Plastic

Dichromated Gelatin.
Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Plastic

Post by Tony DCG »

I've been shooting some objects that are plastic maybe like a polyethylene similar to the green plastic army men we played with as kids (and maybe still do)
I'm still having issues with movement and wanted some advice.
So imagine gluing an object to a flat surface, then rotated 90 degrees and shot. So the object is only attracted by its base. The result is movement on the hologarm.
Yesterday I tried propping the object up from behindby adding a metal rod. I also tried gluing the base with a different glue (was 5 minute epoxy to super glue).
It still showed movement.
I have a metal object next to it that is secured with screws and that is my reference that did not move indicating it is just the plasic moving.
Today I drilled a hole on top of the object and placed a metal rod to see if that would help, will shoot later this week.
I was wondering if there is something else going on such as the material itself expanding or contracting or if even the couple of mw2 is causing some expansion. Can I spray the object with some sort of harding spray that can help?
Can anyone shed some light of this?
Thanks
Tony
lobaz
Posts: 280
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Plastic

Post by lobaz »

Hi,
what are the exposure time and the settling time?
Petr
Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Plastic

Post by Tony DCG »

Thanks Petr
Settling time is around 20-30 minutes.
Exposure time is around 4 minutes

Oh and just to be clear on the metal object I use as a reference it is adjancent to the plastic one.
Again the platic object shows a dark image while the metal is pretty sharp while rotating the hologram
holomaker
Posts: 772
Joined: Wed Jan 07, 2015 8:01 am

Plastic

Post by holomaker »

The need to thermally stabilize your object , is this a denisyuk ? Allow a lot more time to settle like an hour or more......
lobaz
Posts: 280
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Plastic

Post by lobaz »

Four minutes is a lot for a plastic toy. First, I would try normal orientation (i.e. not 90 degrees), just to make sure this is not the origin of the problem - maybe thin parts try to follow gravity. Settling time 20-30 minutes sounds quite short to me. I remember when I was making a hologram of a (gold) pocket watch (single beam Denisyuk, exposure time about 30 s, setup on a Melles-Griot table in the basement), settling times shorter than 15 minutes did not work. Your object does not behave as a spring as the watch, but the exposure time is much longer. I would try overnight settling.
Thermal issues could be source of problems as well. I would try to make a styrofoam box around the setup (excluding laser).
Can you read something from the pattern of the stripes? Are they parallel, circular, ...?
Petr
holomaker
Posts: 772
Joined: Wed Jan 07, 2015 8:01 am

Plastic

Post by holomaker »

Yes agree generally if a denisyuk is being made you can simply place a cardboard box over the entire setup and just cut a small hole to allow the one beam in and allow to settle as long as your patients will last!
Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Plastic

Post by Tony DCG »

Many thanks guys
lobaz wrote:Can you read something from the pattern of the stripes? Are they parallel, circular, ...?
I've seen both strips and circular.
Can you tell me what each indicate?
I know I hvae seen thinner glass cause circular patterns.
I've seen it were as you tilt the hologram there is a bright image followed by a dim one as I tilt it.
I've also seen areas of complete darkness, these are generally were the object is thinnest.

Can the laser itself be enough to heat up the material?

I really like the 90 degree idea and will also incoorperate a box

Thanks again
Tony
Steven

Plastic

Post by Steven »

I have shot holograms containing a plastic object (possibly a form of acrylic) using exposures longer than 20 minutes.
However, the object was very reflective (silvered "happy birthday" cake topper), so it didn't get much heating from a power density of about 100 µJcm2.

I allowed a settling time of a couple of hours or so and placed plenty of material around my table to reduce drafts.
The holograms were shot in simple Denisyuk with the DCG plate placed face down.
The depth of the holograms were 15-20mm.

As others have said, I suspect that it may be a thermal expansion issue.

A useful list of coefficients of linear thermal expansion for various materials can be found here:
http://www.engineeringtoolbox.com/linea ... -d_95.html

HTH,
Steven.
Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Plastic

Post by Tony DCG »

Thanks Steven, that was extremely helpful.
142laser
Posts: 453
Joined: Wed Jan 07, 2015 10:14 am
Location: Tampa, FL

Plastic

Post by 142laser »

Wow I really learned something reading this. I had NO idea it took any real time for an object to "settle". I suppose is depends heavily on the kind of object and the environmantal conditions. Amazing. Makes some sense though.
Post Reply