Diffraction of Helium-Neon Laser

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.    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:

-To find out the wavelength of helium-neon(He-Ne) laser (by diffraction gratings).

-and to Observe the interference pattern produced when laser light passes through multiple slit grating (diffraction grating).



3-Tools of The experiment

·       Laser source (He-Ne) laser of wavelength (630 nm).

·       screen.

·       diffraction grating.


·       metric ruler.

4. Steps and methods of the experiment:

1. Switch on the Laser apparatus and notice the red beam.

2. Arrange the diffraction grating so that the Laser will be transmitted through the diffraction grating and incident on the screen.

3. Move the screen forward and backward until you get the clearest fringes on the screen.

4. Measure the distance between the center of the central fringe and each of the bright fringes.

5. Graph between D (y-axis), X(x-axis).


6. Apply Snell’s Law : n λ = d sinθ.


5-ParametersTheory And Final Law of The experiment


n=order of Diffraction.

λ= wavelength of laser

d= spacing between the slights (width of single slit for diffraction grating)


D= distance between the diffraction grating and screen


slope=ΔD /ΔX

n λ = d sin θ

n λ = d sin X/D……………………

Hence 1/slope= ΔX/ΔD

d= (2.54 cm) / (15000 line)

n=1 , …………………… λ=?

λ= (d*1/slope)/n


Final Law:

n λ = d sin θ

6 -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.

AlsoThe 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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