Re: [ATM] Large Amateur Telescope

["matt" <mariusrf@bellsouth.net>]

    so to make a long story short, light is light , photons are photons .
More or less redshifted but photons . Instead of behaving like a
misunderstood person, why don't you actually explain WHAT you're trying to
do, NOT HOW  you're doing it ?
    Just state what you are trying to accomplish please and leave the
particulars of your implementation for a later stage. Explain the principle
of what you want to do.
    You started arguing the merit of various details before telling us WHAT
it is you want to prove, check, verify, measure, or disprove, or whatever.
    I do have somehow a feeling of dejavu , all these explanations resemble
an old friend of mine who tried in vain for about 2 months in the first year
of college to invent a perpetuum mobile . He wasn't quite sure either what
principle he was going to use, all he knew was that if he used this
combination of wheels, gears, pulleys, plus an outstanding number of other
complicated contraptions it would just work. When we tried to understand
what it was he was doing, he delved just like you into lots of gory details
, and became very frustrated at our ignorant attempts of convincing him that
it wouldn't and shouldn't work. After all he was inventing it and we had no
idea of the details, so how dared we argue with him without knowing. He even
tried to build the thing !

best regards,
matt tudor


-----Original Message-----
From: Thomas Miller <tommy81@comcast.net>
To: atm@atmlist.net <atm@atmlist.net>
Date: Monday, November 01, 2004 10:43 PM
Subject: Re: [ATM] Large Amateur Telescope


>Matt wrote:
>
>>Optical fiber has a fairly high level of PMD (polarization mode
>>dispersion) which would render your measurement worthless.  Just flex it a
>>little and watch your phase change go all over the map, or rotate the
>>polarizer you've got at the end (you DO have a polarizer on the fiber
>>exit, don't you) and change the phase.
>
>Our device works for any polarization state, including unpolarized
>light.  We are not measuring the phase of light.  We are measuring the time
>delay of a chopped-light waveform.  The phase we refer to is the "phase
>shift" (really a time delay) of the chopped waveform caused by the 300m
>fiber delay loop.  This phase shift is easily seen on the oscilloscope in
>real time in the lab with a bright light source, and it most certainly does
>not jump around when you flex the fiber.  And no, we don't have a polarizer
>on the fiber exit.  This is not only unnecessary, but would attenuate 50%
>of our scarce photons.
>
>We use 200 micron core multimode (MM) fiber.  If we were using single-mode
>fiber, we might have to take PMD into account, but I'm not sure:  I don't
>know much about the quirks of single-mode optics.  I wish we could use
>single-mode (SM) fiber, as it has much less fiber attenuation than MM, but
>it's tough enough stuffing starlight into a 200 micron MM orifice, let
>alone the 8 microns or so for SM.
>
>Perhaps you were assuming that we were using a fairly well-known method of
>lightspeed measurement using opto-electrical choppers (Pockel's cells) for
>which polarization concerns are paramount.  However, we are using a
>mechanical chopper akin to the toothed wheel employed by Fizeau around 1850
>in the first direct lightspeed measurement.  I wish we could use the
>Pockel's cell method, as the chop frequencies are much higher than for
>mechanical choppers, and the fiber delay would be shorter, the fiber
>attenuation less.  The main problem with Pockel's cells, for our purposes,
>is their narrow bandwidth.
>
>The bottom line is that our device is not just a design on a piece of
>paper.  It has been built and tested and it works.  All "theoretical"
>objections seem to have been addressed.
>
>* * *
>
>When someone tells you something can't be done, don't believe it,
>especially if the objection is of a theoretical nature.  The "laws of
>physics" prevented the use of radio waves to create images of the human
>body:  the wavelength was too long, and there was some law about spatial
>resolution being on the order of a wavelength.  Yet MRI uses radio waves to
>create such images.
>
>We were told by engineers at the company that manufactures the fastest
>commercially available mechanical optical chopper that the "laws of
>physics" put a limit on mechanical optical choppers at about 50 kHz.  We
>are now pushing 600 kHz with our latest design.  (We thank this company for
>graciously loaning us their prototype micro-slotted disks.)
>
>
>>In any case, light goes at different speeds thru different materials, so
>>to measure the speed accurately, you have to know the index of refraction
>>accurately, which is tough to do with optical fiber.
>
>Well, to be truthful, we don't actually measure the speed-of-light in
>absolute terms.  We measure the speed-of-light as a ratio to the
>speed-of-light for a standard lab source.  We assume that our lab source
>has a "normal" lightspeed, but we don't actually measure the absolute speed
>of the lab source or the star:  we just compare them.
>
>
>Tom-
>
>
>_______________________________________________
>ATM mailing list http://www.atmlist.net/
>

_______________________________________________
ATM mailing list http://www.atmlist.net/