Birefringent optical retardation
For a homogeneous plane-parallel transparent plate at normal incidence with two effective indices for the common wave-normal direction, optical path retardation is Γ=d(n_slow−n_fast).
Key knowledge
For a homogeneous plane-parallel transparent plate at normal incidence with two effective indices for the common wave-normal direction, optical path retardation is Γ=d(n_slow−n_fast). Phase retardation at vacuum wavelength λ₀ is Δφ=2πΓ/λ₀. Under crossed polarizers, interference depends on phase difference and the angle of the principal vibration directions to the polarizers; an extinction orientation can hide birefringence.
Values and equations
Γ=d(n_slow−n_fast); Δφ=2πΓ/λ₀
- Γ,d,λ₀
- optical path retardation, plate thickness and vacuum wavelength m
- n_slow,n_fast
- effective refractive indices of the two vibration modes 1
- Δφ
- phase retardation rad
Conditions and scope
- d is physical plate thickness in this normal-incidence model. Neglect spatial beam separation and interface complications; use effective indices for the section, wavelength and wave-normal direction, not automatically the mineral's maximum index difference. Oblique anisotropic propagation needs separate phase/path geometry.
- White-light interference colour depends on wavelength dispersion and thickness as well as birefringence. The emergent superposition need not remain linearly polarized; colour alone is not a unique mineral identifier.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read the actual Γ=t(N−n) travel-time derivation and vibration/extinction sections. Δφ is an explicitly disclosed wavelength conversion; excluded the incorrect blanket statement that arbitrary out-of-phase components always yield linear polarization and uninspected colour-chart numerical inference.
2026-10-10 · Independent AI editorial review: All73 exact supplement compact statements, conditions, displayed equations and247 origin semantic links read; all109 combined original36+supplement73 author-source rows, exact locators, hypotheses, exclusions and disclosed derivations assessed. Original36 exact scientific content is independently approved in the linked receipt. All18 inherited Earth compact references and shared Math/Physics/Measurement methods were considered in the full practical Earth inventory. Targeted actual primary sections listed below; not every source body/proof or every possible university elective independently reread. AI editorial reference review, not human certification, full-degree proficiency, new experimental validation or a claim of whole combined Earth-and-Cosmos approval. Receipt: earth-completion-independent-content-inventory-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-earth-optical-retardation
- Revision
- core.1
- Structured reference record
- University core expansion