In this tutorial, we'll attempt to follow Einstein's dictum so you can make holograms easily.
"Everything should be made as simple as possible, but not simpler." — Albert Einstein
The procedures we propose herein are as simple as it is physically possible. In the process, we make holography not only as simple as possible, but safer, less expensive, and more accessible to young people.
Most of the essential items described in this article can be found in our Integraf hologram kits or are available separately. The kits let you make many kinds of holograms, including the reflection hologram (viewable with whitelight) and transmission hologram (viewable and projectable with laser light) described in this tutorial.
2. Overview on How to Make a Hologram
Before diving into the details, here's a super duper quick overview on how a hologram is made. Making a hologram involves recording the interference pattern that occurs when light coming from a stabilized laser meets its own light bouncing back from the object it's illuminating. The key is to set up the laser, the object, and the recording film or plate in a way that captures the interference pattern. Once that's done, we simply need to expose the object and film plate with the laser light and then develop the exposed film plate. Once you get the hang of it, the whole process can be completed in 3 minutes.
Our holograms kits include everything you need to make holograms, including step-by-step instructions and tips.
Since we need to capture microscopic interence pattern exactly as it is at one moment in time, you can imagine how movement of the object, the film plate, or laser can mess things up. In fact, movement of any element by more than 1 millionth of a meter is enough to ruin your hologram. For that reason, we have to make sure our set up is super stable, i.e. no movement, no vibrations, no noise, no air currents, etc.
3. Holography Supplies
You will need the diode laser discussed below, a supply of PFG-03M 2.5 x 2.5 inch film plates (63mm x 63mm), and a JD-4 processing kit (or alternatively, PFG-01 plates with JD-2). All of these items are included in the HOLOKIT hologram kits or available separately from our catalog.
Though slightly trickier and thus not recommended for first-time holographers, one can also use PFG-01 holographic film sheets sandwiched and clipped between two glass plates instead of using holographic plates. Develop with JD-2. For the instructions below, substitute the properly sandwiched film sheet for the holographic glass plates. See our article on how to use holographic film sheets for important details.
3.1 The Laser
To make holograms, we take off the collimating lens of the laser to shine its pure, naturally spread beam right on to the holographic plate and object.
The figure below shows a Class IIIa diode laser with an output of 3 to 4 mW when operated by 3.0 v dc. If the power is supplied by batteries, its red light of wavelength 650 nm achieves a coherence length exceeding 1 m after a warm-up period of a few minutes. The traditional helium-neon laser, on the other hand, operates on dangerously high voltages, is prone to breakage, has a shorter shelf life, and a coherence length of approximately 30 cm.
Unlike many laser diodes and laser pointers, the laser shown below and in our catalog has a stabilized frequency output (a must for holography), good coherence length (also a must), and a removable collimating lens. With the spring-loaded collimating lens mounted on the laser, the output beam can be adjusted to focus at any arbitrary distance.
To make holograms, we'll actually take off the collimating lens. Without the lens, the direct output from the laser spreads out with a highly eccentric elliptical profile. Since the beam encounters no external optical elements, the light has no mottled patterns caused by interference and diffractions, and appears perfectly clean. In other words, we'll be shining this pure beam right on to the holographic plate and object.
The responsible parent or teacher is advised to remove the lens and the small tension spring before allowing the student to use the laser. This way, the power density received by human eyes will not exceed that received when looking at an ordinary grocery store laser scanner. When the laser is not in use, replace the collimating lens (with or without the tension spring). This helps ensure that you won't lose the lens and, more importantly, will help keep dust out of the laser.
If you are using your own "laser pointer" for making holograms, know many laser pointers and diodes do not have frequency stabilizing circuits (like the one above), which is required for holography. Moreover, since most laser pointers do not have a removable collimating lens, you must buy a special optical lens to spread the beam. With two lenses (four lens surfaces) through which the laser beam must shine, there may be many objectionable patterns on the resulting beam due to the four lens surfaces and the dirt on them.
3.2 Stable Support for Laser
An excellent support for such a small laser is a wooden clothespin, as shown below. For mechanical stability and maneuverability, the clothespin holding the laser is stuck into a cup of sand, salt, or sugar (not pepper!). On the other hand, for schools with available laboratory hardware, the clothespin can be glued to a rod and mounted on a lab stand with a right-angle clamp.