Horizontal stripes on red hologram

[Max]

Hello,

I'm quite new to holography, and I've tried making some holograms for a science project, using an integraf kit (PFG-03M plates).

For now I just make some simple holograms (pinpoint laser and direct contact between hologram and objects). I first made 2 of stacks of coin that did well, then I wasted 4 plates trying to take an eiffel tower that didn't come out (perhaps due to vibrations), and now I made a 5 others that worked more or less, 2 eiffel towers, 1 little car, keys and 1 magnifying glass pointed toward coins.

I experience some problems with these last 5 and I would be glad to get the advice of more advanced holographers.

- Horizontal stripes appear on the objects. It looks like interference fringes, and I can't explain them, and why they appear on these objects but not on the coins. Could it be related to the laser orientation (or polarisation) ? I made these one with a 45-degree incidence, but I had made the coins with a normal incidence (I later realised it was more difficult to look at). These stripes make the eiffel tower look broken.

- With the magnifying glass pointed toward points, I can only see the magnifying glass and not what is behind. I guess this was a bit too ambitious.

I would like to try out interferometry, but obviously I can't while there are these stripes.

Thanks for your help.

[dave battin]

these holograms show object movment. longer settle times, draft exclusion, vibration isolation, and attachinig you object better to the platform ............... good work keep it up.

[BobH]

I'm not accustomed to working with diode lasers, but those lines look more like coherence length lines to me. Could it be that the coins worked because they were relatively flat against the plate with a normal incidence beam? Could you describe the laser?

For fringes like that to be object motion, the object would have to be vibrating with a regular period for the whole exposure. I think it's coherence length.

[Joe Farina]

I'm not accustomed to working with diode lasers, but those lines look more like coherence length lines to me. Could it be that the coins worked because they were relatively flat against the plate with a normal incidence beam? Could you describe the laser?

For fringes like that to be object motion, the object would have to be vibrating with a regular period for the whole exposure. I think it's coherence length.

Yes, it seems like coherence length to me also. As Bob said, since the coins are flat, it's possible that the depth-contours (light/dark bands which indicate coherence length) are not showing up. Diode lasers can be unpredictable, sometimes they mode-hop.

[dave battin]

yes this is also possible, i kinda dismissed this idea,as the multimode holograms i have seen the lines are very much uniform unlike these... :think:


what laser are you using?

[Colin Kaminski]

Once you have seen both forms of interference they are easy to tell the difference. Motion happens around a pivot point un-related to an optical axis. This makes concentric spheres that appear to emanate from that point. With coherence problems the fringes appear to come from the diverging point of the laser beam. Without rocking the hologram it is hard to tell but that looks like a diode modehop to me. A mode hop is making a hologram with two distinct frequencies. An interferogram of sorts.

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[Max]

Thanks for you answers,

For fringes like that to be object motion, the object would have to be vibrating with a regular period for the whole exposure

Yes, that's what I thought (I don't think random vibrations would produce coherent interferences), and the system was quite well isolated...

This makes concentric spheres that appear to emanate from that point. With coherence problems the fringes appear to come from the diverging point of the laser beam

Indeed the concentric spheres are moving (becoming thinner) with the viewpoint, but don't seem to be around a point of the object.

The diode laser I use is described on integraf's website. It claims it has a 1-meter coherence length... isn't mode-hopping weird in this case ? (I go back to school in one week, I may be able to make measures with a michelson then...)

I found similar symptoms described here by jeff-blyth (However this is about a 100 mW pinpoint laser (!) while mine is a 3 to 4 mW) :

However strong horizontal stripes ran across the image. These moved as you moved your viewing position. Symptomatic of “mode hopping” I understand.

I will make some few holograms this evening, I will try varying incidence and will try waiting a longer time for laser stabilisation.

Thanks again.

[dave battin]

as it could easily be anyone of these issues(or all of them), could you post a picture of your setup? as im still thinking movement is involved here, how long exposuer? how is the film/objects held?

[Max]

Excuse me for not answering earlier, unfortunately I haven't any photo of the setup, but it was quite the same described on integraf's website, the object was enlightened from above, I just laid the hologram on the object while holding a black paper in front of the laser, waited a few seconds to let things settle, removed the shutter for a 15-20 sec exposure and put the shutter back. As for vibration isolation, I did it at my school on a heavy metallic slab which was in a lab for isolation purposes.

I haven't had the time to make other attempts as I said the other day, but I certainly will in the course of this week. Moreover, as I return to school next week, I will be able to use a "true" laser they have there, with a spatial filter. I will share progresses here if it doesn't bother you.

[Tom B.]

I just laid the hologram on the object while holding a black paper in front of the laser, waited a few seconds to let things settle, removed the shutter for a 15-20 sec exposure and put the shutter back. .

Even with glass plates, much more than a few seconds are generally needed for things to settle just due to air currents etc. A few minutes at least are advisable. If the object is made of plastic or other non-rigid material and it is under stress from the added weight of the plate, it may never settle - it could just keep sagging as it slowly deforms under the extra weight. You may need a better plate support that keeps the plate close to the object without stressing it.

I've seen contour lines from both object/plate movement and from multimode lasers and my bet here would be object or plate movement, pivoting at the bottom. Multimode or mode hops in my limited experience usually produce sharper lines. It would help to know what the object material and setup was.