Lighting for holograms

On: Sun, May 26, 02 05:48:23 AM

Tom B. wrote:

Anyone have any suggestions on types of bulbs, shades and optics etc. for wall display of reflection holograms? My ceiling height limits the distance of the source from the hologram to 2-3 feet, and the small halogen lamps and bulbs I've tried produce a fairly ugly non-point source beam with spillover light much wider than the claimed spot angle. For 2-3 foot distance, I would like a nice smooth 6 inch spot which works out to 9-14 degrees. Don't need a lot of wattage - 50W spots are way too bright as is.


Colin Kaminski - Sun, May 26, 02 01:39:14 PM

I have used mini-halogen spots at 35W and 10 degrees. The problem I have has is you need a UV filter to keep from damaging the hologram long term. If money is no object then there are very small instruments for stage lighting that would have a flatter beam profile. I have only used them on stage once and am not sure who made them. I rented them.

Thilo K. - Tue, May 28, 02 01:47:28 PM

Do you know how to light rainbow holograms ? Commercial rainbow hs seem to have a shiny surface fixed to the back of the hs, so lightning from front of the h is possible. But I have not found a suitable material to connect with yet. Spreading 'chrome' paint on back of the h didnīt help. Have you stuck to illuminating these hs from behind, or have you already found a suitable method of coping with this problem ?

Colin - Tue, May 28, 02 11:28:28 PM

I have not tried it yet but I have some mylar and some optical cement I will try someday.

Tom B. - Wed, May 29, 02 03:48:11 AM

Interesting - I haven't been much interested in making rainbow holograms just because of the difficulty of lighting them, but a reflective backing might be just the ticket. I just now tried laying a transmission holo over some mirrorized mylar and it produced a decent rainbow-blurred image, but not quite as clear or bright as from direct lighting. It probably IS best to use an index-matching optical adhesive to reduces losses and internal reflections. Re lighting, just found a company that makes VERY high power white LEDs - up to 120 lumens for the 5W model: They make other colors too. Prices are not too outrageous, about ten bucks for the 1W models and $36 (U.S.) for the 5W. I think with the addition of a small collimating lens these MIGHT do just what I want - worth a try, at least. Would need to buy or build a power supply, heatsink, etc. as well. Just what I need, another project :) (sigh)

Andrew - Thu, Jun 06, 02 09:40:32 AM

Tom, You refer to Index-matching Optical adhesive. What is that actually? I am a scultor who is currently experimenting with transparencies over metals. I am interested in an adhesive for this purpose. Thanks would like to see some holograms you make.

Colin - Fri, Jun 07, 02 02:43:09 AM

I get mine from Thorlabs. I have used many of their part numbers, Here is an example: NOA60

Tom B. - Fri, Jun 07, 02 03:36:46 AM

When you lay film over any rigid flat surface, inevitably there will be a thin layer of air trapped underneath. Index matching refers to eliminating reflections caused by the change of refractive index as light passes from film (index N= 1.5?) to air (index N= 1.0?) and back again by replacing the air with a medium that has a refractive index that is closer to film. Optical adhesives, such as those made by Norland, are clear one-part adhesives that are set by exposure to ultraviolet light. Norland's glues have refractive indexes in the 1.52-1.56 range. sells the stuff at about $20 for a 1 oz. bottle. I recall having seen more detailed product info on Norland's site. If you want to experiment with the effect, you could try various liquids such as water (N = 1.33), or mineral oil or glycerine (N = 1.475). Higher index liquids, such as toluene (N= 1.496) tend to be unpleasantly toxic.

Colin - Fri, Jun 07, 02 11:15:37 PM

For reference we should add that when index matching two transparent materials: "Ideally, this should be the geometric mean of the refractive indexes of the film and glass. In practice it is difficult to find a liquid that is chemically and physically acceptable and has exactly the right refractive index." Graham Saxby, Practical Holography, 1988 Many of the chemicals I have seen recommended would require a hood to ventilate the toxic fumes. So play safe. Fortunately a better match than air bubbles is not to hard.

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