Over the weekend I had the time to start testing the latest batch of photopolymer from Polygrama and I have to tell you that it was a pleasure to work with. But let me back up a bit and take you to the beginning of the testing session.
[first posted Tuesday, March 15. 2005]
[updated 3/30 with the latest round of results & consolidated into one post]
Not having a supply of slide glass available, on Saturday I cut a stack of glass plates ranging in size from 19x38x2mm to 38x38x2mm. I was planning on starting out with the smallest plates and working up to the largest depending on the results.
Early Sunday morning I got up and gathered together the rest of the tools I’d need for testing. A small container to hold the polymer, a syringe and needle for removing the polymer from the bag it came in, backup tape, clamps for holding the glass together, a 75W halogen bulb and a test subject.
With the room lights off and my blue safelight on, I attempted to remove the polymer from the container with a needle and syringe that I’d had from times when we had to give medicine to sick pets but quickly found that the polymer was so thick that it wouldn’t go through the needle. I gave up on that and just snipped a corner off the bag and emptied the contents into a small container. Then taking the syringe, sans needle, I sucked the polymer up into the syringe. It’s still there and the syringe will serve as the permanent container for as long as the polymer lasts. I put the syringe in a light-tight box so I could prepare the plate and table setup.
With the lights back on, I took one of the medium sized glass plates and put it on my processing table. I then took the backup tape and snipped off about an inch and a half and put the tape across the plate near one edge. Static held it down while I repeated this for the opposite edge.
Turning the room lights back off, I took the polymer syringe and put a small drop of polymer onto the glass dead-center, placed another piece of glass on top and clamped the two together using two paper clamps and placed this into a light-tight box so I could set up the table. The drop of polymer ultimately expanded to cover the most of the glass.
The table setup was a simple single-beam reflection setup using my 30mW HeNe laser, ½ wave plate and spatial filter. The subject was a layer of small white alphabet blocks glued onto a white card. The setup was configured so that the plate containing the polymer would be leaning right on the face of the cubes. I set spatial filter far enough from the subject so that the beam was expanded to about 2” diameter.
With the laser shutter closed I placed the first plate against the blocks, set the computer for a 20 minute settle time and a 60 second exposure. After the exposure was done I took the plate off the table and exposed it to the 75W halogen for a few seconds and then set about looking for an image, which I almost immediately found. It wasn’t bright, it wasn’t clean, but I unmistakably had a hologram in between the two plates of glass.
The hologram has some odd dark spots which I hope are signs of the polymer moving and a few bubbles but the rest of the polymer shows a decent image of the blocks.
I thought that was too easy so I quickly set up a plate using the largest of the glass, threw that on the table and set it up for a 20 minute settle and 90 second exposure. Once again, I got a hologram that isn’t especially bright but is clearly there. Two for Two.
At this point I decided I needed to stop for the night, closed up shop and went back to bed.
During the day Sunday I wondered about the polarization of the laser beam. I’d had a ½ wave plate in the beam from a previous setup but hadn’t re-aligned it for use with the single-beam setup I’d created. That evening I checked it and it was indeed set 90 degrees off the ideal when shooting at Brewster’s angle. I fixed that and set about doing another test using the large glass. After a 20 minute settle and 90 second exposure I got a slightly brighter hologram.
Last for the day I decided to replace the subject with a mirror and attempt a simple reflection grating. Another 20 minutes and 60 seconds later I had a hologram of a mirror in my hand.
Four for four. This is a polymer that clearly works. I’m not getting the brightness claimed by Polygrama but I’m also doing exposures that are longer than any I’ve attempted in quite a long time and there’s a possibility that the table isn’t stable enough or (I hope more likely) that the polymer was still moving slightly, or perhaps the polymer was too old (it’s almost a month old).
Monday evening I cut some more glass for further tests and made up two plates for use on Tuesday morning. I wanted to see how the results changed when using plates that had had more time for the polymer to settle.
I also changed the setup so that I was using the blocks as subject and re-aligned everything so the plate was reflecting as little light as possible.
This morning I simply turned on the laser, dropped the plates into the holder and made two exposures, one at 60s and another at 90s. Both holograms came out decent with the first showing no sign of movement. Unfortunately the second does show some signs of polymer movement. I didn’t have time to take pictures (barely had time to finish the tests) but will take some more soon.
I ran a couple of horizontal (meaning the plate was sitting horizontally rather than vertically) tests and found that the images were coming out noticeably brighter. Unfortunately not yet bright enough to rival silver-halide or DCG. Hopefully that will come with more development on the part of Polygrama.
In the eveneing Andres came over and we shot another polymer hologram and again we got a relatively bright hologram.
This morning I thought I’d see what alcohol would do. Unforturtunately I don’t have any PEG so I decided to sacrifice one of my tests to the gods of isopropyl alcohol. The results? It does increase brightness but also causes the the polymer to come away from the glass if left more than a 1-2 seconds in the alcohol. Interestingly enough, I think (but haven’t tried yet) that the polymer might be strong enough to work as a small sheet and apply to another surface.
Here’s a shot of a hologram that had been very dim (relative to the others) before alcohol treatment and brightened up considerably afterwards. I’d guess that it doubled (at least) in brightness.
Looking at the light coming off my fingers you can see that the hologram isn’t nearly as bright as current silver and DCG but it’s reliable so far and I’m certain that Polygrama will continue to work on the efficiency.
For those that don’t know, I normally keep two setups going at the same time, one for mastering and one for copying. I took some time to reset my master layout to make a reflection HOE with the reference beam at 45 degrees and the object beam at normal to the plate. After another 20 minutes (settle time) and 60 seconds I had a reasonably bright reflection HOE that was basically a mirror. Given the results I’d had with alcohol on the other hologram I decided to try it here as well. Unfortunately it caused the polymer to crack and ripple and separate but once it was pressed between two pieces of glass it smoothed out a fair amount and I could again see a much brighter “mirror”.
Late in the evening I modified the setup to produce a transmission HOE with the polymer.
The dot on the bottom is being produced by the HOE and the dot on the top is the transmitted beam. If you look carefully you’ll see that the bottom dot is both slightly larger and brighter than the top dot. The HOE is easily >50% efficient and the expansion is due to my using a sharply diverging beam for the “object” light when making the hologram.
Having produced a transmission HOE, it was time to see what 70% alcohol would do. I carefully pried apart the glass, put a single drop of alcohol onto the polyer and put the cover glass back on.
Here’s the alcohol treated transmission HOE.
Things to try next:
o Use cling-wrap for the spacer.
o Use rain-x on one piece of glass to allow it to be removed. Sub the other piece of glass.
o Pre-hardening the emulsion with heat, brief white light or UV?
o Compare with a 60 and 90 second exposure using PFG-01.
o See if the polymer can be removed as a sheet and applied to another surface without destroying the image.