I am experimenting with a 20 mW diode and single-beam setup since about one year. With the BB640 plates I obtained really nice holograms almost from the beginning. But since these plates aren't available anymore I had to change to films. I am now using Slavichs PFG-O1 films(102 mm x 127 mm). My problem now is: I don't know how to mount the film properly. The sandwiching technique (film between two glass plates) doesn't work fine. There are always fringes (ring-like structures) on my holograms. I found out that these fringes are newtonian rings. They are not provoked by instabilities but by different optical path lengths because the glass plates are not totally flat. One can easily see them by pressing two glass plates together- breething against one plate to have some moisture on the surface - and holding it into the diverging beam of the diode. You can now see the rings - and they are moving if you squeeze the plates (it's actually a nice way to test a setups stability). If have tried several things to get rid of the fringes: e.g. glueing the film to only one glass plate - but there are problems with air bubbles and there are always traces of the glue visible on the hologram. Does anybody know a way of gluing a film to a glass plate? I've heard of people using trichlormethane, and others are using sticky foils. Actually I have tried to fix my film with tape to the glass plate. This works fine (there are no more fringes or multiple reflections - you don't even have to care about the brewster angle) but only for small pieces (about 4x4cm2). When I used larger pieces of film (like 127x102 mm2) the film always moved a little bit - mainly in the center where it is not fixed - destroying the interference (therefore leaving a dark patch in the middle of my holograms). An even better way of holding the film might be that of using no support like glass plates at all - but only a frame. Does anybody have experience with such a film holder? Greetings from Bavaria Tom
Colin - Thu, May 24, 01 11:22:26 AM
Tom, I still use plates but I have read that big labs use vaccum platens to hold film stable. I would make one from aluminum and drill very small holes on very close centers. Have the whole plate black anodized. Then you have to build a back plate that can hold vacuum. For a vaccum pump you can use an old refigerator compressor. In California a few years ago they made it mandatory to recycle R12 refigerent. All of the old vaccum pump in the automotive and refigeration trades are oblolete and I was able to obtain one for free. The pumps are small and very quiet but I would still put it in another room. If you try this and it works let me know. Plates are very expensive. Also have you tried lamp oil in you sandwich? That is the advice people have given me. 63.193.192.103
Joe Farina - Thu, May 24, 01 11:36:26 AM
I've used the following technique with Agfa film. It involves using a single piece of glass and index matching fluid. The index matching fluid I used is known as "mineral spirits" in the U.S. This is ordinary paint thinner, sold as a substitute for turpentine. In my neighborhood, it is available in hardware stores, often having the phrase "100% mineral spirits" on the label. Clean your glass plate and put some drops of mineral spirits in the center. Then put the film in position(emulsion side facing up, not in contact with the mineral spirits) by bending it downward toward the center, so that the center of the film contacts the pool of fluid first (so that bubbles will tend to be pressed out to either side). Then place a layer of about 3 paper towels on top, and remember the orientation of the film. Take a rubber roller (called a "brayer" in art supply shops) which is as long as the width of your film. Press down through the paper towels onto the center of the film. Then using a back-and-forth motion, rock the brayer back and forth while pressing down. This method helps to prevent air bubbles, and the paper towels protect the emulsion while soaking up any excess fluid which is squeezed out the edges. 216.65.161.130
Vidar - Mon, May 28, 01 07:27:33 AM
Index matching with oil or white spirit is simply very nice. I have been using this method with film for many years and is very please. More infromation can be found in Practical Holography, Graham Saxby.
For thin film like the pfg you may have to use mineral oil instead of white spirit and use a window cleaner to attach the film firmly to the glass. Works nice for both transmissions with a black painted glass and for reflections. Good luck. 213.236.155.35
Frank DeFreitas - Mon, May 28, 01 10:51:49 PM
When running test after test working with diodes in the now "early" days, I had to come up with a way of not going broke using glass plates -- while also keeping the quality of the holograms intact and consistent -- so that any problems would be from the laser test itself, and not the set-up. Of course, this meant working with film (AGFA-8E75HD at the time).
With both time constraints and the shear number of test shots, I quickly became aware that wet-mounting was just too much to do each time. So here's what I did:
Since the very nature of holography requires that glass plates be manufactured to exacting specs in regards to flatness, I took two old plates and placed them in a standard Clorox bleach solution. Within several minutes, the emulsion turns to a white paste and can be rinsed off with water -- leaving just the glass substrate. This took care of the problem with commercial glass and it's inconsistent "flatness" for sandwiching. NOTE: Since this IS a chemical reaction taking place, when removing the emulsion with bleach, use a fume-hood or do this outdoors.
Once rinsed, clean the glass off with any standard window cleaner and take care to store them so they do not become scratched. Any scratch will show up in the final hologram -- and, if it is deep enough, actually create a shadow -- due to the angled surface of the physical scratch itself.
Then, just take your film and sandwich it between the two pieces of glass. My method was to "squeeze" the glass together with a twisting motion while applying downward pressure. If done properly, you will create your own vacuum and the entire sandwich will stay together as one unit. When you REALLY get the hang of it, you'll find it hard to get it apart!
Now, for the set-up: You will need a polarized laser and make sure that the polarization is properly oriented to your plateholder. You will also need to bring your reference beam (or single beam) in at "exactly" brewsters angle. One way to determine this is to set up your plateholder at brewsters and place a single piece of glass in it. Hit the glass with your spread beam. The glass is going to reflect some of the light hitting it, so place a white card in this reflected light path (in order to view it). If you rotate your laser head, you will notice that this reflected light becomes brighter and dimmer. Find the spot within the rotation where the reflected light is at it's dimmest on your white card, and you've got it. There should be two spots for this with every 360-degree of rotation. With my HeNe, it is at the 3:00 and 9:00 position(s) for side-reference (parallel to table). With the diode, it is at 12:00 and 6:00. With a HeNe, you'll always have a "little" bit of light reflected. With a properly-running diode, the reflection will go completely out on the card (100% -- or VERY close to 100% -- transmission through the glass).
For side referencing, also make sure that your plateholder is not angled toward or away from the incoming laser light, too. It should be straight up and down in relation to the reference beam. This also means making sure that your incoming laser light stays parallel to the surface of the table . . . and is not directed upwards or downwards in any way toward the plateholder during it's travel. If you're using an overhead reference, then it should not be angled in any way from either SIDE. In other words, the ONLY "angle" present should be the reference angle -- no matter what table geometry or set-up you're using.
Place your sandwich into the plateholder and give it time to "settle". It will take much longer with film than with a glass plate. I usually use this time to get chemistry ready, or go upstairs and have a cup of tea and relax, etc.
Do your exposure as you normally would. If you have everything set-up properly as stated above, you will have a film hologram that is every bit as clear, bright and clean as one on glass plates -- without the cost of plates and without any type of index matching fluid or the associated mess and/or extra time.
In closing, I have heard that the .mil thickness of the new film out there is less than it was previously with AGFA . . . so this may require a few "tweaks" here-and-there with settling time, etc.
Regards,
Frank 208.59.249.8
Guillermito - Wed, Jun 06, 01 06:22:45 AM
Frank, while you're back, and because you don't read your email, so i post here, what about sending me the missing IC in my power supply kit, or just give my money back, which i would prefer? That's more than one year, you know. I've bought other lasers since then. You're certainly a good holographer, but a borderline businessman, and it's very annoying. At least you could put some info on your page, or remove the DS Laser page if you don't have anymore, so people could understand. I decided i want this stuff resolved before this summer. And look, i'm even open for a deal: instead of sending my money back, you can pay me with an hologram, as i am an avid collector. You can contact me at [guillermito@pipo.com] or [guillaume@molbio.mgh.harvard.edu]. Frank, let's end this matter quickly. Please. 132.183.191.178
Tom Naiser - Sun, Jun 17, 01 07:37:57 AM
Thanks for your good advice. Finally I have managed to make some good holograms without fringes, dark patches etc. I have tried several methods. Using white spirits (one was a turpentine replacement, the other a highly volatile mineral oil derivate) I had at an improvement (in getting rid of the fringes) but I had quite some problems with air bubbles as the liquids have a rather low viscosity. And the fumes are not very healty,too. I have also tried using old BB- holo plates for sandwiching, but the 2.5"x2.5" format I used is probably too small. I guess it works well with larger plates.
The method I use know, and which works really fine is this: Take a glass plate (not necessarily a holo plate, window glass works fine too) and put a few drops of lamp oil (that is liquid paraffine) on it. Put the film with the emulsion site onto the glass plate (into the oil - this doesn't harm). Use paper towels to press the film onto the plate and squeeze out the air bubbles. The film sticks very well to the glass plate - perfectly flat - and it doesn't come off easily (for days). Only at the edges there might be small bubbles enclosed (due to the films rigidity). You can treat is now as a holo plate (apart from the fact that the emulsion site is pointing towards the glass plate). Another advantage of the lamp oil is that it is not that poisonous as the other stuff, it doesn't produce fumes and you can easily wash it off with water (maybe with a few drops of detergents). 217.48.209.145