Glossary

17.2 Applications of Diffraction, Interference, and Coherence

4 min read•june 25, 2024

Wave behaviors shape our world in fascinating ways. From mirrors reflecting light to prisms dispersing colors, these phenomena are everywhere. Understanding how waves interact with matter unlocks applications in optics, imaging, and communication technologies.

gratings and resolution limits are crucial in optics. These concepts determine how well we can separate and analyze light waves. By manipulating wavelengths and apertures, we can push the boundaries of what's visible, enabling powerful tools for scientific discovery and everyday tech.

Wave Behaviors and Their Applications

Wave behaviors in real-world applications

Top images from around the web for Wave behaviors in real-world applications

  • Young’s Double Slit Experiment | Physics View original

    Is this image relevant?

  • Thin Film Interference | Physics View original

    Is this image relevant?

  • Young’s Double Slit Experiment | Physics View original

    Is this image relevant?

1 of 3

Top images from around the web for Wave behaviors in real-world applications

  • Young’s Double Slit Experiment | Physics View original

    Is this image relevant?

  • Thin Film Interference | Physics View original

    Is this image relevant?

  • Young’s Double Slit Experiment | Physics View original

    Is this image relevant?

1 of 3
  • Reflection
    • Mirrors
      • Plane mirrors produce virtual images that appear to be behind the mirror surface
      • Curved mirrors (concave and convex) focus or diverge light to create real or virtual images
    • Reflective coatings
      • Optical filters selectively reflect certain wavelengths of light while transmitting others
      • Reflective insulation reduces heat transfer by reflecting radiant energy (space blankets)
  • Refraction
    • Lenses
      • Converging lenses (convex) focus light rays to a point, used in cameras and telescopes
      • Diverging lenses (concave) spread light rays apart, used in eyeglasses to correct nearsightedness
    • Prisms
      • Dispersion of light separates white light into its constituent colors (rainbows)
    • Atmospheric refraction
      • Mirages occur when light rays bend due to temperature gradients in the atmosphere (desert mirages)
      • Apparent position of celestial objects shifts due to refraction in Earth's atmosphere (sunset colors)
  • Diffraction
    • Single slit diffraction
      • Spreading of waves around obstacles explains the bending of sound waves around corners (concert halls)
    • Diffraction gratings
      • Separation of light into its constituent wavelengths enables spectroscopic analysis (identifying elements)
    • Aperture effects
      • Resolution limits in imaging systems determine the smallest features that can be resolved (telescopes, microscopes)
    • Double slit interference
      • Constructive and patterns demonstrate wave-particle duality (Young's double slit experiment)
    • Thin film interference
      • Anti-reflective coatings reduce glare by destructively interfering with reflected light (camera lenses, eyeglasses)
      • Iridescent colors in nature result from thin film interference (soap bubbles, oil slicks, butterfly wings)
    • Lasers
      • Coherent light sources for precision measurements and communication enable applications like barcode scanners and fiber optic networks
      • Recording and reconstructing three-dimensional images relies on the coherence of laser light (security holograms on credit cards)
      • Random interference pattern produced by coherent light scattered from a rough surface, used in laser speckle contrast imaging

Diffraction Gratings and Resolution Limits

Calculations for diffraction and wavelengths

  • Diffraction gratings
    • : dsin⁡θ=mλd \sin \theta = m \lambda
      • dd grating spacing determines the angular separation between diffraction orders
      • θ\theta angle of diffraction depends on the wavelength and order of diffraction
      • mm order of diffraction (integer) determines the number of wavelengths that fit within the grating spacing
      • λ\lambda wavelength of light affects the angle of diffraction for a given grating spacing and order
    • : R=λΔλ=mNR = \frac{\lambda}{\Delta \lambda} = mN
      • Δλ\Delta \lambda minimum wavelength difference that can be resolved is limited by the total number of grating lines
      • NN total number of grating lines determines the resolving power of the grating
  • Resolution limits
    • : sin⁡θ=1.22λD\sin \theta = 1.22 \frac{\lambda}{D}
      • DD aperture diameter limits the minimum angular separation between resolvable points
    • : d=λ2nsin⁡θd = \frac{\lambda}{2n \sin \theta}
      • dd minimum resolvable distance is determined by the wavelength and the of the imaging system
      • nn refractive index of the medium affects the minimum resolvable distance
  • Wavelength changes in different media
    • Wavelength in a medium: λn=λ0n\lambda_n = \frac{\lambda_0}{n}
      • λ0\lambda_0 wavelength in vacuum is reduced when light enters a medium with a higher refractive index
      • nn refractive index of the medium determines the factor by which the wavelength is reduced

Diffraction gratings vs double slits

  • Diffraction gratings
    • Advantages
      1. Higher resolving power compared to double slits allows for better separation of closely spaced wavelengths (atomic emission spectra)
      2. Ability to separate closely spaced wavelengths enables precise spectroscopic analysis (identifying chemical compounds)
      3. Multiple orders of diffraction for increased dispersion provide a wider range of wavelengths for analysis (ultraviolet to infrared)
    • Limitations
      • More expensive to manufacture than double slits due to the need for precise grating spacing and a larger number of grating lines
      • Requires a larger aperture for a given resolving power, which can limit the light-gathering ability of the system
  • Double slits
    • Advantages
      1. Simpler and less expensive to manufacture than diffraction gratings, making them suitable for educational demonstrations
      2. Suitable for demonstrating basic interference patterns and the wave nature of light (Young's double slit experiment)
    • Limitations
      • Lower resolving power compared to diffraction gratings limits the ability to distinguish between closely spaced wavelengths
      • Limited ability to separate closely spaced wavelengths makes double slits less suitable for precise spectroscopic analysis
      • Fewer orders of interference for reduced dispersion result in a narrower range of wavelengths that can be analyzed simultaneously

Advanced Optical Techniques

    • : Mathematical approach to analyzing optical systems using Fourier transforms, enabling advanced image processing and filtering techniques
  • : Non-invasive imaging technique using low-coherence interferometry to produce high-resolution cross-sectional images of biological tissues
  • : Imaging technique that converts phase shifts in light passing through a transparent specimen into brightness changes, enhancing contrast in biological samples

Key Terms to Review (26)

Abbe Diffraction Limit: The Abbe diffraction limit, also known as the diffraction limit, is a fundamental constraint on the resolution of optical imaging systems, such as microscopes and telescopes. It establishes the minimum distance at which two distinct points can be resolved or distinguished in an image, based on the wavelength of the light used and the numerical aperture of the optical system.
Angular Resolution: Angular resolution refers to the ability of an optical system, such as a telescope or a microscope, to distinguish between two closely spaced objects or features. It is a measure of the smallest angle between two points that can be resolved or distinguished by the system.
Augustin-Jean Fresnel: Augustin-Jean Fresnel was a French physicist who made significant contributions to the understanding of the nature of light, particularly in the areas of diffraction, interference, and coherence. His work laid the foundation for the wave theory of light and had a profound impact on the development of modern optics.
Coherence: Coherence refers to the degree of correlation or consistency between different waves or parts of a wave. It is a crucial concept in the understanding of wave interactions, diffraction, and interference phenomena.
Coherence Length: Coherence length is a measure of the spatial or temporal coherence of a wave, indicating the distance or time over which the wave maintains a fixed phase relationship. It is an important concept in the study of interference, diffraction, and other wave phenomena.
Constructive Interference: Constructive interference is a phenomenon that occurs when two or more waves of the same frequency and phase combine to produce a wave with a larger amplitude. This concept is fundamental to understanding the behavior of various types of waves, including sound waves, light waves, and electromagnetic waves.
Destructive Interference: Destructive interference occurs when two waves of the same frequency and amplitude, but opposite phase, combine to cancel each other out, resulting in a reduction or elimination of the wave amplitude at the point of interaction.
Diffraction: Diffraction is the bending and spreading of waves as they encounter an obstacle or opening. This phenomenon occurs when waves, such as light, sound, or electromagnetic radiation, interact with a barrier or aperture that is comparable in size to the wavelength of the waves.
Diffraction Grating: A diffraction grating is an optical device that uses the phenomenon of diffraction to split and disperse light into its constituent wavelengths. It is a crucial tool in the study of interference, coherence, and the applications of these wave phenomena.
Fourier Optics: Fourier optics is a branch of optics that utilizes the mathematical principles of Fourier analysis to describe the propagation of light and the formation of images. It provides a powerful framework for understanding the behavior of optical systems and the manipulation of light waves.
Fraunhofer Diffraction: Fraunhofer diffraction is a specific type of diffraction that occurs when a wave, such as light or sound, encounters an aperture or obstacle and the resulting diffraction pattern is observed at a large distance from the object. This phenomenon is particularly relevant in the study of optics and the behavior of electromagnetic waves.
Grating Equation: The grating equation is a fundamental relationship that describes the diffraction patterns produced by a diffraction grating, a device that splits and diffracts light into its component wavelengths. It is a crucial concept in the study of the applications of diffraction, interference, and coherence.
Holography: Holography is a technique that uses the interference of light waves to create a three-dimensional image of an object. It involves the recording and reconstruction of light waves to produce a lifelike, detailed representation that can be viewed from different angles.
Huygens-Fresnel Principle: The Huygens-Fresnel principle is a fundamental concept in wave optics that describes the propagation of light and other waves. It states that every point on a wavefront can be considered as the source of secondary spherical wavelets, and the new wavefront is the envelope of these wavelets.
Interference: Interference is the phenomenon that occurs when two or more waves interact with each other, resulting in the creation of a new wave pattern. This interaction can lead to either constructive interference, where the waves reinforce each other, or destructive interference, where the waves cancel each other out.
Interferometer: An interferometer is a device that uses the interference of waves, typically light or sound waves, to make precise measurements or to analyze the properties of those waves. It is a fundamental tool in the fields of optics, spectroscopy, and metrology, with applications ranging from the detection of gravitational waves to the study of the structure of atoms and molecules.
Numerical Aperture: Numerical aperture (NA) is a dimensionless quantity that describes the range of angles over which a lens or other optical system can accept or emit light. It is a measure of the light-gathering ability of an optical system and is a key parameter in determining the resolution and depth of field of an optical instrument.
Optical Coherence Tomography: Optical Coherence Tomography (OCT) is an imaging technique that uses low-coherence interferometry to capture high-resolution, cross-sectional images of the internal structure of materials, including biological tissues. It is a non-invasive, non-contact method that provides detailed information about the subsurface composition and morphology of the imaged object.
Phase Contrast Microscopy: Phase contrast microscopy is an optical microscopy technique that enhances the contrast of transparent and colorless specimens by converting variations in phase of the light passing through the specimen into variations in amplitude, which can then be detected. This allows for the visualization of details in samples that would otherwise be difficult to observe using a standard brightfield microscope.
Rayleigh Criterion: The Rayleigh criterion is a fundamental concept in the study of diffraction, interference, and coherence. It establishes a threshold for the resolution of two closely spaced objects or features, determining the minimum angular separation required for them to be distinguished as separate entities.
Resolving Power: Resolving power is a measure of the ability of an optical instrument, such as a telescope or a microscope, to distinguish between two closely spaced objects or to separate two closely spaced features of an object. It is a fundamental concept in the applications of diffraction, interference, and coherence.
Speckle Pattern: A speckle pattern is a random interference pattern that is created when coherent light, such as laser light, is reflected off a rough surface or scattered by a medium with random inhomogeneities. This interference pattern arises due to the random phase shifts of the scattered light waves, resulting in a granular, high-contrast image.
Thomas Young: Thomas Young was a renowned 19th century English polymath who made significant contributions to the understanding of wave optics, including the principles of interference and diffraction. His work laid the foundation for many applications of these wave phenomena.
Wave Optics: Wave optics is a branch of optics that deals with the behavior of light as a wave, focusing on phenomena such as interference, diffraction, and coherence. It provides a comprehensive understanding of how light interacts with various media and structures, going beyond the basic principles of geometric optics.
X-ray Crystallography: X-ray crystallography is a technique that uses the diffraction of X-rays by the atoms in a crystalline solid to determine the arrangement and structure of those atoms. It is a powerful tool for studying the molecular structure of materials at the atomic level.
Young's Double-Slit Experiment: Young's double-slit experiment is a fundamental experiment in the study of wave optics, which demonstrates the principles of diffraction and interference of light. It was conducted by the English physicist Thomas Young in the early 19th century and has become a cornerstone in the understanding of the wave nature of light.
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Back
Practice QuizGlossary
Practice QuizGlossary
Next guide