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).
(1) In the book I am using the separation of bright fringes is indicated as being ##\Delta y=\frac{\lambda}{d}##, where ##d## is the separation of the slits so on a screen of width ##W## I would see ##\frac{W}{\frac{\lambda}{\frac{1}{N}}}## bright fringes. I don't see why the text of the...
Textbook examples usually involve a plane monochromatic wave that is diffracted by a plane grating.
If one places an ideal focusing lens behind the grating one will get a diffraction pattern in the back focal plane of the lens.
The geometric size of this diffraction pattern is proportional to...
I know that in order for the two lights to be distinguishable from one another they have to be separated by an angle of at least theta = 1.22(wavelength)/(width of aperture). I tried drawing the given picture below and then using trig to find L in terms of d/2 and theta/2. However, this ended up...
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...
I am wondering if it is possible to use principals of diffraction to cause a collimated beam of light (laser) to become divergent. I see that zone plates are most always used for focusing the light from a source, unless they are used in reverse. This is why zone plates are seemingly always...
When the crystal above is illuminated with light of intensity ##I_0##, what is the intensity at the central maximum? (The picture shown above is a 4 x 4 unit cell of the crystal)
The answer is ##(\frac {5} {16} )^2 I_0##. Why?
Apparently, Electric field is proportional to the transparent area...
First question: When shining a laser (##\lambda = 630nm##) through a 2D crystal, diffraction patterns are observed. Why?
Possible reasons:
1. Atoms and the space between them act as diffraction gratings.
2. Bragg Diffraction, although in this case the pattern would be observed on the same...
In a diffraction grating experiment, what can be the sources of error and also what effect do these sources have on the unknown quantity (wavelength) in the experiment?
I have been seeing interference and diffraction problems involving the double slit and single slit equations that ask for things like the "highest order maxima" or minima, which I have learned are basically found by setting the angle to 90 degrees. My question is are there any real world...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
I know the textbook definitions and descriptions of the phenomenon, but I'm hoping for a fundamental WHY.
I can see that when a water wave passes an obstacle, the wave spreads out into that object's shadow because the wave's energy is not constrained to any direction and so it will move out in...
Hello!
I'm very interested in knowing your opinion on how close my model is to the Fresnel Diffraction by an opaque barrier, as seen here:
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/difopa.html#c1
My model:
Sorry for the low quality image.
Hi.
The angular resolution is calculated through
$$\theta=1.22\frac{\lambda}{D}\enspace.$$
It's the first zero of the intensity function (in small-angle approximation) of the Airy disk...
when a single photon is supposed to form a diffraction pattern, they hit the detector by different angles at the slit.
so then what cancels this photon's momentum change? what happens to the photon's energy/frequency?what measurements has been done to confirm the answer?
Homework Statement
In picture, first-order reflection from the reflection planes shown occurs when an x-ray beam of wavelength ##0.260 nm## makes an angle ##\theta=63.8°## with the top face of the crystal. What is the unit cell size ##a_0##?
Homework Equations
Bragg law
$$d=\frac{ n...
I've recently come across this problem:
Answer true or false. If light shines through 2 slits, will the diffraction pattern always be within the interference pattern.
I don't understand this question, however. How can the interference and diffraction pattern be separated in this situation...
Hey, I am currently busy with studying solid state physics and looking at diffraction theory. Following link explains Frauenhofer diffraction pretty good: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/mulslid.html#c3
Let's assume a N=6 multiple slits. Its diffraction pattern depends on slit...
Homework Statement
Homework Equations
Path difference is nλ at maxima, (n+0.5)λ at minima
The Attempt at a Solution
I think the phase difference between S1 and S2 is not 0 anymore, because the wave effectively takes a longer distance by going through S2. Thus, there is no longer a central...
Homework Statement
Suppose you wanted to be able to see astronauts on the moon. What is the smallest diameter of the objective lens required to resolve a 0.60 m object on the moon? Assme the wavelength of the light is near the middle of the visible spectrum: 550 nm yellow light.
(in m)
A...
Homework Statement
Two slits (of width ##a=39 \mu m##) are lighted up with a monocromatic wave of ##\lambda=632,8 nm##. The distance between slits and the screen id ##D=4 m##. The distance between the slits id ##d=195 \mu m##.
In front of the slits there are a convergent lens with focal length...
Hi all,
I'm trying to simulate the Fresnel diffraction by using this expersion :
$$ A(x')=\frac{1}{j\lambda z}e^{jk(z+\frac{x'^2}{2z})}F(A^{trans}(x)e^{jk\frac{x^2}{2z}})_{u=\frac{x'}{\lambda z}} $$
So when I use this formula my problem is that I don't know how to take the good frequency, here...
Homework Statement
If a green laser is (wavelength = 532nm) sent through two slits with a separation of 127 um, how wide (in total) would the 11 green dots formed be if they were projected onto a screen 1.25m away from the slits?
Refer to this diagram sorry for bad quality...
Homework Statement
The Attempt at a Solution
Hi All,
I have two issues with this question. First of all when I put the given values into the Bragg condition for diffraction I get two different wavelengths when the question implies there is only one. Secondly, I don't know how I can...
I was reading a book called Catching the Light; a book on the history and other interesting things about light. There is a discussion in the book about refraction such as one might see when looking at a stone at the bottom of a pond when viewed at an angle. I've always just thought of the...
Homework Statement
A triangular lattice of lattice spacing ##a=2 ## angstroms is irradiated with x-rays at time zero of wavelength 20 angstroms at an incident angle of ##\alpha =135##.
1) What is the maximum wavelength of the incident x-rays?
2) What is the scattering angle ##\Omega## for...
If I understand the phenomenon correctly; whenever we capture an image using a telescope, because the light that's emitted from a distance object acts like a wave, we notice a diffraction pattern in our image. Now, in the double slit experiment (I didn't create the image, excuse the "slot"...
Hi,
I recently tried to create diffraction gratings using the negative film of a disposable camera. I designed them so the 'slits' were black and the rest was white so on the negative film the slits would be transparent and the rest would be opaque. It didn't work however. Does anybody have any...
In his second lecture of the QED series (see below), Prof. Richard Feynman explains the phenomenon of reflection from a plane mirror, and then the working of a diffraction grating with his theory of arrows (probability amplitudes), and we see that how the new theory, which is much moved from the...
Homework Statement
Consider the crystal in the attached image (https://ibb.co/ftMrBH) (a triangular lattice of white atoms with a triangular basis of grey atoms attached to them at angles of 0, 60 and 120. From a previous problem the fractional coordinates of the atoms in the basis are (0,0)...
Homework Statement
Low-energy electron diffraction (LEED) experiments are carried on to study a deposition of argon (Ar) and
xenon (Xe) on the surface of a graphite single crystal. In the regime of vapor pressure considered, 75% of Ar
and 25% of Xe are adsorbed on the (hexagonal) crystalline...
Homework Statement
Homework Equations
The Attempt at a Solution
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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...
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...
Hi everyone. I am having some difficulty understanding the formulas of single slit diffraction and diffraction gratings. This is partly because the formulas that I have been given in class do not reflect what I have found online entirely.
As we know, the formula for single slit destructive...
Abu
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Here's a picture that was in my textbook - they are the patterns of interference and diffraction of a light wave. I don't get why the interference amplitudes are all equal. Aren't they supposed to be higher in the middle and lower as they move away from the center??
Homework Statement
So I'm trying to determine the slit separation of a 2-D grid (as I understanding it, basically a grid with a lot of parallel, equally spaced slits in the x and y directions). I know I have to use some form of the formula d*sin(theta) = m*lambda, and I'm having some trouble...