common type of channel for optical communications. The transmitters in optical fiber links are generally light-emitting
diodes (LEDs) or laser diodes. Infrared light, rather than visible light is used
more commonly, because optical fibers transmit infrared wavelengths with
less attenuation and dispersion. The signal encoding is typically simple intensity modulation, although historically optical phase and frequency modu-
11
lation have been demonstrated in the lab. The need for periodic signal regeneration was largely superseded by the introduction of the erbium-doped
fiber amplifier, which extended link distances at significantly lower cost.
Text 3
Signal lamps
An air traffic controller is holding a signal light gun that can be used to
direct aircraft experiencing a radio failure (2007).
Signal lamps (such as Aldis lamps),
are visual signaling devices for optical
communication (typically using Morse
code). Modern signal lamps are a focused
lamp which can produce a pulse of light.
In large versions this pulse is achieved by
opening and closing shutters mounted in
front of the lamp, either via a manually
operated pressure switch or, in later versions, automatically.
With hand held lamps, a concave mirror is tilted by a trigger to focus the
light into pulses. The lamps are usually equipped with some form of optical
sight, and are most commonly deployed on naval vessels and also used in
airport control towers with coded aviation light signals.
Aviation light signals are used in the case of a radio failure, an aircraft
not equipped with a radio, or in the case of a hearing-impaired pilot. Air
traffic controlers have long used signal light guns to direct such aircraft. The
light gun's lamp has a focused bright beam capable of emitting three different colors: red, white and green. These colors may be flashing or steady, and
provide different instructions to aircraft in flight or on the ground (for example, "cleared to land" or "cleared for takeoff"). Pilots can acknowledge
the instructions by wiggling their plane's wings, moving their ailerons if
they are on the ground, or by flashing their landing or navigation lights during night time. Only 12 simple standardized instructions are directed at aircraft using signal light guns as the system is not utilized with Morse code.
Text 4
Photophone
The photophone (originally given an alternate name, radiophone) is a
communication device which allowed for the transmission of speech on a
beam of light. It was invented jointly by Alexander Graham Bell and his
assistant Charles Sumner Tainter on February 19, 1880, at Bell's 1325 'L'
Street laboratory in Washington, D.C.
12
Bell believed the photophone was his most important invention. Of the
18 patents granted in Bell's name alone, and the 12 he shared with his collaborators, four were for the photophone, which Bell referred to as his
'greatest achievement', telling a reporter shortly before his death that the
photophone was "the greatest invention [I have] ever made, greater than the
telephone".
The photophone was a precursor to the fiber-optic communication systems which achieved popular worldwide usage starting in the 1980s. The
master patent for the photophone (U.S. Patent 235,199 Apparatus for Signalling and Communicating, called Photophone), was issued in December 1880,
many decades before its principles came to have practical applications.
Text 5
Free-space optical communication
Free-space optics (FSO) systems are generally employed for 'last mile'
telecommunications and can function over distances of several kilometers as
long as there is a clear line of sight between the source and the destination,
and the optical receiver can reliably decode the transmitted information.
Other free-space systems can provide high-data-rate, long-range links using
small, low-mass, low-power-consumption subsystems. More generally,
transmission of unguided optical signals is known as optical wireless communications (OWC). Examples include medium-range visible light communication and short-distance IrDA, using infrared LEDs.
Text 6
Heliograph
Heliograph: Australians using a heliograph in
North Africa (1940).
A heliograph (Greek: Ἥλιος helios, meaning
"sun", and γραφειν graphein, meaning "write") is a
wireless solar telegraph that signals by flashes of
sunlight (generally using Morse code) reflected by a
mirror. The flashes are produced by momentarily
pivoting the mirror, or by interrupting the beam with
a shutter.
The heliograph was a simple but effective instrument for instantaneous optical communication
over long distances during the late 19th and early
20th century. Its main uses were in military, surveys and forest protection
work. They were standard issue in the British and Australian armies until
the 1960s, and were used by the Pakistani army as late as 1975.
13
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UNIT REFLECTION
Terminology
conventional
converge
curved mirrors
fraction
frequency
hard X-rays
interface
magnify
media
metallic coating
propagation
refractive index
specula
thin-film optics
VHF
visible
wavefront
Task 1. Answer the questions:
1. What phenomenon is depicted in the photo?
2. What is the definition of that phenomenon?
3. Where else can you meet it?
4. How is it used in engineering?
5. What do you know about Maxwell and
Fresnel?
Mount Hood in
Mirror Lake 1
Task 2. Find information about Maxwell and Fresnel on the net or
some other source and share it with your group mates.
Task 3. Match the words to their meanings.
1 wavefront
2 interface
3 undergo
4 specular
5 incident
6 shallow angle
7 enhance
A плотный
B подвергаться
C сохранять
D фронт волны
E толщина/глубина поверхностного слоя
F усиливать
G граница
14
8 retain
9 skin depth
10 transparent
11 boundary
12 dense
H зеркальный, отражающий
I малый угол
J падающий
K поверхность раздела
L прозрачный
Task 4. Explain the meanings of the following international words
and those you have studied in Unit Optics (Terminology) in English.
angle, incidence (a physical term), acoustics, sonar, radar, reflect, polarity, inversion, image, spherical, parabolic, rotate, tunnel.
Task 5. Read the text and write down its plan.
Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium
from which it originated. Common examples include the reflection of light,
sound and water waves. The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle
at which it is reflected. Mirrors exhibit specular reflection.
In acoustics, reflection causes echoes and is used in sonar. In geology, it
is important in the study of seismic waves. Reflection is observed with
surface waves in bodies of water. Reflection is observed with many types of
electromagnetic wave, besides visible light. Reflection of VHF and higher
frequencies is important for radio transmission and for radar. Even hard
X-rays and gamma rays can be reflected at shallow angles with special mirrors.
Reflection of light is either specular (mirror-like) or diffuse (retaining
the energy, but losing the image) depending on the nature of the interface.
A mirror provides the most common model for specular light reflection,
and typically consists of a glass sheet with a metallic coating where the reflection actually occurs. Reflection is enhanced in metals by suppression of
wave propagation beyond their skin depths. Reflection also occurs at the
surface of transparent media, such as water or glass.
In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive
index. In the most general case, a certain fraction of the light is reflected
from the interface, and the remainder is refracted. Solving Maxwell's equations for a light ray striking a boundary allows the derivation of the Fresnel
equations, which can be used to predict how much of the light is reflected,
and how much is refracted in a given situation. Total internal reflection of
light from a denser medium occurs if the angle of incidence is above the
critical angle.
15
Total internal reflection is used as a means of focusing waves that cannot effectively be reflected by common means. X-ray telescopes are constructed by creating a converging "tunnel" for the waves. As the waves interact at low angle with the surface of this tunnel they are reflected toward
the focus point (or toward another interaction with the tunnel surface, eventually being directed to the detector at the focus). A conventional reflector
would be useless as the X-rays would simply pass through the intended reflector.
When light reflects off a material denser (with higher refractive index)
than the external medium, it undergoes a polarity inversion. In contrast, a
less dense, lower refractive index material will reflect light in phase. This is
an important principle in the field of thin-film optics.
Specular reflection forms images. Reflection from a flat surface forms a
mirror image, which appears to be reversed from left to right because we
compare the image we see to what we would see if we were rotated into the
position of the image. Specular reflection at a curved surface forms an
image which may be magnified or demagnified; curved mirrors have optical
power. Such mirrors may have surfaces that are spherical or parabolic.
Task 6. Why are the following words special? What do these words
mean? Look up for information in the dictionary if necessary.
medium/media, phenomenon/phenomena, speculum/specula, index/ indexes(indices)
Task 7. Mark the following statements T (True), F (False), N (Not
mentioned). Find the proof in the text.
1. Light is reflected by any media.
2. There are three laws of reflection.
3. A mirror is a metallic sheet with glass coating.
4. The phenomenon of reflection is used in radars.
5. It is impossible to suppress hard X-rays and gamma rays.
6. Specular reflection can be the simplest variant of a mirror reflection.
7. A conventional reflector cannot be used in X-rays telescopes.
8. Light changes its polarity if the reflecting material is of higher density.
9. Maxwell was the first to formulate the theory of reflection.
10. Diffuse reflection does not allow obtaining the exact image.
Task 8. Answer the questions. Either find the proof in the text or prove
it in some other way.
1. What do mirrors exhibit?
2. What are echoes caused by (in acoustics)?
3. What part of light is usually reflected?
16
4. What is the condition for the total reflection to take place?
5. Why are mirrors necessary for X-ray telescopes?
6. What is mathematics used in optics for?
7. What are the peculiarities of reflection from curved surfaces?
8. When is light reflected off a surface in phase?
9. What industries/areas is the phenomenon of re-
flection used in?
10. When is a reflected image reversed?
Task 9. Look at the picture on the right. Give the
name to the depicted phenomenon and explain it.
Task 10. Work with a partner to complete the
word families in the table below. Translate the words
while filling in the table.
Verb Noun Adjective Other parts of speech
diffuse
…
occur
predict
…
…
…
…
converge
…
…
suppression
…
…
derivation
…
propagation
equations
…
…
…
…
…
…
…
…
…
…
…
curved
…
…
…
…
…
solving
…
…
…
…
Task 11. Skim the text and write out the sentences where the word
would is used. Translate them.
Task 12. Read and translate the information about using the word
would. Find the corresponding explanation(s) of using the word would in
the sentences you have written out in Task 11.
1. used for talking about what was going to happen in the past, used for
showing what someone expected, intended, promised etc when they were
thinking or talking about the future
For example: Most analysts expected that there would be a change in
policy.
2. used for talking about the possible results of a situation that is unlikely to happen or that did not happen
17
For example: What would happen if there was an earthquake?
would have done something:
If I’d known you were coming, I’d have got your room ready.
3. used for saying what someone used to do in the past
For example: The Campbells would sometimes invite us over for the
weekend.
4. used for politely asking someone to do something or to let you do
something
For example: Would you mind waiting outside?
Would it be all right if I used your phone?
Task 13. Search the Internet and other possible sources to learn more
about the usage of the word would. Share the information you have found
with your group mates.
Task 14. Translate the following linking words. Find the sentences
where they are used in the text and translate those sentences.
either… or
even
so that
beyond
in the most general case
toward
eventually
Task 15. Use the linking words from Task 11 in sentences of your
own.
Task 16. Write an essay of 150 words on one of the topics.
1.Visible light
2. Seismic waves
3. Acoustics
4. Types of mirrors
5. Light polarity
6. The main characteristics of light.
Task 17. Look through the text again and get ready to speak about reflection using your plan and the figure below.
18
Additional tasks to Unit Reflection
Task 1. Describe the picture. Include in
your description the information about
1. The source of light
2. The density of two different media
3. The angle of reflection
4. The energy of light before and after the re-
flection
Task 2. Fill in the gaps with the following words. One word is extra.
1 equal 2 incident 3 angle 4 enhance 5 equations 6 specular 7 reflected
8 surface 9 reflecting
If the A… surface is very smooth, the reflection of light that occurs is
called B… or regular reflection. The laws of reflection are as follows:
1. The C… ray, the reflected ray and the normal to the reflection at the
D… point of the incidence lie in the same plane.
2. The E… which the incident ray makes with the normal is F... to the
angle which the reflected ray makes to the same normal.
3. The G... ray and the incident ray are on the opposite sides of the nor-
mal.
These three laws can all be derived from the Fresnel H….
Task 3. Answer the questions. Find out necessary information if you
cannot answer the questions.
1. What is a dipole antenna?
2. What do you know about Huygens?
3. What does quantum electrodynamics deal with?
Task 4. Read the text and give it a heading.
In classical electrodynamics, light is considered as an electromagnetic
wave, which is described by Maxwell's equations. Light waves incident on a
material induce small oscillations of polarisation in the individual atoms (or
oscillation of electrons in metals), causing each particle to radiate a small
secondary wave in all directions, like a dipole antenna. All these waves add
up to give specular reflection and refraction, according to the Huygens–
Fresnel principle.
In the case of dielectrics such as glass, the electric field of the light acts on
the electrons in the material, and the moving electrons generate fields and
become new radiators. The refracted light in the glass is the combination of
19
the forward radiation of the electrons and the incident light. The reflected
light is the combination of the backward radiation of all of the electrons.
In metals, electrons with no binding energy are called free electrons.
When these electrons oscillate with the incident light, the phase difference
between their radiation field and the incident field is π (180°), so the forward radiation cancels the incident light, and backward radiation is just the
reflected light.
Light–matter interaction in terms of photons is a topic of quantum electrodynamics, and is described in detail by Richard Feynman in his popular
book QED: The Strange Theory of Light and Matter.
* in terms of – касательно, с точки зрения, с учётом, если иметь в
виду, в терминах
Task 5. Look at the picture. Make the comparison
and give the definition to the diffuse light.
Task 6. Translate and explain the following in-
ternational words:
luminance, photometry, radiance, radiometry, co-
sine, mechanism, polycrystalline, diffuse, organic
Task 7. Match the words to their definitions.
1 bounce
2 is due to
3 reflectance
4 due to
5 observation
6 cell
7 fiber
A the fraction of the total radiant flux incident upon a surface that
is reflected and that varies according to the wavelength distribution
of the incident radiation
B hit surface and move away
C because of something
D the process of watching something carefully in order to find
something out
E is caused by
F a very thin piece of a natural or artificial substance similar to a
hair in shape
G the smallest part of a living structure
Task 8. Translate the text. Compare your translation with that of your
partner. Choose the best variant.
When light strikes the surface of a non-metallic material it bounces off
in all directions due to multiple reflections by the microscopic irregularities
20
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