Holography Help

On: Sun, May 19, 02 05:04:49 PM

Alex wrote:

RESPONSES

Colin Kaminski - Sun, May 19, 02 09:51:44 PM

It would help greatly if we knew what laser, film and developing system you are using. Some first things to check. STABILITY. This is usually the problem. Make sure there are no air currents in the room. Make sure there is no noise in the room. Wait till no cars are driving by outside. Make sure the object sits perfectly flat and does not wobble. Make sure to warm up the laser. I put my film on the table and leave the room for 15 minutes to wait for everything to settle. Then I carefully and gently return and lift out the shutter card. The whole exposure time I either don't breathe or I take very shallow breaths. If you provide more information we will have more ideas. Don't get discouraged! We all have had bad exposures. 64.167.149.189

Alex - Mon, May 20, 02 08:50:44 AM

Oops, I guess that info would help... I am using all the items suggested in "Shoebox Holography". I am using BB-640 plates, the "Infinter200" diode laser operating at 650nm. I am also using a -12x-12(not sure how to write it) lens to spread the beam. I am using two concrete slabs with the shockobsorbing feet and a large piece of metal on top with magnets to hold the plate. I am using a little figure placed about 1cm behind the plate. O and the plates are 2.5" square and I am exposing them for 15 sec(but I tried 10sec also after I developed the first because I thought it turned dark relatively quickly and that didn't work etiher). Those are the specifics of the setup. 168.213.1.134

Colin - Mon, May 20, 02 01:37:27 PM

I have used magnets to hold the plate and found unless I had the poles aligned correctly I could not hold the film tightly. It should be obvious which way is better when you flip one magnet and test it. Something to look for is a faint image of the magnet. It was likely very stable durring the exposure. Another thing to try is to touch the object to the plate. When they are in contact they tend to move together. In a single beam set up it is only the plate to object relationship that needs to be stable to 1/8 of 650nm. On some of my exposures I find the image is there but really faint and takes me some time to find. The sun works well to find dim objects. Flip and rotate and change the angles sometimes a flash of color will go by that turns out to be a part of your object. Make sure the object is very white. Single beam holograms often have very poor object to reference beam ratios and white objects are better. I often use a white porcelain figurine for single beam work. If you place a white card behind the figurine and look at it's shadow you will see how evenly illuminated it is. There is no need to spread the beam any wider than the plate. Check that there is not any wobble between the concrete and the metal. I use very thin foam between by concrete slap and metal plate. Your are just looking to even out the contact not to float the steel so make sure it is very well compressed. It could have been a random movement in the ground when you made your exposures. Don't be afraid to waste some film sorting it out. Looking in my log book I did not get a perfect exposure till my 7th plate. I got an image on my first but not my second or third tries. I do not use BB-640 so perhaps one of the group with more experience as some ideas about finding the proper exposure time. With my system I can go by image color. Did you tape the edge of the plate facing the laser? If not you should have at least rainbow stripes. 64.167.149.189

Alex - Mon, May 20, 02 02:13:00 PM

Thank you very much, Colin. I will definetly try that today. I appreciate all your help. -Alex 65.34.72.187

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