Optical Properties of Materials 재료의 전자기적 성질 Part II. Optical Properties of Materials 2015년 11월 20일(금요일) 또는 21일(토요일) 중간고사 2:

The Optical Constants 7 Goethe (1749-1832): “Treatise on Color” Color is not an absolute property of matter (such as the resistivity), but requires a living being for its perception and description. If the color blue is removed from the spectrum, then blue, violet, and green are missing and red and yellow remain.” Thin gold films are bluish-green when viewed in transmission. These colors are missing in reflection. Consequently, gold appears reddish-yellow.

7.1 Introduction THz

7.2 Index of Refraction, n Index of refraction: Dispersion: optically thin Index of refraction: the refraction is caused by the different velocities, c, of the light in the two media optically dense Dispersion: The magnitude of the refractive index depends on the wavelength of the incident light which we called dispersion.

7.3 Damping Constant, k Electromagnetic Wave Equation Metals damp the intensity of light in a relatively short distance. Thus, an additional materials constant is needed to characterize the optical properties of metals. Electromagnetic Wave Equation Trial Solution Complex index of refraction, Set where, k is called the damping constant

For insulators (s=0), :complex index of refraction Absorption :complex index of refraction :complex dielectric constant Maxwell relation For insulators (s=0),

Damped amplitude Undamped wave

7.4 Characteristic Penetration Depth, W, and Absorbance, Damping Term Characteristic penetration depth The inversion of W is sometimes called the (exponential) attenuation or the absorbance, a. Inversion of W : It is related to the energy loss

7.5 Reflectivity, R, and Transmittance, T : Transmissivity N is generally a complex quantity, By definition R has to remain real. Thus, the modulus of R becomes (Beer equation)

(1) (2)

7.6 Hagen-Rubens Relation Find out the relationship between reflectivity and conductivity. For small frequencies (i.e., u<1013 s-1), in the IR region, with e~ 10 Hagen-Rubens Equation (neglecting 2n+1<<2n2) Set, s=s0 States that in the infrared region, metals with large electrical conductivity are good reflectors (DC conductivity) (only valid at frequencies below 1013 s-1, or wavelengths larger than 30 mm)

In the case of no conductivity: Summary: In the case of no conductivity: When there is a conductivity: Hagen-Rubens equation