Is it safe to store DCG emulsion in a red tupperware container? It is not opaque, but is more opaque than transparent. Just wondering if I can forgo more extreme measures.
I read about somebody boiling their hologram for 60 seconds and reprocessing for brighter and more broadband results. Do you need to be in a darkroom when reprocessing? I figured the water could make the emulsion sensitive to light again. Or is it chemically changed into something non-soluble now?
Just finished coating my first ~1"x1" plates. Boy, did I underestimate the difficulty of getting an even coating... I think it's easier with larger plates, as the accumulation of emulsion near the bottom is wiped away or scraped off afterwards to aid in sealing. I don't plan on sealing any of the first few holograms I make (if any), I just need the morale boost of knowing I can do it, haha.
Another question here out of curiousity -- what would happen if you let a cube of dichromated gelatin harden then exposed it per usual? Is there any chance that it would produce a volumetric representation of the target object? I imagine it would be pretty hard to dehydrate it, but is there any other reason it wouldn't work?
Thanks!
Storing DCG emulsion (also some misc questions)
Re: Storing DCG emulsion (also some misc questions)
I cannot answer you the DCG related questions. But I can comment this:
By the way, very thick "layers" are utilized in holographic data storage.
If the recording medium is thick (= thicker than a few um), then the Bragg selectivity starts to affect diffraction. This is also the reason why the Denisyuk holograms can be illuminated by white light and reflect just a single colour. Thicker layer = more selectivity. Thus, if you make a very thick layer (several millimeters), the Bragg selectivity would be so strong that almost no light from the white light source would be reflected. Instead, you should use very, very narrowband light (such as a laser) with wavelength perfectly matched to the diffractive structure.pluto wrote:what would happen if you let a cube of dichromated gelatin harden then exposed it per usual
By the way, very thick "layers" are utilized in holographic data storage.
Re: Storing DCG emulsion (also some misc questions)
You mean inside the cube? If so, why not simply dip your object directly into the gloop before it hardens, then harden it.pluto wrote:what would happen if you let a cube of dichromated gelatin harden then exposed it per usual? Is there any chance that it would produce a volumetric representation of the target object?
If you mean you're trying to record on a cube, say 1" x 1" x 1", then you'd get nothing. Firstly, a 25,000 micron emulsion is too deep to record onto, and secondly because dcg absorbs the wavelengths that you're recording with (how else would the emulsion react to your light?). If the light travels through 25,000 microns, I doubt that there'd be any light left to illuminnate the object.
Re: Storing DCG emulsion (also some misc questions)
Thanks for the answers! Since this forum seems to be on life support, I may as well ask another question I've had kicking around my head.
I was thinking about how DCG emulsion is capable of recording images of inordinately high resolution.
What would you see if you looked at a very crisp DCG hologram under a microscope and proper lighting? Say, 10-100x magnification.
Would you be able to see very fine details, as if you were actually examining the object through a microscope?
What is the actual resolution of DCG emulsion? Say, per square centimetre.
Thanks!
I was thinking about how DCG emulsion is capable of recording images of inordinately high resolution.
What would you see if you looked at a very crisp DCG hologram under a microscope and proper lighting? Say, 10-100x magnification.
Would you be able to see very fine details, as if you were actually examining the object through a microscope?
What is the actual resolution of DCG emulsion? Say, per square centimetre.
Thanks!
Re: Storing DCG emulsion (also some misc questions)
The resolution of the recording material has nothing in common with the resolution of a holographic image reconstructed by it. The former determines how well a fringe pattern can be recorded in the material. The fringe pattern itself, not the image reconstructed by it. The resolution of a reconstructed image depends on the source size used to reconstruct it, distance from hologram to image, and the aperture of the hologram.
Re: Storing DCG emulsion (also some misc questions)
As Bob says, the resolution of the materia has nothing to do with the resolution of the image, whatever that means.
When you record a hologram, you're "encoding" the data of the object, as it is represented by an object beam. In other words, when the light reflects off the object, the reflected light has within it the data of the object as it pertains to the various depths and wrinkles of the object. In terms of resolution, the resolution of this object light depends on the smallest level of detail that's carried by the reflected object light. That is, can it differentiate between two electrons in an atom of the object? No. Can it distinguish between two atoms of the object? No. Can it distinguish a thousand molecules of the object? That is, can I tell, from the shape of the object beam, detail to a resolution of a thousand molecules? Probably, depending on the wavelength of the object beam. There are mathematical methods of determining how fine a structure the object beam "carries" within it, such as Rayleigh's Limit, but as a rule of thumb, the limit on the detail of the object as it's encoded within the object beam is about half a wavelength of the reflected light.
Now, the object beam meets the reference beam at the plate. The reference beam is a "clean" beam, it has no data encoded on it at all (unless the mirror's etc are dirty). The object beam carries "object data". Where they meet, the references beam, because it's clean, "references" the object beam. That is, the reference beam acts as a level against the various pits, lands and wrinkles of the object as it's encoded on the object beam (to borrow a term from the optical disk folks). <This> part of the object is so much higher than the reference beam, <that> part of the object has a wrinkle and so is a little bit lower than the reference beam, and so on. These variations of the object beam as against the level of the reference beam is translated into some physical manifestation of the material; in dcg, the various heights and depths are encoded as variations in hardness of the material, as determined by some level of basic hardness. So, if the basic hardness of the dcg - before exposure - is given a figure of, say, 5, then the light from both object and reference raises the basic hardness by a "dc" level to, say 9. Now the variations of the object as encoded in the object beam vary the hardness by, say, 2. So, across the emulsion, every point on the emulsion has a hardness between 7 (9-2) to 11 (9+2). Thus, the variations in the depths and heights of the object is translated into a variation of hardness inside the emulsion.
As I mentioned, the "resolution" of the object beam is about half lambda ( 216nm for a 532 green beam). So, to properly represent the object, the emulsion must vary between 7 and 11, at best, within of 216nm. or about 4,200 lines/mm (the usual measure of resolution is how many lines can you distinguish in 1 mm). Thus to accurately represent the object beam, whatever physical quantity changes, can it change between it's maximum value and minimum value within half lambda? In some materials,no because the physical structure itself (the size of the molecule, say) is larger than 216nm. In some materials, yes, because the physical structure is smaller than 216nm. In the case of dcg, it's resolution is about 6000 l/mm so the answer is yes (in this particular example).
Now, you reconstruct the hologram. The reconstruction light must interact with the physical manifestation - hardness, in the case of dcg - and create a new form of light. That is, the recon beam is altered into another beam. If the recon is done properly, the recon beam will transform into an exact copy of the object beam. If not, you get what are call "aberrations" and you'll get a distorted copy of the original object beam. The amount of distortion determines how distorted the object reconstruction is. If you're reference is way off, you'll get nothing. If you're close, you'll get something close - the image may bulge in some places, for example. So, there's one limit on the resolution of the holographic image. Another is the fact that one "form" of light from one single source will create one object beam. If there are more than one source, each source will create it's own object beam, which will superimpose on each other. In practice, any source of light has multiple sources (the filament of a light bulb, for instance, has a source from every point along the filament). All of the multiple object beams will create images that' are all slightly displaced from each other. Thus you have a blurring of the image. If the source is "fine" enough (an led, for example) you won't notice the blurring. If the source is "broad" (a fluorescent lamp, for example) then you'll notice the blurring.
When you record a hologram, you're "encoding" the data of the object, as it is represented by an object beam. In other words, when the light reflects off the object, the reflected light has within it the data of the object as it pertains to the various depths and wrinkles of the object. In terms of resolution, the resolution of this object light depends on the smallest level of detail that's carried by the reflected object light. That is, can it differentiate between two electrons in an atom of the object? No. Can it distinguish between two atoms of the object? No. Can it distinguish a thousand molecules of the object? That is, can I tell, from the shape of the object beam, detail to a resolution of a thousand molecules? Probably, depending on the wavelength of the object beam. There are mathematical methods of determining how fine a structure the object beam "carries" within it, such as Rayleigh's Limit, but as a rule of thumb, the limit on the detail of the object as it's encoded within the object beam is about half a wavelength of the reflected light.
Now, the object beam meets the reference beam at the plate. The reference beam is a "clean" beam, it has no data encoded on it at all (unless the mirror's etc are dirty). The object beam carries "object data". Where they meet, the references beam, because it's clean, "references" the object beam. That is, the reference beam acts as a level against the various pits, lands and wrinkles of the object as it's encoded on the object beam (to borrow a term from the optical disk folks). <This> part of the object is so much higher than the reference beam, <that> part of the object has a wrinkle and so is a little bit lower than the reference beam, and so on. These variations of the object beam as against the level of the reference beam is translated into some physical manifestation of the material; in dcg, the various heights and depths are encoded as variations in hardness of the material, as determined by some level of basic hardness. So, if the basic hardness of the dcg - before exposure - is given a figure of, say, 5, then the light from both object and reference raises the basic hardness by a "dc" level to, say 9. Now the variations of the object as encoded in the object beam vary the hardness by, say, 2. So, across the emulsion, every point on the emulsion has a hardness between 7 (9-2) to 11 (9+2). Thus, the variations in the depths and heights of the object is translated into a variation of hardness inside the emulsion.
As I mentioned, the "resolution" of the object beam is about half lambda ( 216nm for a 532 green beam). So, to properly represent the object, the emulsion must vary between 7 and 11, at best, within of 216nm. or about 4,200 lines/mm (the usual measure of resolution is how many lines can you distinguish in 1 mm). Thus to accurately represent the object beam, whatever physical quantity changes, can it change between it's maximum value and minimum value within half lambda? In some materials,no because the physical structure itself (the size of the molecule, say) is larger than 216nm. In some materials, yes, because the physical structure is smaller than 216nm. In the case of dcg, it's resolution is about 6000 l/mm so the answer is yes (in this particular example).
Now, you reconstruct the hologram. The reconstruction light must interact with the physical manifestation - hardness, in the case of dcg - and create a new form of light. That is, the recon beam is altered into another beam. If the recon is done properly, the recon beam will transform into an exact copy of the object beam. If not, you get what are call "aberrations" and you'll get a distorted copy of the original object beam. The amount of distortion determines how distorted the object reconstruction is. If you're reference is way off, you'll get nothing. If you're close, you'll get something close - the image may bulge in some places, for example. So, there's one limit on the resolution of the holographic image. Another is the fact that one "form" of light from one single source will create one object beam. If there are more than one source, each source will create it's own object beam, which will superimpose on each other. In practice, any source of light has multiple sources (the filament of a light bulb, for instance, has a source from every point along the filament). All of the multiple object beams will create images that' are all slightly displaced from each other. Thus you have a blurring of the image. If the source is "fine" enough (an led, for example) you won't notice the blurring. If the source is "broad" (a fluorescent lamp, for example) then you'll notice the blurring.
Re: Storing DCG emulsion (also some misc questions)
Simply said: definitely yes, if everything is done properly.pluto wrote:Would you be able to see very fine details, as if you were actually examining the object through a microscope?
In fact, holographic microscopy is a very active field, especially digital holographic microscopy where you don't record a hologram on a photochemical plate, but on a common digital sensor such as the one found in every digital camera. Then, of course, the digital sensor captures the interference pattern (a very complicated pattern of "light" and "dark" spots), not the magified image. In order to observe the image, it is necessary to simulate light behavior computationally, i.e. to simulate what happens if such an interference pattern was illuminated by a proper reconstruction beam. As we are in digital now, we can simulate a perfect reconstruction beam with exactly one wavelength, infinite coherence length, perfect wavefront shape, etc., and to apply digital signal processing to enhance the reconstructed image.