Not getting an image

[hearbob50]

Hi, I have been trying to make a reflective hologram. I am not getting any image and feel I am not understanding something basic. This is what I have.
1) a class IIIa laser putting out 1.4mW. film is PFG-01 made in Sept of 2024 kept in a fridge.
2) it is reflected off of a front surface mirror
3) the beam then passes through a 20mm double concave lens
4) the dispersed laser hits the film which is facing emulsion out.
5) the subject, have tried both a 4 inch white plastic chair and a gold metallic one, is placed directly behind the film with a white reflector behind it
6) processed in JD-2 chemistry for 2 1/2 minutes
7) it's all done under a green safelight.
8)exposer was started at 8 sec, then a test strip of 15, 30 and 45. Then 3 minutes, then 5 minutes then 15.

I just feel I am not understanding something very basic that I'm not getting. Thanks

[Din]

Hi, I have been trying to make a reflective hologram. I am not getting any image and feel I am not understanding something basic. This is what I have.
1) a class IIIa laser putting out 1.4mW. film is PFG-01 made in Sept of 2024 kept in a fridge.
2) it is reflected off of a front surface mirror
3) the beam then passes through a 20mm double concave lens
4) the dispersed laser hits the film which is facing emulsion out.
5) the subject, have tried both a 4 inch white plastic chair and a gold metallic one, is placed directly behind the film with a white reflector behind it
6) processed in JD-2 chemistry for 2 1/2 minutes
7) it's all done under a green safelight.
8)exposer was started at 8 sec, then a test strip of 15, 30 and 45. Then 3 minutes, then 5 minutes then 15.

I just feel I am not understanding something very basic that I'm not getting. Thanks

A number of questions:
1) how large is the film?
2) is the 20mm the focal length or the diameter. If one, what is the other?
3) What is the angle between the ref and the film? It should be about 50 - 60 degrees. Too shallow (< 50 - 60 deg) and the recon light will reflect off the film. Too steep (> 60 deg) and the exposure increases)

Important factors:
1) The beam divergence, and the power/cm². If the film is large or the beam diameter is much larger than the film, the film may be getting too low a power. The laser beam should mostly hit the film, with a little overspill. If the 4 inch chair is as large as the film, then the object is too large; the object should be about a third of the film dimension in whatever orientation the film is. Don't use any metallic objects; the reason is that metallic objects throw reflected light off the film. The object must be uniformly diffuse. However, having said this, we used to spray paint metallic objects with matt white.

2) Is the orientation of the chair such that most of the reflected light hits the back of the film? Ratio is important, so as much as the reflected light from the object must hit the film, not be reflected away from it.One test is to take a white card and run it around the object on the back side of the film. If most of the light is reflecting away from the film, the light on the white card will be bright.

3) The emulsion should be facing the object, not be facing out. The reason is that if the first surface the reflected light hits is glass, some (or most, depending on any polarisation present) of the reflected light from the object is reflected from the glass (first surface to 'see' the reflected light) which loses light that actually hits the emulsion, where the hologram is recorded.

4) If the film was in a fridge, did you let it dry before using it? Film kept in a fridge will have a layer of moisture on it and it's important to leave the film long enough to allow the moisture to evaporate.

5) How dark did you take the development? To check darkness, look at the safelight through the developed film (obviously before bleaching it). For PFG-01, the safelight should be reduced by about 100 times - it should look pretty dark, almost non-existent, relative to looking at it directly. If the safelight is still pretty bright, it needs more development. As a general rule of thumb, it should take about 3 minutes to go dark enough to pretty much dim out the safelight - too quick and you've overexposed, too long and you've underexposed.

I would also get rid of the white reflector. The reason is that the white reflector may be reflecting more light than the object, swamping any reflected light from the object. The white reflector may also be throwing light away from the film.

And, on top of it all, is the stability of your setup. The chair should be glued down onto a stiff surface that itself is not prone to motion, ie don't glue it down to a plywood surface, a solid metal block is good. A good technique, just before you're going to shoot, is to tap the object, the film holder and the optics (I assume the film is firmly attached to the film holder?). If, when you tap, you hear a pinging or reverberation, something is not tied down enough.
A diagram of your setup would be useful.

[hearbob50]

hi, thank you for the reply. this won't address all of the questions you asked and I am working on that. my setup is not ideal. I am working in the largest light tight space our school has which is also our alternative photo lab, cyanotype, platinum etc. I have attached two photos. the film is 4x5. I am using a 4x5 negative carrier that has a clamping system to secure the film, so no glass is holding the film. the double concave is 20mm DIA, EFL is -20, BFL is -20.55. Again thanks for the help. I am trying to work out how to do this for future classes

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[Joe Farina]

I am using a 4x5 negative carrier that has a clamping system to secure the film, so no glass is holding the film.

This could easily be the source of the problem. I don't think film that isn't supported on glass will work for holograms. I haven't used PFG-01 film (don't know what the plastic film material is), but in the days of Agfa film, I used mineral spirits (from the hardware/paint store) as an index-matching fluid. I placed a few drops on a piece of glass, applied the film (the plastic side touching the mineral spirits, with the emulsion facing up) and used a rubber roller to flatten and squeeze out excess fluid (paper towels can be used between the rubber roller and film to catch fluid that comes out from the edges). I'm sure others here can suggest better methods to use specifically with PFG-01. To support the film/glass sandwich on the table, you could try something as simple as office binder clips standing on edge https://www.amazon.com/Coofficer-Binder ... 541&sr=8-6 Also, your laser is quite weak (and judging from the photo, it looks like the beam is spread out far too much). If your exposure times are long, your table needs to be quite vibration-free and stable. The relationship between the film and object must remain rock-steady during the exposure.

[Din]

I agree that the film is not secured enough, the idea of securing it between glass plates with index matching fluid is a good idea. Clips is also a good idea, we used to secure the film in a holder inside two arms of a U channel with screws (below).

I notice that the mirror is being held at the base. A large mirror being held only at the base causes back-and-forth motion since the top and sides of the mirror are not secured. Can you use a smaller mirror, since the mirror only reflects the raw laser beam? Also, the mirror, lens and film mounts are just placed on the table. This could cause motion of the film holder,mirror and lens because the mounts are not secured on the table; if you've got hot glue, I'd suggest gluing the mounts to the table.

I see the chair is tilted away from the beam direction. This may be throwing light away from the back of the film. It might help if you rotated the chair to more face the laser.

Also agree that the laser is too spread out. I suggest moving the lens a lot closer to the film. If the beam is less spread out, the exposure should reduce quite a bit, which should mitigate motion issues. You should aim for a beam about 6 - 8in in diameter.

[hearbob50]

Hi, Thank you all for the responses. As mentioned the set up is not ideal. However this room is our alternative lab and anything I do is temporary so I will do the best I can. I understand the concerns about the film mount. This is a 4x5 negative carrier. The clamps hold the film down as well as pull it laterally. It's actually flatter than if I had used a glass carrier with anti-newton glass. I will see what I can do to improve in the areas I am able to.

[Joe Farina]

The clamps hold the film down as well as pull it laterally. It's actually flatter than if I had used a glass carrier

It's not the flatness that matters, it's the micro-stability of the plastic film. The thermal expansion/contraction of plastic is quite high, and if there is some kind of pulling force applied to it by the film holder, that sounds worse. The stability needs to be within around a half wavelength of light (if memory serves, Din can state this more precisely than I can). So, the plastic film cannot move more than (say) 300 nanometers or 0.0003mm. I would like to see you succeed in making holograms, and recommend that you try affixing the film to glass with a fluid.
https://holowiki.org/wiki/Index_Matching per the article: "For the Slavich materials sandwich the film in between two glass plates. This can be done with index matching fluid."

[hearbob50]

thank you. I did not understand that that was the issue with how the film was secured. (i.e. micro stability) I assumed it had to do keeping it flat and it seemed to me the extra layers of glass presented more of an issue.