Lecture handout including QS - Department of Materials Science ...

BH8 Course B: Materials for Devices BH8
Birefringence and Polarized Light Microscopy
Light passing into an optically anisotropic, or birefringent, material is resolved into two components,
along the two permitted vibration directions (PVDs): fast (lower n), with its vibration direction parallel
to the fast direction in the material, and slow (higher n), with its vibration direction parallel to the
slow direction. For example, plane polarized light entering a sample:
A Polarizer defines
the direction of
polarization of the
incident light
2 perpendicular
PVDs in sample
The fast component (lower n) travels faster than the slow component (higher n)! Hence, the two
components take different times to reach the end of the sample. Or, put another way, there is an
optical path difference (o.p.d.) between them:
Direction of
polarization of
incident light (at 45°
to vertical axis)
o.p.d. = Δn.t
€
As illustrated above, this difference in speed between the fast and slow components leads to a phase
δ
difference, δ, between the light in these two vibration directions:
2π = Δn.t
λ