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Introduction in Optics Dipl.Ing.Nicoleta PRICOPI

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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

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The classical description of the light

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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 10 8 m/s.

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SubunitSymbolm centimetersCm10 -2 millimetersMm10 -3 micrometers m nanometersNm10 -9 ÅngstromsÅ picometersPm femtometersFm attommetersAm Wavelength ( ) Frequency f=c/ SubunitSymbolHz KilohertzkHz10 3 MmegahertzMHz10 6 GigahertzGHz10 9 TerahertzTHz10 12 elecron-volt [1 eV ~ 2.41 x Hz]

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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.

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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 J·s (Joule x Second) = 4,14 x eV.s (Electron volt x Second)

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Bohrs atom model Niels Bohr postulated that: the electrons in the atoms move in orbits about their nuclei with only certain allowed energies

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Energy E1 E2 h Bohr defined the term energy level of an atom one of the allowed energy values that an electron can have

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The Colors and how we see

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Rod cells Cones cells The photoreceptors

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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

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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

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Snell's Law: N 1 x sin( 1 ) = N 2 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.

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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 splitting of light into its component colors by a prism.

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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 smaller than the lights wavelength and will spread out.

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INTERFERENCE of the light Interference is the interaction between waves traveling in the same medium.

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Constructive Interference Destructive Interference

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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.

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Basic Elements of Optical Systems LENSES

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Single Lens Conventions n The object is placed to the left of the lens. n Real images fall to the right of the lens. n Virtual images fall to the left of the lens. n The object distance d o, is always positive. n The image distance d i, is positive for real images and negative for virtual images. n The focal length, f, is positive for a converging lens and negative for a diverging lens. n The magnification, m, is positive for an upright image and negative for an inverted image.

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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.

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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

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LIGHT SOURCES L ight A mplification by S timulated E mission of R adiation A LASER is a device that creates and amplifies a narrow, intense beam of coherent light.

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Absorption and Emission Stimulated Emission

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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.

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