Download Diapositiva 1 - Instituto de Astronomía

OptoMechanics
Clase 04:
Nature of Light
Dr. Alejandro Farah
Instituto de Astronomía, UNAM
Posgrado de Ingeniería, UNAM
content…
2. Nature of Light:
The student will learn the implication of the physical behavior of
light in optomechanics and understand the meaning of the influence
of the mechanical restraints in optical components.
2.1
Description of the light wave motion.
2.1.1
Types of wave: elastic and electromagnetic.
Definition of optical path.
Posgrado de Ingeniería, UNAM
…first of all…a few words…
absence of darkness
energy
Information
facilitates the ability to view
…
Posgrado de Ingeniería, UNAM
2.1
Description of the light wave motion.
Light:
An electromagnetic radiation, part of which stimulates the sense
of vision Light.
A device that produces light, such as: lamp, an architectural device
A concept of weight
Michael Bosanko
Posgrado de Ingeniería, UNAM
2.1
Description of the light wave motion.
Wavelength
The frequency of the electromagnetic wave
can be varied over the entire positive
range, but cannot be reduced to zero.
The energy in the wave is continuously
variable, with a minimum energy of any
non-zero value, and no maximum value.
Posgrado de Ingeniería, UNAM
2.1
Description of the light wave motion.
Since light is a repeating waveform in motion, it is possible to measure
the physical distance between matching points of adjacent cycles of the
waveform. This is shown here:
The symbol used to represent this distance is the Greek letter "Lambda" (λ).
Posgrado de Ingeniería, UNAM
2.1
Description of the light wave motion.
In the case of light, the wavelength is so short that a specific distance,
called the ångstrom (Å), has been defined.
One ångstrom = 10-10 m or 10-8 cm.
Visible light  3900 Å to 7700 Å
Electromagnetic energy outside this range is no longer visible to the human eye.
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http://sleevage.com
Posgrado de Ingeniería, UNAM
2.1
Description of the light wave motion.
Speed of Propogation
The speed at which light travels through any medium is determined by
the density of that medium.
Speed of light in a vacuum = 2.997925 ± 0.000002 x 1010 cm/sec.
As made famous in Einstein's equation, the letter c is used as a general
symbol for the speed of light.
Posgrado de Ingeniería, UNAM
2.1
Description of the light wave motion.
Frequency and Period
The period of any wave, measured as
some amount of time per cycle, is in fact
the time interval that corresponds to the
physical wavelength of the signal.
The basic mathematical formula that relates wavelength, frequency, and
the speed of light is:
c = fλ
The frequency of the wave is the inverse or
reciprocal of the period.
Posgrado de Ingeniería, UNAM
2.1.1
Types of wave: elastic and electromagnetic.
Definition of optical path.
Elastic wave:
A wave propagated by a medium having
inertia and elasticity (the existence of
forces which tend to restore any part of a
medium to its original position), in which
displaced particles transfer momentum to
adjoining particles, and are themselves
restored to their original position.
where
r is the density,
u is the displacement,
K is the bulk modulus (change in volume of a solid substance as the pressure on it is changed
μ is the shear modulus (Stiffness as Hooke´s law)
Posgrado de Ingeniería, UNAM
2.1.1
Types of wave: elastic and electromagnetic.
Definition of optical path.
Electromagnetic wave:
Electromagnetic waves are formed when
an electric field (shown as blue arrows)
couples with a magnetic field (shown as
red arrows). The magnetic and electric
fields of an electromagnetic wave are
perpendicular to each other and to the
direction of the wave.
http://science.hq.nasa.gov
where
Maxwell Equations (1831-1879)
∇ is the divergence
x is the curl
π is the constant pi
E is the electric field
B is the magnetic field
r is the charge density
c is the speed of light
J is the vector current density
Posgrado de Ingeniería, UNAM
2.1.1
Types of wave: elastic and electromagnetic.
Definition of optical path.
HomeWork: 2.1.1
i) The range of visible light is 3900 Å to 7700 Å.
Why are our eyes can not see in other wavelengths?
Justify your answer in no more than 10 lines and include
some scientific references.
ii) What is the spectral resolution of the vision of a black widow
spider and a bat?
Why a bat can fly at night?