Glossary
180-degree phase change
A specific phase shift (or π radians) that occurs when light reflects from a medium with a higher index of refraction than the medium it is currently traveling through.
Example:
Light traveling in air that reflects off a glass surface will undergo a 180-degree phase change, effectively flipping its wave crests to troughs.
Absorption
The process where light energy is taken in by a medium and converted into other forms of energy, such as heat.
Example:
Wearing a black shirt on a sunny day makes you feel warmer because the dark fabric causes significant light absorption, converting light energy into thermal energy.
Antireflective Coatings
Thin layers applied to surfaces, designed to reduce unwanted reflections by using destructive interference of light reflected from the coating's two surfaces.
Example:
The purplish tint on high-quality camera lenses indicates the presence of Antireflective Coatings, which minimize glare and maximize light transmission for clearer photos.
Constructive Interference
Occurs when two waves are in phase, meaning their crests align with crests and troughs with troughs, resulting in a combined wave with increased amplitude.
Example:
In a concert hall, sound waves are designed to exhibit Constructive Interference in the audience seating areas, making the music louder and clearer.
Destructive Interference
Occurs when two waves are out of phase, meaning the crest of one wave aligns with the trough of another, resulting in a combined wave with reduced or zero amplitude.
Example:
Noise-canceling headphones work by generating sound waves that cause Destructive Interference with incoming ambient noise, effectively silencing it.
Film thickness
The physical dimension of a thin layer of material, which is a critical factor in determining the type of interference (constructive or destructive) that occurs.
Example:
The varying film thickness across a soap bubble is what creates its iridescent rainbow colors, as different thicknesses enhance different wavelengths of light.
Incident light's angle
The angle at which light strikes a surface, influencing the path length difference and thus the interference pattern in thin films.
Example:
The appearance of a CD or DVD changes as you tilt it because the incident light's angle affects how light reflects and interferes from its microscopic grooves.
Indices of Refraction
A measure of how much the speed of light is reduced when passing through a medium, which determines the extent of bending and phase changes upon reflection.
Example:
The difference in indices of refraction between water and air explains why a straw appears bent when partially submerged in a glass of water.
No phase change
The absence of a phase shift when light reflects from a medium with a lower index of refraction than the medium it is currently traveling through.
Example:
If light travels from glass and reflects off an air boundary, it experiences no phase change, maintaining its original wave orientation.
Normal incidence
A specific condition where light strikes a surface at a 90-degree angle, maximizing interference effects and simplifying calculations in thin film problems.
Example:
For the simplest analysis of an antireflective coating, physicists often assume normal incidence, meaning the light hits the coating straight on.
Phase Change
A shift in the phase of a light wave, typically occurring upon reflection, which depends on the relative refractive indices of the materials involved.
Example:
When light from air reflects off a denser material like glass, it experiences a phase change, which is crucial for designing antireflective coatings.
Reflection
The process where light bounces back from the boundary between two media, returning to the original medium.
Example:
Looking at your image in a still pond demonstrates reflection, as light from your body bounces off the water's surface back to your eyes.
Refraction
The bending of light as it passes from one medium to another, where its direction and speed change but its phase remains constant.
Example:
A prism separates white light into a spectrum of colors due to refraction, as different wavelengths bend at slightly different angles.
Thin Film Interference
A phenomenon where light interacts with layers as thin as its wavelength, causing colorful patterns due to the combination of reflected light waves.
Example:
The vibrant colors seen on a puddle with an oil slick are a classic example of Thin Film Interference, where different thicknesses of the oil film cause specific colors to be enhanced or canceled out.
Transmission
The process where light passes through a new medium after encountering a boundary between two different materials.
Example:
When sunlight hits a clear window, most of the light undergoes transmission, passing through the glass into the room.
Wave Interference
The phenomenon where two or more waves combine to form a resultant wave, which can have a larger or smaller amplitude depending on their relative phases.
Example:
When two ripples from separate drops meet on a pond, they create a complex pattern of Wave Interference, with some areas of larger waves and others of cancellation.