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Interferometry test
March 17 2004 at 1:57 AM
  (Login javamiggs)

This is my first time to make holograms and Im testing my optical table for stability using Michelson interferometer set-up. Here is what I observed:

1. Multiple parallel black lines appear in my screen.
2. If Im not doing anything, the fringes are not moving or blurring. If I shout or clap my hands, it doesnt affect the fringe pattern too.
3. If I stomp or drag some objects in the floor, the fringes blur.

Is my table suited for recording or I still have to do something to avoid the blurring? If the fringes I observed are not blurring, does it mean my table is stable enough for recording?

My setup is going to be split-beam.
 
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Colin Kaminski
(no login)
Re: Interferometry testMarch 17 2004, 3:55 AM 

So far it sounds pretty good. The finges (black lines) you observe are what you will be recording. The can not move during an exposure so don't stomp or drag things on the floor while shooting.

Another thing to consider, how long does it take bluring fringes to settle? Watch you interferometer for a long time. What happens when the water heater or refigerator turns on? How about when a car drives by?
 
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(Login javamiggs)
Re:March 17 2004, 10:54 PM 

Im going to have holography interferometric studies. By the way im a student and this is my research work. There's no one working on holography in our university before and this is a first attempt. Professors just taught me the concepts, they havent actually made an actual recording.

Im lucky because our laboratory has two air-cushioned optical tables. Im looking at it and looks very heavy. It takes atleast 6 people to lift it. It has never been used before for holography.

If the fringes doesnt blur, is this enough to conclude that my table is suited for recording a hologram? Is there any other way to test?
 
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(Login javamiggs)
instantly..March 17 2004, 11:09 PM 

By the way, after I aligned the beam and obtained the fringes, it's not blurring, it's like projecting a picture of lines in the wall. I havent seen it blurring first and then settles down later.

It just blur during aligning period and when I stomp and drag things in the floor. Sometimes if the beam are not properly aligned, the fringes are dancing. Sometimes I just let it dance for a while. It's fun watch.
 
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(Login MichaelHarrison2)
Re: Interferometry testMarch 17 2004, 4:56 AM 

In addition to what Colin has suggested, get someone to go about the house:

o walking normally.
o walking by stomping their feet
o opening and closing all the doors
o opening and slamming all the doors
o turning on/off heaters and fans (don't forget any small ones, especially the ones you think wouldn't affect your table).
o opening and closing the garage door.
o turning on/off the washing machine and dryer.
o turning on/off each AC unit.
o playing the various TVs or radios loudly.
o running a lawn mower outside.
o running the car outside.

In other words, get someone else to do go around making every noise you can think of while you watch (or better yet, video record) your fringes. Through this you'll learn what affects your table so that if someone bad happens you'll know how long you have before the table settles and if you just had a recording affected or if you need to cancel the recording and re-start the settling process.

Also, if you can stomp or walk around the table and see the fringes move, build a remote shutter so that you never have to wonder if you caused the dim image you got.




---------------------------
If someone says it can't be done but they haven't tried it, don't believe them.
http://www.dragonseye.com/Holography
 
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holofloh
(Login holofloh)
Re: Interferometry testMarch 18 2004, 1:33 AM 

you wrote: My setup is going to be split-beam

don't begin a with split beam for your first hologram sessions. there are too much things they can make the setup not working. for the first time it is better to make denisyuk holograms.
glue the film holder and the object near together on a thick plate of steel or pressed wood. i have used hot-glue for that.


 
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(Login javamiggs)
Ok. Here's what I really want to do.March 18 2004, 2:43 AM 

I am planning to do a real-time holographic interferometry. Applying it to some sort of scientific study. This would be very ambitious I think for a beginner (But Im gonna do it no matter what..), . Im not doing display holography so Im not worrying about the quality of hologram i may made.

My only concern is to be able to set-up the entire split-beam configuration and succesfully record my reference hologram and be able to study the fringe pattern that would arise upon distorting my reference object.

I have a couple of plates for starter. Yes I will try your suggestion to have a feel of recording and developing a hologram.

This is not a project that has a deadline next week. I have plenty of time. Im doing it step by step, and at the same time learn much on it, with the help of you people. I would have to thank this forum.

Right now I just want to be sure if my table is well enough fit to record holograms. I think this is the first thing to settle.
 
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(no login)
Re:Ok. Here's what I really want to do.March 18 2004, 3:31 AM 

What you are experiencing with your fringes is perfectly normal for a passive vibration isolation table (air cushioned without real time monitoring with feedback compensation). As long as the fringes settle and stay settled you will be able to record the constructive and destructive interference differences. Do test to see what kind of external noises, movements and such cause the fringes to move or dim.

Also, air currents play a big role in fringe degradation.

I do agree with holofloh, do some Denisyuks as processing the hologram is also a technique that needs to be mastered.

You could also do interferometry with a Denisyuk by exposing once, stress the object slightly, then expose again as a second step.

Peace, and have fun!!!
 
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Bob
(no login)
Re: Ok. Here's what I really want to do.March 18 2004, 9:39 AM 

It sounds to me like you're ready to do the set-up! I'd recommend that you:
A) make both path lengths equal (regardless of the laser you're using), +/- about half an inch.

B) use washers on all the bolts used to attach components to the table.

C) touch the bottom of all bases with a flat file to remove burrs (formed by dropping them when not in use) before putting them in the set-up.

D) tighten all bolts so that you need a tool to take them apart (post-component, postholder-base, base-table).

E) don't worry to much about processing the hologram because cosmetic quality of the hologram is not critical to your application.
 
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(Login MichaelHarrison2)
use a single-beam setup...March 18 2004, 9:57 AM 

for your first attempts.

I thought I'd start a new sub-thread to reinforce what others have suggested.

Firmly attach your optics to your mounts and your mounts to your table.

Firmly attach your object to your table.

Use a single-beam setup so that you only have to worry about movement between the plateholder and object.

Use a white cup (or something similar) for your object and make the first exposure. Without changing or moving any part of your setup put a paper just put a paper clip (the large black ones that are used to hold stacks of paper) over the lip of the cup and after settling, make the second exposure.



---------------------------
If someone says it can't be done but they haven't tried it, don't believe them.
http://www.dragonseye.com/Holography
 
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(Login javamiggs)
The fringe somewhat "shifts".March 19 2004, 3:06 AM 

Quoting JonhFP "Also, air currents play a big role in fringe degradation."

I let the aircondition run and sometimes I see the black parallel lines moves smoothly back and forth from their original positions. I was able to magnify the black line's thickness to 1 inch and I could see clearly that it moves very little. It doesnt blur, it just move. Is this an implication of "fringe degradation"? Do I need to avoid this?

The laboratory Im working is totally sealed. Turning the aircondition off would transform it into an oven.
 
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(no login)
Re:The fringe somewhat "shifts".March 19 2004, 3:43 AM 

Movement degrades the image. If the fringe moves more then half the thickness of a fringe you will not get a hologram. You can keep the air conditioner on but just turn it off when you do you exposure. For a test, watch your fringes just after you turn the Air off. See how long it takes for the fringes to remain stable. Use this time to settle after turning the air off. Make your exposure, then turn the air back on.

Another alternative it to design a cover for your table that baffles the air movement. Basically design a frame and line with plastic. A very basic cover could simply be a standard table put on your Holographic table with plastic taped at the top and allowed to hang down all four sides, making a sort of tent.


 
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(Login MichaelHarrison2)
Re: Re:The fringe somewhat &quote;shifts&quote;.March 19 2004, 4:47 AM 

You'll probably find that if you just turn off the AC prior to a shoot that your settling times will still be fairly long. It take a while for a large mass of air to stop moving.

If you can swing it, create a cover for your table using one of these two methods...

1) If you use a flexible cover such as plastic, try to create a canopy that extends above the table several feet and below the table at least a foot. Make sure it doesn't touch the table or is heavy enough that random air currents won't move the canopy, causing movement in the table. There's a visual example of one way to do this on my site.

2) Create a hard canopy out of wood that can be hinged up to work on the table and hinged back down when you're shooting. There's a visual example of one way to do this on Colin's site.


 
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(Login javamiggs)
Ready to make my first hologramMarch 24 2004, 7:48 PM 

Finally I was able to make my optical table vibration free and ready to make my first hologram. I'll do a reflection type first as what Holofloh had suggested. Is the PFG-01 plates suitable for reflection hologram?

My real aim is to have a two beam set-up and make a transmission hologram. Our lab has only 4 50/50 beam splitters with a cube mount. My other questions is, how can I make a 4:1 (ref:obj) beam ratio out of these? Does it really need to be 4:1?
 
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(no login)
Re: Ready to make my first hologramMarch 24 2004, 11:39 PM 

PFG-01 is perfect.

Since the object wont reflect much light you will need much more light on the object than the reference. A microscope slide used as a beam splitter might work for you. Take 90% and send it to the object and 10% to the reference. Then expand the object beam till it is larger that the object till the brightest reflection off the object is about 1 to 1.
 
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(Login javamiggs)
bright objectsMarch 25 2004, 8:03 PM 

Im thinking that if my object is very reflective (e.g. very shiny peice of metal), I could still use my 50/50 beam splitter and be able to get enough reflected light. Just a thought. Would this be possible?

Again I'll inform everyone that I am not doing a display holography. So Im not really concerned about the beauty of my object.

I got a hard time planning how to mix my developer (I have JD-2) and finding a place to install a temporary sink. I guess I have to postpone making hologram next week.
 
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(no login)
Re: bright objectsMarch 25 2004, 8:20 PM 

Better would be flat white so you don't make an Optical Element on accident and not be able to figure out what you are looking at. Then expand the reference beam so you are wasting a lot of it. This is your best bet. You are looking for a beam ratio of about 1 to 1 on the brightest parts of the image.
 
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