Introduction in Optics

Dipl.Ing.Nicoleta PRICOPI

Outline

• What is light?–Relevant theories

• The Colors and how we see• Reflection, Refraction,

Dispersion, Diffraction

Interference and Polarization of the light

• Elements of Optical Systems

• Light Sources–LASER

What is Light?

Light is a type of radiation

Light can be thought of as a wave or as a particle

Wave-Particle Duality Nature of Light

The classical description of the light

Wave properties Wavelength (); Frequency (no. of oscillations/sec); Amplitude (the “height” of the wave)–the square of the amplitude = intensity of the wave; Energy; Velocity = c = 3 x 108 m/s.

Subunit Symbol m

centimeters Cm 10-2

millimeters Mm 10-3

micrometers m 10-6

nanometers Nm 10-9

Ångstroms Å 10-10

picometers Pm 10-12

femtometers Fm 10-15

attommeters Am 10-18

Wavelength ()

Frequency f=c/

Subunit Symbol Hz

Kilohertz kHz 103

Mmegahertz MHz 106

Gigahertz GHz 109

Terahertz THz 1012

elecron-volt [1 eV ~ 2.41 x 1014 Hz]

• I part (optical spectrum) includes: the spectrum of visible light, IR spectrum and UV spectrum;

• the IInd part comprises: microwaves spectrum, radio-frequencies spectrum and power frequences spectrum;

• the IIIrd part contains: X-rays spectrum and gamma-rays spectrum.

The quantum mechanical description of the light

- Light = particles called photons (quanta of electromagnetic energy).

- In 1900 Max Planck introduced of the idea of quantization of energy postulating that: “the energy of any oscillator can not be any desired value, but only the value related to its frequency”.

- Planck described light as discrete bundles of energy and proposed that the energy of a single photon is:

E=h·f where:• f is the frequency of the light;• n is the index of refraction of the medium (n = 1 for open space);• h is the Planck constant, which has the value:

h = 6.62 x 10-34 J·s (Joule x Second)= 4,14 x 10-15 eV.s (Electron volt x Second)

Bohr’s atom model

Niels Bohr postulated that: “the electrons in the atoms move in orbits about their nuclei with only certain allowed energies”

Energy

E1

E2h

Bohr defined the term energy level of an atom one of the allowed

energy values that an electron can have

The Colors and how we see

Rod cells Cones cells

The photoreceptors

REFLECTION of the light

The reflection of light can be roughly categorized into two types of reflection: • specular reflection defined as light reflected from a smooth surface at a definite angle

•diffuse reflection, which is produced by rough surfaces that tend to reflect light in all directions

REFRACTION of the light

Refraction (or bending of the light) occurs as light passes from a one medium to another when there is a difference in the index of refraction between the two materials.

Refractive index (N) is defined as the relative speed at which light moves through a material with respect to its speed in a vacuum.

The index of refraction, N, of other transparent materials is defined through the equation:

By definition, the refractive index of a vacuum is defined as having a value of 1.0

Snell's Law: N1 x sin(1) = N2 x sin(2)

When N(1) is greater than N(2), the angle of refraction is always smaller than the angle of incidence.

Alternatively when N(2) is greater than N(1) the angle of refraction is always greater than the angle of

incidence.

When the two refractive indices are equal (N(1) = N(2)), then the light is passed through without

refraction.

dispersion of the light

The index of refraction varies with the frequency of radiation (or wavelength) of light. This is occurs with all transparent media and has been termed dispersion.

As the wavelength of light increases, the refractive index decreases.

It is the dispersion of light by glass that is responsible for the familiar splittingof light into its component colors by a prism.

diffraction of the light

Diffraction is the process by which light waves traveling throught a small hole or slit that is phzsically the approximate size of even smallerthan the light’s wavelength and will spread out.

INTERFERENCE of the light

Interference is the interaction between waves traveling in the same medium.

Constructive Interference

Destructive Interference

polarization of the light

Light waves can vibrate in many directions. Those that are vibrating in one direction – in a single plane such as up and down –are called polarized light.

Basic Elements of Optical Systems

LENSES

Single Lens ConventionsSingle Lens Conventions The object is placed to the left of the lens.The object is placed to the left of the lens.

Real images fall to the right of the lens.Real images fall to the right of the lens.

Virtual images fall to the left of the lens.Virtual images fall to the left of the lens.

The object distance dThe object distance doo, is always positive., is always positive.

The image distance dThe image distance dii, is positive for real images and negative , is positive for real images and negative

for virtual images.for virtual images.

The focal length, f, is positive for a converging lens and The focal length, f, is positive for a converging lens and negative for a diverging lens.negative for a diverging lens.

The magnification, m , is positive for an upright image and The magnification, m , is positive for an upright image and negative for an inverted image.negative for an inverted image.

Reflection of Light-Mirrors

The image in a plane mirror is upright,

left-right reversal, same size,

and located as far behind the mirror

and the object is in front of the mirror.

Spherical Mirrors

–Radius of Curvature (R)

–Center of Curvature (C)

–Focal point (F)

–Focal length (f)

–f = 1/2R

Concave Mirror Images

Convex Mirror Images

LIGHT SOURCES

Light Amplification by Stimulated Emission of Radiation

A LASER is a device that creates and amplifies a narrow, intense beam of coherent light.

Absorption and Emission

Stimulated Emission

Population Inversion

Characteristics of Laser Light

1.Coherence. Different parts of the laser beam are related to each other in phase. 2. Monochromaticity. Laser light consists of essentially one wavelength, having its origin in stimulated emission from one set of atomic energy levels.3.Collimated-laser beams are very narrow and do not spread very much.