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. Axel Togawa

    I Heisenberg Microscope: Exploring Single Photon Diffraction

    In the thought experiment proposed by Heisenberg, a single photon is scattered by the electron that we want to observe, and entering the microscope lens (the photon), it will create a diffraction pattern that gives the uncertainty on the position according to the law of optics. I wanted to ask...
  2. Dickie

    Diffraction of RF - how is it affected by frequency?

    I'm currently trying to get my head around the properties of UHF vs VHF propagation, specifically to do with diffraction around terrain and obstacles of various sizes (i.e buildings, vegetation etc). I understand from experience that UHF is generally more suitable in built up, urban...
  3. xpell

    B How small is the smallest hole that would still allow you to see through it?

    This is not for a homework or anything, I'm just a curious person who was wondering... that: how small is the smallest hole in an opaque material that would still allow to see the "world beyond it", using your eye or any kind of existing or prospective technology? (English is not my mother...
  4. P

    Evanescent Waves in near field for aperture > lambda (diffraction)?

    We have two different accepted formulas for the far field and near field respectively. I want a numerical program that works for both, furthermore I want to use it to calculate power through the aperture after confirming it in the far field vs near field. I start off by treating the far field...
  5. guest948

    Why does the intensity vary when the detector is moved away from the slits?

    I guess C: constructive interference pattern along the central line. Am I correct?
  6. S

    B Converting Lux to W/m^2 for Solar Radiation Measurement

    For a physics project, I'm planning to investigate the relationship between the number of slits in a diffraction grating and the intensity of the central maxima. The light meter which I'm planning to use to measure the intensity gives me a result in LUX. I know the wavelength of the red laser...
  7. rannasquaer

    MHB Thermal Diffraction and Expansion

    Does anyone know how I can relate the diffraction in a circular crack to the thermal expansion of that crack? Something that I relate the gap radius with the distances between the light and dark fractions of the diffraction figure.
  8. aspodkfpo

    Diffraction of light around slits forming shapes

    Just wanted to confirm whether or not the images formed by light shining through hexagonal slits are hexagons rotated by 90 degrees. In the solutions, a hexagon was not rotated 90 degrees.
  9. P

    How do my successive diffraction patterns look?

    I feel like I am "exactly wrong" ; In the far field I get more variation in the same xy-space and in the near field I get less variation. I feel like the opposite would be true. I'm trying to create a diffraction pattern by replacing the aperture with a thin cylinder with a uniform volume...
  10. hairey94

    Diffraction of Light (Single Slit)

    My initial guess... Third dark fringe is 2nd order dark fringe and second bright fringe is 1st order bright fringe. Is this the correct guess?
  11. P

    Plotting a Bessel Function for Diffraction (Fraunhofer)

    From my understanding of diffraction pattern is supposed to result in something like this However when I plot it I get the central peak without the ripples (even when broadening the view). My result My code is as follows %1) Define the grid. Define vectors so that they include 0...
  12. M

    Effect of stacking diffraction gratings

    Hi I have a basic question about the effect of transmitting a laser beam through multiple diffraction gratings. Suppose a diffraction grating was used to produce many spots as follows: Would adding a second grating of the same pattern result in more spots/maximas? If so, would the resulting...
  13. mike2020

    Strange optical phenomenon: lighting a candle in front of a TV screen

    I observed a strange optical phenomenon when lighting a candle in front of a tv screen, in the dark (attached picture). There seems to be two lines forming an 'X' figure with a colored pattern (of diffraction, I suppose). I think it must be related to the material structure of the TV screen...
  14. Y

    Diffraction, interference, single and double slit setups

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  15. 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...
  16. K

    Real Fresnel diffraction experiment

    I'm wondering if I can perform an actual experiment to observe Fresnel diffraction. I would like to do it with a rectangular aperture and of course, visible light. What should its dimensions be? And from which distance from it can I expect to start seeing a decent diffraction pattern? I know I...
  17. K

    Exploring the Limitations of Diffraction: Fresnel vs. Fraunhofer

    I have only seen Fresnel and Franhoufer diffraction being discussed in textbooks. Is it because they are the only two tratable types of diffraction? I mean, in the sense that one can really work out the equations to get results.
  18. B

    Diffraction using a circular aperture

    Here is the following question I have been trying to answer I have drawn a quick simple sketch of what I believe is happening in the set up. Also because the angle that I am dealing with is very small, I made the assumption that sin(theta) = 12.9mm/X (where X in this case is the max distance...
  19. H

    A diffraction grating formed by parallel adjacent tracks on a CDROM

    (d)sin(40.6)=(475*10^-9)(1) d=730*10^-9 (m) prof says answer is 1460*10^-9 (m) tho
  20. B

    Angular position for 2nd order diffraction

    Here is my problem I have given this a go and get 26.77 degrees as my angular position My concern is do I double this angle to get the angular width between both 2nd order maxima's (which would be 53.53 degrees) or do I just leave it as 26.77 degrees? Thanks for any help!
  21. ChrisXenon

    Photographing diffraction grating interference patterns

    If I direct a laser pointer onto a diffraction grating and place a screen beyond it, I see a diffraction pattern - a line of dots - as expected. If I move the screen further away from the grating, the distance between the dots increases - again as expected. If I place a camera where the screen...
  22. ChrisXenon

    Is the diffraction grating formula wrong?

    So, two wave fronts leave adjacent "slits" in a grating and head for a screem When they get to a point of local maximum, they will have interfered constructively, and so they must be in phase. Therefore the path different will be a whole multiple of the wavelenth. People routinely draw a right...
  23. Amartansh

    Diffraction tomography, inverse scattering

    What are some good books which covers topics like diffraction tomography, inverse scattering, RF imaging and Fourier optics?
  24. L

    How can a single slit diffraction create an interference pattern?

    I explained that Huygens principle states that each point on the wave front act as a point source which produces spherical waves which produce the interference pattern. Now his question is that where are these points and wouldn't there be infinite number of points on each wave front creating...
  25. fsonnichsen

    Sodium Vapor Lamps (low pressure) for spectral calibration and diffraction work

    Just curious if anyone out there is using the old low pressure sodium vapor lamps for spectral calibration and diffraction work. I was surprised that I do not see any bench ready laboratory lamps from the usual vendors. I understand that the last manufacturer of the low pressure bulbs, Philips...
  26. F

    I Why Won't Observation in a 2 Slit Experiment Cause 1 Slit Diffraction?

    From what I understand, if the two-slit experiment is performed while observing a slit for particles, two distinct bands appear rather than interfering. This is a little confusing, as, from what I understand, diffraction is caused by measuring a particle's position (i.e. using a slit to narrow...
  27. K

    Measuring the Distance between the Fringes of a Diffraction Grating

    I have been preparing for a physics practical on diffraction. More specifically, we will use a CD as a transmission grating (by peeling off the reflective layer), and measure the distance between the fringes for a specific distance between the CD and the viewing wall. However, it is unclear...
  28. C

    I Why the reflected angle is the same as incident in x-ray diffraction?

    I'm reading about x-ray diffraction in the context of crystal structure determination. Usually this discussion begins with Bragg's law, $$2d\sin\theta=n\lambda,$$ where ##\theta## is the angle of incoming and "reflected" x-rays. This is the bit that bothers me. I understand that the...
  29. K

    Diffraction Grating: Possible variables for Experiment

    For my High School Physics course, I have been tasked to design an experiment investigating the properties of a CD diffraction grating, and we MUST make a graph. Unfortunately, we only have two lasers of different wavelength, so changing the wavelength and measuring ##theta## would be a bad...
  30. 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...
  31. K

    Do Multiple Diffraction Gratings Affect Interference Patterns?

    Here is my thinking: Let's replace the second diffraction grating with a screen. Then, after passing through the first grating, I would expect there to be an interference pattern on the screen. Depending on the distances between the first grating and second, I could have several difference...
  32. Daniel Petka

    B Poisson Spot Madness: Laser & Coin Lens Experiment

    Recently, I started to experiment with a laser and a coin used as a lens, being inspired by an old Cody's Lab video. My initial assumption was that through diffraction, the laser will be focused onto a spot on when the coin is a certain distance away from the wall. In a way, I imagined it as an...
  33. U

    X-ray Diffraction and Bragg's Law

    Hi, I know the material being studied is FeCO3.H20 (hydrated siderite) and the wavelength for a D2 diffractometer with a Co tube is 1.79026. In order to use Bragg's Law to calculate the peak positions, I think I need to first calculate d using the equation with the Miller indices and a which...
  34. Charles Link

    Learn the Fundamentals of the Diffraction Grating Spectrometer

    Continue reading...
  35. 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...
  36. 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...
  37. 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%...
  38. D

    Equation to find the intensity of diffraction patterns: explanations please

    I = I0[ sin (φ/2)/(φ/2)]2 Given such equation I don't understand why in sin(φ/2) are used degrees and in (φ/2) at the denominator radians. If there is any reason for it i forgot about it 😓. Is there anyone so kind to explain to me why is like that? Thanks in advance
  39. T

    Strange Optical Effect: See CD Fully Visible & Ruler Bulging

    In the picture a CD is held in front of a ruler. The light source is an ordinary lamp. You can see a shadow of the CD on the ruler. Remarkable is the shadow on the screen behind it, because you can see that the CD is fully visible and the ruler bulges instead. Does anyone know this optical...
  40. RealKiller69

    Diffraction -- Calculate the interference lost orders due to diffraction

    I have calculated the diffraction part for each one of the slits but I am not getting any lost order.
  41. A

    I Area under a diffraction curve

    Hi, consider the following curve: f(\theta) = \frac {I_0sin^2(n\theta/2)}{sin^2(\theta/2)} When the area over a cycle from ##0## to ##2π## is evaluated it gives ##(2πnI_0)##. This is exactly ##\frac {I_{max} + I_{min}}{2}## , since ##I_{min}## is ##0##. Is this a coincidence, or is...
  42. J

    Pinhole Diffraction of a Spherical Wave

    Case (a) is the textbook of a planar incident wavefront and below it in the figure is the known simple formula for the central spot and fringes, or minima and maxima, angular distribution with respect to the optical axis. So, the question here is regarding case (b). The position (usually...
  43. T

    Light Diffraction physics problem

    Been trying to figure this problem out for a couple hours now, if i use 400 nm into the equation it comes out to 800: 400=sin(30). If i do 700 nm it comes out to 1400: 700=sin(30). I feel like i’m doing somethingwrong with the problem but i can’t figure out what.
  44. T

    Reciprocal lattice for FCC and diffraction peaks

    My issue is more with the steps to approach rather than the calculations. I was just wondering if someone could confirm my approach to be correct. As it asking for the reciprocal lattice of an FCC I assume this would mean I need to use the points on the BCC to calculate the geometrical...
  45. DPMF6973

    Index of refraction and wavelength

    The problem is multiple choice. A) refraction b) diffraction c) reflection d) dispersion An explanation would also be greatly appreciated!
  46. M

    How can I find the width of the central diffraction maximum.

    If I am given the width of the slit (b), wavelength of the light (λ), and the distance of the slit from the screen (D), how can I find the width of the central maximum (d)? My book says d/2=Dλ/b, but with no explanation and I don't understand why. Where does this formula come from? Thank you...
  47. 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...
  48. R

    B Particle properties conclusion from no-slit diffraction

    Is it possible to infer particle properties from 2 sources diffraction with no slit/slits involved? Some explanations of experiments i can find, if i understand them correctly at all, relate to the possibility of concluding particle momentum, from absorption lines, when emanating from a single...
  49. A

    I What is “quantized momentum transfer” and can it account for interference patterns?

    In https://www.sciencedirect.com/science/article/pii/S0378437109010401, the author claims that the interference pattern obtained in the double-slit experiment does not need a wave description of matter, and can be accounted for by the "quantized momentum transfer" from the slits to the electron...
  50. R

    Electron Gun diffraction and undeflected spot diameter

    Hi I am doing an electron gun diffraction right now and I wonder why the angle below is 2 phi. What I think about it that it's actually the results of two waves one is shown below and the other is a wave with the same accident angle but negative "those two rays will be symmetric around the...
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