Wood Grain Effects on Colourholographic BB Plates

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John Sonley

Wood Grain Effects on Colourholographic BB Plates

Post by John Sonley » Sun Oct 10, 2010 3:08 pm

Hi Jem, I’ve just spent two days experimenting with your Colourholographic BB plates. We may be getting there slowly but I'm not happy with the results so far

Having seen from their web site that the apparent sensitivity of your plates is only 1/10th of the old AGFA film I use, I so I was not surprised when giving an exposure of 1 minute 15 seconds (the exposure I gave the old AGFA film Temp Laminated on to glass) and developing with CW C2 followed by an EDTA bleach, the film was clearly very underexposed, I noticed heavy wood graining in the plane of the film and I believed it due to the reference beam hitting the edge of the glass. The image formed was rather dim

For the next plate I increased the development time to 2 1/2 minutes with the same chemical processing. The film plate was still under exposed but not as bad and with such a long exposure I believed the wood grain effect was in fact a temperature based movement - I don't now think that

For the third plate I decided to use a special fast developer similar to Zip1 that I used to use in my early days of holography at a temperature of 34 degrees centigrade (Mike Burridge’s recipe) followed by the dichromate bleach. I sensitised and swelled the plate with 5% TEA and with a 1 minute exposure; the plate went almost black after 10 seconds development. (I had washed out the TEA before development). The image is moderately bright but with this severe wood grain effect in the plane of the plate. Please see the photograph in this link

Image

which you will understand was difficult to take but it does show the problem. Looking at the green image, produced with a white light reconstruction beam, suggests that the ‘Sea Shell’ may re-construct brighter in green light than in red HeNe light.

Thinking about this wood grain effect immediately suggests incorrect polarisation of the HeNe – but it’s the same set-up I use regularly with my old AGFA film temporarily laminated on to glass and no wood grain effect at all

In the past I have had wood grain type effects when sandwiching film between glass plates but here there is no sandwiching at all and in my last attempt I shaded the age of the plate on both sides to prevent internal reflection effects I have experienced before.

I don't want to waste any more of your plates, but I found a box of AGFA plates I had forgotten about and will continue my studies with these when I find an answer to this 'brushed silk' type wood grain effect.
A sure-fire way of checking whether it is an ‘s’ ‘p’ polarisation problem is to make one more image on my old AGFA plates and if I get the same wood grain effect turn my HeNe through 90 deg. and see if the problem disappears … it’s a bit difficult physically as the 33mW laser is within a square section housing and the feet are not adjustable

BRgds

John

John

Colin Kaminski

Wood Grain Effects on Colourholographic BB Plates

Post by Colin Kaminski » Sun Oct 10, 2010 4:29 pm

John,

You likely know this but for other people that end up on this thread from search engines, here are some links:

http://www.holowiki.com/index.php/Brews ... Discussion
http://www.holowiki.com/index.php/Mirro ... n_Rotation

Are you pre-sensitizing the BB640? I found it was faster if soaked in water first or better yet TEA. Then I liked long exposure times and short development times. I only had a few plates to play with so I did not get very far. Some of the brightest silver holograms I have seen were made on BB640 by Tom B.

BobH

Wood Grain Effects on Colourholographic BB Plates

Post by BobH » Mon Oct 11, 2010 4:36 am

I don't have any experience with the BB film, but am wondering if the "wood grain" you're seeing might be caused by a very bright object beam. The BB material might be transmitting more light to the object, decreasing your beam ratio. The object light hitting the plate near normal incidence that's polarized orthogonally to the reference beam will only make "noise gratings" and the "wood grain" you show.

Presuming that you're doing a Denisyuk geometry, I'd recommend windows for the plateholder with AR coatings on the outsides only and index-matched to the film. You might also have an index mismatch between the base of the film and the glass you're mounting it to. I'd look closely at the index of everything in the stack in the plateholder. :wink:

Tom B.

Wood Grain Effects on Colourholographic BB Plates

Post by Tom B. » Mon Oct 11, 2010 5:05 am

My (mostly good) experience with BB-plates is almost entirely limited to BB-640 reflection holos developed with metol/ascorbic acid (as in JD-4) and bleached with Fe3 EDTA, because that's what worked best for me. I had very limited success with transmission holos for reasons still unknown. Woodgrain was a problem. Were you making transmission holos? One thing I've been meaning to try for transmission holos is to paint the glass side black with some easily peelable paint. I bet that would help a lot.

Also, probably not your problem but maybe helpful, I did notice that dried TEA solution on the glass side of the plate left an oily scum that degraded the contrast in various ways. Wiping the glass side clean with a damp paper towel after TEA treatment and drying produced much cleaner results.

John Sonley

Wood Grain Effects on Colourholographic BB Plates

Post by John Sonley » Mon Oct 11, 2010 2:15 pm

Colin Kaminski wrote:John,

You likely know this but for other people that end up on this thread from search engines, here are some links:

http://www.holowiki.com/index.php/Brews ... Discussion
http://www.holowiki.com/index.php/Mirro ... n_Rotation

Are you pre-sensitizing the BB640? I found it was faster if soaked in water first or better yet TEA. Then I liked long exposure times and short development times. I only had a few plates to play with so I did not get very far. Some of the brightest silver holograms I have seen were made on BB640 by Tom B.
Yes Colin, I pre-sensitised the film with 5% TEA and with a 1 minute exposure time and 10 second development time, I think I'm following the principles you recommend
BRgds
John

Ed Wesly

Wood Grain Effects on Colourholographic BB Plates

Post by Ed Wesly » Mon Oct 11, 2010 2:19 pm

Maybe the plates weren't totally dry from the TEA?

John Sonley

Wood Grain Effects on Colourholographic BB Plates

Post by John Sonley » Mon Oct 11, 2010 2:26 pm

BobH wrote:I don't have any experience with the BB film, but am wondering if the "wood grain" you're seeing might be caused by a very bright object beam. The BB material might be transmitting more light to the object, decreasing your beam ratio. The object light hitting the plate near normal incidence that's polarized orthogonally to the reference beam will only make "noise gratings" and the "wood grain" you show.

Presuming that you're doing a Denisyuk geometry, I'd recommend windows for the plateholder with AR coatings on the outsides only and index-matched to the film. You might also have an index mismatch between the base of the film and the glass you're mounting it to. I'd look closely at the index of everything in the stack in the plateholder. :wink:
Bob, the light ratios were not too far off optimum - maybe a slightly brighter object beam than the ideal 4:1. As measured the extremes around the centre of the plate were between 2.3:1 to 3:1 - but I've used such ratios in the past with film temporarily laminated to glass and absolutely no evidence of wood grain
The set-uo wasn't Denisyuk it was a twin beam illuminated object transmission hologram with 30 deg side reference beam
BRgds
John

John Sonley

Wood Grain Effects on Colourholographic BB Plates

Post by John Sonley » Mon Oct 11, 2010 2:38 pm

Ed Wesly wrote:Maybe the plates weren't totally dry from the TEA?
Didn't think of this option Ed but I think I did a good job with my rubber blade and then dried with a hairdryer for about half a minute. I then left the plate in my light proof bag for about quarter hour to stabilise, made a final adjustment to the spatial filter, safe light on and mounted the plate in my ball bearing aligned plate holder, a further half hour for the lab to stabilise and then remote activation of the non-contact laser shutter followd by washing, development and bleaching, as previously detailed - all this procedural stuff is standard for each hologram I attempt but this is the 1st time I've used glass plates, all previous experience is with film temporarily laminated on to glass and never a problem with woodgrain
BRgds
John

BobH

Wood Grain Effects on Colourholographic BB Plates

Post by BobH » Mon Oct 11, 2010 2:47 pm

I think the 30 degree reference beam is the issue then. Like Tom mentioned, you might try using a backer plate of smoked glass index-matched to the plate. That should do it. Or paint the plate like many others do. I'd also recommend a much higher beam ratio for a transmission hologram. More like 10, measured with the detector pointed toward the center of the object and the source (Ed might disagree here :whistle: ).

John Sonley

Wood Grain Effects on Colourholographic BB Plates

Post by John Sonley » Tue Oct 12, 2010 3:57 pm

BobH wrote:I think the 30 degree reference beam is the issue then. Like Tom mentioned, you might try using a backer plate of smoked glass index-matched to the plate. That should do it. Or paint the plate like many others do. I'd also recommend a much higher beam ratio for a transmission hologram. More like 10, measured with the detector pointed toward the center of the object and the source (Ed might disagree here :whistle: ).
Hi Bob - having calculated the beam ratio - yes it is a bit too strong on the object side - I'll shift the variable beam splitter a smidgeon to the left .. that should do it and I'll try my 1st test plate with the new light ratios and my 2nd plate (if the woodgrain still exists) with my HeNe turned on it's side (90 deg)

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