L7

Question 1

What is the scale for guiding and confining light?

Answer 1

• Micrometer scale (~100μm).
• Example: Glass (n1=1.3) in air (n2=1), n1>n2 -> TIR (Total internal reflection).

Question 2

Define evanescent wave.

And when does it occur?

Answer 2

• An exponentially decaying wave with an imaginary wave vector.
• It occurs when light is trapped at an interface with moderate refractive index (n<2), leading to imperfect confinement.

Question 3

What is the penetration depth (dp) of an evanescent wave for visible light?

and how is it affected by changing refractive index?

Answer 3

• 50-100 nm for visible light.
• Depth decreases with increasing refractive index.

Question 4

What is evanescent coupling?

Answer 4

• The interaction of an evanescent wave with a material
• Often used in biosensing to detect shifts in resonance caused by biomolecules.

Question 5

What is Fresnel Romb?

Answer 5

An optical device used to produce elliptical or circular polarisation by introducing a phase shift between the p and s components of vibration after reflections.

vibration?