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.
5th Test Hologram (8 x 10 AGFA) 1/16/99
Holograms will be on display at The Discovery Center of Science
and Technology at Lehigh University soon.
(NOTE: Holograms are not 3-dimensional on your computer monitor).
The above hologram should lay to rest any concerns for film/plate size or depth limits using a laser pointer (same $7.99 model as other holograms). This hologram shows depth back to 8 inches (yes, 8 inches!) into this 8 x 10 single-beam reflection hologram shot on an AGFA 8E75HD glass plate. If you remember, Steve Michael reported high-contrast fringes out to 10-inches during his interferometry tests of his diode -- and wondered in an Email today if he could have gotten more. With single-beam (Denisyuk) holography, Graham Saxby states: (practical holography, prentice-hall, page 136) "the image depth is limited to half the coherence length of the laser beam". So, can we be correct in assuming that the 8-inch depth displayed by this hologram makes the coherence length of the laser pointer *at least* 16-inches?
I would say it is quite more than "satisfactory" with brightness, but doesn't exhibit the brightness of the 4 x 5 digital camera shot on BB-Plates from Germany (see page 4). However, it is certainly consistent with any other single beam, 8 x 10 reflection that I have shot with my 15mW HeNe (which took 36 payments to own). When I look at that tiny little laser pointer with 3 AA batteries hooked up to it I feel like I'm dreaming this or something. As a side note: the green you see is not algae, it is uneveness in the squeegeeing of the TEA. Although, in this case, this green "mistake" fits right in!
The above photos show two different perspectives of the coral hologram: (left): straight on; (right): looking down showing depth into hologram. The flat, non-dimensional photo on the right makes it look like the coral is going up to the top of the plate, but actually you're looking down at it -- and it is receeding into the hologram.
With fresh batteries (the new AA DuraCell ULTRA's), the reference reading measured a 50 on the 3 scale of the Science and Mechanics light meter. The exposure time worked out to 7.5 seconds (according to a forumula I use), but I added 2.5 to round it off to 10. With single-beam holograms there is no opportunity to adjust beam ratios as there is with split beam, so the brightness/reflectivity of the object itself has to be taken into account. With metallic/silver objects (like the camera), I do not add any additional time to the exposure. With the coral, I added approx. 20 percent. With a darker object, I may add 50% all the way up to actually doubling the exposure (although this does add to the noise/scatter of the finished hologram).
I did not spread the beam out as much with this hologram as I did with the 4 x 5's (relatively speaking, size for size). One thing that I noticed with the beam profile of the diode/pointer is that it is very consistent side to side, up and down. Which means, I do not see as much variation in beam intensity across the width of the plateholder (drop-offs in intensity moving away from the center) as I do with a "tight" HeNe spread. With a HeNe, I've always had to waste quite a bit of perimeter light to get the light falling on the plate to have equal readings all over. It remained very "hot" in the center until it was spread quite a bit larger than the area needed. Not so with the pointer. I spread the pointer beam out to cover the 10-inch width, with just a very little overshoot onto the plateholder sides. The Light reading showed an amazing amount of equality across the width of the plate. So I left it tight. Doing this with the 4 x 5's should cut exposure time as well.
Another attribute worth mentioning is that the beam is rock-solid stable. With HeNe lasers there is noticeable "drift" over time -- requiring a fine adjustment of the spatial filter, etc. if you return to a set-up after any considerable length of time. With the pointer, I have not had to make any adjustments at all. It remains "as-is" from one day to the next.
The emulsion was pre-swelled using a 10% solution of Triethanolomine, both for color-control and hyper-sensitizing the emulsion. Processing was PyroChrome (pyrogallol developer, dichromate bleach). I should mention at this point (which I've failed to do so far) that tap water should be avoided at all costs when processing a hologram -- especially if your local water is heavy on chlorine. The chlorine in some tap water will render what could be a great hologram dim beyond belief. This is especially important for mixing of your chemistry. Buy distilled/de-ionized water for your chemistry -- and use if for rinsing as well when possible.
So, there you have it folks -- an 8 x 10 single-beam reflection hologram with 8-inches of depth using a $7.99 laser pointer. And yes, I know I'm asking you to believe quite a lot. I would find it hard to believe myself, to tell you the truth. This has come a long way since the dim, little "frosty the snowman" hologram before Christmas.
I have a 10mW, 640nm diode coming in shortly. In the meantime, I may set up and try a split-beam. My next goal is to do a 4 x 5-inch holographic stereogram portrait. The single-beams are working out so good, that I do not want to take any time to do just a regular split-beam reflection hologram. The BB-Plates are so bright and crisp with single-beam that I feel that split-beam is not necessary with them (and single beam reflection holograms are always illuminated so much better and evenly than trying to adjust the effect of a second object beam).
The holographic stereograms start out by using a 35mm camera to capture individual frames of a person (or scene/object). I use reversal processing of Kodak TMAX100 film (Kodak sells special reversal kits for TMAX). By reversal, I mean that the negative is actually a positive when processing is finished (like a 35mm slide, only black and white).
To begin, I move the camera horizontally past the person, taking individual exposures along the way. It's possible to include a small amount of "action" or motion, such as winking an eye, or waving, etc. When the hologram is finished and on the wall, the person will wink at you as you walk by.
These individual frames are then all transferred as "slits" onto an individual master laser transmission hologram (H1). This master is then used to send all of the slits as one combined image to a white-light reflection copy (H2).
On my usual stereogram portraits, I shoot the master laser transmission holograms (H1) on film and then transfer over to plates for the reflection copies. I'm not quite sure if 5mW is going to do it, but I'm going to try (always try). I'd like to do one with the 5mW pointer before switching over to the 10mW -- just so it can be shown that an over-the-counter, out-of-the-box laser pointer can do it.
I have my first laser pointer workshop to teach on Monday. If you'd like to come in and learn how to do this hands-on and make your own hologram, just call the number above to arrange a workshop. The studio is an easy drive from New York, Phila., and the Baltimore-DC area.
Stay tuned for the laser pointer stereogram journey. I'll put up pages each step of the way: from the initial photo shoot, through making the master and then reflection copy. Any good-looking models out there?
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Frank DeFreitas Holography