Here is my table's construction, which is relatively cheep, and to date, ultra stable. here is the construction from the ground up: felt and cinderblocks stacked 3 high then rubber racquet balls as my first line of vibration defense, then 1/2" plywood, sorbothane, 3" concrete, sorbothane, and 1/2" steel. The table is 2'x2', and was designed to test the concept of the table's design, and to allow single beam reflection and transmission holograms on 2-1/2" plates. I cut the size and thickness of the sorbothane to filter out lower frequencies at the concrete/wood interface, and higher frequencies at the concrete/steel interface. sorbothane's website www.sorbothane.com has a free windows program for calculating the proper sorbothane size and thickness to tune the vibrations. I can set up an interferometer on my table, bang the ground with a hammer, and see no movement of the fringes. The one last thing I need to do is add a layer of tarpaper or heavy aluminum tape to the bottom of the steel plate to remove high frequency vibrations.
Colin Kaminski - Wed, Mar 28, 01 01:14:14 PM
I have been looking into sorbthane. What parameters did you use in your analysis? I have the software from sorbothane but I am unsure of the inputs. What sizes of sorbothane did you decide to use? I was able to damp out the high frequencies of my steel plate with a layer of 1/4" Expanded Polyethylene Closed Cell Foam (very cheap). If I hit my table the sound damps out very quickly but the low frequencies last about 1.5 sec. (as measured by my interferometer). 64.167.151.5
Jonathan - Fri, Mar 30, 01 01:16:17 PM
I'm curious to know of your experiences with your interferometer, and whether your interference pattern is a series of more or less parallel lines or whether it's a series of concentric circles. I've found the pattern of circles is much more sensitive, especially to path length differences caused by temperature changes or component drift. It's easily produced by having one beam slightly less diverging than the other, and then you have a zone plate, producing a "bulls-eye" pattern. This leads to being able to calculate the degree of path length change when you detect movements of the bullseye. For example when the bullseye changes from red to black you would be seeing a half wavelength path length change between the beams (for an ideally produced zone plate, which is produced from a spherical wavefront coinciding with a plane wavefront). When you see a flutter type movement of the pattern you are looking at a sensitivity in the interferometer measured in fractions of a wavelength. What I found the most interesting is the comparison between my 15 mW He-Ne and a 30 mW diode laser. The He-Ne took longer to settle down (about an hour to stabilize the power level) and didn't ever really a produce rock solid pattern. The diode would settle almost immediately (say 10 seconds) but would "fuzz-out" occasionally for the first hour and a half, after which it would be safe to shoot. I presume this is mode-hopping. 142.194.47.132
Colin - Fri, Mar 30, 01 03:17:09 PM
I have used the configuration that produces horizontal lines. I will change the set up to produce a bulls-eye. I have a split beam set I am happy with right now so it may take a week or so. I don't fully understand the term "Mode Hopping". I am told it results from changes in temperature of the diode. Lasermax supplies a peltier based temperature stabilization system with their interferometers. I believe it is a change in the frequency of the diode. 64.167.151.134
BLUEEYEDPOP - Thu, Apr 05, 01 07:45:40 PM
I don't recall exactly what parameters I used 8(. What I recall was just trying to divide the weight about several equally shaped blocks of Sorb., and see what the frequency isolation efficiency was. I will download the prog. as soon as I can, and look into it.
64.63.88.51
- Thu, Apr 05, 01 08:06:56 PM
OK.
I downloaded the software.
I'll be calling them tomorrow if I get a chance.
I do not understand. 64.63.88.51