ORWO spectral plates

holo_cyware · Post by **holo_cyware** » Sat Oct 03, 2009 5:00 am

The lines are thin, and look like the fingerprints (they are curved).

The reflection is from the lightsource, I don't have enough skills to take a pic of a hologram yet.

holo_cyware · Post by **holo_cyware** » Sat Oct 03, 2009 9:59 am

Ok - just found out: the lines are the "Newton's wood" effect, caused by the lack of Brewster's angle and the angle of the plate to the laser light (something like 60 degrees)

Joe Farina · Post by **Joe Farina** » Sat Oct 03, 2009 11:04 am

The "wood" bands will appear in the plane of the emulsion. With mode-hopping, the bands will closely follow the contour of the object. Mode-hopping results in very short coherence lengths; the bands on the object represent areas where it's going in and out of coherence zones. Hard to tell from the photo.

holo_cyware · Post by **holo_cyware** » Sat Oct 03, 2009 12:13 pm

It's not mode hopping then (and it shouldn't be); the lines are clearly on the surface of the emulsion folowing it in length, and have nothing to do with the objects. I also observed that with different holograms the lines are less visible/not visible, as I the plates were shot on different angles.

On the other hand, a laser with a coherence so short that even a holo of some coins would be "bread sliced" would be rather pathetic. I guess a green pointer could beat that.

Joe Farina · Post by **Joe Farina** » Sat Oct 03, 2009 12:38 pm

holo_cyware wrote:a laser with a coherence so short that even a holo of some coins would be "bread sliced" would be rather pathetic

It does happen. The lines can be on the order of 1 to 2mm. I've made some myself

JohnFP · Post by **JohnFP** » Mon Oct 05, 2009 12:44 pm

I still think it is polarization and Brewsters problem. It look like woodgrain, not sliced bread because it is evident where there is no object.