Observing fringes - Superferometer Part 2

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Justin W

Observing fringes - Superferometer Part 2

Post by Justin W »

Howdy All

I've just recently slapped together a bunch of posts and mirrors and some lenses and crap and I'm going to try to use it all to make some holograms. I've built this infernal contraption on the surface of a 4' x 6' x 8" thick Newport table. This is a table seeing at least its third owner and has a few miles on the odometer by now. I don't know if such a bohemian lifestyle has effected this things' rigidity in any way, but I'll say it sure was a big heavy slab of thick heavy rigid damn metal when it showed up, it was moved in and set up in a sensible fashion, looks real flat, and keeps laser beams where I left them for days and weeks now.

The Superferometer idea occurred to me back when I was first aiming beams around in a small sandbox. It's not surprising to hear that it's been done before, but it just seemed ike a good idea as I was trying means of mounting a parabolic mirror over a film holder. I was pretty used to watching the crazy green laser fuzz, and in even an otherwise apparently still beam of light, I saw twitches - tiny dances in the fuzziness. It took a while to note this and it was only eventually that it occurred to me that I might not be stable and rigid and junk. So I figured on aiming the parabolic straight back at the spatial filter, blah blah blah made an interferometer that uses all the stuff I'm considering imaging with.

Much easier to do on this table. And stays where I left it! I took Colin's advice and incorporated the film holder into the beam train, which is working out just fine. I also discovered some instability in the 2-axis adjustable mirror mount that I built from odds and ends (the base needed leveling and my initial mounting was ridiculous), so I shored up some weak spots, oh and object lighting mounting was overhauled as well, for stability reasons - all because I've had the opportunity to watch these fringes!

Things I feel like I can say I've noticed about laser fringes that rely on my imaging components:

Now that the one adjustable mirror is more solid, the fringes don't blur for as long after moving that beam.

After adjusting anything, moving anything, or handling anything involving the beam trains, the fringes will for the next period of time find themselves migrating in one direction. It is my belief that this is the settling process.

During the periods when the fringes are in steady or regular movement they seem much more sensitive to vibration and air currents.

It took about 45 minutes for my fringes to settle. When they did, they did. Locked in. My clever shutter idea is going gangbusters and goes unnoticed by superferometer fringes.

This is not a daytime camera. Jitter detected.
BobH

Observing fringes - Superferometer Part 2

Post by BobH »

One very usefull thing I've done is to set up a video camera to put the fringes on a monitor in another room. That way the heat and air movement caused by your body doesn't disturb the fringes you're trying to observe. :wink:

You'll want to find the source of that creep. It's probably play in the adjustment screws on your mirror mounts. You want clean solid contact between the table top and your mount bases. Hit them with a fine file before putting them on the table. Bases pick up little burrs during rough handling and storage, making them slightly unstable on the table.

Build a nice, durable set of table enclosure components. Keeping the air on the table still is every bit as important as keeping the components from vibrating or settling.
Justin W

Observing fringes - Superferometer Part 2

Post by Justin W »

Thank you Bob!

The source of the creep I believe to have been my first reference beam relay mirror - it was secured to one of my home-made steel posts that wasn't threaded tightly to the table. I do still see a couple short moments of fringe crawl immediately following adjustment of my 2-axis mount I fabricated - regular-quality pointed steel screws seating at a dynamic angle into brass bits pulled from tiny copier shafts... No surprise. I could put time into checking my Thorlabs 2-axis jobbie for screw-point creep, but it's brand new lab sh*t, and is more of a set n forget thing anyhow.

Oh, yes - I achieved something similar to the video monitor idea - a fine suggestion but by the time I read this I had already steered my superferometer output through a loose lens and off my collimator and with my lab door open a crack I was watching fringes from out here where I'll be chuting. A digital video observation arrangement really would be a huge evolutionary step for doing that; ability to record, motion detection, timekeeping.... But today is not the day I can afford a much better webcam than the one I have.

Bob, I believe you with all my heart about the air currents. You made a great post some time ago where you explained very nicely about how vibrations (our most despised enemy) really only lower effective beam ratios while air currents do the real damage... I can attest to the vibration thing from my own sandbox experience: I couldn't make a transmission hologram any higher than 6:1. Air currents push around fringes while vibration just jitters them or blurs them a bit. In my empty-bedroom-size laboratory with the door closed my superferometer fringes will settle into stillness then not react to any air currents until I swing open the door and bow into the room and start fanning air over my optics. Could I be one of those rare cases where my darkroom is small enough and isolated enough (with central heat/air off) that baffling for more than light may be unnecessary?
dave battin

Observing fringes - Superferometer Part 2

Post by dave battin »

Justin W wrote: Could I be one of those rare cases where my darkroom is small enough and isolated enough (with central heat/air off) that baffling for more than light may be unnecessary?
As its been said before, until you test it you will never know. There many good tips given here at this site and ALL of them added together will make you brighter holograms. Listen to what the successful holographers say, they are not trying to waist your time, but instead trying to accelerate your learning curve! ISOLATE your table from drafts!

i also see your power supply on the table in you face book pictures, if this get warm it would be a good idea to remove this from the table as the fluxuation in temps(on vrs off) will distort you table top!
Justin W

Observing fringes - Superferometer Part 2

Post by Justin W »

Hi Dave
Baffle for air currents I shall!
Maybe a rubber mat between my controller and table would make a good thermal insulator...
Colin Kaminski

Observing fringes - Superferometer Part 2

Post by Colin Kaminski »

Justin W wrote:Hi Dave
Baffle for air currents I shall!
Maybe a rubber mat between my controller and table would make a good thermal insulator...
When I got to visit Lon Moore's lab he had two tables each in a sepeerate room. One had a 5W Verdi laser and appeared to be the work horse of the lab. It was a very large Newport with every optics one could imagine. That room had a large cabinet that contained spares for every optical thing you could imagine.

The other was a sand table with a large HeNe. The Power supply on the Hene was adding lots of air currents to the table. He had made a box (just cardboard and tape) that directed the heat flow away from the table.

He ran a HEPA fan in the main room to help with dust and mentioned that he did not turn it off for exposures.
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