ok people tend to be saying that a stiff isolation table is much better than a heavy one. Does this mean that if the object and plate are fixed extremely strongly on to , for example a 2 inch thick piece of steel, that isolation from movement is no longer needed?
Ken Dunkley - Tue, Nov 07, 00 01:06:50 AM
Hello Ian
I'm almost saying that. What I am saying is that if you had an "ideally stiff" table, then isolation from movement is no longer needed. Example: If you had a 24" square (1/4 to 3/8" thick) of steel plate, you could make ordinary (fresnel)holograms on it regardless of what floor your apartment was located. Note that adequate baffling from air movement is still required. There is a paper titled "coffee table holography" that appeared in the early 70's that describe holograms made on an ordinary coffee table.
However, if you increased the size of the table to say 4 x 8 feet and if you intend to operate above ground floor levels, then I'd start to get nervous. Operating on ground floor levels is safe (with or without vibration isolation). The brightness of your images will depend on how well you provided baffling or a table enclosure/hood around your set up. My experiments have shown that baffling is much more important than vibration isolation when operating at ground floor levels.
Remember, don't get hung up worrying about vibration. The first thing you need to do is to set up a Michaelson interferometer test (use 80 cm arms)on the ground where you wish to locate your table. Baffle the beams from air currents by running the beams through cardboard tubing. Take readings of fringe drift (time to go from bright to dark fringe) at the beginning an at 15 minute intervals. After 1.5 hrs or before, if your fringes appear rock steady over a 10 plus minute period...great. Your next step is to install a table (with or without a vibration isolation system) and test it using the same Michaelson setup. The results will be better, equal, or worse than the results gotten from the floor alone. However, if your plate exposure times are well under 30 seconds you should be ok. Baffling your system is the key to receiving bright fringes.
Best regards
Ken 152.163.206.192
Ken Dunkley - Tue, Nov 07, 00 01:20:52 AM
Ian, One important addition is that when you set up the Michaelson, make absolutly sure that no laser light is returning back into the laser resonator/cavity. If you set up your beam splitter mirrors at a perfect 45 degree angle to the beam as indicated in numerous drawings illustrating the interferometer, then laser light will automatically return to and re-enter the laser cavity. Light returning to a cavity can alter the overall character of your fringes. This is very important and cannot overemphasized. To eliminate this possibility, alter the angles of the splitter and your mirrors.
Ken 152.163.206.192