Diffraction Of Helium Neon Laser

Introduction to the Diffraction of Helium-Neon Laser 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.

Aim Of The Diffraction Of Helium Neon Laser

To find out the wavelength of helium-neon(He-Ne) laser (by diffraction gratings).
To Observe the interference pattern produced when laser light passes through multiple slit grating (diffraction grating).

Tools Of The Diffraction Of Helium Neon Laser

·Laser source (He-Ne) laser of wavelength (630 nm).
·screen.
·Diffraction grating.
·Metric ruler.

Steps And Method Of The Helium Neon Laser 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.

Parameters, Theory And Final Law of The experiment

Theory

∴ slope = ΔDΔX

nλ = d sin θ

nλ = d sin (X/D) …………

Hence: 1slope = ΔXΔD

d = 2.54 cm15000 lines

n = 1 , …………… λ = ?

λ = d × 1/slopen

Final Law

nλ = d sin θ

Medical Applications Of The Helium Neon Laser Experiment

The diffraction of helium neon 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.

Frequently Asked Questions About the Helium Neon Laser Experiment

Why use a diffraction grating instead of a single slit?

A grating with many closely spaced lines produces sharper, more clearly separated bright fringes than a single slit, making it easier to measure diffraction angles accurately and calculate wavelength.

What does the "order" (n) in the diffraction equation represent?

It refers to which bright fringe is being measured — n = 1 is the first bright fringe on either side of the central maximum, n = 2 is the second, and so on. Each order corresponds to an additional full wavelength of path difference.

Why does pupil size affect visual acuity through diffraction?

As the pupil narrows, light diffracts more strongly, spreading the image on the retina and reducing sharpness — this is why extremely small apertures (like a pinhole under ~1mm) can actually blur vision instead of improving it.