FAQ - Making Holograms
Like learning to ride a bicycle, expect some pitfalls on the way. The most common error made by beginers are:
The film or holographic plate moved during exposure. Make sure the holographic film or plate set solidly at a location very near the object (touching it is best!). If you are using our Budget Holokit (which uses holographic film instead of plate), make sure the film us clamped tightly between the glass plates, and also let it set for 5 minutes in the dark before the exposure is made. This allow time for the air trapped between the glass plates to to escape and the ensemble to stop moving.
The object moved during exposure. Use solid and heavy objects and those that look bright under red laser light. Do not use cloth, paper, or rubbery object which once deformed, takes a long time to recover its shape. Metallic and porcelain are preferred. Lean the film-glass sandwich on the object to prevent relative motion during exposure. See other sources of movement in the next question below.
Another common error may be that one is simply not looking at the finished hologram correctly. In other words, the hologram is okay but you just need to modify the way you're looking at it. To learn more about how view a hologram, take a minute to read our short article "How to View Your First Hologram".
If you still have encounter problems after trying again, we'd be glad to help you. Simply email us. Include photos of your set up and resulting hologram, if you it can. We can usually diagnose and fix the problem right way.
If your object or holographic film plate moves even one thousandth of an inch during exposure, your hologram will not likely turn out the way you want. That's because a hologram is a recording of the microscopic interference pattern resulting from the light coming from the laser meeting its light bouncing off the object. When there is movement, the interference pattern cannot be clearly recorded.
Listed below are just a handful of less obvious causes of movement you want to AVOID:
- Choosing an object that is not hard enough. Paper, cloth, furry dolls, and don't make good holograms.
- Setting up your hologram lab near a window, vent, or other place where a draft may flow through.
- Changing the temperature of the object or film plate. If you hold the object with very warm hands, for example, and then expose while the object is cooling down to a cooler room temperature, you're hologram may not look ideal. That's because the object may expand slightly from the heat of your hand and then shrink thereafter to room temperature thereafter. Yes, this counts as movement!
- Breathing next to the exposure area, which may create a slight draft or temperature change
- A neighbor playing loud music next door may cause unwanted vibration (Sorry. Van Halen and holograms don't mix!).
- Walking around your set up with clunky shoes.
Aren't there some situations where it's okay to have just a little movement? Actually yes. You may actually want to capture microscopic movements on specific experiments (this is what's part of the practice of holographic interferometry). We had one young customer who actually made a hologram of a mushroom growing. Another made a hologram of an egg . . . with a baby chick inside! Movements were so minor that that the holograms worked out and, in fact, showed black lines where movement occurred. You can read more about how to do this in Experiment 7, found in Laser Holography: Experiments You Can Do. This booklet is included in any of our HOLOKITs, and can also be purchased separately from our online catalog.
A five minute warm up time is very important! A critical part of making holograms lies having a stable frequency output from the laser. Not all diode lasers can do this, but the holography diode laser in our catalog can because it has a special built-in circuit. One needs to take make sure this laser is warmed up five minutes before making exposures. We looked at the laser's output through a Fabry-Perot interferometer on an oscilloscope and saw that its frequency stops shifting after about five minutes. Thereafter, any disturbance such as touching the laser or even blowing some air across the laser during operation can shift this frequency. If this happens, wait about a minute and it will settle again.
When you shine the laser light on the plate at any angle other than straight-on, some light will enter the edge of the plate that is nearest to the laser. This light then bounces back and forth inside the plate by internal reflection and interferes with the reference beam. In other words, whenever you see these straight lines of color, you have actually made a very good hologram of a beam of light, even though you didn't want to!
To prevent this, use a black marker and paint the top edge of the plate to prevent the light from entering through it. Or, use an obstacle such as a ruler or a piece of paper to cast shadow over this edge during exposure.
No, Stop! Don't do it! Don't do anything to the emulsion. Once the emulsion is dried, there is nothing you can do about it.
The answer is to keeping a hologram clean is prevention. When removing the wet hologram from the Photoflo bath, carefully inspect it. It should be evenly wet. If you blow dry the hologram, note that dust may deposit on the wet hologram. Every speck of dust will cause a local blemish on the hologram.
Here is how the "pros" keep holograms looking great. After treating the hologram to a Photoflo bath, treat the hologram with distilled water so that the wet hologram is completely free of bubbles or streaks. Then place the bottom edge of the wet hologram on top of a paper towel and lean it against a vertical surface in a dust-free area. Allow the hologram to dry by itself. This may take more than an hour depending on the humidity.