1. Clase 04: Nature of Light Dr. Alejandro Farah OptoMechanics Instituto de Astronomía, UNAM

2. 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.

3. Posgrado de Ingeniería, UNAM …first of all…a few words… absence of darkness energy Information facilitates the ability to view …

4. Posgrado de Ingeniería, UNAM 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 2.1 Description of the light wave motion.

5. Posgrado de Ingeniería, UNAM 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. 2.1 Description of the light wave motion. Wavelength

6. Posgrado de Ingeniería, UNAM 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). 2.1 Description of the light wave motion.

7. Posgrado de Ingeniería, UNAM 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. 2.1 Description of the light wave motion. http://sleevage.com http://bankstreetblog.files.wordpress.com

8. 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 10 10 cm/sec. As made famous in Einstein's equation, the letter c is used as a general symbol for the speed of light.

9. 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 frequency of the wave is the inverse or reciprocal of the period. The basic mathematical formula that relates wavelength, frequency, and the speed of light is: c = fλ

10. 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)

11. 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 Maxwell Equations (1831-1879) where ∇ 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

12. 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?