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Spectral Reflectance and emittance changes with..
Wavelength and temperature
Spectrale reflectance and emission may also change with...
Light polarization and surface roughness/condition
Emittance: For spectral, directional, hemispherical analysis...
Directional average of e' over outgoing directions
Emittance: Total directional
Spectral average of e'
Emittance: Total Directional, hemispherical
Directional and spectral average of e'
Aborptance depends on?
Spectral, hemispherical absorptance...
Depends on incoming radiation (and therefore entire temperature field), so it is not a pure surface property
For blackbodies, what does spectal emissive power depend on?
Wavelength and temp. only
For real surfaces, what does emissive power depend on?
Direction of the observer to the surface (characterized by theta and/or the vector s).
For recombining plasma
Texc > Teq
For Ionizing plasma..
T exc < Teq
Texc = Teq
For thermodynamic equilibirum..
- -Each process is balanced with its reversed process.
- -Radiation follows the Planck formula
For technical processes, LTE
- LTE= local thermal equilbirum.
- Collisions dominate excitation at higher pressure
- Boltzmann distribution are valid
Describe Spontaneous emission
Excited state is created, and photon emitted in an arbitrary direction
Describe Induced emission:
- delta e=hv already hits an excited stated,
- "induced emossion is emitted in the same direction as the incoming photon.
Descroibe LASER (Light Amplification by Stimulated Emission of Radiation)
- -Excited states generated through pump source
- -Induced emission is containted in a cavity through mirriors
- -Standing wave is formed to maintain the simululated emission process
- -Part of the standing wave is extracted through one side of the cavity
Emission characterizes the upper state (T or F)
Absorption characterizes the lower state (T or F)
What does absorption lead too?
An exponential decrease of incident radiation
Define line strength
It is the spectral integration over the absorption coefficient.
What four processes may emission and absorption lines be broadened through?
- 1) Natural Broadening
- 2) Doppler Broadening
- 3) Collisional Broadening
- 4) Zeeman Broadening
Describe the Doppler Effect.
It states that a wave moving from an emitter will increase in frequency if the emitter is moving towards the observered.
It will decrease in frequency if it is moving away.
Describe the three factors in collision broadening:
- 1) Van der Waals: collision with neutrons
- 2) Resonance: collisions with "like" species particles
- 3) Stark: Interactions with ions or electrons. Specific for each transition/line
Describe a Gauss profile:
Half widths of a gauss can be combined quadratically.
99% of transition energy reached in 2 HWHM
Describe a Lorentz profile:
Half widths of Lorentz profile can be summed linearly.
90% of transition energy within 6 FWHM
99% is reached after 50 HWFW
Used when both a Gauss and Lorentz is present.
Combination of one Gauss and one Lorentz width.