Lippman photos as filters?

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Lippman photos as filters?

Post by ErikZ » Mon Nov 02, 2009 11:01 pm

I was looking for narrow notch filters having dichroic filters in mind, but came across holographic filters. To me these seemed to be closely related to Lippman plates so I turned to looking for information about them.

Does anyone have experience with this or any information or suggestions on this subject? Notch filters would correspond to reflection colours, bandpass filters to transmission colours, how does one get one or the other version?

The filter is intended for use with a laser, will the coherence of the laser be an advantage in producing the filter, or could it lead to problem with speckle noise? Swelling could be a severe problem if the filters doesn't match the wavelength used to produce it, but also an opportunity if the shift is such that it can be trimmed back to the desired wavelength by angular adjustments. I guess angles off the perpendicular direction causes a redshift so that the filter should be blueshifted e.g. due to shrinkage after having been produced under moist conditions.

The holographic filters I found information on were quite thick which I assume may be required for obtaining the narrow bandwidth. What bandwidths could be expected with Lippman photos?

Erik Z

Ed Wesly

Lippman photos as filters?

Post by Ed Wesly » Mon Nov 16, 2009 9:33 pm

Boy, you picked a doozy of a topic! I can see what you are getting at, and to some degree you could accomplish what you are describing, however the main limitation will be the holographic recording material you will be using.

What you are describing is sometimes called a conformal mirror, making a hologram with the mirror in contact with the recording material. If you ever get the chance to visit the International museum of Photography at George Eastman house in Rochester, NY, and ask to see the box of stuff from Herbert Ives, you will be rewarded with a peek at a conformal mirror made Lippmann/holographically in 1907! As a test of spectral sensitivity, Ives exposed Lippmann plates to a variety of spectral sources passed through a pinhole, (a spatial filter!) and recorded essentially holograms of mirrors with the plates backed by mercury.

So you are on the right track, and can even get some decent results using silver halide plates. The problems as you have noted are shrinkage for wavelength shifts, but what will be a bit more vexing is that there will be more than one wavelength reflected.

With the typical silver halide plates whose thickness is about 6 to 7 microns, you will get a strong color reflected, at the recording wavelength, thanks to the Lippmann-Bragg diffraction or constructive interference from a thick dielectric stack or whatever you want to call it. But other colors will also be reflected, due to constructive Bragg diffraction/interference, but not as strongly, with some disappearing completely due to destructive Bragg diffraction/interference! (Gaps in the spectra!)

To witness this phenomena, look at the highlights in any reflection hologram, especially highlights deep in the image space. You will see a bright glowing blob at the replay color, but you will also see a spectral line of colored highlight dots pointing to a reflection of the reference source.

The efficiency of the material is the limiting factor for the amount of bandpass, and with the typical silver halide emulsions I wouldn’t expect things to be higher than about 80% or so. Some of those super duper Raman notch filters made by Kaiser are pretty thick DCG, processed narrow band, with densities of 6 or so, meaning only 10^6 or one millionth of the wavelength to be rejected gets through! If all that rejection is due to reflection, then the efficiency would be like 99.999999%!

It would be a fun exercise to play with, although you will get more modest efficiencies than the above, but you could make some neat beamsplitters! See for instance, "HOE for Holography", T. Jeong, E. Wesly, Proceedings of the First International Congress on Holography, Varna, Bulgaria, 1989.


Lippman photos as filters?

Post by Jeffrey » Sat May 15, 2010 7:33 am

Well, while quoting Rich Rallison, don't forget to search for any of his publications. He showed me a dichromate mirror he made, which appeared clear, but could entirely reflect a laser beam, leaving NONE of the beam transmitting through to my hand. I never saw such efficiency before.