Fraunhofer diffraction

• Alan Tam
As in the following link of diffraction grating experiment:http://www.practicalphysics.org/go/Experiment_120.html?topic_id=1&collection_id=20

Alan Tam

We look at a lamp at a distance through a slit form the halves of a broken razor blade and a diffraction pattern is observed.

My questions are:

1. Is it a Fraunhofer diffraction? Our eyes are close to the slit, but one of the conditions for fraunhofer diffraction to occur is the screen far from the slit.

2. Why does the line filament need to be parallel to the line of slit?

Thanks

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Alan Tam said:
We look at a lamp at a distance through a slit form the halves of a broken razor blade and a diffraction pattern is observed.

My questions are:

1. Is it a Fraunhofer diffraction? Our eyes are close to the slit, but one of the conditions for fraunhofer diffraction to occur is the screen far from the slit.

No, you're not. You're looking at the image of the slit.

What happens when light passes through the a slit is that the diffraction pattern that you are seeing is really a Fourier transform of the slit itself. But here's the interesting part. If you put a lens after that at the RIGHT spot (i.e. where you would get a focused image), then the lens essentially does an inverse Fourier ttransform and you get back the image of the slit!

2. Why does the line filament need to be parallel to the line of slit?

Thanks

What filament?

Zz.

As in the following link of diffraction grating experiment:

http://www.practicalphysics.org/go/Experiment_120.html?topic_id=1&collection_id=20 [Broken]

To derive the diffraction gratig formula, we assume the rays emerging from the slits are parallel which requires the screen to be far from the grating. In the experiment, do our eyes act as a screen? But it is close to the grating.

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If you have a long light source, and you allign it perpendicular to the slit, then you will end up with an incoherent source, because different parts of the light source will have unequal angle of entry into the slit.

Zz.

What is Fraunhofer diffraction?

Fraunhofer diffraction is a phenomenon that occurs when a wave, such as light or sound, passes through an aperture or around an object, causing the wave to spread out and produce a diffraction pattern.

How is Fraunhofer diffraction different from other types of diffraction?

Fraunhofer diffraction is different from other types of diffraction, such as Fresnel diffraction, because it occurs in the far-field of the diffracting object, where the wavefront is approximately planar. This allows for simpler mathematical calculations and analysis.

What is the mathematical equation for calculating Fraunhofer diffraction?

The mathematical equation for calculating Fraunhofer diffraction is the Fraunhofer diffraction integral, which takes into account the wavelength of the wave, the size and shape of the aperture or object, and the distance between the object and the observation point.

What are some common applications of Fraunhofer diffraction?

Fraunhofer diffraction is commonly used in fields such as optics and acoustics, for analyzing diffraction patterns produced by various objects or apertures. It is also used in X-ray crystallography to study the structure of crystals.

What is the significance of the Fraunhofer diffraction pattern?

The Fraunhofer diffraction pattern provides information about the size and shape of the diffracting object or aperture, as well as the wavelength of the wave. It is also used in various scientific and engineering applications, such as determining the resolution of optical instruments and measuring the size of particles in a suspension.