Diffractive Optics

As part of the Light & Optics tutorial on diffraction, I was seeking to produce a series of images that demonstrate some of the basic diffraction experiments with light.

I came up with some basic drawings for a single & double slit, and then decided to make a pinhole aperture to complement a set of apparatus for use with optics demonstrations.

Single & Double Slit Experiment

In order to demonstrate the principles of diffraction through a single and double slit, you will need to construct the slits, however there are many ways the slits may be constructed.

For the best resolution, the edges of the slit should be sharp and the width of the slit be able to be controlled.

Diffraction Slit Drawings
Single Slit
Double Slit

The following images are of actual photographs taken of the patterns produced by the above single and double slits. A Helium-Neon laser with a wavelength of 632.5nm was used as the light source.

Single Slit Diffraction Pattern

Double Slit Diffraction Pattern

I have made availble my plans and drawings for construciton of the single and double slits.

Download Drawings:

  File: FRS_DiffractionSlits.pdf

Pinhole (circular Aperture) Experiment

To perform the demonstration of passing light through a circular aperture, this can be accomplished by making a hole in aluminium foil with a pin.

However, the smaller (and more accurately circular) the hole is, the better the resolution of the resulting patterns.

In the case for my pinhole, this was created by the use of a Q-Switched ND:YAG laser. The laser is focused with the use of a lens, with the foil positioned at its focal point.

Pinhole Aperture

The following photograph taken of the pattern produced by a circular aperture. A Helium-Neon laser with a wavelength of 632.5nm was used as the light source.

Circular Aperture Pattern

Q-Switched ND:YAG Laser
Q-Switched ND-YAG Laser Cavity

Over the many years, I have been fortunate to have been able to obtain several laser systems, which has given me invaluable experience with many different types of lasers.

One of my first pulsed solid-state lasers that I obtained, was the small ND:YAG lasers cavities which came out of the Coherent 7900 series ophthalmic lasers used for YAG Laser capsulotomy following cataract surgery.

Originally, the cavity was non-functional due to a failed flash-lamp, however I was able to repair the laser with the use of a Xenon flashlamp (which was of the same length as the original) from an old photoflash unit.

The result was successful and was able to obtain a working laser cavity which also was able to be powered from 4 'AA' batteries.

The cavity is small, measuring 112mm long x 48mm wide x 25mm high. The actual ND:YAG rod is 3mm x 80mm

This laser cavity was used to produce the above circular pinhole with the use of an objective from a CD Player optical block.

The measured energy produce by the cavity is 118 millijoules.

- Flavio Spedalieri -
Written: 29th December 2020

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