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METR 415/715

METR 415/715. Wednesday February 6 2013. Imaginary part of index of refraction. When n i is non-zero, absorption of an EM wave occurs as it passes through a medium. n i is sometimes referred to as the absorption index n i depends on the wavelength

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METR 415/715

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  1. METR 415/715 Wednesday February 6 2013

  2. Imaginary part of index of refraction • When ni is non-zero, absorption of an EM wave occurs as it passes through a medium. • ni is sometimes referred to as the absorption index • nidepends on the wavelength • Figure 4.1 (page 77) shows values of nifor water and ice – small for visible and higher for UV and IR

  3. Intensity as a function of travel through a medium • Eq 4.2, p.77 • Βa= absorption coefficient

  4. Intensity as a function of travel through a medium • Eq 4.3, p.77

  5. Transmittance t • The fraction of radiation intensity that survives the trip over the distance x. • The fraction that was NOT transmitted must have been absorbed and thereofre converted to another form of energy such as heat

  6. Beer’s Law • The intensity of a beam of monochromatic radiation falls off exponentially as it traverses a uniform medium • The rate at which it falls off is proportional to βa

  7. Penetration Depth • Defined as the value of x for which t(x) = e-1 or approximately 37% • Check Figure 4.2 on page 79 for water and ice • How does that influence color of pools water? Light penetration into the ocean?

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