Introductions

Holography related topics.
Ed Wesly
Posts: 501
Joined: Wed Jan 07, 2015 2:16 pm

Re: Introductions

Post by Ed Wesly » Tue Feb 02, 2016 6:43 pm

And a lot of students learned from these: http://edweslystudio.com/Pedagogy/PedagogyFrameset.html
"We're the flowers in the dustbin" Sex Pistols

lobaz
Posts: 272
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Introductions

Post by lobaz » Wed Feb 03, 2016 2:15 pm

hologram wrote:and it's just a matter of time until i'm pleading for help with my DCG holograms :lol:
Start with silver halide. No kidding. :)

hologram
Posts: 10
Joined: Mon Jan 25, 2016 2:03 am

Re: Introductions

Post by hologram » Wed Feb 03, 2016 7:56 pm

lobaz wrote:
hologram wrote:and it's just a matter of time until i'm pleading for help with my DCG holograms :lol:
Start with silver halide. No kidding. :)
why do you say that? i wanted to start with DCG because i didn't like the idea of having to buy film. DCG seems like it's dirt cheap, doesn't have to be ordered from special suppliers and also produces brighter holograms. i'm fine with initial failure as long as i'm not wasting expensive film.

i've also invested in a green laser so it's probably too late to go back, haha

User avatar
admin_jsfisher
Site Admin
Posts: 106
Joined: Sun Jan 04, 2015 12:35 am

Re: Introductions

Post by admin_jsfisher » Wed Feb 03, 2016 8:30 pm

What sort of green laser? A 100 - 150 mW diode module from eBay is unlikely to work very well.

hologram
Posts: 10
Joined: Mon Jan 25, 2016 2:03 am

Re: Introductions

Post by hologram » Thu Feb 04, 2016 1:37 am

admin_jsfisher wrote:What sort of green laser? A 100 - 150 mW diode module from eBay is unlikely to work very well.
i bought a 100mw microgreen from holomaker, so it is SLM. although he recommends that it isn't run at full power continuously, so at least 50mW. maybe more, i have no experience with these lasers. anybody have a microgreen from holomaker? if so i'd be interested to hear how they use it for holography.

is 50mW decent for DCG? would doubling the exposure time give me the same result as a 100mW laser?

lobaz
Posts: 272
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Introductions

Post by lobaz » Thu Feb 04, 2016 4:29 am

lobaz wrote:Start with silver halide. No kidding. :)
hologram wrote:why do you say that? i wanted to start with DCG because i didn't like the idea of having to buy film.
I suppose you did not make any hologram yet. First thing to learn: when making a hologram, anything can go wrong **very** easily. Holography is very sensitive, but until you try it, you have no idea how bloody sensitive it is.

Something in the setup can move, there can be a problem with a laser, exposure time can be wrong, processing can be flawed. Any error completely destroys the hologram - and without prior experience, you don't know what went wrong. If you want to make your own DCG plates, add several serious problems: the emulsion itself can be bad, you have no idea how to determine exposure time, and as exposure times are **much** longer than for silver halide, your optical setup must be super super super stable.
hologram wrote:i've also invested in a green laser so it's probably too late to go back, haha
No problem here, there are plates sensitive to green as well. You can try Harman HoloFX Green (available from Harman eshop), Slavich VRP-M (available e.g. from Integraf together with chemistry) or Ultimate U08 Green (available from Ultimate eshop together with chemistry). Trust me: order a few plates for first experiments and proceed step by step.

lobaz
Posts: 272
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Introductions

Post by lobaz » Thu Feb 04, 2016 4:49 am

hologram wrote:is 50mW decent for DCG? would doubling the exposure time give me the same result as a 100mW laser?
You can use 50 mW for small plates. Doubling exposure time is tricky: longer exposure increases chance that something moves, air circulation affects the hologram, laser must keep its properties twice as long... I don't make DCG, so maybe I am wrong with this one, but at least in silver halide the law of reciprocity holds just for short exposures (i.e. 100 mW for 1 s equals to 50 mW for 2 s); for longer exposures (minutes), you must use even longer exposure than predicted by the law.

Just to get some numbers in: sensitivity of a silver halide plate is about 150 uJ/cm^2. If you have a plate 10x10 cm, you must expand your beam to a circle of radius about 10 cm, i.e. to area 314 cm^2. It means 50 mW spreads to this area, i.e. we have 50/314 = 0.16 mW/cm^2 = 160 uW/cm^2. (Note I supposed that the energy spreads evenly, which is not true, and you have no losses, which is also not true.) Clearly, the exposure time should be about one second, or in practice several seconds.

A DCG plate has sensitivity about 2.5x10^5 uJ / cm^2. It means you should expose for 2.5x10^5 / 160 = 1562 seconds = 26 minutes. Clearly, holding your setup still for 1 s is much easier than for 26 minutes! Of course, a plate 2x2 cm does not require large beam spreading, thus power per area is much higher, thus exposure time is shorter. That's why I told "you can use 50 mW for small plates".

hologram
Posts: 10
Joined: Mon Jan 25, 2016 2:03 am

Re: Introductions

Post by hologram » Thu Feb 04, 2016 5:31 am

i've read quite a few posts by people claiming to have made denisyuks on a concrete floor, does that sound possible to you? i will only have a beam expander between the laser and the plate.

i think i'll give it a shot with DCG, but resort to AgX if i can't produce any holograms whatsoever. even marginal success is motivation enough for me to continue, plus it gives me a reference point from which to incrementally improve.

the holography gods must be laughing at my unwarranted optimism :D

lobaz
Posts: 272
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Introductions

Post by lobaz » Thu Feb 04, 2016 10:19 am

hologram wrote:made denisyuks on a concrete floor
It is definitely possible if your concrete floor is still enough (read: in the basement, no traffic in the neighborhood, no air currents). Remember that even your presence in the room makes air circulate! If you breathe, it is even worse. For first experiments, glue everything together. If you succeed, slowly relax, e.g. glue almost everything :)
hologram wrote:even marginal success is motivation enough for me
That's the biggest trouble: a beginner rarely achieves a marginal success. You either succeed (i.e. you have a hologram), or end with a blank plate. Nothing in between.

User avatar
admin_jsfisher
Site Admin
Posts: 106
Joined: Sun Jan 04, 2015 12:35 am

Re: Introductions

Post by admin_jsfisher » Thu Feb 04, 2016 10:34 am

Well, since you seem locked into the DCG-first idea, I wish you well, but offer the following advice and caution:

Here's a link to holowiki you should read. http://holowiki.org/wiki/Dichromated_Gelatin

The image there is a of 2"x3" Denisyuk made with a 10mW 532nm laser. The plate was in physical contact with the 1/4"-20 screws. If I recall correctly, the exposure time was 5 minutes.

Probably the most important thing on that wiki page is this:
Chemical safety is always important. In DCG-based holography, the gelatin and water used are completely safe; isopropyl alcohol and dichromates are not. Alcohol is highly flammable, especially at the higher concentrations used in drying a hologram; dichromate is a strong skin irritant and a known carcinogen. Treat them both with the respect they deserve.
Under no circumstances let anything from you holography work area into your kitchen...not even your kitchen sink, especially not your kitchen sink.

Post Reply