Writing on film with a laser

[carllooper]

I've always been interested in holography.

I recall someone making an animated hologram on Super8 (or 8mm) from a long time ago. I can't recall the details of how that one was done, but I know that the hologram was, of course, very tiny: the size of the 8mm frame. The projector had a laser light source, and no lens. You basically stared into the projector gate to see the hologram.

Lately I've been exploring how to digitally synthesise a hologram, where one would then just print that, by conventional "film out" means onto film. And project laser light through it.

Lasers are now very cheap. Think of those laser pointers you can pick up for less than $10.

While these can be used for holography there are versions specifically made for holography, that are not much more expensive. They use the same diodes. The following one is able to produce holograms up to the size of 4" x 5" (102 x 127mm) which is more than enough considering the size of Super8 (or 16mm for that matter).

http://www.integraf.com/shop/holography-laser



The same site has a tutorial on simple holography:

http://www.integraf.com/resources/artic ... -holograms

Now making a traditional hologram isn't what I actually have in mind - but its the techniques used that are of interest. And how they might adapted for some experimental film making. In any experiment along these lines the first task is always to just deal with the basic raw materials and get some physical feel for the interaction between the materials.

For example: just using the laser like a pen, and literally "drawing" directly onto raw film stock with it. A work in it's own right can be done in this way. Just move the laser around over the film stock and process the results. Build up a feel for the difference between moving the pen quickly vs moving it slowly. One can then get a bit more technical and note the approximate distance/time involved in each move of the pen. To get an understanding of the difference in density of the result.

And one needn't go any further than this. A work made by drawing directly on film with a laser pointer.

For what I have in mind, it's the same thing: drawing on film with a laser. Its fundamentally no different. But one elaborates the laser by putting a filter in it's path. A simple filter can be made from some junk film off the cutting room floor. Especially if it has some image. For this will create a complicated pattern on the film when held between the laser and the raw film stock. The details in the filter film will diffract the laser light causing complex interference patterns to appear on the print film. One can get some wild abstract results with such.

Now an interesting thing here is that while the filter might contain a pictorial image, and the pattern exposed on the film is an abstract interference pattern, there is a physical relationship between the two that in principle allows the abstract pattern to be transformed back into the pictorial image that was otherwise employed as a filter. Of more interest to me is not reconstructing this filter image, but doing the opposite: creating an abstract interference pattern, that when illuminated by laser light, creates a pictorial image on the print film.

Now it goes without saying that doing this would need a bit more work than waving the laser and filter around by hand. But not too much more work. A simple way to do this is to make a filter on film and run it through a film projector where the light source for the projector has been replaced with a laser. And the print film runs through a camera. In other words: an optical printer setup. However unlike an optical printer there's no lens between the filter film and the camera film. It's a lensless printer. No focusing required.

But the very complicated part of this process is not the mechanical setup but computing the filter. Or at least it is in my take on this. To compute an interference pattern, that when illuminated by laser light, creates a pictorial image on the film.

Which is what I like about this particular project - simple mechanics but a complex digital problem to solve.

In the mean time I'll have some fun drawing some doodles on film with a laser pointer.

C

[Mmechanic]

Not to critizise or diminish anything of your post but LASER and LED or very different sources of light.

L. A. S. E. R., Light Amplification by Stimulated Emission of Radiation, has to do with a medium that is hit by light from a separate source like a ruby encircled by a discharge tube. The medium’s atoms are made to transfer the energy their way which is light (in most cases) bouncing to and fro within the medium. A full mirror and a half mirror at both ends of the ruby rod collimate the light rays so that a bundle of parallel beams leaves the half mirror. The LASER beam is thus not only very accurately parallel but also of one wave length and harmonic. The beam waves are in synch. That light allows to make holography by interference.

The LED, Light Emitting Diode, is a DC, Direct Current, semiconductor element. The interface of a negative doted and a positive doted surface diode emits light upon the electric current. Nothing collimates the light, no amplification occurs. The only means of making the light converge are lenses such as the plastic hood and additional outer lenses and reflectors. LED light is narrow-banded to within about 10 nm. Compared to LASER light it’s not monochromatic. Above all, mind you, LED light is never harmonic.

I think it will be problematic to produce holographic images with LEDs.

[carllooper]

Not to critizise or diminish anything of your post but LASER and LED or very different sources of light.

L. A. S. E. R., Light Amplification by Stimulated Emission of Radiation, has to do with a medium that is hit by light from a separate source like a ruby encircled by a discharge tube. The medium’s atoms are made to transfer the energy their way which is light (in most cases) bouncing to and fro within the medium. A full mirror and a half mirror at both ends of the ruby rod collimate the light rays so that a bundle of parallel beams leaves the half mirror. The LASER beam is thus not only very accurately parallel but also of one wave length and harmonic. The beam waves are in synch. That light allows to make holography by interference.

The LED, Light Emitting Diode, is a DC, Direct Current, semiconductor element. The interface of a negative doted and a positive doted surface diode emits light upon the electric current. Nothing collimates the light, no amplification occurs. The only means of making the light converge are lenses such as the plastic hood and additional outer lenses and reflectors. LED light is narrow-banded to within about 10 nm. Compared to LASER light it’s not monochromatic. Above all, mind you, LED light is never harmonic.

I think it will be problematic to produce holographic images with LEDs.

I'm not quite up on the specific internals of the diode laser mentioned in my post. I'm familiar with the more conventional (and more expensive) ones using mirrors. But from what I've read, diode lasers employ the same idea and are actually lasers - not just an led. As I understand it there is an optical cavity (similar in principle to the mirror cavity) in which the light is syncronised with itself, through stimulated emission, to produce a measure of coherence - at least enough to be exploited for interference experiments in which a reasonable holographic image can be created.

"In the absence of stimulated emission (e.g., lasing) conditions, electrons and holes may coexist in proximity to one another, without recombining, for a certain time, termed the "upper-state lifetime" or "recombination time" (about a nanosecond for typical diode laser materials), before they recombine. Then a nearby photon with energy equal to the recombination energy can cause recombination by stimulated emission. This generates another photon of the same frequency, travelling in the same direction, with the same polarization and phase as the first photon. This means that stimulated emission causes gain in an optical wave (of the correct wavelength) in the injection region, and the gain increases as the number of electrons and holes injected across the junction increases. The spontaneous and stimulated emission processes are vastly more efficient in direct bandgap semiconductors than in indirect bandgap semiconductors; therefore silicon is not a common material for laser diodes."

http://en.wikipedia.org/wiki/Laser_diode

C

[Mmechanic]

Well, my old time knowledge seems to be outdated. If such LASER-LEDs exist, alright, have fun!
Please accept my apologies for having wanted to teach the knowing. I am on a different continent anyway.

[carllooper]

Well, my old time knowledge seems to be outdated. If such LASER-LEDs exist, alright, have fun!
Please accept my apologies for having wanted to teach the knowing. I am on a different continent anyway.

That's fine. I wasn't too certain on the details myself. I was just taking it on faith that they were actually lasers. After reading your post I had to go and read up on such.
So, a win-win situation. We are now, both of us, a bit more up to date.


Apart from using the laser as a pen to draw on film, the project I have in mind is to try some computer generated holograms, through which to print. This article here goes over the basics: on such

http://corticalcafe.com/prog_CGHmaker.htm

The author prints his computer generated holograms onto acetate. The print looks like this:



He then just shines a laser through it:



So the idea is to do something similar, but where the computer generated hologram is printed onto 16mm (or Super8). The simplest way is to just photograph the computer generated hologram off a high definition screen. The processed result is then run through a film projector, where the light source has been changed to a laser. At this point one could hold a piece of paper in front of the projector and obtain a real image on the paper. The projector has no lens, but there will be a focus plane, encoded in the hologram, and the paper will need to be held at that distance, in order to obtain a focused image.

Now the results of this process can be very rudimentary, depending on what finesse you bring to the process. If one prefers images with clean smooth surfaces, you may be quite fustrated with this process. There can be a lot of strange noise in the result. By doing it on cine film (as opposed to still film, or printing to acetate) the noise component (or grain) can be engineered to cancel out, in the same way that normal grain in conventionally exposed film does so. The grain will still be there (whether large or small) but now as dancing grain, and one is better able to "see through" this dancing grain, to the signal. And this has it's own kind of magic. However the grain discussed here is a function of the hologram rather than the film stock, so the cancellation needs to be engineered (rendered) into the computer generated holograms in some way.

Now a downside in all of this, is that the hologram is computer generated rather then optically derived. It's a synthesised hologram. And it will exhibit certain systematic limits. But in doing it this way one is able to test the basic concepts of holography and work out a good theoretical framework for a particular set up. The next task is to replace the synthesised hologram, with an alternative way of generating holograms - of which there are all sorts of possibilities.

C