Hair/wire laser diffraction interference pattern

In summary: These edges act as two point sources, one left and one right. The two point sources interfere, and the wavefronts that were blocked by the wire are replaced by a diffraction pattern.In summary, the interference pattern formed by a laser shining on a hair or wire follows the single-slit interference equation nλ = d (y/D). Experimentally, the pattern appears to be a single-slit pattern, but when considering the edges of the hair or wire, it can also be seen as a result of double-slit interference according to Babinet's principle. The edges of the hair or wire act as two point sources, creating a diffraction pattern and resulting in an interference pattern.
  • #1
esdoublelef
2
0
Hair/wire laser diffraction interference pattern - does it follow single-slit or double-slit?

for single-slit interference, the equation nλ = d (y/D), (d is the width of the single-slit, y is the distance between central BRIGHT fringe to the nth DARK fringe, D is the distance from slit to screen)

for double-slit interference, the equation nλ = d(y/D), (d is the width of the single-slit, y is the distance between central BRIGHT fringe to the nth BRIGHT fringe, D is the distance from slit to screen)

How about for a laser shining on a hair (to find the thickness of hair/wire?), what does nλ = d (y/D) mean for the interference pattern?

Experimentally, the actual interference pattern I observe in class is that it looks like a single-slit (the next bright fringe isn't very bright, quite dim) . But when I draw a diagram to show how light bends around the edges of the hair, it looks like double-slit.

More importantly, what does y mean for the hair-laser experiment?

thanks!
 
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  • #3
The pattern of light forming on the other side of the hair is a result of diffraction and interference and of cause some of the undistrubed beam getting past the hair. Is this pattern formed by a single source of light?
 
  • #4
andrevdh said:
The pattern of light forming on the other side of the hair is a result of diffraction and interference and of cause some of the undistrubed beam getting past the hair. Is this pattern formed by a single source of light?

Yup it's a single source of light, and i suppose it'll be the same as single slit experiment. It's just trying to understand why, but i got to draw out the lines to understand it. Thanks all!
 
  • #5
esdoublelef said:
Yup it's a single source of light, and i suppose it'll be the same as single slit experiment. It's just trying to understand why, but i got to draw out the lines to understand it. Thanks all!
I don't think it's easy to understand Babinet's principle by drawing rays or wavefronts. Instead, the elementary explanations that I've seen generally use an indirect argument. The link I posted gives a brief explanation. More of this type of argument can be found by web search and also here on the forum:
https://www.physicsforums.com/threads/why-does-laser-on-a-hair-wire-creat-a-single-slit.465358/
 
  • #6
The wire presents the wavefronts coming from the laser with two edges, one on the left and one on the right.
 

1. What is a hair/wire laser diffraction interference pattern?

A hair/wire laser diffraction interference pattern is a pattern that forms when a laser beam is shone onto a hair or wire. The light is diffracted, or scattered, by the hair or wire, creating a pattern of alternating light and dark bands.

2. How is a hair/wire laser diffraction interference pattern created?

A hair/wire laser diffraction interference pattern is created when a laser beam is shone onto a hair or wire. The light from the laser is scattered by the hair or wire and creates the pattern on a surface behind it.

3. What information can be obtained from a hair/wire laser diffraction interference pattern?

A hair/wire laser diffraction interference pattern can provide information about the thickness, density, and refractive index of the hair or wire. It can also be used to study the properties of light and the phenomenon of diffraction.

4. How is a hair/wire laser diffraction interference pattern different from other types of diffraction patterns?

A hair/wire laser diffraction interference pattern is different from other types of diffraction patterns because it is created by a single hair or wire, rather than a regular pattern of slits or openings. This allows for more precise measurements and analysis.

5. What are some real-world applications of hair/wire laser diffraction interference patterns?

Some real-world applications of hair/wire laser diffraction interference patterns include measuring the diameter and structure of individual hairs in forensic science, studying the properties of materials in materials science, and analyzing the structure of DNA molecules in biology and genetics.

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