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. D

    X-Ray Diffraction: Single Crystal Peak?

    Hello all, I have a basic question with the theta-2theta technique in XRD. Here it is: If I have a single crystal material and I perform the above mentioned characterization. Should I get one diffraction peak associated to the orientation of the bulk crystal or should I get many peaks...
  2. K

    Light from Element X through a diffraction Grating

    Homework Statement Light emitted by Element X passes through a diffraction grating having 1200 lines/mm. The diffraction pattern is observed on a screen 75.0 cm behind the grating. Bright fringes are seen on the screen at distances of 56.2 cm, 65.9 cm, and 93.5 cm from the central maximum. No...
  3. H

    Electron Single Slit Diffraction

    Homework Statement Electrons pass through a 10-6m wide slit with a speed of 1.5 x 106m/s. How wide is the electron diffraction pattern on a detector 1 m behind the slit. Homework Equations \lambda=h/mv (matter waves) asin\theta=m\lambda (path length difference for constructive...
  4. J

    What is the actual explanation of diffraction?

    I've done plenty of problems over the course of my degree that involve waves passing through slits of widths comparable to their wavelengths, and spreading out. As far as I'm aware though, I haven't been told what is actually going on there, just that it does happen. I know that we can...
  5. D

    Order of Diffraction Explained: Animation & Detailed Explanation

    Hi. I cannot understand what the order of diffraction means. Could anybody give me some link with animation or detailed explanation? I do not understand why it should be integer to create constructive interference?
  6. $

    Collimating light from diffraction grating

    Homework Statement Consider the following, A collimated light source impinges on a plane diffraction grating and diffracts via the well known diffraction equation. The diffracted light is then collimated by a 1 metre focal length lens (good quality one). It is experimentally verified that the...
  7. C

    How Does Light Interact with a Slit in Single Slit Diffraction?

    When light goes through a narrow single slit it diffracts. And you can explain this with the uncertainty principle or the wave-like nature of light. But if a photon can only be in one medium at a time then how does it know its going through a slit , How is it interacting with the edges of the...
  8. K

    Spherical Huygens Waves and Diffraction: Why Does the Situation Look Different?

    Short question, but I can't figure it out - when we have a diffraction on any obstacle, which is construction of spherical Huygens waves, why the situation presents as it is shown on the first picture and not like on the second picture, what could actually be expected, as we consider spherical...
  9. P

    How Do You Solve the Diffraction Intensity Problem with Different Units?

    Homework Statement [PLAIN]http://img714.imageshack.us/img714/8205/65617184.jpg Homework Equations I = I_{0} [\frac{sin[\pi a(sin\theta)/\lambda]}{\pi a(sin\theta)/\lambda}]^{2} The Attempt at a Solution Here is my attempt: I = I_{0} [\frac{sin[\pi (50)(sin\1)/632]}{\pi...
  10. L

    Monochromatic Red Light Diffraction: Exploring the Effects on Rainbow Fringes

    Consider one slit white light diffraction which produces rainbow fringe - black fringe - white fringe-black fringe-rainbow fringe. That is, continuous spectrum (or...two continuous spectrums). My question is, instead of white light, project monochromatic red light. What happens then leaving all...
  11. fluidistic

    Optics, Diffraction Homework: Intensity Expression on Far Screen

    Homework Statement On a screen there's a square aperture (hole) whose sides are 2a lengthy. We put a square of lengths a in the center of the hole. We illuminate the aperture with an He-Ne laser (\lambda =632.8 nm). We put a screen far from the screen with the square aperture, so that we...
  12. C

    Build a Homemade Diffraction Grating - Ideas & Buying Guide

    Does anyone have an idea on how to build a homemade Diffraction Grating . If its too hard I could buy one there not that much. It would be cooler to build one tho.
  13. T

    Why Does Single-Slit Diffraction Create a Pattern of Maxima and Minima?

    When waves diffract through one slit why does it form a series of maxima and minima when there is no interference?...our teacher won't tell us and its really annoying me...and i have no idea why it should. please help! ~sorry if this is in he wrong place
  14. J

    Spacing of diffraction grating

    Homework Statement You will need to know the spacing d between grooves on the diffraction grating used in the lab. If the this diffraction grating has 13400 grooves per inch, how many grooves per meter does it have? Homework Equations 1 inch = 39.37 meters The Attempt at a...
  15. T

    Aperture size of a diffraction grating

    Homework Statement From the intensities of the first-order peaks in the spectrum of a diffraction grating with monochromatic (633 nm) light shining on it, estimate the aperture size. Also known: grating constant (20 nm), distance from grating to screen (25 cm), positions of first-order peaks...
  16. T

    Diffraction due to a narrorw slit

    Homework Statement Light of wavelength 490 nm is incident on a narrow slit. The diffraction pattern is viewed on a screen 3.6 m from the slit. The distance on the screen between the central maximum and the third minimum is 2 cm. What is the width of the slit? Homework Equations The...
  17. B

    Can Diffraction Effects be Removed with an Interferometer?

    Diffraction is obviously a limiting constraint on high-precision imaging instruments. But is it possible, given a known aperture shape, to remove the diffraction caused by that aperture? At this point, I know that the diffraction pattern of an aperture or slide film brought to rear focus is...
  18. T

    Finding the width of a diffraction slit

    Homework Statement Single-slit diffraction can be observed with any type of electromagnetic wave (not just light). Suppose you want to make a diffraction slit whose width is seven times larger than the wavelength for the following cases. How wide would the slit be? (a) A radio wave for...
  19. S

    Wave length for a bragg diffraction from a incident x-ray.

    A cubic crystal with a lattice constant "a" is mounted with a [100] direction parallel to the incident x-ray beam. what would be the wave length for a bragg diffraction to occur from (110) and (111) planes? So Bragg's law is: 2d sin (theta) = n wavelength. So my thoughts are: This is...
  20. fluidistic

    Question about waves, maybe diffraction related

    I don't know why my intuition tells me that generally if a monochromatic wave goes toward an aperture smaller than its wavelength (or half its wavelength maybe), the wave can't go through the aperture. Is it true? I don't think so now... I see no reason why it would be true. And we couldn't...
  21. J

    Young's Double Slit Experiment (Diffraction)

    A lecturer is demonstrating two-slit interference with sound waves. Two speakers are used, 1.9 m apart. The sound frequency is 1220Hz and the speed of sound is 343 m/s. Students sit facing the speakers in a row of sear 5.4 m away. Along the row of students, what is the spacing between the...
  22. D

    Fraunhofer Diffraction for two unequal slit widths

    Homework Statement Consider a Fraunhofer diffraction pattern due to two unequal slits. Let a and b be the unequal slit widths and c the distance between their centers. Derive an expression for the intensity of the pattern for and diffraction angle \theta, assuming the arrangement to be...
  23. O

    Why does thin hair create a horizontal diffraction pattern?

    So I understand that thin hair or wire can make a diffraction pattern, but why would the diffraction pattern be horizontal when the hair is vertical?
  24. J

    Single Slit Diffraction and Monochromatic light

    Monochromatic light with a wavelength of 419 nm passes through a single slit and falls on a screen 88 cm away. If the distance of the first-order dark band is 0.29 cm from the center of the pattern, what is the width of the slit? My knowns are as follows: L= 88 cm (distance from slit to...
  25. M

    X-ray Diffraction, Intensity vs. Wavelength Graph

    Homework Statement http://b.imagehost.org/0607/Question_7.png Homework Equations [PLAIN][PLAIN]http://d.imagehost.org/0813/Untitled_6.jpg The Attempt at a Solution I was able to get question b, which ends up being 73pm, but as for questions a and c, I was unable to come up with...
  26. S

    Calculating Distance to Screen in Double Slit Diffraction Experiment

    Homework Statement Light of wavelength 460nm falls on two slits spaced .3 mm apart. What is the required distance from the slit to a screen if the spacing between the first and second dark fringes is to be 4mm?Homework Equations dsin(theta)=(m+1/2)lambda where d = .3mm y=4mm lambda = 460nm...
  27. D

    Diffraction Limited Object Size

    Homework Statement What is the diffraction-limited object size (at 25 cm) imposed by the numerical aperture of the eye (if the eye is a diffraction-limited optic)? Use 4mm for the iris diameter and 550 nm for the wavelength. Homework Equations Rayleigh criterion states: for angular...
  28. M

    Planes of simple cubic structure and X-ray diffraction experiment

    In the book of the Dr. Ronald Askeland the problem about x-ray diffraction use the next planes indices to calculate the interplanar distance, but I don't understand why to use such planes indices? Are these planes all of planes in a cubic structure? (111) (200) (211)...
  29. S

    Answer: Diffraction Maxima: Angular Locations of 1-4th Maxima

    Homework Statement Show that the angular locations of the first to fourth secondary maximas are \alpha = a sin \Theta/\Lambda = 1.43030 2.45902 3.47089 4.46641 respectively. a is the slit width = 0.00016m \Lambda wavelength of laser 650nm Homework Equations I(\Theta) = I0...
  30. G

    Dark fringes for single-slit diffraction

    How many dark fringes will be produced n either side of the central maximum if light (its wavelength is 651 nm ) is incident on a single slit that is 5.47x10^-6 m wide? sin (theta) = m.wavelength/w
  31. I

    About diffraction (conceptual problem)

    I have read that the wavelength must be according to the size of aperture to get diffraction phenomena. Considering normal incidence on the aperture, please explain why the wavelength should be of the order of aperture, as wavelength is perpendicular to the diameter of aperture, & any wave can...
  32. T

    Diffraction & Grating: Uses in Everyday Life

    I wonder is there any application for diffraction and diffraction grating in daily life except for lab purposes?:bugeye:
  33. T

    Circular Aperture Fresnel Diffraction

    Homework Statement A circular aperture, with diameter 3.1 mm, is illuminated by a monochromatic plain wave. On the screen, which lays 1m ahead, we observe that the center of the diffraction pattern is dark. When we start to move the screen gradually backwards, the center becomes bright, then...
  34. J

    Diffraction plane & image plane

    Hi Please can someone explain in a simple way what the Diffraction plane & image plane are Thanks
  35. P

    Diffraction Grating experiment

    Hi guys, I currently have a few doubts with diffraction grating (mostly theoretical-wise), so minimal calculations are involved. I basically did an experiment on diffraction grating, involving looking through a diffraction grating and observing the spectra, aiming a laser beam at the grating...
  36. S

    Single slit diffraction experiment

    I'm a novice at this quantum business and was just trying to understand the single slit diffraction experiment and when an electron's position is getting measured in particular. Given my understanding it looks like the electron's position gets measured twice. Once when it is just about to...
  37. Useful nucleus

    X-ray diffraction for 2-D crystal

    Is it possible to perform x-ray diffraction for 2-D crystal like Graphene? If poossible how does the bragg interference criteria look like here?
  38. N

    How do I calculate diffraction intensity for a 2D lattice?

    Homework Statement How do I figure out the intensity of diffraction spots after doing Bragg diffraction on a particular 2D lattice? Homework Equations The Attempt at a Solution I'll guess I make 1 spot in the diffraction pattern the strongest, and the diffraction spots around it...
  39. 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...
  40. T

    How Does Light Behave Before Passing Through a Slit in Diffraction Experiments?

    I have a question regarding light bundles and the diffraction of waves. I've been trying to wrap my head around the processes that govern how diffraction works and it all seems to make sense to me regarding water waves and sound. If I just apply Huygens' principle that every point in a wave is...
  41. I

    What causes light to bend when passing the edges of objects?

    I know the concept of diffraction of light, but not yet understood why light should bend passing the edges of objects ! I mean what makes it bend?
  42. L

    Single slit diffraction distance

    What happens to the distance between fringes as the width of the single slit become larger? Does the distance between fringes increases? What happens to the centre bright fringe? Does it become larger with an increasing single slit width? My hunch is: Increasing the width increases the size of...
  43. R

    Feynman Lec, problem with diffraction

    Homework Statement It is a thing feynman doesn't explain, it is meant to be obvious, but for me and some friends is not. If you have the first book, chapter 30-6, "Diffraction by opaque screen", he is talking about the approssimation of the two path: for finite distance is h^2/s, and is...
  44. E

    Why is wave diffraction around object better at longer wavelength?

    Wikipedia: Does the wave theory itself (the mathematical formulation) imply that diffraction is more efficient at longer wavelengths? I just want the logical connection of why (for example) radio waves diffract and bend around objects better than visible light. :confused: Thank you.
  45. L

    Single slit diffraction - distance between 1st&2nd order dark fringes

    Homework Statement Monochromatic light with wavelength 580nm passes through a single slit 2.60um wide and 2.10m from a screen. Find the distance between the first- and second-order dark fringes on the screen. Homework Equations y=(n*lamda*L)/d The Attempt at a Solution...
  46. G

    Is the Diffraction Grating's Line Count Accurate?

    This is an intro lab-based question. Homework Statement I took a 650 nm red laser and shined it through a diffraction grating that claimed it had 13500 lines/inch, which comes to 5315 lines/cm in civilized people units. The grating was placed 30 cm away from a piece of paper on the wall...
  47. P

    How Do You Calculate Fringe Spacing in Single Slit Diffraction?

    Homework Statement Monochromatic light with wavelength 580nm passes through a single slit 2.20um wide and 1.80m from a screen. Find the distance between the first- and second-order dark fringes on the screen. Homework Equations The Attempt at a Solution y=n\lambdaL/2d...
  48. O

    Diffraction grating wavelengths question

    Hey guys this is the problem i need to solve: Light consisting of two wavelengths which differ by 160 nm passes through a diffraction grating with 2.50 x 105 lines per metre. In the diffracted light, the third order of one wavelength coincides with the fourth of the other. What are the two...
  49. A

    Why the term diffraction in XRD

    Why the term "diffraction" in XRD When there is selective reflection of x-rays from crystals, why the phenomena is called "diffraction"? As we know that diffraction is associated with the bending of waves at the corners of any obstacle, here there does not seem to be any bending around the...
  50. B

    Diffraction Gratings - N narrow slits

    A grating having 600 lines per mm is illuminated with sodium light of mean wavelength 589.3 nm. Determine the maximum order of diffraction that can be observed. By differentiating the expression: d sin θ = m λ, calculate the angular separation in arc minutes in second order for the two...
Back
Top