What is Diffraction pattern: Definition and 64 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. A

    B Explanation for bright fringes in Single Slit Diffraction

    In Young's Double Slit Experiment, we were shown the complete derivation for location of fringes, width of fringes etc. on interference by two point sources of light and all was well. In Single Slit Diffraction we were just asked to remember the formulae as they were with little explanation. I...
  2. B

    Engineering Determining the Bragg plane spacing from diffraction pattern

    1.1) I see 4-fold rotational symmetry about the axis going through the center of the diffraction pattern perpendicular to the plane of the page 1.2) and 1.3) This is where I'm stuck. Once I get the horizontal spacing between adjacent lattice points, ##d^*##, the repeat distance in the crystal...
  3. Mr Fallspring

    I Double-Slit Experiment: Does rate of photon emission matter?

    Hi there! High school physics teacher hoping to pick the brains of people who know more than I do here. I'm curious whether the rate of photon emission has any noticeable effect on the diffraction pattern generated by the double-slit experiment. To be clear: I understand a diffraction pattern...
  4. belbin09

    Single Slit Interference Pattern: Increased Distance

    ATTEMPT AT SOLUTION The effect on the pattern when the screen is moved further away is the bright fringes would become wider, the light intensity of the bright fringes would decrease, and the bright fringes will appear closer together. REASONING I answered this question based on how light...
  5. nmsurobert

    B Number of fringes in a 2-slit diffraction pattern

    When looking at a diffraction pattern made by two slits, and trying to calculate wavelength, what do we count as fringes? For example, in this picture are there five total fringes or, like, 25? I've been trying to set up a lab for my high school physics 2 class and the math says that every...
  6. Douglas-Stinson

    A Calculating Fresnel Diffraction Pattern from Circular Apertures

    I am attempting to calculate the Fresnel difraction pattern from different diameter circular apertures for specific source to aperture and aperture to sensor distances. I'm generally following the procedure given in Klaus D. Mielenz "Algorithms for Fresnel Diffraction at Rectabngual and Circular...
  7. O

    I Umbrella fabric and diffraction pattern

    It is sometimes said that a distant street lamp seen through a dark coloured umbrella fabric appears like dotted diffraction pattern, as in figure A. However, I have tried several umbrellas but all of them produce a blurred cross, as in figure B. The umbrella fabric superficially looks like a...
  8. S

    I How Can One Derive the Diffraction Pattern Formula from a 1D Aperture?

    I've been trying to derive a formula for diffraction pattern formed by casting a plane-wave through a generic 1D aperture onto a screen distanced ##L## from the aperture. The aperture is described by an opacity function ##f:\mathbb{R} \rightarrow [0,1]## so it can be a single slit, multiple...
  9. S

    Determine horizontal separation of fabric from diffraction pattern

    Do I need to use formula to answer this question? Can't I just divided the horizontal distance in the picture by 2. so the horizontal separation of the thread is 54.8 / 2 = 27.4 mm? Thanks
  10. H

    What is the effect on a diffraction pattern when reducing the width of the slit?

    Monochromatic light is normally incident on a diffraction grating. The mth order line is at an angle of diffraction angle θ and has width w. A wide single slit is now placed in front of the grating and its width is then slowly reduced. As a result: A. both θ and w increase B. both θ and w...
  11. P

    Programming a Diffraction Pattern by the (pseudo?) method of images

    I oriented a magnetic dipole perpendicular to the hole (parallel to the ŷ ŷ y^ŷ direction) with one end at it's origin and I get the following pattern I was really looking for something like this As you can see I'm getting almost the exact opposite of what I want since I'm going for...
  12. jisbon

    Single lens creating a diffraction pattern?

    Hi all, So far all the problems I dealt with is dealing with double slits when working with dark and bright fringes. In this case, what should I do in regards with a lens? Also, what does the question mean when it asks for the minimum distance that the lens can resolve on the screen? Does it...
  13. O

    Diffraction pattern due to a lens with focal length f

    Suppose one light up with a laser on a grid with grid constant g. The grating is followed by a focusing lens with a focal length of f. In the focus (or immediately in front of it) the maxima have a distance d. How large was the distance of the maxima immediately after the grating? scheme: Laser...
  14. shahbaznihal

    Location of a diffraction pattern

    I am trying to make a spectrometer. At the moment, I have an optical setup consisting of a laser, diffraction grating and a screen/detector in a straight line. I am trying to understand how to estimate the location of the diffraction pattern of the slit on the screen? Is it the same location on...
  15. T

    A I made a website to index TEM diffraction patterns

    Hi, I spent some time during my PhD with the task of indexing TEM diffraction patterns, usually made with selected area diffraction. All available software I found online was either too complicated or too expensive (or both). So I decided to make my own: https://www.odpin.com It's 100%...
  16. M

    Controlling light diffraction angle with a holographic "lens"

    I'm a physics student, and working on a class project that requires coming up with a method to control the exit angle (diffraction angle) of a monochromatic light source. For example, taking a laser (monochromatic, coherent light source), spreading the beam, and directing the light at a piece...
  17. S

    Fraunhofer diffraction pattern

    Homework Statement A square aperture with a side of length 0.5 mm is illuminated with light of wavelength 550 nm. At what distance from the aperture would the Fraunhofer diffraction pattern have a central maximum with a width also equal to 0.5 mm? What can you say about the Fraunhofer condition...
  18. S

    Fraunhofer Diffraction Pattern Ratio of Power Densities

    Homework Statement Find an approximate expression for the ratio of the power densities at the principal maximum to that at the first secondary maximum on either side, in the Fraunhofer diffraction pattern of an N-slit multiple aperture. Assume that the slits are much narrower than their...
  19. MermaidWonders

    MHB Solving for Slit Width-Wavelength Ratio at $\pm90°$ Diffraction Pattern

    For what ratio of slit width to wavelength will the first minima of a single-slit diffraction pattern occur at $\pm 90°$? The thing is, when I did it, I used the formula $sin\theta = \frac{n\lambda}{a}$, and used the fact that $m = 1$ and $\pm 90°$ to solve for $\frac{a}{\lambda}$. However, I...
  20. Pushoam

    Center of diffraction pattern

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] I did not understand what is meant by the center of the pattern here. a) I have ## \delta \theta_{hw} = \frac { \lambda }{Nd \cos{\theta }} ## For central maximum ## \theta = 0##, so central line has less width than...
  21. Paddyster

    How does the diffraction grating in Canadian currency work?

    Hi, This is my first post so apologies if I'm not clear enough or if I am posting in the wrong place. I am doing my 3rd year project at university and I am creating diffraction gratings. My supervisor shown me a Canadian note and if you shine a laser through the maple leaf it will shine on the...
  22. J

    Abbe theory: diffraction pattern to primary image

    I have been attempting to unravel Abbe’s theory, of the role of diffraction in microscopic vision, in a ‘nuts and bolts’ sort of way, meaning in terms that I can understand: diffraction, interference and so on. While Fourier transforms are clearly at the heart of the process the assertion that...
  23. S

    Intensity of Diffraction Pattern

    Homework Statement An interference pattern is produced by light with a wavelength 580 nm from a distant source incident on two identical parallel slits separated by a distance (between centers) of 0.480 mm . Let the slits have a width 0.320 mm . In terms of the intensity I_0 at the center of...
  24. A

    A source's effect on diffraction pattern

    I am quite aware of the effect of slit width and wavelength in a single-slit diffraction pattern. However, my teacher has never touched on the effect of a source moving towards or away from the slit. Neither can I find any satisfactory or comprehensible response to this phenomenon. While my...
  25. A

    Diffraction pattern for large number of particles

    Why does a large number of identical particles randomly distributed produce a diffraction pattern same as that of a single particle?
  26. M

    Analyzing diffraction pattern with ImageJ

    Hey! I have a very unusual question. It is about using ImageJ to analyze diffraction patterns from TEM. 1. Homework Statement To calculate lattice parameter I need Miller Indices from planes I can recognize in the picture, wavelength of electrons and camera length. In our instructions for...
  27. 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?
  28. 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...
  29. 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...
  30. A

    Single slit diffraction pattern in 2D

    Hi all, I was looking at previous exams and I saw a question with single slit diffraction. Please look at picture. So, this made me think: "Wow, I never thought single slit diffraction could be applied in 2D with one pattern horizontal and the other vertical." Then, I thought why is...
  31. B

    Archived Lab Help: Find Miller Indices from Diffraction Pattern?

    I'm currently in a modern physics class and one of our labs was an electron scattering experiment that required the use of a cathode ray tube and a target foil. We aim the electron beam through one of four quadrants on the target foil and measure the diameter of the ring diffraction pattern...
  32. P

    Find Distance for 1.2cm Circular Diffraction Pattern

    Homework Statement You want to photograph a circular diffraction pattern whose central maximum has a diameter of 1.2cm . You have a helium-neon laser (λ=633nm) and a 0.13-mm-diameter pinhole. How far behind the pinhole should you place the viewing screen? Homework Equations Y = λx/b...
  33. R

    What's the x-ray diffraction pattern of triangular atoms?

    What would happen to the XRD pattern if instead of having spherical atoms, we had triangular atoms? I found the optical diffraction pattern for a triangular aperture, but I'm not sure if optical diffraction patterns would be the same as XRD patterns.
  34. A

    Diffraction Pattern of Buckminsterfullerene

    Hello, I was wondering if anybody knows of some studies or recent work showing the diffraction patterns observed when shining a laser on buckminsterfullerene. The curiosity stems from the idea that its more-or-less "spherical" structure and uniform composition might lend some intriguing (and...
  35. B

    Help With Simple Single Slit Diffraction Pattern?

    Homework Statement Plane light waves are incident on a single slit of width 2.45 cm. The second dark fringe is observed at 44.3° from the central axis. What is the wavelength of the light? Homework Equations θ=pλ/a... where theta is in radians, p =2 (second light minimum), and a = slit...
  36. R

    Physics Introductory Diffraction Pattern Problem

    Homework Statement Light of wavelength 588 nm illuminates a single 0.70 mm wide slit. At what distance from the slit should a screen be placed if the first minimum in the diffraction pattern is to be 1.82 mm from the central maximum? Homework Equations Im not sure on the equation, someone...
  37. A

    What is the explanation for this diffraction pattern?

    http://asymmetricphotons.davehewitt.com/__oneclick_uploads/2012/03/asymm.JPG While playing with lasers in a simple home setup, I have produced asymmetrical diffraction patterns and have been unable to locate explanations in the public domain. By using a green led laser and two parallel panels...
  38. D

    Single-slit diffraction diffraction pattern

    Homework Statement A single slit forms a diffraction pattern with monochromatic light. The 6th minimum of the pattern occurs at an angle of 23° from the central maximum. The number of bright bands on either side of the central band is closest to: A) 16 B) 13 C) 14 D) 15 E) 17 Homework...
  39. A

    A Fraunhofer diffraction pattern is produce on a screen

    Homework Statement A Fraunhofer diffraction pattern is produced on a screen 218 cm from a single slit. The distance from the center of the central maximum to the first-order maximum is 7620 times the wavelength (lambda). Calculate the slit width. Answer in __m Homework Equations...
  40. S

    Diffraction pattern to crystal structure

    How do crystallographers go from a diffraction pattern to actually determining the structure of the crystal? http://pwatlas.mt.umist.ac.uk/internetmicroscope/micrographs/microscopy/decr5a-a-big.jpg
  41. K

    Quasicrystal diffraction pattern

    hey all. i was wondering what's the diffrance between quasicrystal diffraction pattern and normal crystals (single and multiple).. where can i find some info about the diffrences? thanks , alon
  42. P

    Intensity of light in Fraunhofer diffraction pattern

    Homework Statement The intensity of light I in the fraunhofer diffraction patter of a single slit is I=I0(sin\gamma/\gamma)2 where \gamma=\piasin\theta/\lambda Show that the equation for the vaules of \gamma at which I is maximum is tan\gamma=\gamma well, intensity is...
  43. C

    Predicting a diffraction pattern without the limiting assumption

    Hello all. I have a relatively simple question. I have learned very recently about wave optics and the resulting diffraction patterns. The experiment by Thomas Young was used to explain the topic and the equations were solved with the assumption that L >> d >> lambda. I was curious how one would...
  44. K

    Single slit diffraction pattern

    Homework Statement A single slit forms a diffraction pattern, with the first minimum at an angle of 40 from the central maximum. Monochromatic light of 410 nm wavelength is used. The same slit, illuminated by a different monochromatic light source, produces a diffraction pattern with the...
  45. sophiecentaur

    How long does a diffraction pattern take to form?

    I was idly musing (as you do) and I was thinking of Fermat's principle which says that light takes the 'shortest route'. That, however, must refer to the classical situation. Take the simplest diffraction situation of two slits - or forming the really complex diffraction pattern from a large...
  46. S

    Fourier optics for diffraction pattern

    I need to determine the diffraction pattern of 2 different kinds of prisms. 1. For a right angled prism. 2. For a symmetric prism For a right angled prism, the transmission function is exp[2ipixa]*rect(x/d) where d is the base width of the prism, a is a conastant. So the diffraction...
  47. A

    Diffraction pattern of a light beam from a narrow slit

    Actually, I'm studying for my entrance exams to college. I think the professor made a mistake. So , the question says : A diffraction pattern of a light beam from a narrow slit and from a thread are : a)Completely identical b)Totally different c)Identical except for the center. He...
  48. P

    Diffraction: how to know the amount of slits from a diffraction pattern?

    Homework Statement There are at least two different situations. If you have N-2 middle minimums, the amount of slits is N. Please, see the bottom left http://scienceworld.wolfram.com/physics/DiffractionGrating.html" . The case with no such thing is the question about. How can I determine the...
  49. J

    Exploring Wave-Particle Duality and the Diffraction Pattern

    Hi, I’ve got a general question about wave-particle duality, and the experiments done with slits. When a laser is beamed through a small slit, we get a diffraction pattern. This pattern is interesting because it contains dark bands. When it comes to explaining the existence of...