Interference, Diffraction, and Optical Filters

Interference

Superposition of overlapping waves creating patterns.

Diffraction

Bending of light around obstacles.

Young's Experiment

Demonstrates light wave interference using slits.

Constructive Interference

Waves combine for increased amplitude at bright fringes.

Destructive Interference

Waves combine for decreased amplitude at dark fringes.

Path Difference

Difference in distance traveled by two waves.

Fringe Pattern

Alternating bright and dark bands on a screen.

Sinc Function

Mathematical function describing diffraction patterns.

Airy Disc

Central bright spot in diffraction pattern.

Resolution Limit

Minimum separation to distinguish two images.

Rayleigh Criterion

Condition for resolving two close objects.

Diffraction Grating

Multiple slits creating enhanced interference patterns.

Grating Equation

d sin q = nλ relates angle and wavelength.

Resolving Power

Ability to distinguish closely spaced images.

Slit Width (d)

Distance between adjacent slits in a grating.

Wavelength (λ)

Distance between successive peaks of a wave.

Angular Deviation (q)

Angle at which light is diffracted.

Order of Diffraction (n)

Integer representing the fringe number.

Central Maximum

Brightest point in an interference pattern.

Dark Fringe Location

Position of minimum intensity in interference.

Bright Fringe Location

Position of maximum intensity in interference.

Example Calculation

Using given values to find fringe positions.

Slit Separation

Reciprocal of lines per mm measurement.

Angular Deviation

Angle of light change due to diffraction.

Grating Density

Number of lines per mm on a grating.

Order of Bright Fringe

Number indicating the fringe's position.

Laser Filters

Must sharply cut on/off due to narrow wavelengths.

Long Pass Filter

Transmits wavelengths above a specified cut-on.

Short Pass Filter

Transmits wavelengths below a specified cut-off.

Band Pass Filter

Transmits a narrow range of wavelengths.

Neutral Density Filter

Reduces intensity without wavelength discrimination.

Absorption Filter

Colored glass that absorbs unwanted light.

Dichroic Filter

Redirects light at 45° angle, allows transmission.

Diffraction

Departure from geometric optics causing light patterns.

Interference

Interaction of light waves causing patterns.

Thin Film Interference

Light reflected at interfaces alters interference patterns.

Interference Filters

Reflect unwanted wavelengths using thin layers.

Constructive Interference

Waves combine to amplify light intensity.

Destructive Interference

Waves combine to reduce light intensity.

Dielectric Material

Insulating material used in interference filters.

Bragg's Dielectric Mirrors

Used to direct light in different spectral regions.

Optical Filter Design

Determined by layer thickness and light angle.

Dichroic Definition

Greek for 'two colors', used in filters.

Filter Thickness Calculation

Based on wavelength and refractive index.

Dichroic

Greek term for two colors in filters.

Dichroic Filter

Reflects and transmits specific light wavelengths.

Transmitted Light

Light that passes through a filter.

Reflected Light

Light that bounces off a surface.

Absorptive Filters

Filters that absorb unwanted light wavelengths.

Coloured Glass Filters

Filters made of dyed glass or plastic.

Fluorescence

Emission of light by a substance after absorption.

Bandpass Filters

Allow specific wavelength range to pass.

Full Width at Half Maximum (FWHM)

Width of a bandpass filter at half peak transmission.

Notch Filters

Inverted bandpass filters that block specific wavelengths.

Long Pass Filters

Allow wavelengths longer than a cutoff to pass.

Short Pass Filters

Allow wavelengths shorter than a cutoff to pass.

Fluorescein (FITC)

A fluorescent dye with specific excitation/emission wavelengths.

Interference Filters

Filters using interference to selectively transmit light.

Blocking Properties

Ability to prevent unwanted wavelengths from passing.

Transmission Properties

Ability to allow desired wavelengths to pass.

Neutral Density Filters (N.D)

Reduce light intensity without wavelength discrimination.

Beam Splitters

Divide light into two or more beams.

Optical Filter Evaluation

Assess filter performance using stained particles.

Light Loss by Optics

Reduction of light transmission through optical materials.

Quartz Filters

Used for wavelengths < 450 nm.

Spectrofluorometer

Instrument for measuring fluorescence and filter performance.

Filter Lifetime

Duration before filters degrade and need replacement.