Question

Consider a planar waveguide used for attenuated total reflection measurement of a film coated on one surface of the waveguide. For a given angle of incidence, the sensitivity of attenuated total reflectance increases as the thickness of the waveguide decreases. Explain why. (The waveguide can be less than$\mathbf{1}\mathbf{\mu m}$thick.)

Short answer

The rise in sensitivity of attenuated total reflectance as the waveguide thickness decreases.

Step-by-step solution

Definition of Reflectance and waveguide

• The proportion of perpendicularly incident light reflected from a component relative to that reflected from a standard of established reflectance is known as reflectance.
• A device (such as a duct, coaxial cable, or glass fibre) for confining and directing the propagation of electromagnetic waves (such as light), particularly a metal tube for channelling ultrahigh-frequency waves.

Determine the sensitivity of attenuated total reflectance increase as the thickness of the waveguide decreases

• It is necessary to explain why the sensitivity of attenuated total reflectance increases as the waveguide thickness decreases.

• The number of reflections inside increases as sensitivity increases, and the waveguide expands as well. Because each reflection has a certain amount of attenuation.
• The number of reflections is inversely proportional to the waveguide at a constant angle of incidence.
• As the waveguide shrinks, the number of reflections grows.

• The rise in sensitivity of attenuated total reflectance as the waveguide thickness decreases was explained.