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With your gelatin and dichromate, you should be dissolving in about 35 mls of water. However, most dcg holographers us ammonium dichromate, not potassium. Potassium dichromate is less sensitive than ammonium dichromate and you need a longer exposure than you'd normally use. As a rough estimate, I'd use about 30 to 40 mJ/cm² for the ammonium salt, and about 50 to 60 for the potassium. The fact you may be under-exposing may explain the dim images.

How do you pre-harden before the water wash? You may be pre-hardening too much, which would explain the blue image.

One thing that strikes me is the stability of the mirror. If you gently hold the mirror and gently twist it to-and-fro, it should not rotate. If it does, you need to tighten the mirror. You could also hit the mirror with a raw beam (un-expanded) and tap the mirror. If the reflected raw beam moves, the mirror needs tightening.

My dcg lotion is 4.5g gelatin: 0.88g potassium dichromate.I used denisyuk for my design light path.I'm not sure if my laser has etalon installed.Then I also discovered that I wasn't very good at photographing objects other than metal objects. I can only photograph objects with highly reflective surface materials or metallic luster.
I drew my light path diagram and put a photo of the laser on it. Does this laser contain etalon?
I will try your method next time I make a hologram, it really inspired me a lot.

I'm sorry I can't make out the image you uploaded. As I understand, you placed a lighter underneath the plate, and a coin next to it. If the lighter was about 5 mm thick, the coin was 5 mm below the lighter?
If this is all correct, the coherence of your laser is very probably more than 5 mm, and therefore I'd suspect motion. A couple of points:
1. Is the lighter simply lying on it's side, or is it glued down? It should be glued down. To make sure, glue it down, then tap it with a fingernail; it should not move.
2. Is the coin also not glued down? Coins are generally pretty flat, so they usually don't need to be glued down, but if the surface is not flat, the coin may move.

Did you make your own DCG? If so, can you give me the formula? Your picture shows a deep blue image with green blobs (we call those "greenies"), so I suspect either over-exposure, or over heating of the emulsion during preparation, or both.
Insofar as the coin, you should diffuse the coin's reflection - we sprayed bright metallic objects with a matte white spray paint - the reason being that a bright coin will act as a mirror giving you a sort of second reference, not only giving you multiple references, but also swamping the reflection from the lighter and making a mess of your ratio. While you're at it, spray paint the lighter also with matt white.

Can you show, or describe, the geometry? Was the reference generated by a mirror directly above plate/lighter/coin?

As I said, it's highly unlikely that the problem is coherence, Argon lasers tend to have a coherence length of a few inches without an etalon (I assume you do not have an etalon). However, the best way to determine coherence length is with a Michaelson (below, diag 1). M1 and M2 are mirrors, BS is a beamsplitter, d1 and d2 are the distances between mirror and beamsplitter and the output goes to a matt white surface. If the distances of mirrors-beamspliter are the same (d1 = d2), then you'll get a series of stripes. As you pull back one mirror, say M1, d1 gets longer than d2 and the contrast fades. When the contrast is too weak to discern, the coherence length is the difference (d1 - d2).
Another quick-and-dirty way is to get a solid rod or plank and make marks, say half an inch apart (below, diag 2). Now tilt the rod/planck so the marks go away from the plate and shoot it. There'll come a distance where you can no longer make out distinct marks and this is a measure of coherence. Any questions, let me know.
[attachment=0]michaelson.jpg[/attachment]

I've been struggling with this issue lately. I don't know why the holograms I shot cannot record more "deep" information. If I place my subject farther away from the DCG glass plate, I won't be able to capture anything. I'm not sure if this is due to vibration or lack of coherence in the laser?

I don’t know why I can’t add attachments normally, so. I uploaded this zippo lighter hologram to ins. https://www.instagram.com/p/C0Hh1AOCftr/

Sorry, when I add an attachment to my reply, I don't know why it always prompts me that the addition failed.
This is a dcg I made recently, taking a picture of a zippo lighter and using a jdsu 2211d as the laser. I don’t know if I can upload it accurately. What I want to express is that I actually placed a coin next to the lighter, but I don't know why I can't see the coin pattern in this hologram. I wonder if it's because the coin is further away from the DCG glass plate than the lighter. Does this mean that the coherence length of 2211d is not enough, and I need to replace the laser to obtain a better coherence length. And whether the obis series of products are qualified for this, and whether they perform better than 2211d.

[quote=creamierpanties post_id=72977 time=1700916000 user_id=11861]
Sorry, I forgot to post the picture supporting 488nm. The laser is a parameter of a 488nm wavelength laser.
The reason why I want to ask whether this device supports shooting holograms is that I previously purchased a meteorological ion laser to shoot holograms. The model is jdsu 2211D. The depth of field of the hologram shot with this laser is not particularly sufficient. After the optical path is lengthened to one meter, the depth of field connection will become very shallow, only about two millimeters. When I shoot with 2211D, I need to control the length of the exposure light path within 50cm, so that I can get a depth of field of about 5mm. My guess is that this argon ion laser is not coherent enough, so I want to replace it with a different laser.
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Sorry, not quite sure I understand what you mean by "depth of field". In photography, this term refers to the sharpness of the image in terms of the depth of the image field. In holography, the depth of the field usually refers to the depth of the image itself, ie how far the image extends in the z direction (assuming the plane of the hologram is x-y). So, when you say: "After the optical path is lengthened to one meter", do you mean the optical path difference? That is, the length of the object is 1 m? Also, "the depth of field connection will become very shallow, only about two millimeters", are you referring to some sort of resolution?

In a hologram, the depth of the object, the difference between the point nearest to the film and the furthest from the film is determined by the coherence length. So, if you're shooting a rod of, say, 2 metres, and the coherence length of the laser is 1.5 metres, you'll effectively lose half a metre of the object ( this is not quite true, since the image does not abruptly disappear after the coherence length, it just fades away). The coherence length is given by the bandwidth of the laser, or the linewidth. The larger the bandwidth, or the linewidth, the shorter the coherence length. This ( https://www.rp-photonics.com/coherence_length.html ) is a good reference for calculating the coherence length from the linewidth, as given by your parameters.

In terms of your statement of getting a depth of field of 5mm, if you're referring to resolution, then, so long as you're within the coherence length, the resolution is theoretically the wavelength of light, half a micron. Again, this is not quite true because aberrations will limit the resolution, however, the resolution is probably ~ 1mm within reason. Bear in mind also, the resolution of the image depends on the mismatch between the source size illuminating the hologram, and the spatial coherence of the laser (which is why spatial coherence is important). Therefore, as you increase the size of the illuminant, you tend to lose detail along the depth of the image. Another important point is that the size of the illuminant refers to the size as "seen" by the hologram; the further away the hologram is from the source of the illuminant, the smaller the hologram "sees" the source and the sharper is the depth.

I am assuming you're referring to a display hologram. If you're referring to, say, an interogram another set of criteria come into play. If you give me further details on your depth of field for your application, I could be more explicit.

By the way: "here are the parameters", there are no parameters.

here are the parameters

Sorry, I forgot to post the picture supporting 488nm. The laser is a parameter of a 488nm wavelength laser.
The reason why I want to ask whether this device supports shooting holograms is that I previously purchased a meteorological ion laser to shoot holograms. The model is jdsu 2211D. The depth of field of the hologram shot with this laser is not particularly sufficient. After the optical path is lengthened to one meter, the depth of field connection will become very shallow, only about two millimeters. When I shoot with 2211D, I need to control the length of the exposure light path within 50cm, so that I can get a depth of field of about 5mm. My guess is that this argon ion laser is not coherent enough, so I want to replace it with a different laser.

[quote=creamierpanties post_id=72963 time=1700720460 user_id=11861]
I noticed that there are many waveband products to choose from in the obis series, and I want to use the 488nm band laser as the light source for making holograms. Here are some parameters, I want to know how this is different from 315m, what are the advantages and disadvantages. I only know that this band is very efficient when exposing DCG dry plates.
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None of the lasers in your series reference the 488 band. The 315 lasers only emit in the 532 nm band, as far as I know. The disadvantage is that DCG is 5 times less sensitive to 532 than to 488nm. In other words, an exposure of, say, 1 minute at 488 is equivalent to approx 5 minutes of exposure at 532 (dyes apart, which you did not mention). The 315 can get very hot, and you need to mount it on some sort of heat dump, or it'll turn off very quickly.

My wife is a Senior Research Engineer who works with technical holograms all the time. According to her, the M² for some these lasers is too high, creating a larger spatial coherence, and, she says, the polarisation ratio is not ideal. As far as the lasers they're very compact.