Laser Application for Measuring Multi Slit

Content of this page :

1.    Introduction of the experiment.

2.    Aim of the experiment.

3.    Tools of the experiment.

4.  Steps and methods of the experiment.

5.    Parameter, Theory and Final law of the experiment.

6.    Table of The Readings.

7.    Medical application and advantages of the experiment.

1. Introduction of the experiment:

The helium–neon (HeNe) laser can emit several lines in the visible and infrared range, but most commercially available lasers are based on the red line at 632.8 nm, with a power of several milliwatts. HeNe lasers have exceptionally low gain and efficiency, and their cw output does not exceed 100 mW. Their applications are limited to low-power tasks.

2. Aim of the experiment:

1-Observe Fraunhofer diffraction and interference from multiple-slit (a diffraction grating).

2-Calculate the slit spacing of a diffraction grating.



3-Tools of The experiment

Helium-Neon laser

Multi slit (grating)




4-Steps and Method of The experiment

a) Place the grating in the laser beam (close to the screen, not far away).

b) Measure the distance from the plane of the grating to the screen (D) and record it in an Excel spreadsheet.

c) Record the labeled ruling density (grooves/mm) in your Excel spreadsheet.

d) Tape a piece of paper across the screen. Mark carefully the positions of the principal maximum and the interference maxima. Remove the paper from the screen and attach it to your lab report.

e) Measure the distance of each interference maximum from the principal maximum (Xn) and record them in a paper as 1nd fringe (X1), 2nd fringe (X2) and record them and so on.

plot a graph between number of diffraction (n) and Xn.


5-ParametersTheory And Final Law of The experiment


n: (number of diffraction)

X(n): (order of the fringe)

d: (the width of slit)

Final Law: d sin θm = mλ



6. Table of the Readings:

7 -Medical Application:

The He-Ne laser is used for a variety of therapeutic purposes such as promoting wound healing, encouraging healing of skin grafts, in skin diseases and in blood disorders.

Also, The colored tissue at the front of eye that contains the pupil in the center. This iris helps control the size of the pupil let more or less light in to the eye. The iris adjusts the size of the pupil and controls the amount of light that can enter the eye. All light waves undergo diffraction as they pass through a small opening. Thus the iris produces a diffraction pattern on the retina. Generally, normal pupil size in adults range from ( 2-4 )mm in diameter in bright light to (4-8) mm in the dark. However, if the pupil becomes much smaller, for example 1.0 mm, diffraction produce measurable effect on visual acuity. You can demonstrate this effect by reading an eye test chart through a 0.75 mm hole: you should notice a decrease in your ability to read the small letters.




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Download The Data Sheet

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