INTRODUCTION Characteristics of Thermal Radiation Thermal Radiation Spectrum Two Points of View Two Distinctive Modes of Radiation Physical Mechanism of Absorption and Emission Transition of Energy States Physical Mechanism of Scattering

Characteristics of Thermal Radiation 1.Independence of existence and temperature of medium Ex) ice lens black carbon paper ice lens

2. Acting at a distance electromagnetic wave or photon conduction photon mean free path volume or integral phenomena ballistic transport diffusion or differential phenomena as long as continuum holds free electron solid: lattice vibration (phonon) fluid: molecular random motion Ex) sky radiation

d Phonon  Phonon-Boundary Scattering  = 300 nm d < 60 nm (channel length of SOI transistor)

Silicon layer thickness (nm) Thermal conductivity (W/mK) 40 Phonon boundary scattering predictions Asheghi et al. (1998) Savvides et al (1973) Yu et al. (1998) Ju & Goodsen (1999) Escoba & Amon (2004) T = 300 K Bulk silicon 10 4 Thermal Conductivity of Silicon

adibatic wall cold wall at T c L a) m << L : normal pressure b) m ~ L : rarefied pressure c) m >> L gas adibatic wall hot wall at T h

3. Spectral and Directional Dependence quanta history of path surface emission CO 2 at 830 K, 10 atm

Thermal Radiation Spectrum   1 1  10  10 2  10 3  ultra violet infrared visible thermal radiation

Two Points of View 1.Electromagnetic wave Maxwell’s electromagnetic theory Useful for interaction between radiation and matter 2. Photons Planck’s quantum theory Useful for the prediction of spectral properties of absorbing, emitting medium

EM theory Two Distinctive Modes of Radiation 1.Thermal radiation through transparent media: surface radiation Theoretical frame work Micro- physical properties r, ,  Optical constants n,  Solid state theory qTqT Surface radiative properties , ,  Transport theory Geometric integral eq.

Transport theory Radiative Transfer Eq. (RTE) 2. Thermal radiation in participating media: gas radiation Theoretical frame work Molecular or particle parameters Radiation properties a,  qTqT Quantum theory Mie theory

Physical Mechanism of Absorption and Emission composition of radiating gas: molecules, atoms, ions, free electrons photon: basic unit of radiation energy emission: release of photons of energy absorption: capture of photons of energy 3 types of transition bound-bound bound-free free-free

bound state free state ionized energy Energy transition for atom or ion E 1 = 0 E2E2 E3E3 E4E4 EIEI bound-bound absorption bound-bound emission bound-free absorption free-bound emission free-free transition

Bound-Bound Transition When a photon is absorbed or emitted by an atom or a molecule and there is no ionization or recombination of ions or electrons Magnitude of energy transition: related to frequency of emitted or absorbed radiation E 3  E 2 emission, E 3 - E 2 = h a photon emitted with h or fixed frequency associated with the transition of energy level

E 1  E 2, E 3, E 4 absorption in the form of spectral lines 

Broadening Effect natural broadening (Heisenberg uncertainty principle) Doppler broadening collision broadening Stark broadening (strong electric field) 

Carbon dioxide gas at 830 K, 10 atm

Transition of Energy States 1.bound-bound transition molecules: rotational states vibrational states electronic states atoms: electronic state

electronic state 1 Internuclear separation distance (diatomic molecule) Energy dissociation energy for state 1 dissociation energy for state 2 electronic state 2 vibrational state rotational state Transition between rotational levels of same vibrational state in same electronic state Transition between rotational levels in different electronic state Transition between rotational levels in different vibrational states of same electronic state

1)Rotational transition within a given vibrational state: associated energies at long wavelength 8 ~ 1000  m 2) Vibration-rotation transition: at infrared 1.5 ~ 20  m 3) Electronic transition: at short wavelength in the visible region 0.4 ~ 0.7  m Engineering industrial temperature: vibration-rotation transition

2. bound-free transition sufficient energy of ionization or recombination bound-free absorption (photoionization) free-bound emission (photorecombination) continuous absorption coefficient 3. free-free transition in ionized gas (bremsstrahlung)

reflection, refraction, diffraction Scattering Redirection of photons

Elastic scattering (coherent) Inelastic scattering Isotropic scattering Anisotropic scattering Dependent scattering Independent scattering

Scattering Regime size parameter:  D/ Rayleigh scattering: molecular scattering  D/  Mie scattering: Mie theory  D/  Geometric scattering: principle of geometric optics  D/ 