Optical intensity, coherence and fringe visibility
For scalar co-polarized fields, averaged intensity includes a cross-correlation term.
Key knowledge
For scalar co-polarized fields, averaged intensity includes a cross-correlation term. Define γ₁₂=⟨E₁*E₂⟩/√(⟨|E₁|²⟩⟨|E₂|²⟩); then phase scanning gives visibility V=2√(I₁I₂)|γ₁₂|/(I₁+I₂). Correlation over delay describes temporal coherence and over separated positions describes spatial coherence.
Values and equations
I=I₁+I₂+2√(I₁I₂)Re(γ₁₂e^[iφ]); V=(I_max−I_min)/(I_max+I_min)
- I,I₁,I₂,I_max,I_min
- Intensities W m⁻²
- γ₁₂,V
- Complex normalized coherence and fringe visibility
- E₁,E₂
- Complex electric-field envelopes V m⁻¹
- φ
- Scanned relative phase rad
- i
- Imaginary unit
Conditions and scope
- Same detection/polarization normalization, nonzero arm intensities and a defined averaging interval; |γ|≤1 by Cauchy–Schwarz.
- Intensity imbalance can reduce visibility even for |γ|=1. Vector polarization mismatch and nonstationary fields require the appropriate vector/time-dependent correlation; intensity is not generally the sum of separate intensities.
Sources · 1
References
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Evidence and review
Optics 2.71: Wave optics lecture 11 (2014): Pages 1–5, equations 1–25: complex-field superposition, Michelson time correlation and Young spatial correlation; normalized coherence and visibility follow expansion of the same field sum.
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Entry details
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- physics-optical-interference-coherence
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- University core expansion