Search found 405 matches

by Din
Thu May 09, 2024 9:41 pm
Forum: General Holography
Topic: noise due to a large (extended) object
Replies: 10
Views: 910

Re: noise due to a large (extended) object

Did you want me to try a simplified explanation without Gabor's "gobbledygook" ? I think you once said on this forum that conversations must, at some point (probably sooner than later!), get technical/scientific (with language and/or formulas not understood by the vast majority), or the p...
by Din
Wed May 08, 2024 8:37 am
Forum: General Holography
Topic: noise due to a large (extended) object
Replies: 10
Views: 910

Re: noise due to a large (extended) object

I'd already got the paper. Did you want me to try a simplified explanation without Gabor's "gobbledygook" ?
by Din
Tue Apr 30, 2024 12:57 pm
Forum: General Holography
Topic: noise due to a large (extended) object
Replies: 10
Views: 910

Re: noise due to a large (extended) object

I'm still confused about the difference between "objective" and "subjective" speckle. I'm not sure where these two terms originated from, but it may have been from the 1970 paper by Dennis Gabor "Laser Speckle and Its Elimination." I suspect it's older than 1970, since...
by Din
Mon Apr 29, 2024 2:45 pm
Forum: General Holography
Topic: noise due to a large (extended) object
Replies: 10
Views: 910

Re: noise due to a large (extended) object

With speckle, I assume that a rough surface of an object causes small "spots" of destructive interference along the surface of an object, making the object look grainy. This effect would be due to the laser light only (having nothing to do with the hologram) and the hologram merely record...
by Din
Tue Mar 19, 2024 12:03 pm
Forum: General Holography
Topic: beam ratios: silver vs. polymer vs. DCG
Replies: 6
Views: 1593

Re: beam ratios: silver vs. polymer vs. DCG

Having done my first few photopolymer holograms (Bayfol HX200), it seems that polymer is more dependent on beam ratio equality (ideally ~1:1 for a reflection hologram) compared to DCG. It reminds me of silver halide, but perhaps not as extreme. Maybe this is due to the dyes present in polymer and s...
by Din
Sun Mar 10, 2024 9:51 am
Forum: General Holography
Topic: One-step real-image reflection hologram?
Replies: 4
Views: 1538

Re: One-step real-image reflection hologram?

Yes, a 2f-2f geometry will create the real image on the other side. But, you have to consider aberrations, particularly coma and astigmatism. Coma will distort the image and astigmatism will cause a variation of the focus through the depth of the image. To avoid this, the lens has to be much larger ...
by Din
Mon Feb 19, 2024 2:18 pm
Forum: For Sale / Want to Buy / Trade
Topic: Donate and Help Conservation Research?
Replies: 14
Views: 5909

Re: Donate and Help Conservation Research?

Given your extensive experience in creating and testing -- 1. Would you agree that UV light exposure is the biggest risk to black-backed SHG holograms? P.S. We found that UV filtering plexiglass did not impair our image reconstruction. 2. Do you agree with the Wise article's statement about heat ex...
by Din
Fri Jan 26, 2024 9:41 am
Forum: For Sale / Want to Buy / Trade
Topic: Manual for the Coherent Sapphire 532-300
Replies: 7
Views: 2626

Re: Manual for the Coherent Sapphire 532-300

There's no such thing as a zero divergence beam. Any plane wavefront would have to be infinite in extent to have zero divergence. Diffraction causes any finite plane wavefront to diverge: "Diffraction causes light waves to spread transversely as they propagate, and it is therefore impossible to...
by Din
Thu Jan 25, 2024 9:36 am
Forum: For Sale / Want to Buy / Trade
Topic: Manual for the Coherent Sapphire 532-300
Replies: 7
Views: 2626

Re: Manual for the Coherent Sapphire 532-300

... it is reasonably collimated. (But divergence looked rather substantial.) Joe Joe a laser cannot be collimated and have a divergence. The beam exiting the laser is always diverging because it's in the nature of the Gaussian profile (I can give you the mathematics of it if interested). There is a...
by Din
Tue Jan 23, 2024 1:37 pm
Forum: For Sale / Want to Buy / Trade
Topic: Donate and Help Conservation Research?
Replies: 14
Views: 5909

Re: Donate and Help Conservation Research?

Thanks, Din, this paper is new to me, and I appreciate it. The paper is disappointing, because it's more of a "survey" of art, rather than a technical study. It did have an interesting list of potential problems with silver halide materials. I think this might be useful for the original p...