2. Nature of Light Optical Waves Waves • Longitudinal Waves or P waves (Eg. Sound/Spring waves) • Transverse Waves or S waves (Eg. String wave) • Longitudinal Waves + Transverse Waves (Eg. Sesmic/Earthquake wave) A transverse wave is one in which the displacement is perpendicular to the direction of travel. In longitudinal waves, the displacement is parallel to the propagation direction. The "closer together" region is called a compression, and the "farther apart" region is called a rarefaction. Frequency : number of oscillation f 1 T Earthquake Waves The faster earthquake waves is called the primary wave (P wave). It is a longitudinal wave, as it spreads out, it alternately pushes (compresses) and pulls (dilates) the rock. The P waves are able to travel through solid rock. The slower earthquake wave through the rock is called the secondary wave (S wave). It shears the rock sideways at right angles to the direction of travel. The other type of earthquake wave is called the surface wave. Its motion is restricted to near the ground surface. The surface waves in earthquakes can be divided into two types. The first is called a Love wave. It has no vertical displacement; it moves the ground from side to side in a horizontal plane but at right angles to the direction of propagation. The horizontal shaking of Love waves is particularly damaging to the foundations of structures. The second type of surface wave is known as a Rayleigh wave. It moves both vertically and horizontally in a vertical plane pointed in the direction in which the waves are traveling. Love waves generally travel faster than Rayleigh waves. A person is located from the epicenter of the earthquake. When earthquake occurs, he/he moves forwards and backwards, firstly. And then she/he vibrates up and down. Constructive/Destructive Interferences Phase Velocity and Group Velocity Example of Observing Phase VelocityBarber’s Pole Electromagnetic Spectrum • Radiometry • ( :1mm~1nm) • infrared light, visible light, ultraviolet • light in optoelectronics • Photometry • ( : 400~700nm) • visible light in human vision Representations of Electromagnetic Waves • In EE theory, the electric and magnetic field components of the z-propagating light are often jkz expressed by H yˆH e E xˆE0 e jkz 0 E( z, t ) xˆE0 cos(t kz ) • In Physics, the electric and magnetic field components of the z-propagating light are often expressed by jkz jkz E xˆE e ˆ 0 H yH 0 e E( z, t ) xˆE0 cos(kz t ) TE-polarized: the electric field ⊥ the plane spanned by the incident and the normal lines TM-polarized: the magnetic field ⊥ the plane spanned by the incident and the normal lines General Traveling Wave Expression in Homogenous Medium Maxwell’s EM Wave Equations in Simple Medium Oblique Incidence for TE-polarized Light Oblique Incidence for TM-polarized Light Normal incidence at interface Regardless of polarizations, Photon Photon energy: E hf (J) • h : planck’s constant • f : frequency of radiation (Hz) • Joule (J) is the unit of energy, and Watt (W) is the unit of power. • Power is the energy generated/dissipated per time interval. Note: 1 W=1 J/sec Radiometric and Photometric Units Flux—to describe a flow phenomenon Radiometric flux Photometric flux Symbol w p Unit watt (w) lumen (lm) Relationship : 1 W 555nm 683lm Radiometric and Photometric Intensity Radiometric intensity: radiometric flux density per steradian (w/sr) IR R (W/sr) Photometric intensity: luminous flux density per steradian IP P (lm/sr or cd) Eg. Photon population P hotonenergy at 555 nm 8 3 10 19 E hf 6.6261034 3 . 582 10 J 9 555 10 1 1 lm 1.464103 W 683 Number of phot onper second for one lumen 1.464103 15 photons n 4 . 087 10 19 s 3.58210 Efficacy Conversion from Radiometric Flux to Photometric Flux Definition of efficacy Efficacy: k P R where k = efficacy (lm/w) P = photometric flux (lm) R = radiometric flux (w) 0 [Eg-1] 40w incandescent lamp delivers 460 lumens . (Assume that 90% 0 of the power is radiated and 10 % is conducted away as heat) R 40 90 0 0 36 W (radiometric flux) P 460lum ens (photometr ic flux) efficacy: k 460 12.8 lm w 36 [Eg-2] 40w fluorescent lamp delivers 3200 lm . efficacy: k 3200 88.9 lm w 40 90 0 0 Note : fluorescent lamp > incandescent lamp in efficacy . Efficacy of Thermal Radiators Block-body radiation – perfect radiator (absorber) Stefan-Boltzman law : total radiation I T 4 : Stefan-Boltzman constant ( 5.67 108 watt m2 o K 4 ) T : degree Kelvin( oK ) Wien’s displacement law: m T const. ( 3000) m: maximum radiated wavelength (m) Radiant profiles I I O cos 2 1 Point source Lambertian source Exponential intensity source I()=I0 (=constant) I()=I0 cos I()=I0 cosn I(): intensity in direction of angle (Lambert’s cosine law) n :radiation pattern exponent I0 : intensity in direction of symmetry axes Radiant Incidence and Illuminance Radiant incidance: Radiant flux distribution on a surface ER R A (W/m2 ) R : radiant flux (W) A : area of flux distribution (m2 ) Illuminance : Ep p A (lm/m2 , lux or lx)) P : luminousflux (lm) Eg. Illumination from a point source s I cos A d2 For 0 (source surface) Illuminat on i : E I E 2 d Eg. Illumination from a wide-area Lambertian source Intensity in the direction of the receiver: Flux into the receiver: I I o cos r S AR cos cos (S I o ) 2 d S : source flux AR: receiver area : receiver direction from the perpendicular to the source : receiver-angle from the perpendicular d: source-receiver distance (m)

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# Radiometric flux Photometric flux