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Spectral Reflectance and emittance changes with..
Wavelength and temperature
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Spectrale reflectance and emission may also change with...
Light polarization and surface roughness/condition
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Emittance: For spectral, directional, hemispherical analysis...
Directional average of e' over outgoing directions
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Emittance: Total directional
Spectral average of e'
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Emittance: Total Directional, hemispherical
Directional and spectral average of e'
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Aborptance depends on?
Incoming intensity.
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Spectral, hemispherical absorptance...
Depends on incoming radiation (and therefore entire temperature field), so it is not a pure surface property
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For blackbodies, what does spectal emissive power depend on?
Wavelength and temp. only
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For real surfaces, what does emissive power depend on?
Direction of the observer to the surface (characterized by theta and/or the vector s).
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For recombining plasma
Texc > Teq
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For Ionizing plasma..
T exc < Teq
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Boltzmann Distribution
Texc = Teq
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For thermodynamic equilibirum..
- -Each process is balanced with its reversed process.
- -Radiation follows the Planck formula
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For technical processes, LTE
- LTE= local thermal equilbirum.
- Collisions dominate excitation at higher pressure
- Boltzmann distribution are valid
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Describe Spontaneous emission
Excited state is created, and photon emitted in an arbitrary direction
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Describe Induced emission:
- delta e=hv already hits an excited stated,
- "induced emossion is emitted in the same direction as the incoming photon.
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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
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Emission characterizes the upper state (T or F)
True
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Absorption characterizes the lower state (T or F)
True
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What does absorption lead too?
An exponential decrease of incident radiation
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Define line strength
It is the spectral integration over the absorption coefficient.
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What four processes may emission and absorption lines be broadened through?
- 1) Natural Broadening
- 2) Doppler Broadening
- 3) Collisional Broadening
- 4) Zeeman Broadening
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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.
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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
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Describe a Gauss profile:
Half widths of a gauss can be combined quadratically.
99% of transition energy reached in 2 HWHM
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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
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Voigt Broadening
Used when both a Gauss and Lorentz is present.
Combination of one Gauss and one Lorentz width.
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