Short time reference beam

[John Klayer]

I was shooting a set of cave holograms a while back using two fibers - one for the reference and one for illumination. During one shot the reference fiber fell out of its holder sometime during the exposure. So I don't know how much shorter than the object exposure the reference exposure was but that image turned out the best by far of the set. Just seems strange. I tried a little bit to duplicate the result in the lab without much success, I might try it again some day.

[Steven]

Maybe the bright hologram was the result of having a better beam ratio?

Steven.

[John Klayer]

Yeah, I thought that too but wouldn't the extra object light without the accompanying reference beam have just added noise to degrade the image, not improve it?

[Ed Wesly]

Depends on whether or not the object light alone was under the exposure threshold of the material. It could also be that this one was properly exposed, the other less bright ones were overdone.

[Din]

Yeah, I thought that too but wouldn't the extra object light without the accompanying reference beam have just added noise to degrade the image, not improve it?

Not necessarily.

Consider the reason for the noise. If you over-modulate with a higher object beam, you "flatten" the sinusoidal peaks. This results in Fourier components in your grating. Some of these components are low frequency. Thus, the low frequency grating diffract at small angles and throw a halo around the object - noise. So, it very much depends on the ratio (I'm assuming you did have some reference - your statement "without the accompanying reference" seems to indicate that there was no ref), the way you develop, the angle of the ref, which presumably was not the angle you intended, since the ref fibre fell out and, also presumably, hit the floor and so hit the plate at some other angle than the one intended, among other factors. Also, was there a colour shift? It may be that the photopic at the colour of the recon is greater than that of the previous shots, thus making it seem brighter.