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.
Necklace with Overhead Reference Beam 1/21/99
(NOTE: Holograms are not 3-dimensional on your computer monitor).
The above hologram was shot on a new batch of BB-Plates from Germany that were sent to me last week for testing by Dr. Joachim Vinson of Vin-Teq, Ltd. (listed on link page). The previous test (of the digital camera) was made on plates over 2 years old. The only difference (that I noticed) turned out to be a much shorter development time to reach desired density (2.0-2.5). This turned out to take approx. 3.5 minutes. So, the plates hold up very well, at least for 2+ years.
With objects that cause specular reflections it's very easy to "burn" the emulsion. Luckily, the necklace was not in contact with the plate or there may have been trouble. Overall, the Austrian crystals are very bright and sparkle beautifully. More light could have been directed to the lower portion of the plate -- but otherwise, it's definitely a frameable shot if matted down to only the necklace itself.
The plate was pre-swelled with a 5% solution of triethanolomine, both to move the image away from the 650nm wavelength of the pointer and to hypersensitize the emulsion. Exposure time was 18 seconds. I used an overhead reference beam this time around (see below). Using a 10x objective and 25-micron pinhole, distance from pinhole to mirror was 35-inches, and 3 inches (avg.) from mirror to plate.
I do notice some woodgrain effect to the emulsion (when held at a steep angle, not visible at viewing angle), but this is probably due to the (1) extra glass used in the set-up, (2) angle of mirror to plate or a combination of both. In any case, it is the fault of the set-up, not the plates.
The above photos show the set-up used for exposure. The photo on the left is looking down to the set-up from the pointer and spatial filter. The photo on the right is a side view.
Basically, the necklace had to lay flat, which eliminated the possiblity of shooting it with the plateholder tilted in the sand. I used a simple "sandwich" arrangement on a sandtable, which included (from bottom up), (1) a layer of felt to absorb stray light, (2) an 8 x 8-inch by 1/4-inch thick steel plate, (3) a 4 x 5-inch white card, (4) 4 beveled rubber plumbing washers as spacers to create a shadow on the white card for depth, (you can see one of the black washers in the upper left-hand corner of the hologram photo at the top of the page), (5) the clear glass plate that held the necklace, (6) 4 more beveled rubber plumbing washers as spacers, and lastly, the holographic plate (not shown, obviously). The large flat-plane, front-surfaced mirror was pushed down into the sand with the felt material surrounding it to protect the surface. It was then tilted to the proper reference angle to direct the incoming spread reference beam down onto the plate.
The holographic plate was not held in position by anything other than its own weight resting on the rubber washers. Frankly, this would not be considered a very stable set-up, and I had my concerns on whether it would work. Turns out, it worked fine, but one has to wonder if even better results would not have been achived by a more fixed or rigid construction. I did allow close to one-half hour settling time hoping to compensate.
With this test, I just wanted to try out the newer BB-Plates and a new set-up. I don't particularly like placing any mirror after the laser light has been spatially filtered -- since I like to go from the filter directly to the plate without hitting another surface. But in this case, it was easier to use an overhead reference beam.
I could have mounted the laser pointer and spatial filter on a tripod and shot the reference beam down at the required angle. Remember, the ONLY part of your system that needs to have vibration isolation with single-beam holography is the object and the plate. The laser and lens/spatial filter does NOT have to be isolated or even located on the table.
Along with other plans, I am working on a very "portable" isolation set up that will not be much larger than the 8 x 8-inch steel plate used in this set-up. A 4 x 8-foot sandtable is pretty-much overkill for this single-beam work -- although the diamond-braced design that I use for this table (thanks to Gary Kline of the Discovery Center at Lehigh University) is very, very stable.
Still to come:
1. Split-beam / stereogram test
2. 8 x 10 using my 10mW, 640nm diode when it arrives (should be soon)
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Frank DeFreitas Holography