What is Diffraction: Definition and 1000 Discussions

Diffraction refers to various phenomena that occur when a wave encounters an obstacle or opening. It is defined as the bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.

In classical physics, the diffraction phenomenon is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets. The characteristic bending pattern is most pronounced when a wave from a coherent source (such as a laser) encounters a slit/aperture that is comparable in size to its wavelength, as shown in the inserted image. This is due to the addition, or interference, of different points on the wavefront (or, equivalently, each wavelet) that travel by paths of different lengths to the registering surface. However, if there are multiple, closely spaced openings, a complex pattern of varying intensity can result.
These effects also occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance – all waves diffract, including gravitational waves, water waves, and other electromagnetic waves such as X-rays and radio waves. Furthermore, quantum mechanics also demonstrates that matter possesses wave-like properties, and hence, undergoes diffraction (which is measurable at subatomic to molecular levels).

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  1. J

    Physics - Single Slit Diffraction

    Hi Guys, my textbook mentioned that how the equation for the minima for single slit diffraction was derived: Consider a slit of width W with 2 light rays, one emitting from the edge, one emitting from the center. Their path difference is W/2 sin T . If the path difference is 1/2 lambda, then...
  2. D

    Crystal Diffraction: The Mystery of (1 1 1) Plane in Lattice SC, BCC, and FCC

    Hi, this is my first post. I have a problem to solve: "Given the plane (1 1 1) of 3 lattice sc, bcc and fcc, says in which case there is diffraction" I hope that someone helps me... Thanks for helpers
  3. C

    Number of interference fringes visible in the central diffraction peak

    Homework Statement How many interference fringes are visible in the central diffraction peak if the ratio of slit separation to slit width is 3.125? Homework Equations d*sin(θ) = m*λ for interference maxima with slit separation d, maxima are at m = 0, 1, 2, 3 ... a*sin(θ) = m*λ for...
  4. 0

    Need simulate program for fresnel biprism diffraction

    need simulate program for fresnel biprism diffraction(urgent) Dear friends I am student learning phyisics (8th term or 4th year) this is my last term and I have optic My teacher told us that he want some programs to simulate some optice expriments like : prism - young expriment - loid...
  5. C

    Light passing through a lens diffraction phenomenon

    A light passing through a lens will be focused for a converging lens. However, to look at it carefully, it'll not converge to a single point but to a certain size. The size of it and some fringes surround it is actually a diffraction phenomenon. I don't really understand that the usual...
  6. M

    Chiral nematic liquid crystals - describing light diffraction

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  7. S

    Exploring 2D Diffraction Spacing and Light Transmittance in 40um x 40um Lattice

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  8. R

    Understanding the Absence of [001] Diffraction Peak in X-Ray Diffraction

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  9. M

    Diffraction of Sound: Exploring Why Wavelength Matters

    When the wavelength is bigger than an obstacle, then the sound waves bend around the obstacle. so why I can't imagine this at all I read this page and watched the animations of it but it doesn't tell me the answer http://www.acoustics.salford.ac.uk/feschools/waves/diffract.htm reflection of...
  10. G

    Diffraction grating spectrometer

    Homework Statement Suppose that you have a reflection diffraction grating with n=140 lines per millimeter. Light from a sodium lamp passes through the grating and is diffracted onto a distant screen. How wide does this grating need to be to allow you to resolve the two lines 589.00 and...
  11. G

    Double-slit diffraction with thin film interference

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  12. mishima

    X-ray diffraction: history and theory

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  13. A

    Diffraction Grating Overlapping Orders

    Homework Statement The same diffraction grating is used with two different wavelengths of light, λA and λB. The fourth-order principal maximum of light A exactly overlaps the third-order principal maximum of light B. Find the ratio λA/λB. Homework Equations sin theta = m lambda /...
  14. C

    Fresnel zone plate diffraction

    Homework Statement A zone plate is to be set up on an optical bench, where it will be used as an enlarging lens. Its innermost zone is to be 0.2250 mm in diameter and monochromatic blue-green light of wavelength 480 nm from a cadmium arc is to be used. If the magnitude of the enlargements is...
  15. K

    Diffraction of blue and red light on a prism

    Could someone help me with the path taken by the emergent ray for blue light if it is refracted most than red light rays.the emergent ray for the red light lies on the boundary of the prism after being diffracted and forms the criticle angle(c). Is the path taken by the refracted blue light ray...
  16. U

    What is the correct equation for finding path difference in CD diffraction?

    Homework Statement White light was shone vertically down on a cd tilted 5°, with adjacent tracks d = 720 nm. An observer some distance away observes a color of light. Determine that wavelength of light observed. (Refer to picture attachment) Homework Equations finding path...
  17. V

    Bragg diffraction / Solid state physics

    Homework Statement Homework Equations n\lambda = 2dsin(\theta) The Attempt at a Solution a) solving for d I get \frac{n*\lambda}{2*sin*(\theta)} = d substituting in the first value 50.85 to solve for d, with n=1 I get d= 1.754*10^-10m How do I solve the miller indices from the inter...
  18. C

    Diffraction through a single slit

    This isn't a homework question per se, I'm just wondering about something in my textbook (Halliday & Resnick) that isn't clear to me: This figure shows intensity as a function of angle (0 degrees is the center) for three experiments that use single slits of different width. The one on the...
  19. T

    Effect of apperture diffraction and fourier plane

    Dear All, I appreciate the efforts and support of members/admin here toward the goodness of education. I am confusing a few concepts regarding diffraction, kindly help me out. I came up with following questions, 1. Is apperture required for diffraction or any finite wave will diffract...
  20. B

    Diffraction grating problem involving two wavelengths.

    Homework Statement A diffraction grating has 4,200 rulings/cm. On a screen 2.00 m from the grating, it is found that for a particular order m, the maximum corresponding to two closely spaced wavelengths of sodium (589.0 nm and 589.6 nm) are separated by 1.54 mm. Determine the value of m...
  21. P

    Diffraction Through a Sub-Wavelength Sized Slit?

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  22. P

    Intensity of light in Fraunhofer diffraction pattern

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  23. bearcharge

    X-ray diffraction in the presence of an electric potential

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  24. bearcharge

    X-ray diffraction in the presence of electric potential

    Hi, I was conducting an experiment on a material using XRD and I investigated two cases. One case is the presence of outside electric potential, that is, the material being connected to a electric circuit. The other case is the absence of this electric potential. I found that the two XRD...
  25. L

    Why is there a spectrum on the back of a CD or DVD?

    Homework Statement When i see the back of a CD or DVD, there is a spectrum, in which the various colours are overlapping with each other(continuous spectrum) Homework Equations What is the reason for this phenomenon, diffraction or dispersion? The Attempt at a Solution Diffraction...
  26. fluidistic

    Physical meaning of a result in Bragg's diffraction

    Homework Statement The distance between crystal planes in a KCl crystal is about 3.14 \times 10 ^{-10}m. Calculate the Bragg's reflexion angle of first order for electrons with kinetic energy of 4keV. Compare it with photons that have the same energy.Homework Equations \lambda n =2d \sin...
  27. M

    Understanding Light diffraction

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  28. P

    Single Slit Diffraction find central maximum

    Hi, I have tried tackling these question but I am simply absolutely lost... 1. A single slit of width 1.50 um is illuminated with light of wavelength 500.0 nm. Find the angular width of the central maximum. I have no attempt for number 1. 2. Microwaves of wavelength 2.8 cm fall on...
  29. C

    Diffraction grating angular separation

    Homework Statement Light consisting of two nearly equal wavelengths L and L+dL, where dL << L, is incident on a diffraction grating. The slit separation of the grating is D. Show that the angular separation of these two wavelengths in the m'th order is dTheta = dL / ((D/m)2+L2)0.5...
  30. P

    Diffraction from Sub-Wavelength Features

    I was wondering what occurs when a diffraction grating is produced with features smaller than a wavelength of visible light. If the pits in a CD were made to be only a few tens of nanometers wide, what would we see?
  31. P

    Why Do Some Diffraction Orders Go Missing?

    Explain the concept of missing orders in case of double and n slit diffraction.
  32. S

    Calculating Diffraction Intensities

    Hi, I'll start with the background so perhaps you can understand my problem better. I want to write some requirements for diffraction with electrons. I know that typically an electron diffraction pattern would need ~1e6 electrons, I could justify this because I also know (and can show...
  33. R

    Diffraction Patterns: Calculate Wavelength of Light

    Homework Statement A beam of monochromatic light is incident on a single slit of width 0.560 mm. A diffraction pattern forms on a wall 1.35 m beyond the slit. The distance between the positions of zero intensity on both sides of the central maximum is 2.32 mm. Calculate the wavelength of the...
  34. P

    What is the relationship between diffraction and resolving power?

    Hi, Going through a Physics problem in class today my teacher stated that we could only resolve if: θ = λ/b. Why? Is it because when that does not follow, there is no "black spot", therefore that light source can merge with another one? Thanks, Peter
  35. P

    Diffraction and Semi-Conductor Lithography

    I was curious as to how semiconductor manufacturing gets around the fact that diffraction should prevent processors with transistors on the scale of tens of nanometers from being possible. How do we get around this if the diffraction of light is a fundamental limit to how small we can do any...
  36. P

    Diffraction and Aperture Size: How Does It Affect Image Resolution?

    Hi there, I understand somewhat how diffraction works in terms of the aperture of a camera lens and the resulting loss in resolution in the image, but my question is: Is the degree of diffraction only dependent upon absolute aperture size, or the size of the entrance pupil? For example, f/22...
  37. N

    Diffraction grating & young double slit -light not perpendicular to grating

    Homework Statement I was a asked a question from an experiment: What happens if the light shone into the diffraction grating or a double slit is not perpendicular to the diffraction grating or double slit? What will happen?The Attempt at a Solution Straight away i can tell that the light...
  38. H

    Alternating violet and red fringes in Diffraction Grating

    When white light is passed through the slits in the grate and hits a screen some distance away from the grate, different order spectra appear. My textbook tells me that violet light is always closer to the zeroth order bright fringe than red light because it has a shorter wavelength. However...
  39. I

    Help me understand interference and diffraction better

    Homework Statement I've been reading a book about waves. I skipped the test earlier this year because I had not done any problems and thought it would be a waste of time to try. But now I kind of have to do it, I've re-read the book but it's much to understand and remember. Especially the...
  40. N

    Diffraction - Why must slit width be comparable to the wavelength of light?

    Hey guys, In diffraction of light, why must the slit width be of comparable size to the wavelength of the light being shone on it for diffraction to be noticed most? Thanks
  41. M

    Question about electron diffraction

    When firing electrons at a small slit, does the resulting interference pattern appearing on a screen behind the slit change significantly depending on whether the electrons are "aimed" at the center of the slit compared to the edges of the slit? Any references with more info about this?
  42. khurram usman

    How Does Coherence Affect Interference and Diffraction in Light Waves?

    if i have two in coherent waves then will interference and diffraction be noticeable? if yes then to what extent and what factors matter?please xplain
  43. S

    How/why does diffraction occur?

    What is the mechanism of diffraction? Let's consider water waves and not light; if we consider water an aggregate of little molecules, why would a chain of molecules moving up and down (the wave) suddenly turn once passed through a slit? I hope I'm clear enough.
  44. H

    Software to calculate diffraction figure at focal point of concave mirror?

    Classic paraboloidal mirror. Incoming flat wavefront of known wavelength (500 nm, green light), propagating parallel to the major axis of the mirror. The wave hits the mirror and is being sent back towards focus. At the focal plane, there's a flat CCD or some other light detector. Upon hitting...
  45. H

    What is the 'first order' diffraction peak?

    Could someone explain what the 'first order' diffraction peak is?
  46. H

    Electron diffraction diameter measurement

    Hello In an electron diffraction experiment usually the diffraction rings are blurred. My question. If measuring the diameter, should I measure to the inside of the ring, the outside, or take a guess where the middle of the ring is and measure to there? Thanks
  47. zimo

    Fraunhofer diffraction, multiple slits

    Homework Statement A system consisting of 5-slit (completely identical) that the distance between their centres, d, is four times the width of a slit, b. Calculate the relation between the major maximum at the center and the next maximum (can be given that position of the maximum is...
  48. H

    Why does X-ray Diffraction Show Disappearing Peaks in CaCoH3?

    -------------------------------------------------------------------------------- Hope somebody can help me. I am studing perovskite hydride CaCoH3 using X-ray diffraction. CaCoH3 crystallizes with a cubic in space group Pm-3m. At phase transtion point, all peaks weakened gradually, and...
  49. BruceW

    Classical light diffraction round corner

    I know how photons are diffracted round a corner in quantum mechanics. But is there also an explanation in classical electromagnetic theory (i.e. by Maxwell's laws?) Imagine there was an EM wave traveling purely normal to a slab of material which is highly attenuating, but which has a small...
  50. E

    Understanding Diffraction in a Double Slit Experiment

    i just don't understand diffraction in a double slit , ? how is it related to interference?? like if i want to find how many bright fringes within the central bright fringe of the diffraction envelope? or how many bright fringes are found between the bright fringes of the first and second of...
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