School of Holography
LASER POINTER / SEMICONDUCTOR LASER HOLOGRAPHY
by Frank DeFreitas Holography Studio
Creative Holography Using
My magical journey of making
Inexpensive Laser Pointers
holograms with a $7.99 laser pointer
and inexpensive laser diodes.
3rd Test Hologram (Multi-Color) 1/8/99
(NOTE: Holograms are not 3-dimensional on your computer monitor).
Above is my first test shot at creating a multi-color hologram using the $7.99 laser pointer. Overall, it doesn't have the "snap" that the gold, single-color digital camera hologram has (previous page) and appears a little weak (thin) like the first test hologram. But for a single beam, it's not bad. For a multi-color hologram made with a $7.99 laser pointer, it's hard to believe! The blurring is a focusing problem due to holding the hologram a little too close to the camera (no zoom lens), it's actually quite sharp. I also find it hard not to get room reflections in the glass. After all these years, I still have not developed any talent at photographing holograms. Obviously, the hologram is of two Crayola crayons -- and both the red and green exposures were done with the 650nm (red) pointer. What I find amazing (even more so than the crayons) is the plateholder edge (made out of pressboard). You can see it run along the bottom edge on the inside of the plate. See it? It's tan . . . just like the actual plateholder. I'll have to ponder this unexpected, interesting result at a later time.
The first exposure was for green, swelling the emulsion 14% with TEA (triethanolomine). The second exposure was red. The TEA is washed out of the emulsion for the red exposure. It is always best to do the red exposure last, instead of first, since the photo-flo and water soak before exposure to remove the TEA actually leaves the emulsion a little hyper-sensitized, and gives a better balance with other colors than if the red exposure were done right out of the box (before the other colors). For newbies, when I mention "color" I am referring to the wavelength(s) of light that the hologram uses to reconstruct the object(s). There are no actual "physical" colors in a hologram (nor any "physical" image as in photography).
The set-up was the same as for the digital camera, so I just divided the 6-second exposure into two equal exposures of 3-seconds. Processing, once again, was PyroChrome technique at 2 minute development. For this hologram, I did not adjust exposure times or table geometry for each color.
In any case, with this process (which is actually called pseudo-color), it really is a hit and miss affair. Even after the holograms are completed and framed you will notice color shifts due to temperature and humidity changes. In fact, this coming summer I wouldn't be surprised if the red exposure on this test plate actually moves close to the deep-red and becomes a little dim (actually only dim to the eye). Indoors in the winter, the red may move closer to the gold considering the hot air heat in my home. Expansion and contraction of the emulsion -- even if it's sealed.
EVEN SO . . . there are certainly many positive uses for TEA:
TEA MAY BE THE ANSWER -- Using Triethanolomine (TEA) may allow the creation of holograms with longer wavelength diodes -- which are readily available, powerful and cheap.
When you shoot a reflection hologram and process using the PyroChrome technique (pyrogallol developer and potassium dichromate bleach) the hologram will reconstruct with the same wavelength of light that was used to expose the plate. For example, when you use a HeNe laser at 633nm, the hologram will "play back" at that color -- unless steps are taken during the processing technique to alter the color, such as adding sodium sulfite to the developer or using triethanolomine as a pre-swelling technique before exposure. Both of these will move the final color of the hologram away from the red and have it reconstruct in a shorter wavelength such as yellow, gold, green or blue, depending on the concentration.
At present, the best price/power ratio with laser diodes is not with the shorter 635nm diodes but at the longer wavelengths such as 650 and 670. For instance, a 15mW 635nm diode made by Hitachi (model HL6322G) sells for approx. $195. But their 35mW 658nm diode (model HL6501MG) sells for only $41.
Now keep in mind, that the eye is much less sensitive to 658nm than it is to 635nm (actually around 6-8 times less sensitive). A hologram created using 658nm will be *perceived* as being much less brighter than one created using 635nm, all things the same. This is where TEA comes in. If you pre-swell the emulsion before exposure with the 658nm diode (say 10%-12%), you will find that the resulting image will move away from the 658nm playback wavelength into the more eye-sensitive area of yellow or green. (Note: slightly higher percentages of TEA would be required to get the same results as it would using a HeNe since you're moving away from 658nm instead of 633nm.) Thus, you're putting a 35mW diode into your studio for $41, that is giving you the amount of power found in the upper end of HeNe lasers costing thousands of dollars.
So now we know that it is certainly possible to create multi-color, single-beam reflection holograms using a an inexpensive laser pointer. Now it's time to work on improving the quality and brightness of the image. All of the holograms produced so far were done using batteries. Next, I will do a test image using the power supply and see if the AC/DC conversion, voltage or current has an adverse (or positive) effect on making one.
From the little bit of research I have done into diodes in the past few weeks it appears to me that they are very sensitive to many factors including voltage, current and temperature. The slightest change can alter wavelength and power output and cause what is known as "mode hopping" -- where the laser jumps from one wavelength to another abruptly -- certainly not good at all if this happens during an exposure over several seconds or more.
I think it is to everyone's advantage to feed the diode the cleanest and most constant electrical currrent possible. This could mean an inexpensive power conditioner that filters and controls the electricity. I know Radio Shack sells one which conditions and protects against spikes. An even better choice would be the ones sold for electronic devices such as computer equipment which monitors the voltage and current and continuously makes adjustments. They are sold with one to many outputs, and I believe the models that have one output are rather inexpensive.
I am also going to attach a small temperature probe alongside of the diode to monitor any thermal shifts. Once again, you can pick these up in any electronic supply store and most measure to tenth's of a degree.
Of course, we don't want to spend a fortune doing this. The whole point of this is to have an affordable way to introduce people to holography -- and the holograms produced so far (without ANY fancy gear) are without a doubt in the same league as those produced using any 5mW HeNe laser.
One goal is to create an 8 x 10 "reasonable quality" single-beam hologram with this laser pointer. The big test (even more so than the 8x10 I believe) will be split-beam holography of any size. If split-beam is possible, the next step is a simple animated stereogram portrait.
Check back for updates to this on-going project and also tune-in to HoloTalk for my internet radio talk show which will be following work by myself and others as part of the broadcasts. Also, don't forget to visit Steve Michael's site.
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Frank DeFreitas Holography