emulsion thickness

Silverhalide Emulsions / Chemistry.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

Re: emulsion thickness

Post by Din »

BobH wrote: Sun Dec 05, 2021 9:28 am Regardless, it will work fine as I used the technique for many years while at Digilens.
Perhaps you could explain to Mr Pratheep, who asked the question, how you actually conduct the experiment, assuming you know this. Since he asked the question, I think that he deserves to get details of your method. Simply saying "Use a spectrometer" and adding no further details is a little like intellectual strutting. How do you 'use' a spectrometer? How do you translate the results on the spectrometer into a measurement of emulsion depth? What did you use it for? An emulsion depth measurement, or some other displacement? What was the error? Were these errors taken into consideration? Were they random errors? Was there any statistical analysis at all at Digilens? Did Digilens publish results? Do you have a reference? Do you have a theoretical basis, or any calculations? Perhaps you could point Mr Pratheep to someone at Digilens to discuss their results? I think Mr Pratheep needs a little more than intellectual posing for the fan base.

Whatever you did, or did not do at, Digilens, without details of method and/or a reference and/or some theory, the 'spectrometer method' seems of no value to Mr Pratheep. It also depends on the application; for most applications, emulsion depth to an error of 10% or even more is acceptable and that may be the reason for the Digilens result, assuming there was one. Since the rms (Did you take account of the rms at Digilens?) is usually below this, a certain inaccuracy is acceptible.However, for different applications, an rms of 10% may be disastrous. For example, an rms of 10% in a high speed communication channel with an FBG would lower the bandwidth, perhaps considerably
Joe Farina
Posts: 814
Joined: Wed Jan 07, 2015 2:10 pm

Re: emulsion thickness

Post by Joe Farina »

Din wrote: Sat Dec 04, 2021 4:04 pmYou may be able to get one at some university 'sales'. The University of California, San Diego (UCSD) has a so-called 'surplus sale', where equipment is bought for some project or study. Once the study is over, the equipment is put up for sale or auction. Here is the UCSD site, and you may be able to have them ship some item: https://surplus.ucsd.edu/. It's possible that other universities do the same. At any rate, we (Triple Take) got our traveling microscope from a UCSD surplus sale.
Thanks for the info and link. I'm surprised at the variety of equipment they have.

I have a spectrophotometer, which incorporates a spectrometer, so I would be interested in knowing how a spectrometer can be used to measure an air gap.

Noticed this (claiming 0.1micron resolution) for $339 (?):

https://www.amazon.com/Accuracy-Sub-Mic ... B07K358Q3W

https://www.youtube.com/watch?v=wWRWw4Rz2qA
BobH
Posts: 441
Joined: Tue Jan 06, 2015 10:26 pm
Location: Mesa, AZ

Re: emulsion thickness

Post by BobH »

I expect Mr. Pratheep can ask for clarification himself, if necessary after reading the linked information in my response. I used an Ocean Optics USB2000 spectrometer at Digilens for the measurement, and still do today.
Martin
Posts: 131
Joined: Sat Apr 04, 2015 2:36 am

Re: emulsion thickness

Post by Martin »

Martin wrote: Sun Dec 05, 2021 8:19 am So if you aim at very narrow bandwidth, you'd need a thick (I think ~ 1 - 2um or so) recording medium. Volume gratings e.g. currently used to run compact ECL laser diodes at single frequency (see Ondax, now Coherent I believe) would come to my mind.
Sorry for the typo. I meant 1 - 2mm thick recording layers.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

Re: emulsion thickness

Post by Din »

Martin wrote: Mon Dec 06, 2021 4:21 am
Martin wrote: Sun Dec 05, 2021 8:19 am So if you aim at very narrow bandwidth, you'd need a thick (I think ~ 1 - 2um or so) recording medium. Volume gratings e.g. currently used to run compact ECL laser diodes at single frequency (see Ondax, now Coherent I believe) would come to my mind.
Sorry for the typo. I meant 1 - 2mm thick recording layers.
Yes, true.

The reason is that the diffracted wavelengths are a function of the Bragg spacing. If the recording medium is thin, then there are fewer Bragg planes, and the variation of the spacing from the mean may be high (large standard deviation), resulting in a broad range of wavelengths. As the medium gets thicker, the variation from the mean gets smaller (the standard deviation drops), and the resulting wavelength range gets smaller. But 1 - 2 mm (1000 - 2000u) may be a bit excessive however. Bear in mind that the reason the Bragg planes form at all is the absorption of the medium to certain wavelengths. If the medium gets very thick, then the recording beams themselves lose intensity as they travel through the medium. This means that the ratio diminishes and the efficiency decreases. I believe you had this issue with one of Polygramma's polymers at one time. This also happened to one of our clients who had a 1mm cube made to get an extremely narrow bandwidth, the result was a very weak efficiency. I have got a 5nm bandwidth with an emulsion of 100u on DCG.
Martin
Posts: 131
Joined: Sat Apr 04, 2015 2:36 am

Re: emulsion thickness

Post by Martin »

Din wrote: Mon Dec 06, 2021 9:59 am
If the recording medium is thin, then there are fewer Bragg planes, and the variation of the spacing from the mean may be high (large standard deviation), resulting in a broad range of wavelengths. As the medium gets thicker, the variation from the mean gets smaller (the standard deviation drops), and the resulting wavelength range gets smaller. But 1 - 2 mm (1000 - 2000u) may be a bit excessive however. Bear in mind that the reason the Bragg planes form at all is the absorption of the medium to certain wavelengths. If the medium gets very thick, then the recording beams themselves lose intensity as they travel through the medium.
Right. Finding a recording material adequate for such thick layers isn't trivial. The volume holographic gratings for commercial laser systems are based on photo-thermo-refractive glass. Incidentally and interestingly, some of these systems rely on silver-halide doped glass. It's probably safe to say that such technology is out of reach to the average holographer. These VHGs provide extremely narrow bandwidths, For quite some time I was wondering whether the photo-thermo-refractive glass could be replaced by a slightly more "consumer-friendly" recording material.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

Re: emulsion thickness

Post by Din »

Martin wrote: Tue Dec 07, 2021 10:50 am
Din wrote: Mon Dec 06, 2021 9:59 am
If the recording medium is thin, then there are fewer Bragg planes, and the variation of the spacing from the mean may be high (large standard deviation), resulting in a broad range of wavelengths. As the medium gets thicker, the variation from the mean gets smaller (the standard deviation drops), and the resulting wavelength range gets smaller. But 1 - 2 mm (1000 - 2000u) may be a bit excessive however. Bear in mind that the reason the Bragg planes form at all is the absorption of the medium to certain wavelengths. If the medium gets very thick, then the recording beams themselves lose intensity as they travel through the medium.
Right. Finding a recording material adequate for such thick layers isn't trivial. The volume holographic gratings for commercial laser systems are based on photo-thermo-refractive glass. Incidentally and interestingly, some of these systems rely on silver-halide doped glass. It's probably safe to say that such technology is out of reach to the average holographer. These VHGs provide extremely narrow bandwidths, For quite some time I was wondering whether the photo-thermo-refractive glass could be replaced by a slightly more "consumer-friendly" recording material.
It really depends on the bandwidth you want for the application. You're probably right about finding consumer materials for extremely narrow bandwidths for lasers. You can get about 2 or 3 nm with DCG. In the 80's at POC and, before that, at NTS, where I was working on HUDs and laser protection goggles, DCG was considered the material with the highest efficiency (at POC, I got an OD of 4.5, and someone got an OD of 5) and the most flexible material in terms of the ability to tune to any vis wavelength, and control bandwidth up to a point. At Triple take, we did have to get a DCG hologram in the ~5 nm, and I think I could have got it lower. But, getting linewidths on the order of a KHz or so is probably not possible. However, many companies are abandoning DCG for medical reasons, so it no longer seems to be a "consumer-friendly" material.

Now, everyone seems to be using Covestro. Considering that the bandwidth of a hologram results from differential swelling in wet processing, Covestro should be extremely narrow band, since there's no wet processing. But Covestro material does swell a little, so extremely narrow band is probably not possible.

The other problem, as I mentioned earlier, is that the extremely thick materials with a chemical actinic reaction, will absorb, and so the ratio changes along the depth of the material. Therefore, any such material must have an actinic process that does not involve absorption, such as, perhaps, charge transfer. For some years I have considered magneto optical materials.
User avatar
admin_jsfisher
Site Admin
Posts: 117
Joined: Sun Jan 04, 2015 12:35 am

Re: emulsion thickness

Post by admin_jsfisher »

Several posts to this thread that were directed more at each other and not the topic at hand have been moved to "The Dump". Please, let's just let the matter die there.
Post Reply