Questions from a first-timer...

[Antonuzzo]

Hi all,

I’ve just got myself one of those Integraf kits, and I’ve been trying to make holograms with limited success.

My first three were exposed for ten seconds and resulted in holograms that were very faint under white light, and a little less faint under laser light.

The second three were slightly more visible under both, after raising the exposure time to 15-20 seconds.

What was weird was that a couple of the holograms showed better white light visibility when they were wet than when they dried.

Patently, I’m doing something wrong – either getting the exposure times wrong, or the time in the baths wrong (I’m using JD-4 with 03 plates). I noticed that the holograms turned black within 3 seconds of being in developer. I also noticed some black matter in the first wash afterwards (I washed for around 2-3 minutes).

I don’t think it’s vibration – the holograms are clear and well defined, albeit faint.

Any suggestions or observations welcome!

Also – I have a 200mw red laser; how would I adjust the exposure time? Is it linear or logarithmic? And do larger plates need a longer exposure?

Many thanks!

[Ed Wesly]

Do you really have a 200 mW red laser? No He-Ne was ever that big, so I am guessing that if you really do have 200 mW, it must be some sort of a diode device, which may not have much in the way of coherence. Please let us know what you have exactly, as that might be where the problems start.

If you do have 200 mW, and it’s coherent enough, then 10’s of seconds of exposure is going to be way overboard, even with PFG-03M, especially if your beam spread is just big enough to cover the 2 ½” square plates in the kit. You need to make a test strip, directions here: http://nlutie.com/ewesly/PedagogyFrameset.html

And you’re correct, exposure is logarithmic, as that is the way our eyes see!

Any pictures would also be useful in long distance trouble-shooting. Plus if you disclose your location, there may be a member of the Forum in consulting distance!

[BobH]

Hey Ed, I have a picture of a 1W he-ne built in the '60s by Bell Labs. Not commercially available though.

[a_k]

The 1W HeNe must have been a huge monster.

I assumed that Antonuzzo was talking about an Integraf kit with a small 5mW LD.

Also – I have a 200mw red laser; how would I adjust the exposure time? Is it linear or logarithmic? And do larger plates need a longer exposure?

As long as the light intensity is the same you won't need a longer exposure for larger plates. But since for larger plates the beam would be spread more, the intensity would be smaller and thus you would need a larger exposure time.

Within reasonable limits the exposure time is linear with the reciprocal value of the intensity. If the light intensity is way too low, you would need longer exposure times. -> "reciprocity failure"

[holomaker]

As i remember this past summer we shot a couple holograms @ The Laser Teaching Center at Stonybrook U, using the Intergraph kit, the included diode laser put out 5mw or so. Again as i remember we had the one beam split and used 1/2 as the referance and the other 1/2 to rear illumnate the redicle, the exposuer was @ 10 seconds. So based on what we did you are way overexposing, go back and try Ed's method of exposuer testing and this will help you greatly !


PS If it is putting out 200mw you wount be able to manually "shutter" the exposuer fast enought unless you way over expand the beam

Les see some pictures!

[Dinesh]

What was weird was that a couple of the holograms showed better white light visibility when they were wet than when they dried.

Assuming this is a transmission hologram, this is reasonable, depending on what you mean by "showed better". Water sometimes acts in a lenslike manner focusing the light, so that the light is more focused. In this way, the image light appears more intense. However, if you're looking at an image, the image tends to be a little distorted. So, you'll see a bright rainbow-like spread of light, but you may not be able to distinguish the image easily, or at all if this is an H1 geometry. If this was a reflection hologram, then you probably won't be able to see any image until the film is dry.However, you can see bursts of rainbow like colour; this is not image light, just scatter

Patently, I’m doing something wrong – either getting the exposure times wrong, or the time in the baths wrong (I’m using JD-4 with 03 plates). I noticed that the holograms turned black within 3 seconds of being in developer. I also noticed some black matter in the first wash afterwards (I washed for around 2-3 minutes).

The exposure clearly seems to be wrong, but may be too high (see below). I've also noticed that 03 emulsions tend to go black almost instantly. This is why I can't use 03C. I assumed that this was due to fogging (the exposure to white light of an unexposed film), but every single 03 film I've ever used tends to go black almost instantly. The black matter in the wash may well be the emulsion itself. The 03 tends to be a soft emulsion (there are hardening procedures using formaldehyde) and so it's quite likely that bits of the emulsion came off in the wash.

how would I adjust the exposure time? Is it linear or logarithmic?

Exposure time is linear. You have to give the film a certain amount of energy given by the exposure figure for the particular film. The number of milliwatts is the number of millijoules being delivered to the plate every second, since 1 mW = 1 mJ/sec. Typically, a silver halide film has an exposure in inverse relationship to the grain size - the smaller the grain, the longer the exposure. Typically for Slavich, I find that the exposure is in the region of about 100 - 200 microJoules (uJ)/sq cm. on the plate (the area referred to is important, most commercial detectors have an aperture of 1 sq cm so the '/sq cm" is usually left out, since it's understood. If your detector - asuming you're using one - has a smaller or larger aperture you have to alter the exposure acording to the reading). If you have a 200mW laser hitting a small plate with just one mirror and one lens, you may well be hitting the plate with about 150 mW/sq cm. Assuming you want 150 uJ/sq cm, your exposure is 1/1000 sec, since your exposing the plate to 150,000 uJ/sec and you only want the plate to receive 150uJ. In tis case, 1 or 2 seconds is too high. This may be your problem. You can get ndf's (neutral density filters) that "throw away" a large amount of light. Exposure tests are a good idea when you're roughly in the right region of exposure. However, in this case you're three or four orders of magnitude off, so the first course of action is to throw away most of the beam power.

I would strongly recommend you talk to Alec Jeong at Integraf. He's very responsive and will try to find answers for you.

[holorefugee]

The Integraph lasers I have are set to 5mw and adjustable. The kit works well. I have meant to write a article about it all for years but I have been sidetracked. Perhaps when my first book on water comes out I will get back to holography writing.

[Dinesh]

Antonuzzo wrote:What was weird was that a couple of the holograms showed better white light visibility when they were wet than when they dried.

Assuming this is a transmission hologram, this is reasonable, depending on what you mean by "showed better". Water sometimes acts in a lenslike manner focusing the light, so that the light is more focused. In this way, the image light appears more intense. However, if you're looking at an image, the image tends to be a little distorted. So, you'll see a bright rainbow-like spread of light, but you may not be able to distinguish the image easily, or at all if this is an H1 geometry. If this was a reflection hologram, then you probably won't be able to see any image until the film is dry.However, you can see bursts of rainbow like colour; this is not image light, just scatter

One thing I did think about later was that you may have been seeing the reflection image as a transmission hologram. That is, you may have held the still-wet hologram up to the safelight, behind the hologram, and it looked bright. When you dried the hologram and saw it in reflection, it may not have been as bright. This is quite common and has been talked about before. Every reflection hologram appears as a transmission hologram when wet and the image sems brighter sometimes.

[Antonuzzo]

Well, as you can see from the gallery, I had some success... up until it dried out.

I've done a test strip, ran the chemicals at different temperatures, the laser at different distances (and I'm using the Integraf one, by the way) and get the same thing each time; a hologram that shows up whilst wet, and fades when dry. So far, that's twelve plates and not a single hologram

Even the ones that were sort of viewable under laser light are now just blank plates.

The one that's in the gallery now shows a very dim, very vague grey image under white light, and nothing at all under coherent.

[Ed Wesly]

The #1 Killer of holograms is movement. If you've gone up and down the exposure gamut, and still not getting anything, try tapping everything to see if it make a solid thump when when. Usually loose things make a clack or something else. If you sometimes see the "spurious transmission image" but no reflection image the motion might be subtle enough to allow the lower spatial frequency, lower tolerance transmission hologram to be recorded but not the finer fringes of the reflection component.

Which might be your next course of action, to attempt a transmission image. I think the Integraf book might describe something called the Omni-gram, or a configuration where the object is close and off to the side of the holographic plate with a direct reference beam going to the plate, no beamsplitter necessary. You might have more success with that. Also check out

The other option is that the plates are just no good. Are you using the Slavich PFG-03M? They are notorious for failure. If you have the will to persist and prevail, try a different batch or brand.

If you are near someone on this forum, see if you can arrange a rendezvous to trouble shoot in person.

Good luck!