Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Vibration Free Table for Holograms

  1. Mar 31, 2007 #1
    Hello,
    I am interested in making a vibration free table to make holograms. The way I was going to do it was to put innertubes under the corners of a box. Then fill the box with sand. I will test it by putting components on the sand to make a interferometer. Are there better ways of doing this?
    Thanks
     
  2. jcsd
  3. Apr 1, 2007 #2

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    You need to estimate the degree of vibration isolation you need to see if you can get it from a quick homebrew apparatus like this. Get an accelerometer and measure the noise power spectral density in your location. Figure out what your apparatus can tolerate.

    As for your specific design, a big mass (sand) on a spring (inner tubes) will basically act like a low frequency oscillator--give it a push and it will go up and down for a long time. It will also filter high frequencies, but you probably need multiple stages, and damping.

    Characterize the frequencies that your apparatus can tolerate. If your exposure is 0.01 second, for instance, then you had better filter out vibrations with shorter periods, that is, roll off everything at and above about 100 Hz. In practice your 3dB point will be determined by the number of poles (stages) in your filter, so you'll probably be nearer to 1 Hz. How much isolation is required? Then take a look on line for information on mechanical filters. You can use a series of tuned springs and masses, as you have proposed, or alternating lead and foam sheets, etc. Ideally you'll measure and calculate things like spring constants or compliances, damping factors, and filter impulse response to see how you're doing and where you need to go.

    A classical damper is a hydraulic shock absorber, such as is mated with springs and masses in an automobile suspension. The theory of these things is very well established.

    Some suggestions to further improve your chances: 1) work in the early morning (1 to 4 am) when traffic, air conditioning, construction activities etc. are minimal. 2) work in a basement on a concrete slab floor 3) in a rural location
     
  4. Apr 1, 2007 #3

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There are dozens of better ways of making a vibration isolation table - even a passive one. Mostly it comes down to your budget and time constraints and your targeted transmissibility (at desired frequencies). The starting point is site selection, based on measurements of the noise levels in the floor where you're planning to set this up. If you're not in a basement, noise amplitudes are smallest when directly above structural members, and get large, the farther away you go.

    The standard approach for an interferometry setup is to use pneumatic damping/isolation within a heavy+very strong steel structure. These are not easy to homebrew unless you've got access to a good machine shop and welding station. They are, however, easy to buy if you've got access to a good chunk of dough.

    What is your budget for this project? And what is the resolution you wish to have?
     
  5. Apr 1, 2007 #4
    I think it can have some vibrations as long as the frquency a factor of 10 less than the frequency of red light.

    [tex]v=\frac{c}{\lambda}=\frac{3*10^8}{650*10^-9}[/tex]

    That is a big number, but so is:
    [tex]w=\sqrt{\frac{k}{m}}[/tex]
    when partially filled intertubes and a ton of sand is used.

    Maybe putting an innertube and weight in series a few times would work better with a layer or two of sorbothane. Or maybe just doing it once with a ton of sand would work?

    I just moved so I instead of a kitchen table I am making dual purpose table for optics-holograms and eating. I am trying not spend much more than a few hundred isn't feasible for me. I am on the first floor; there aren't basements 'round here. Working in the wee hours sounds like a good way to get rid of sound. I will make an interferometer first. If the fringes don't appear than i know something is wrong.
     
  6. Apr 1, 2007 #5

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    I'm going to suggest that you back up and learn some basic physics and engineering, or team up with someone knowledgeable. I'm not trying to be disrespectful, but your project requires at least some practical and theoretical knowledge of physics, math and engineering to succeed. The content of your posts suggests that you aren't there at this point.
     
  7. Apr 1, 2007 #6
    A big chunk of inertia on top of some kind of damper is the obvious method to isolate something (sounds like a typical optics table really). Sure, if one had gobs of spare money this could be greatly improved upon, but one doesn't. Low-cost semi-successful laser-pointer holograms have been done before. The fact that the OP has already planned to verify the stability (by interferometer) is very encouraging. The only thing that hasn't been mentioned yet, does the OP have suitable (high-res) film?
     
  8. Apr 1, 2007 #7
    I have no practical and theoretical knowledge of physics? That's your opinion.

    http://www.instructables.com/id/EWSD3J2NOBES9J5XZT/
    http://home.moravian.edu/users/phys/mejjg01/interests/apparatus_pages/holography_table.htm

    Seems to have worked for these people. You don't have to understand everything to start playing around with it. As long as I am safe. I am not worrying about getting crushed by the sand. At worst I have a ton of sand in my dining room. I just wondered if other people have done this by making a series of dampers and frequency converters w/ sorbothane, weak springs, and heavy masses. Do you have any suggestions? Other than not to do it?
     
  9. Apr 1, 2007 #8
    No, but I do have an excellent laser. I can buy film, beamsplitter, mirrors, lenses etc from edmington scientific. I was thinking about making my own front side mirrors using tollens reagent or something similar. Maybe not...as soon I am sure how to do it safely.
     
  10. Apr 1, 2007 #9

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    As I said, I was not trying to be disrespectful. Just reacting to your statement that you need to filter vibrational frequencies up to 1/10 that of red light, that is about 5*10^14 Hz.
     
  11. Apr 2, 2007 #10
  12. Apr 2, 2007 #11
    I see what you are saying. Sound frequencies are much lower than that. They were saying in the video that the amplitude of the vibration of film should be less than 1/10 of the of the light wavelength. A little different context.
    Suppose I need a 5 second exposure time. Then the frequency is 0.2. Then I want to cut off everything above 0.2. Much smaller than a subwoofer of around 20 hertz.
    My natural frequency is the square rooot of k/m=1/907 is much less than 0.2. I really don't see what the point of calculating it all out when I have seen examples where it worked. I would prefer to learn by doing.
    I believe you have good intentions. That you didn't mean disrespect when you said I don't have any practical knowledge or theoretical knowledge of physics, math, and engineering. However I disagree with you. I will learn from books and experiment at the same time. I don't think you have to wait around to do cook book experiments. Anyways I realize that post was gibberish about the frequency now. I don't think I should wait a few years or anything to do an experiment because of one post of gibberish
     
  13. Apr 2, 2007 #12

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    EDIT: ah, I deleted this post since it crossed with yours.

    You are on the right track here, except you need to have a filter cutoff probably a factor of 3 to 5 below 0.2Hz to have significant attenuation there. Start with your ton of sand and inner tubes and see what you get.
     
    Last edited: Apr 2, 2007
  14. Apr 2, 2007 #13
    I am sorry for arguing. I don't have any bad feelings. I just wanted to make clear my view points. Thank you for your help I really do appreciate it.

    Anyways, once I put that ton of sand in it is going to be hard to move and mess with the table. I was thinking if I could find small inner tubes like to a fork lift, then I could put sorbothane under them. After I fill it with sand that would be hard because I would have to move the sand first. If I put sorbothane in parellal to make a sorbothane layer, then I wonder where the best place to put it is. My guess is before the tubes.
     
  15. Apr 2, 2007 #14

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    No worries.

    I'm not really familiar with the properties of sorbothane. If it has different effective spring constant (my guess is it's stiffer) then it will just modify the overall spring constant of the foam/inner tube combination. Might or might not be what you want.

    By multiple filter sections I meant you'd put another table/spring on top of the first. Definitely try what you have first.
     
  16. Apr 2, 2007 #15
    Yeah I don't think sorbothane can have that much weight so maybe I will use some on the sand if the sand doesn't do the trick by itself
     
  17. Apr 4, 2007 #16

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    Report back to us later on your results. This is an interesting undertaking!
     
  18. May 26, 2008 #17
    Hello NotMrX!

    I see this is something of an antique post, and I hope it not too late to lend some insight as far as cobbling together a functional holography table.

    First off let me say welcome to the wonderful world of holograms!

    A little background on me: I'm just some guy. I'm a regular cat who got into burning holograms a couple of years ago after developing something of a pop-culture fascination with lasers. I'm certainly no professional scientist nor much of an expert at anything at all. I have, however, slaved over a hot laser for long enough to have gained some practical experience with what works and what does not as far as making basic holograms.

    As far as building your first isolation table is concerned:
    Sand is a great way to get started, but falls way short of ideal for a variety of reasons.
    I'll address first the pros of burning 'grams in a sandbox, then move on the cons.

    Bear in mind these three basic tenets of a holography table: Mass, rigidity and isolation.

    Why sand is cool:
    Sandboxes are easy. They are quick to put together and easy to use. Given enough room, a sandbox is highly versatile - steering beams with mirrors staked in sand is a piece of cake. Setups can be torn down and rebuilt in a short amount of time. They are also very inexpensive to assemble/accumulate.

    Why sand is not cool:
    *Takes deep breath*
    A sandbox alone is not sufficient to isolate from ambient vibration. Any sandbox you use will need to be isolated in the same fashion as any other mass you use. It will take a lot of sand to have sufficient mass. A sandbox is messy and dusty. A sandbox will sag. A sandbox is dusty. Beams will wander and drift over a surprisingly short period of time. A sandbox is dusty. If you plan to incorporate a spatial filter into your setup (highly recommended), it will only stay dialed-in for minutes at a time. Oh, and a sandbox is dusty.

    Please don't think that I am against you building a sandbox to get started in holography. It truly is the simplest way to get started. A sandbox will not, however, be the table you want to stick with for the long haul. At some point in the future, if the holobug has found a suitable host in your bloodstream, you will find yourself desiring a rigid table with a steel top upon which you can magnet your optics. Your rigid steel-topped table will most likely be isolated from vibration by means of inner tubes inflated soft.

    Other issues to address if you plan for success with holography:
    Your laser - In your posts so far you have not given much information as far as the particulars of what you are lasing with. Not all lasers are created equal. Yes, a laser does, by nature of it's basic operation, emit a single wavelength of light, but many lasers do not maintain a stable frequency. You laser is likely to operate in multiple longitudinal modes, and if those modes do not remain "locked in" inside the cavity, you will see mode hops. If your laser hops modes during an exposure, your hologram will forever be marked with "sliced bread" - an irritating phenomenon of fine parallel stripes washing over the surface of your image. You want to avoid mode hops. One way of doing this is to perform your holography with a SLM (single longitudinal mode) laser. This option is expensive. HeNe lasers operate in multimode but are stable after sufficient warm up time. HeNe's are reasonably affordable and a good way to get started, though are bulky and fickle. In an ideal world, you could obtain some green-sensitive film and find a Coherent Compass at a great price. ;)

    A baffling deal on a single mode laser is unlikely, of course, so simply get to know your lasers and find one with a stable output.

    A really helpful hint (and listen up now, hear?) - Don't leave beam ratios or exposure times to chance or think you can eyeball it. Obtain an accurate light meter. If you have the dough, purchase a Coherent LaserCheck. You will never regret this. Just stick that hog in front of your dummy plate (both sides for reflection or one side with beams blocked in turn for transmission) to see exactly how much light your film is seeing. Never regret it, I say. The LaserCheck is AWESOME - it will give you numbers in microwatts (microjoules per second), and calculating accurate exposure times is the kind of math you can do in your head with that tool in your arsenal.

    A final note: I noticed in your previous posts that you are hunting for a beam splitter and I commend this. Split-beam holography is the real deal - but - know this: you will not be successful with split-beam reflection holography until you have a very very stable table.

    Best of luck good sir!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Vibration Free Table for Holograms
  1. Hologram ? (Replies: 12)

Loading...