Re: [ATM] Temperature sensing and adaptive optics

["Peter C. Chen" <peterchenmd@comcast.net>]

Dominic-Luc:

> Another thing I have been thinking about, more
> like bad science fiction than science or engineering, is
> the use of heat differentials to bend optical and other
> surfaces. Surely people have done this, but I am not
> personally aware of and actually application of such a
> method of adaptive optics.

            I guess great minds think alike,  That is not a bad idea at all.

            Andre Couder of the Paris Observatory demonstrated (since the 
1930s) that embedded heater elements could be used to control the figure of 
a telescope mirror.  (A. Couder, Thermal Distortions of Telescope Mirrors 
and their correction,  Vistas in Astronomy, v.1, 372-376, 1955).  The 1.2 
meter mirror at the Observatoire de Haute Provence performed very well for 
many decades using this method.  Until, if I recall correctly, someone who 
did not read instruction manuals plugged the heater into line voltage (220 
ac?) instead of 12 v or so dc.

             You might find this link interesting

http://www.digilife.be/club/Johan.Vanbeselaere/atm/optics/figuring/thermally.htm

>I reckoned it would get out of the problem of having a bunch of expensive 
>precision motors.

             Yes it can for some applications.  But bear in mind that 
thermal motion is slow.  Also, the heat diffuses after a while.  Maintaining 
a steady temperature profile and gradient is difficult.   So the technique 
is more suited to large scale, slow (< 1 hz) adjustments of mirror figures 
(active optics).  It is in general not suited for  small scale (point to 
point), rapid (>100 hz) correction  of atmospheric distortions (adaptive 
optics).

Regards,
P. Chen



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