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).

View More On Wikipedia.org
Recent contents Top users
  1. kelvin490

    Question about dark fringe in diffraction

    In finding the angle for the mth dark fringe of single slit diffraction using Huygen's principle, they usually split the slit into equal portions. For example, to find the first dark fringe the slit is split into two equal spacings and if the path difference between the edge and the middle point...
  2. toforfiltum

    Diffraction grating that gives max intensity

    Homework Statement Homework Equations dsinθ=nλ IαA2 The Attempt at a Solution I chose D because I thought that D gives the max intensity since the amplitudes superimpose over a smaller area. But the answer is C. I can't see why.
  3. K

    Picture of Bragg's diffraction sounds confusing

    This may be a little of a stupid question. But I was looking at a diagram describing Bragg's Law of Diffraction. and I was like...how can an interference happen if wave beam C and wave beam C' are hitting different points on the detector screen?! they are not hitting the same point on the...
  4. H

    Calculating Diffraction Grating Spacing for Red Light | Homework Help

    Homework Statement A diffraction grating produces a third-order maximum, at an angle of 22 degrees, for red light (694.3 nm). Determine the spacing of the lines. Homework Equations for maxima: sin θm = mλ/d where m is the order of the maxima, λ is the wavelength in nm, and d is the spacing...
  5. R

    Harness Sea Wave Energy: Focus Waves w/ Diffraction & Floating Breakwaters

    Would it be possible to use diffraction to focus the enrgy of sea waves, on the principle of the zone plate (https://en.wikipedia.org/wiki/Zone_plate) but reduced to 2 dimensions? This could be done by an array of wave-opaque objects such as floating breakwaters, particularly along coasts...
  6. B

    Why can't diffraction happen if wavelength>slit size

    I get that diffraction takes place when wavelength is smaller than slit size due to interference. I am confused though, if every point on the slit is taken as a new source when a wave passes through a slit, then surely, if the wave had a longer wavelength than the slit, then the let's say...
  7. P

    Blazed, transmission, diffraction gratings

    Does anybody have any experience in using a blazed, transmission, diffraction grating? My specific question is, will inverting the grating, relative to the incident beam, result in a different angle of refraction when maximising efficiency into the, n1, first order of diffraction.
  8. A

    Single slit diffraction confusion

    I've found this a very confusing thing:when we locate the second dark fringes above and below the central maxima,we divide the slit into four parts and claim that pairs of waves interfere destructively as the path difference would be wavelength/2.But what if we just divided it into two parts and...
  9. Coffee_

    Diffraction Question: 0 in 1st Place on Planes Normal to Beam

    Take a cuboid unit cell structure where we put an atom on each of the vertices and a different atom in the center. We have a single crystal of that material. Now take one of the cuboid axes to be the ''a'' basis vector. We send in a diffraction beam parallel to that direction. On the other side...
  10. E

    Angular Spectrum Method and Fourier Transform

    Are the results of the Angular Spectrum Method and the Fourier Transform of a Fresnel Diffraction be different, or the same? Given the same distance between the input and output plane, and the same aperture.
  11. C

    Circular Aperture Diffraction, Angle of First Minimum

    Homework Statement A helium-neon laser ( ##\lambda =633nm##), is built with a glass tube of inside diameter 1.0mm. One mirror is partially transmitting to allow laser light out. From an optical perspective, the laser beam is a light wave that diffracts through a 1.0mm diameter circular...
  12. E

    MATLAB Implementation of Fresnel Diffraction in MatLab

    I'm trying to simulate the Fresnel Diffraction in MatLab using the Fast Fourier Transform syntax. But I'm not getting really good diffraction patterns. Here is the code: %% Fourier Transform for G(p, q) g = layer.*exp(((1i*pi)/(lambda*z))*(r_obj)); G = fftshift(fft2(g)); %% Fourier Transform...
  13. E

    Computer Simulation of Fresnel Diffraction

    Considering this system (from Wikipedia), The Fresnel Diffraction at x, y, and z is ##E \left(x, y, z\right) = \frac{z}{i \lambda} \int \int^{+\infty}_{-\infty} E \left(x', y', 0\right) \frac{e^{ikr}}{r^2} dx' dy'## where ##r = \sqrt{\left(x - x'\right)^2 + \left(y - y'\right)^2 + z^2}##...
  14. S

    The interference of light and diffraction

    Homework Statement https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xft1/v/t1.0-9/11161364_10206082495958864_2429387894279713850_n.jpg?oh=40982e4e4e7647918991060b6f630acc&oe=55C1808A&__gda__=1439347320_8abd4b5ce66baee04bbc345aef15ec68 In terms of the wavelength of the light λ, what is the...
  15. Shahab Mirza

    Diffraction Grating Problem ?

    Hi, 1. Homework Statement Q : A diffraction grating with 10000 lines per CM is illuminated by yellow light of wavelength 589 nm, At what angles is the 2nd order bright fringes seen ?Homework Equations From my textbook , I got this equation , d sin theta = m (λ) The Attempt at a Solution Ok so...
  16. 2

    Is Bragg Diffraction Depicted Accurately in Common Diagrams?

    Hi. So I am studying a bit on acousto-optics and as far as I've gathered, when the Bragg condition is met, the incident ray of light should just be reflected (in a perfect case) with the angle of reflection equal to the angle of incidence. However, this picture does not agree with my thoughts...
  17. S

    Light problem -- diffraction grating distance between adjacent bright fringes

    Homework Statement Light from a laser with a wavelength of 760 nm is directed at a diffraction grating of 1500 lines/cm. If the diffraction grating is located 1.5 m from the screen, calculate the distance between adjacent bright fringes. Homework Equations Δx = Lλ / d 760 nm = 7.60 x 10^-7 m...
  18. CAH

    Diffraction grating and wavelength

    Hi I've attached the question and mark scheme, I don't understand part 6(d)... Why have they used sin90? nλ=dsinθ If there is another order beam how can it be known the angel at which it exists from the zero order? Thanks
  19. H

    Diffraction orders of grazing incidence

    Homework Statement We have a honeycomb lattice. There is an incident wave of 400 nm, whose wavevector has an angle of 75 degree with the surface's normal. This problem is similar to LEEDS ( low energy electron diffraction). Homework Equations What is the condition of diffraction i.e. which...
  20. S

    Diffraction effects in slit experiments

    In double slit experiment with a single source,I am finding the traces of one slit when I have the other one open. I think this is due to diffraction effects.May I know how to tackle this?
  21. Z

    Double Slit Diffraction:Finding Greatest Angle for Minimum

    I'm at wits end. I hate WileyPlus. Part A, B and C are correct. I cannot figure out what Part D is -- all of the answers I am getting are wrong. Homework Statement Homework EquationsThe Attempt at a Solution
  22. G

    Quantum Physics: The Reaction of a Photon Passing Through a Slit in a Plate

    We got a light source and the light comes through a slit in a plate. A photon passes through the slit and ends up somewhere on a screen not in the straight direction due to diffraction. The question is, in quantum physics, does the plate feel the reaction of the photon deflection (1) at the time...
  23. D

    Can a Diffraction Pattern be Solved Without Complete Information?

    Homework Statement A single slit illuminated by light of wavelength λ = 610 nm produces a diffraction pattern with its first minimum at 3.5 mm from the central maximum. (a) Find the slit width, and (b) For the same slit, what wavelength of light would produce a first minimum at θ = 4.0...
  24. S

    Two identical diffraction gratings

    Homework Statement We shine a laser light on two identical diffraction gratings as shown in picture. Calculate ##x##, if in Fraunhofer diffraction image the seventh peak is missing. Homework EquationsThe Attempt at a Solution No idea actually. I know how to do this with one diffraction...
  25. U

    Miller Indices in FCC and BC

    Homework Statement [/B] (a) Show Compression of FCC leads to BCC. (b) State rules for X-rays reflection in FCC. (c) What are the new Miller Indices after compression? Homework EquationsThe Attempt at a Solution Part(a)[/B] I'm quite confused as to what they mean by 'principal axes'. For an...
  26. S

    Find Width of Slit for Diffraction Maxima

    Homework Statement A single slit diffracts laser light of wavelength 650 nm onto a screen 2.00 m away. The distance between the two first-order maxima on either side of the central peak is 2.05 mm. How wide is the slit? Homework Equations a=width of slit y=distance from central max to specific...
  27. A

    Diffraction grating with high intensity in first order

    I'm searching for a reflexive diffraction grating with at least 1500 line per mm and high intensity in first order. Common reflexive diffraction grating don't have enough intensity for my experiment. I need to help for getting such grating. Thanks
  28. L

    Optics cornu spiral and diffraction

    Hi, i am in second year of university and doing optics I have a questions in one ofmy assignment : Fresnel diffraction is observed behind a wire 0.37 mm thick, which is placed 2 m from the light source and 3 m from the observation screen. If the light of wavelength 630 nm is used, find, using...
  29. Anupama

    Diffraction Pattern: Why is Vertical Pattern Observed?

    If you place a thin long wire like object horizontally in the path of a laser passed through a slit in order to obtain a diffraction pattern you will get a vertical diffraction pattern not a horizontal one. Why is it so?
  30. brianeyes88677

    Why Can't We See Diffraction from Metal Surfaces?

    The atoms in a metal (ex. Cu) are arranged as a 3-D grating. But to our common sense ,smooth metal surfaces only reflect lights. Why can't we see diffraction from metal surfaces?
  31. J

    How to photograph a diffraction pattern?

    I want to take a picture of a diffraction pattern directly. If I project it on a wall I see a clear pattern, but when trying to get the pattern on the sensor, I only record a bright green spot. I don't know what the problem is. I'm using a ~50mm focal length lens focused at infinity. Is this...
  32. blue_leaf77

    Fourier shifting theorem in diffraction

    Suppose one has a simple aperture in one dimension across x direction (1D aperture). Illuminated by plane wave, this aperture will produce certain diffraction pattern which, at sufficiently large distance, is just the aperture's Fourier transform, and we place a detector to measure it. Now this...
  33. Robsta

    Calculate focal length of lens by diffraction.

    Homework Statement A collimated beam from a white-light source is incident normally on a transmission grating with 500 lines per mm. The transmitted light then passes through a lens which is used to project the visible (380–780 nm) spectrum of the light source on to a strip of photographic film...
  34. V

    Violation in diffraction? Lagrange (Optical) invariant

    It says you can not change with lenses the value L - radiance. Below I have an example where it proves that you can or where am I wrong? (I made L for 2D case, in 3D case everything the same - L2>L1)
  35. W

    Problem with wave optics - diffraction grating?

    Homework Statement For your science fair project, you need to design a diffraction grating that will disperse the visible spectrum (400-700nm) over 30 degrees in first order. How many lines per mm does your grating need?Homework Equations sin(Θ) = mλ/d y = Ltan(Θ) I'm pretty sure the only...
  36. C

    X-Ray Diffraction peak width due to micro-strain

    I understand that the peak-width of diffraction data increases with increasing amounts of heterogeneous, localized (AKA "micro-") strain. So, if you have a single crystal with atomic impurities in it that each create micro-strain in the lattice, you would expect the amount of peak-broadening...
  37. L

    How's diffraction pattern modied by phonon perturbation?

    Hi there, I have a problem on phonon perturbation's effect on diffraction pattern. Assume atomic planes parallel to (100) of bcc lattice is periodically perturbed by phonon. How will diffraction pattern be modified as a result of such perturbation? Will we see any diffraction peaks in addition...
  38. C

    Index of Refraction Through a Cylindrical Tube

    Hello All, I would like to start learning how to ray trace but the tracing through a tube with a thickness of t has got me stumped. If I have an n1 (outside tube), n2 (Tube), and n3 (inside tube). n1≠n2≠n3. Knowing Θ1 (the angle of incidence in relation to the normal), I can calculate Θ2 from...
  39. W

    X-ray Diffraction: Crystal Structure vs. Electric Dipole

    When x-rays are incident on a crystal structure, do they diffract in the same way as light through a diffraction grating? On the one hand, I've read that a crystal structure acts like a 3D diffraction grating. On the other hand, I have been told that x-rays induce an electric dipole moment in...
  40. K

    Diffraction wavelength of particles in moving frames?

    Here's a question I cannot seem to comply with my understanding of Quantum Mechanics. The characteristic wavelength of a particle is responsible for diffraction interference fringes, which is part of the wavefunction solution to the schrodinger equation. But the wavelength of a particle is...
  41. L

    Diffraction Grating and Dispersion

    1. The problem statement A diffraction grating has a slit separation of 2094.0 nm. What is the dispersion of the 2nd order lines at an angle of 30 degrees (in degrees per micrometer)? Homework Equations dsinΘ=mλ y=(mDλ)/d 3. Attempt at a solution I began by finding λ using the first...
  42. S

    Does a diffraction grating with a shape form fourier image

    i just wanted to get this cleared that a beam falling on a diffraction grating with a shape gives the Fourier images of the grating object which can be reobtained by placing a biconvex lens that would converge the rays and form a focussed Fourier image at its focal length and the image of the...
  43. A

    Minima of a diffraction grating

    Note from mentor: This thread was originally posted in a non-homework forum, so it does not use the homework template. -------------- We have n slits, however suppose half of the middle ones are covered. How could you go about finding the angles at which the minima occur at in the Fraunhofer...
  44. N

    Diffraction of light in a tunnel

    Hi. We all know that light will be diffracted when it goes through a slit that is around as narrow as its wavelength. But what if a plane wave goes through a very long "tunnel" that has a radius around the same size as the its wavelength? What happens then? Do you still get diffraction?
  45. K

    Optical system & diffraction limit

    can you please let me know if this sentence is true about optical systems or not? "Diffraction may limit the resolution achivable by an optical system" Thanks.
  46. J

    Diffraction Gratings: Understanding Spectroscopes Using Pringles Tubes

    Hi, I recently made a spectroscope using a pringles tube. I basically cut a very narrow slit at the metal end and at the plastic lid end I cut a circular shape out of a CD so that it fits inside the lid (I had to strip off the silver lining of course). I have some idea of how it works but would...
  47. A

    Poisson's spot and the circularity of the obstacle

    Homework Statement For poisson's spot to be observed, how accurately circular must the stop be? How is the argument for the Poisson's spot changed if the light is either; white or spatially incoherent? Homework Equations The Cornu spiral for the circular aperture. The Attempt at a Solution...
  48. G

    How to Calculate Intensity and Probability for Double Slit and Diffraction?

    Homework Statement Homework Equations slit width = a , slit separation = b = d (at photo), tanQ=h/L m.λ=b.sinQ λ.b=sinQ B=π.d.sinQ/λ α=π.a.sinQ/λ Iq=Imx(cosB)^2 x (sinα/α)^2// The Attempt at a Solution My first move was to find intensity but I have no idea about the probability of...
  49. N

    Understanding Fraunhofer Diffraction Patterns of Circles and Slots

    Hi, Why is that when a diffraction pattern is created through small circular opening you achieve a diffraction pattern like this; But when we see images of a slot we see this; From; http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraungeo.html#c1 Notice how the diffraction is linear -...
  50. G

    Diffraction Grating: Does Light Excite Electrons or Pass Through Holes?

    Simple question about this: Say you have a wire diffraction grating. Does the incoming light excite the electrons in the metal, which scatter new light *or* does the incoming light simply pass through the "holes" in the mesh and get absorbed by the grating? I've seen it explained both ways, yet...
Back
Top